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Atlantis => the Scientific Atlantis => Topic started by: Adam Hawthorne on April 08, 2007, 11:19:40 pm



Title: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:19:40 pm
It is said that there is no sunken landmass (of the size Plato suggests) in the Atlantic Ocean.

However, I thought it would be worthwhile to investigate ways where a landmass can be submerged, which we shall do now.


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:21:17 pm
(http://upload.wikimedia.org/wikipedia/commons/3/31/Subduction.jpg)

The Juan de Fuca plate sinks below the North America plate at the Cascadia subduction zone.

Subduction


The Juan de Fuca plate sinks below the North America plate at the Cascadia subduction zone.In geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another, with one sliding underneath the other and moving down into the mantle, at rates typically measured in centimeters per year. An oceanic plate ordinarily slides underneath a continental plate; this often creates an orogenic zone with many volcanoes and earthquakes. In a sense, subduction zones are the opposite of divergent boundaries, areas where material rises up from the mantle and plates are moving apart


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:23:12 pm
(http://upload.wikimedia.org/wikipedia/commons/6/6f/Oceanic_spreading.png)
Oceanic plates are subducted creating oceanic trenches


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:24:01 pm
General description

Subduction zones mark sites of convective downwelling of the Earth's lithosphere (the crust plus the strong portion of the upper mantle). Subduction zones exist at convergent plate boundaries where one plate of oceanic lithosphere converges with another plate and sinks below it to depth of approximately 100 km. At that depth the peridotite of the oceanic slab is converted to eclogite, the density of the edge of the oceanic lithosphere increases and it sinks into the mantle. It is at subduction zones that the Earth's lithosphere, oceanic crust, sedimentary layers, and trapped water are recycled into the deep mantle. Earth is the only planet where subduction is known to occur; neither Venus nor Mars have subduction zones. Without subduction, plate tectonics could not exist and Earth would be a very different planet: Earth's crust would not have differentiated into continents and oceans and all of the solid Earth would lie beneath a global ocean.

Subduction results from the difference in density between lithosphere and underlying asthenosphere. Where, very rarely, lithosphere is denser than asthenospheric mantle, it can easily sink back into the mantle at a subduction zone; however, subduction is resisted where lithosphere is less dense than underlying asthenosphere. Whether or not lithosphere is denser than underlying asthenosphere depends on the nature of the associated crust. Crust is always less dense than asthenosphere or lithospheric mantle, but because continental crust is always thicker and less dense than oceanic crust, continental lithosphere is always less dense than oceanic lithosphere. Oceanic lithosphere is generally not denser than asthenosphere but continental lithosphere is lighter. Exceptionally, the presence of the large areas of flood basalt that are called large igneous provinces (LIPs), which result in extreme thickening of the oceanic crust, can cause some sections of older oceanic lithosphere to be too buoyant to subduct. Where lithosphere on the downgoing plate is too buoyant to subduct, a collision occurs, hence the adage "Subduction leads to orogeny". Most subduction zones are arcuate, where the concave side is directed towards the continent. This is especially so where a back-arc basin develops between the subduction zone and the continent. The arcuate configuration probably results from differential friction between the tectonic plates, and the likely agent that would reduct the interplate friction is serpentinite, but a large batch of unconsolidated sediment could cause similar effects as well.

Subduction zones are associated with the deepest earthquakes on the planet. Earthquakes are generally restricted to the shallow, brittle parts of the crust, generally at depths of less than 20 km. However, in subduction zones, earthquakes occur at depths as great as 700 km. These earthquakes define inclined zones of seismicity known as Wadati-Benioff zones (after the scientists who discovered them), which outline the descending lithosphere. Seismic tomography has helped outline subducted lithosphere in regions where there are no earthquakes. Some subducted slabs seem not to be able to penetrate the major discontinuity in the mantle that lies at a depth of about 670 km, whereas other subducted oceanic plates can penetrate all the way to the core-mantle boundary. The great seismic discontinuities in the mantle - at 410 and 670 km depth - are disrupted by the descent of cold slabs in deep subduction zones.



Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:24:44 pm
Subduction causes oceanic trenches, such as the Mariana trench. Trenches occur where one plate begins its descent beneath another. Volcanoes that occur above subduction zones, such as Mount St. Helens and Mount Fuji, often occur in arcuate chains, hence the term volcanic arc or island arc. Not all "volcanic arcs" are arced: trenches and arcs are often linear.

The magmatism associated with the volcanic arc occurs 100-300 km away from the trench. However, a relationship has been found, which relates volcanic arc location to depth of the subducted crust as defined by the Wadati-Benioff zone. Studies of many volcanic arcs around the world have revealed that volcanic arcs tend to form at a location where the subducted slab has reached a depth of about 100 km. This has interesting implications for the mechanism that causes the magmatism at these arcs. Arcs produce about 25% of the total volume of magma produced each year on Earth (~30-35 km³), much less than the volume produced at mid-ocean ridges. Nevertheless, arc volcanism has the greatest impact on humans, because many arc volcanoes lie above sealevel and erupt violently. Aerosols injected into the stratosphere during violent eruptions can cause rapid cooling of the Earth's climate.

Subduction zones are also notorious for producing devastating earthquakes because of the intense geological activity. The introduction of cold oceanic crust into the mantle depresses the local geothermal gradient and causes a larger portion of the earth to deform in a brittle fashion than it would in a normal geothermal gradient setting. Because earthquakes can only occur when a rock is deforming in a brittle fashion, subduction zones have the potential to create very large earthquakes. If this earthquake occurs under the ocean it has the potential to create tsunamis, such as the earthquake caused by subduction of the Indo-Australian Plate under the Eurasian Plate on December 26, 2004, that devastated the areas around the Indian Ocean. Small tremors that create tiny, unnoticeable tsunamis happen all the time because of the dynamics of the earth.



Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:26:09 pm
(http://upload.wikimedia.org/wikipedia/en/thumb/2/21/Subductionfactory.jpg/434px-Subductionfactory.jpg).

Cartoon representation of the Subduction Factory, from Y. Tatsumi JAMSTEC.


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:29:15 pm
Importance
 
 
Cartoon representation of the Subduction Factory, from Y. Tatsumi JAMSTEC.
Subduction zones are important for several reasons:

1.   Subduction Zone Physics: Sinking of mantle lithosphere provides most of the force needed to drive plate motion and is the dominant mode of mantle convection.
2.   Subduction Zone Chemistry: The cold material sinking in subduction zones releases water into the overlying mantle, causing mantle melting and fractionating elements (buffering) between surface and deep mantle reservoirs, producing island arcs and continental crust.
3.   Subduction Zone Biology: Because subduction zones are the coldest parts of the Earth's interior and life cannot exist at temperatures >150°C, subduction zones are almost certainly associated with the deepest (highest pressure) biosphere.
4.   Earth's Mixmaster: Subduction zones mix subducted sediments, oceanic crust, and mantle lithosphere and mix this with mantle from the overriding plate to produce fluids, calc-alkaline series melts, ore deposits, and continental crust. For this reason, scientists increasingly refer to the "Subduction Factory", and we are intermittently and rudely reminded of its operation by earthquakes and tsunamis.
Learning more about the physics, chemistry, and biology of subduction zones requires efforts that are increasingly interdisciplinary and international. Because of the central role that subduction plays in the solid Earth system, as well as its role in maintaining equilibrium between the mantle and the hydrosphere, understanding and teaching how subduction zones operate is a scientific challenge of the first importance.
Subduction zones are also being considered as possible disposal sites for nuclear waste, where the action would carry the material into the planetary mantle, safely away from any possible influence on humanity or the surface environment.

http://en.wikipedia.org/wiki/Subduction


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:31:11 pm
Orogeny
 
Orogeny (Greek for "mountain generating") is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within a time frame.


Orogenic events occur solely as a result of the processes of plate tectonics; the problems which were investigated and resolved by the study of orogenesis contributed greatly to the theory of plate tectonics, coupled with study of flora and fauna, geography and mid ocean ridges in the 1950s and 1960s.

The physical manifestations of orogenesis, the process of orogeny, are orogenic belts or orogens. An orogen is different from a mountain range in that an orogen may be completely eroded away, and only recognizable by studying (old) rocks that bear the traces of the orogeny. Orogens are usually long, thin, arcuate tracts of rocks which have a pronounced linear structure resulting in terranes or blocks of deformed rocks, separated generally by dipping thrust faults. These thrust faults carry relatively thin plates (which are called nappes, and differ from tectonic plates) of rock in from the margins of the compressing orogen to the core, and are intimately associated with folds and the development of metamorphism.

The topographic height of orogenic mountains is related to the principle of isostasy, where the gravitational force of the upthrust mountain range of light, continental crust material is balanced against its buoyancy relative to the dense mantle.

Erosion inevitably takes its course, removing much of the mountains, leaving the core or mountain roots, which may be exhumed by further isostatic events balancing out the loss of elevated mass. This is the final form of the majority of old orogenic belts, being a long arcuate strip of crystalline metamorphic rocks sequentially below younger sediments which are thrust atop them and dip away from the orogenic core.

http://en.wikipedia.org/wiki/Orogeny


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:31:57 pm
History

Before geology, the presence of mountains was explained in Christian contexts as a result of the Biblical Deluge, for Neoplatonic thought, which influenced early Christian writers, assumed that a perfect Creation would have to have been in the form of a perfect sphere. Such thinking persisted into the eighteenth century.

Orogeny was used by Gressly (1840) and Thurmann (1854) as orogenic in terms of the creation of mountain elevations, as the term mountain building was still used to describe the processes.

Elie de Beaumont (1852) used the evocative "Jaws of a Vise" theory to explain orogeny, but was more concerned with the height rather than the implicit structures orogenic belts created and contained. His theory essentially held that mountains were created by the squeezing of certain rocks.

Suess (1875) recognised the importance of horizontal movement of rocks. The concept of a precursor geosyncline or initial downward warping of the solid earth (Hall, 1859) prompted Dana (1873) to include the concept of compression in the theories surrounding mountain-building. With hindsight, we can discount Dana's conjecture that this contraction was due to the cooling of the Earth (aka the cooling earth theory).

The cooling Earth theory was the chief paradigm for most geologists until the 1960s. It was, in the context of orogeny, contested hotly by proponents of vertical movements in the crust (similar to tephrotectonics), or convection within the asthenosphere or mantle (geology).

Steinmann (1906) recognised different classes of orogenic belts, including the Alpine type orogenic belt, typified by a flysch and molasse geometry to the sediments; ophiolite sequences, tholeiitic basalts, and a nappe style fold structure.

In terms of recognising orogeny as an event, Leopold von Buch (1855) recognised that orogenies could be placed in time by bracketing between the youngest deformed rock and the oldest undeformed rock, a principle which is still in use today, though commonly investigated by geochronology using radiometric dating.

Zwart (1967) drew attention to the metamorphic differences in orogenic belts, proposing three types, modified by Pitcher (1979);



Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:33:33 pm
(http://upload.wikimedia.org/wikipedia/commons/thumb/2/20/Taconic_orogeny.png/344px-Taconic_orogeny.png)

Taconic orogeny


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:35:29 pm
Obduction

Obduction is the overthrusting of continental crust by oceanic crust or mantle rocks at a destructive plate boundary. It can occur during an orogeny.


Obduction occurs where a fragment of continental crust is caught with resulting overthrusting of oceanic mafic and ultramafic rocks from the mantle onto the continental crust. Obduction often occurs where a small tectonic plate is caught between two larger plates with the crust, both island arc and oceanic, becoming attached as a new terraine to an adjacent continent. When two continental plates collide obduction of the oceanic crust between is often a part of the resulting orogeny, or mountain building episode. New Caledonia is one example of recent obduction. The Klamath Mountains of northern California contain several obducted oceanic slabs. Obducted fragments also are found in Oman, Cyprus, Newfoundland, New Zealand, the Alps of Europe, and the Appalachians of eastern North America. The characteristic rocks of the obducted oceanic crust are the ophiolites; consisting of basalt, gabbro, peridotite, dunite, and eclogite. There are many examples of oceanic crustal rocks and deeper mantle rocks that have been obducted and exposed at the surface worldwide.

It seems that most obductions are initiated at supra-subduction, back-arc basins. These basins are caused where the edge of the continent collapses seawards, and extension in the back-arc basin enhances volcanism and crustal accretion. Since while the continental crust collapses the upper part of the ductile lithosphere, namely the upper lithospheric mantle, is exposed, and the ophiolitic volcanism accretes on metamorphic lithologic series. As the subduction turns into mountain-building, the ophiolites and their metamorphic basement find their way to mountain tops.


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:38:21 pm
Depression (geology)

Depression in geology is a landform sunken or depressed below the surrounding area. Depressions may be formed by various mechanisms, and may be referred to by a variety of technical terms.
•   A basin may be any large sediment filled depression.[1] In tectonics, it may refer specifically to a circular, syncline-like depression: a geologic basin; while in sedimentology, it may refer to an area thickly filled with sediment: sedimentary basin.[2]
•   A blowout is a depression created by wind erosion typically in either a desert sand or dry soil (such as a post-glacial loess environment).[2]
•   A graben is a down dropped and typically linear depression or basin created by rifting in a region under tensional tectonic forces.
•   An impact crater is a depression created by an impact such as a meteorite crater.
•   A kettle is left behind when a piece of ice left behind in glacial deposits melts.[3]
•   A depression may be an area of subsidence caused by the collapse of an underlying structure. Examples include sinkholes above caves[4] in karst topography, or calderas[5][6] or maars in volcanic areas.
•   A depression may be a region of tectonic downwarping typically associated with a subduction zone and island arc. Fore-arc and back-arc sedimentary basins fill with sediment from an adjacent island arc, or from continental volcanism and uplift.
•   An oceanic trench is a deep depression with steep sides located in the ocean floor. Oceanic trenches are caused by the subduction (when one tectonic plate is pushed underneath another)[7] of oceanic crust beneath either other oceanic crust or continental crust.[8]
•   A depression may result from the weight of overlying material such as an ice sheet during continental glaciation which is subsequently removed resulting in a basin which slowly rebounds. The area around the ice sheet, though not covered in ice itself, may also be pulled down by the weight of the ice sheet, which is known as peripheral depression.[9] Further from the ice, a forebulge may form, which is curved slightly upward.[10]
•   A depression may be a pothole - either a simple roadway depression or a fluvial erosional depression in a river streambed, or area affected by coastal water currents.
One of many impressive depressions is the Great Rift Valley of East Africa. Perhaps even more impressive is the Atlantic Ocean basin.


http://en.wikipedia.org/wiki/Depression_%28geology%29


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:42:21 pm
Map of Sampled Seamounts
(http://seamounts.sdsc.edu/Map_sm_5-12-05.jpg)

It is estimated that there are tens of thousands of seamounts in the world's oceans. They are found in every ocean basins and most latitudes. This map shows the seamounts for which SeamountsOnline currenlty has data. But note that in many cases, we only have records of one or a few species - the number of seamounts which have been well sampled is much smaller. In creating this map, a strict definition of "seamount" was not used - the map includes some features that are less than 1000m tall. If you are aware of sampling that is not represented here, please let us know.

You may use this map, and all materials on SeamountsOnline, freely for non-commercial uses (only) as long as the source is cited. Please cite this map as: K. Stocks. 2005. Map of Seamounts in SeamountsOnline. SeamountsOnline: an online information system for seamount biology. World Wide Web electronic publication. http://seamounts.sdsc.edu.

updated 2005-05-12

http://seamounts.sdsc.edu/



Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:49:38 pm
(http://oceanexplorer.noaa.gov/explorations/05lostcity/logs/lchome/herc_space_600.jpg)

Space shot to our own planet:  ROV Hercules approaches a ghostly, white, carbonate spire in the Lost City Hydrothermal Field, about 2500 feet below the surface of the Atlantic Ocean. Image courtesy of IFE, URI-IAO, UW, Lost City science party, and NOAA.

http://seamounts.sdsc.edu/


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:53:25 pm
(http://oceanexplorer.noaa.gov/explorations/04mountains/logs/summary/media/3d_multibeam_600.jpg)

A multibeam map processed into three-dimensional image of the Manning Seamount complex.
http://seamounts.sdsc.edu/


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:58:06 pm
Hydrographic structure and circulation at the Great Meteor Seamount

This study is part of the DFG programme Analysis of RV Meteor Cruises. The main aim of the project is to investigate the impact of an isolated seamount on the watermass structure and circulation pattern of the surrounding ocean. The area under investigation covers the region of the Great Meteor Seamount in the subtropical North Atlantic Ocean. Interactions between the mean current, tides and the seamount topography force a quasi - stationary, anticyclonic circulation around the flanks of the seamount leading to substantial consequences for the development of ecosystems. Observations as well as numerical simulations reveal two dominant mechanisms of flow at isolated seamounts: the formation of a Taylor column circulation and the resonant amplifaction of seamount trapped waves. An overview is given by Beckmann (1999).

(http://www.awi-bremerhaven.de/Modelling/BRIOS/seamount.gif)

 

Original topography and geographic location of the Great Meteor Seamount from Smith & Sandwell (1997)
Rotating seamount (5Mb)

The characteristics of the mass and current field are described on the basis of CTD, XBT and ADCP measurements along transects across the seamount center, which were carried out during the RV Meteor cruise 42/3 (September 1998). Numerical process studies will help to identify and analyse the physical mechanisms of the different aspects of the circulation at the Great Meteor Seamount with respect to the possibility of the formation of an independent species composition. The Great Meteor Seamount is located far off common fishing grounds and therefore of special interest for the investigation of biological processes depending on one specific oceanographic situation.

Methods and work plan

The hydrographic data set will be postprocessed and summarized in an appropriate database. Numerical process studies will be carried out with SPEM (Sigma coordinate Primitive Equation Model), with terrain - following vertical coordinates (Haidvogel et al., 1991). SPEM is adapted for problems at steep topography and enables high vertical resolution in the near bottom boundary layers over sloping bottom.
Main tasks of the work plan:
•   Postprocessing of the hydrographic data set (CTD, XBT, ADCP).
•   Investigations of the watermass structure and flow path at Great Meteor Seamount from the combination of CTD and current measurements.
•   Configuration and application of SPEM to identify and quantify the dominant physical mechanisms of the circulation.
•   Computation of particle trajectories within SPEM to study interactions between flow dynamics and biological environment.
Results
A dome of cold, less saline and dense water is formed above the seamount summit relative to the surrounding ocean. This pattern is indicative of an anticyclonic eddy-like circulation, wich is generated by either a Taylor cap circulation or the non-linear rectification of seamount trapped waves through resonance with tides.

http://www.awi-bremerhaven.de/Modelling/BRIOS/seamount.html


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:58:55 pm
(http://www.awi-bremerhaven.de/Modelling/BRIOS/ctdvera.gif)

Vertical distribution of potential temperature, salinity and potential density along a CTD transect across the Great Meteor Seamount (density scale inverted).


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 08, 2007, 11:59:54 pm
(http://www.awi-bremerhaven.de/Modelling/BRIOS/ctdhor250.gif)

Horizontal distribution of potential temperature, salinity and potential density on the 250 dbar isobar (density scale inverted).


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 09, 2007, 12:09:37 am
GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L13609, doi:10.1029/2005GL023205, 2005

Evidence of explosive seafloor volcanic activity from the Walvis Ridge, South Atlantic Ocean

J. H. Haxel


Cooperative Institute for Marine Resources Studies and NOAA Pacific Marine Environmental Laboratory, Oregon State University, Newport, Oregon, USA




R. P. Dziak

Cooperative Institute for Marine Resources Studies and NOAA Pacific Marine Environmental Laboratory, Oregon State University, Newport, Oregon, USA




Abstract
Hydrophones moored in the North Atlantic Ocean recorded a sequence of explosive, volcano-acoustic signals originated at the Walvis Ridge in the South Atlantic Ocean. 365 explosive signals were detected from the Walvis Ridge beginning 24 November 2001 continuing through March 2002. The largest swarm began on 19 December at 2329 GMT, and lasted 1.25 hrs producing 32 locatable events. Swarm locations are centered on the northern flank of an unnamed seamount (−32.96°S; −5.22°W), northwest of Wüst Seamount. These signals are interpreted as volcanogenic explosions due to similarities with acoustic signals recorded from a confirmed submarine eruption in the Caribbean in 2001 (Kick'em Jenny volcano). The observations presented suggest recent magmatic activity along the Walvis Ridge may be unrelated to the Tristan da Cunha mantle plume. Furthermore, these events lend support for an extensional fracture-zone model resulting in the recurrence of volcanic activity along older segments of large-scale sea floor lineaments.

Received 11 April 2005; accepted 10 June 2005; published 15 July 2005.

Index Terms: 3045 Marine Geology and Geophysics: Seafloor morphology, geology, and geophysics; 3075 Marine Geology and Geophysics: Submarine tectonics and volcanism; 3035 Marine Geology and Geophysics: Midocean ridge processes.


--------------------------------------------------------------------------------
http://www.agu.org/pubs/crossref/2005/2005GL023205.shtml


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 09, 2007, 12:15:49 am
Tsunamis in the Atlantic Ocean

With the recent December 2004 tsunami that wreaked death and destruction in Indonesia, Sri Lanka, and beyond (view an animation of the tsunami by the National Oceanic and Atmospheric Administration (NOAA) - Apple QuickTime required), many might wonder about tsunamis occurring in the Atlantic Ocean and striking the east coast of the United States; most notably, Maine. Although most people don't put "tsunami" and "Atlantic Ocean" in the same sentence, history and geology tell us that the Atlantic Ocean does experience tsunami activity, albeit on a less catastrophic scale. However, although highly debated in the scientific realm, one of the world's "ticking time bombs" that may trigger a tsunami is located in the Atlantic Ocean!

This Geologic Site of the Month provides background information and characteristics of tsunamis, some of their history in the Atlantic Ocean, and several possible locations where tsunamis could be triggered and impact the east coast of the United States in the future.

Background
What is a tsunami?
A tsunami is a wave produced by a disturbance that displaces a large mass of water - usually a result of geologic activities such as earthquakes, volcanic eruptions, underwater landslides, or in rare geologic cases, meteor strikes. After such a disturbance, displaced water travels outward from its site of origin as a series of unusually large waves at great speeds (Komar, 1996). Tsunamis are often mistakenly referred to as tidal waves, though tides play no role in their formation.  The term tsunami originates from the Japanese words tsu (harbor) and nami (wave). The term was created by fishermen who returned from fishing and found everything devastated in the harbor though they didn't see or notice the wave in the open water (Wikipedia, 2004).


(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-1.gif)


Figure 1 The shape and characteristics of a tsunami are similar to wind-driven waves (Figure 1) - it has a wave crest, trough, wavelength (distance between two wave crests, A and B), and period (time it takes for crests A and B to pass a known point). However, unlike regular wind-driven waves, which generally have wavelengths of up to several hundred meters and periods less than 20 seconds, tsunamis can have wavelengths of several kilometers and periods anywhere from several minutes to upwards of an hour. Their velocity (C), like wind waves, is a function of water depth (h):




where g is gravitational acceleration (9.81 m/s). The rate at which a tsunami loses its energy is inversely proportional to its wavelength. Thus, a tsunami travelling through water depths of 4,000 meters would be moving at approximately 200 m/s, or close to 450 miles per hour! At the same time, because of its very large wavelength, it is losing very little energy. In deep water, a tsunami can pass underneath a ship undetected. This is because its wavelength is on the order of several kilometers. However, when a tsunami reaches the continental shelf and begins to shoal, it will slow and increase in height.

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-2.gif)

Figure 2 shows the generation of a tsunami from an earthquake and how it travels across an ocean. In this situation, an earthquake results from a sudden shift in the subduction zone between continental and oceanic crusts (2a). This abrupt motion displaces the overlying water upwards and downwards, initiating a tsunami. 2b shows the initial tsunami split into a deep ocean (distant) and coastal (local) tsunami, headed in opposite directions. Because the distant tsunami is traveling through deeper water, it is moving much faster. Figure 2c shows amplification of the local tsunami as it passes over the continental slope - this is due to the tsunami encountering shallower water. As it continues towards land, should the trough of the tsunami reach a coastline first, the water level along the coastline appears to fall rapidly, as if the tide is ebbing. This process, called drawdown, is due to the tsunami shoaling, increasing in height, and drawing water seaward.



(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-3.jpg)

Figure 3 summarizes how the characteristics of a tsunami change as the wave propagates through deep water towards the coastline.

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-4.gif)

Figure 4 When a tsunami reaches a coastline, several key factors influence its destructive force. These are the height of the tsunami, its runup height, and its runup distance. Its height is simply the excess height of the tsunami wave (crest) over the normal ocean level as it passes a given point. Its runup distance is the distance from the normal tide line, or shoreline, at the time of the tsunami's arrival to its maximum extent inland. The runup height is the elevation of the point of maximum runup above the normal ocean surface at the time of the tsunami (Figure 4).

The effect a tsunami has on a coastline also depends on the the origin of the tsunami, distance from its point of origin, its size, and the slope and configuration of the bathymetry and coast that the tsunami is approaching. Because of the long period of tsunamis, they can bend around obstacles such as islands, bays, and gulfs. They typically arrive at a coast in the form of suddenly decreasing then rapidly increasing water levels, bore-like waves (similar to a tidal bore), several large breaking waves, or a combination. Tsunamis rarely arrive as a giant breaking wave, as is most commonly depicted, but generally arrive as forceful and rapid increases in water level that violently flood the coastline.

http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05.htm


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 09, 2007, 12:16:50 am
How big can tsunami get?

In general, most tsunamis range from several centimeters to tens of meters. Depending on the distance from the point of origin and various other factors, a tsunami may only appear as brief, discrete elevations of the water level, noted only by tide gauges. On the other extreme is the mega-tsunami, which can reach heights of several hundred meters. The largest recorded tsunami reached an astounding 516 meters (1,720 feet) of runup! This tsunami struck Lituyah Bay, Alaska in July, 1958, the result of an 8.3 magnitude earthquake at the headland of the bay that sent the gigantic wave roaring into the small enclosed bay, tearing up the sides of the bay. An excellent summary and analysis of this event, with pictures, is provided at the Dr. George Pararas-Carayannis website. On the Hawaiian island of Lanai geologists have located three stacked sedimentary deposits from the runup of a giant wave train that may have originated from a nearby submarine landslide about 105,000 years ago (Moore and Moore, 1988). The Lanai deposits, called the Hulopoe Gravel, are found up to an elevation of 375 m (1230 feet) but are more widespread below 100 m (330 feet) inland of the south shore from Kaluakoi to Hulope Bays. This may be the highest known wave runup due to a submarine landslide.

What was the most devastating recorded tsunami?

In terms of human loss, the most recent December 26, 2004 tsunami in Indonesia, which killed over 150,000 people (at the time of this writing), is by far the worst recorded tsunami. A huge tsunami on the order of 30 meters resulted from the explosion of the volcano Krakatoa (in Indonesia) in August 1883, killing over 36,000; while a 1755 earthquake off the coast of Portugal triggered a tsunami that killed over 60,000 in Portugal, Africa, and Spain combined. Although it is under scientific debate, some scientists believe that the most devastating tsunami in terms of global size, may have occurred as a result of a meteor that is believed to have struck the earth near the Yucutan Peninsula some 65 million years ago.



Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 09, 2007, 12:21:18 am
Tsunamis in the Atlantic Ocean and Caribbean Sea

Most tsunamis occur in the Pacific Ocean since it is the hotbed of continental and oceanic plate activity and volcanism. Figure 5 shows the locations of plate margins, recorded earthquakes, and active volcanoes around the world. Note the dominance of both seismically active and volcanic regions in the Pacific Ocean. By contrast, the Atlantic Ocean is home to much less seismic and volcanic activity than the Pacific, which is why the Atlantic has fewer tsunamis. In the Atlantic Ocean, the Mid-Atlantic Ridge is a spreading center and the east coast of the United States is a passive margin; that is, no plates are colliding or sliding against each other as in the Pacific Ocean. The majority of the Atlantic Ocean's active areas in terms of both seismic and volcanic activity is concentrated near the Caribbean Islands, and at the Scotia island arc chain (South Sandwich Islands) near Antarctica. In the Caribbean, just north of Puerto Rico lies the Puerto Rico Trench, the deepest point in the Atlantic Ocean. This is where the North American Plate (moving west) meets the Caribbean Plate (moving east), resulting in relatively active subduction zones and volcanic island-arc systems (Figure 6). The Antilles subduction zone is just southeast of this. Similarly, the South Sandwich Islands in the southern Atlantic also mark an active subduction zone. Here, the Atlantic Plate is being subducted below the Antarctic Plate, resulting in the formation of the volcanic South Sandwich Islands. Since these are well south in the southern Atlantic, they will not be discussed further.

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-5.jpg)
 
Figure 5. Map of the world showing active plate boundaries (blue lines), recorded seismic activity (yellow dots), and active volcanoes (red triangles). Note the general lack of strong seismic volcanic and seismic activity in the northern Atlantic Ocean. The mid-Atlantic ridge is a passive boundary, a spreading center, which is spreading at a rate of about 25 mm/yr. The only active subduction zones are at the Puerto Rico Trench (Caribbean Plate and North American Plate), and at the South Sandwich Islands (image adapted from San Diego State University and NASA).


(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-6.jpg)

Figure 6. Detailed 3-D interpolated image showing the interaction of the Caribbean and North American Plates and the location of the Puerto Rico Trench. The U.S. Virgin Islands and Lesser Antilles are located to the southeast of Puerto Rico (Image courtesy of the U.S. Geological Survey).

The majority of tsunamis in the Atlantic Ocean and Caribbean Sea were triggered by either seismic (earthquake) activity or the result of volcanic eruption. The majority of these resulted in localized damage and death, but nothing on a regionally catastrophic scale outside of the Caribbean. There are many confirmed and unconfirmed tsunami events that resulted in localized flooding, especially in the Caribbean Islands. Lander (1999) determined that there have been over 50 recorded tsunamis, varying in size, in the Caribbean Islands since the year 1530. Zahibo and others (2003a) evaluated past tsunami events and projected the impacts of future potential tsunami activity in the Caribbean.
Numerous websites provide information on recorded historical tsunamis in the Atlantic Ocean and the Caribbean. Several of these include:
•   National Weather Service Forecast Office - Philadelphia/Mount Holly
•   Tsunamis of Volcanic Origin in the Caribbean
•   Tsunami Laboratory - Siberian Division, Russian Academy of Sciences
•   Catalogue of Caribbean Tsunami
The Atlantic Ocean, however, has also been home to several devastating tsunamis, the most notable being the 1755 tsunami that hit Portugal, Spain, and northern Africa. Only the larger of these events are summarized below. At the end of each summary are links to more information on each event.
Large Historic Tsunamis in the Atlantic Ocean and Caribbean Sea (abbreviated list)
1755 Lisbon, Portugal - A near 9.0 magnitude earthquake occurred 200 km from the Portugese coast. This earthquake was generated by convergence between the African and Eurasian Plates at a ridge known as Gorringe Bank. The earthquake itself destroyed much of the Portugese City of Lisbon. Several minutes after the earthquake, a minimum of 3 tsunamis, around 10 meters in height, ravaged the city. An artist's rendering of the destruction of the earthquake and tsunami is provided at the Lisbon earthquake site. The waves also hit Spain and North Africa, and did damage in the Azores, Madiera, and the Canary Islands. Its effects were felt as far west as the Caribbean Islands, where 3-5 meter waves were reported, and as far north as Ireland.
•   Dr. George Pararas-Carayannis
•   University of California - Berkeley
•   Baptista and others (2003, pdf)
•   The Challenger Division for Sea Floor Processes


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 09, 2007, 12:25:55 am
1867 U.S. Virgin Islands - A 7.5 magnitude earthquake occurred in the Aneganda Trough, located between the U.S. Virgin Islands of St. Croix and St. Thomas. The earthquake triggered a series of waves on the order of several meters to over 12 meters that impacted the surrounding Caribbean islands. An 18-meter wave was reported on the island of Guadeloupe, however, this report was considered an exaggeration since it exceeded the maximum wave heights reported closest to the epicenter of the earthquake. However, a 10-meter wave was recorded for two locations on Guadeloupe. A study of the event, including simulations, is provided by Zahibo and others (2003b, pdf).

1918 Puerto Rico - A 7.5 magnitude earthquake occurred 15 km off the northwest coast of the island within the Puerto Rican Trench. The deepest point in the Atlantic, the trench marks the location where the North American plate is being subducted beneath the Caribbean Plate. It produced waves and runup on the order of 4-6 m that killed 40 people on the island (Mercado and McCann, 1998). The effects of the tsunami were recorded as surges in water levels at a tide gauge in Atlantic City, NJ.

University of Southern California Tsunami Research Group - 1918 Tsunami
Puerto Rico Tsunami Warning and Mitigation Program (simulation)
American Geophysical Union EOS, Vol. 85, No. 37, September 2004 (pdf)
1929 Grand Banks, Newfoundland, Canada - This tsunami hit closest to the state of Maine. A 7.2 magnitude earthquake occurred at the mouth of the Laurentian Channel south of the Burin Peninsula on the south coast of Newfoundland, triggering an underwater landslide that caused a tsunami (Ruffman, 2001). The earthquake itself was felt as far as Boston, Montreal, and New York (Figure 7). The underwater slump, however, is deemed by some to be the trigger of the tsunami (Bornhold and others, 2003). A resulting tsunami, including 3 waves ranging between 2-7 m, struck the coast of Newfoundland about 2.5 hours after the earthquake, and it was recorded that the tsunami reached runup heights of 27 m at the heads of the long narrow bays of the Burin Peninsula (Ruffman, 1996). Tuttle and others (2004) recently found onshore tsunami deposits at several locations along the coast of the Burin Peninsula. From field measurements made at one of these locations, it has been determined that the tsunami runup extended 480 m inland to an elevation of more than 8.5 m above sea level (Figure 8). The number of people killed varies based on reports, but ranged from 25-50. The tsunami was registered as far south as South Carolina, and as far east as Portugal. An image and table showing travel times and speeds for the tsunami as it moved down the east coast of the United States are shown in Figure 9.

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-7.jpg)

Figure 7. Limits of the areas that felt effects of the 1929 earthquake that spawned a tsunami that hit Newfoundland. Intensities are from the Rossi-Forel scale and only indicate effects of earthquake shaking, not the tsunami (from Natural Resources Canada).
(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-8a-m.jpg)

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-8b-m.jpg)
Figure 8. Photographs of 1929 tsunami deposits at Taylor's Bay on Newfoundland's southern coast. Photograph (above) shows three sandy units deposited by consecutive waves. Photograph (right) shows fining upward of a single sandy unit probably related to the decrease in velocity of the tsunami (from Tuttle and others, 2004).

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-9.jpg)

Figure 9. Image of tsunami travel times for the 1929 tsunami that occurred off of Newfoundland. The table below the figure provides information on travel times, the approximate distance traveled, and speed of the wave for various locations that recorded the wave along the eastern United States coastline. (Ruffman, 1996).

Canadian Geological Survey
Lost at Sea
Tsunamis in the Gulf of Maine
Only small tsunami events have been recorded in Maine. According to the National Weather Service, events were recorded in 1872 and 1926. In 1872, small waves (less than 50 cm) were recorded by tide gauges in Penobscot Bay, though the source of the waves is unknown. A larger wave hit Mt. Desert Island in 1926. This wave reportedly reached 10 feet and suddenly flooded Bass Harbor. There were no injuries reported. It is thought that these events precipitated from small earthquakes in the Atlantic Ocean. Strangely, there are no records in Maine of the 1929 tsunami that hit Newfoundland (mentioned above).

Tsunami Threat to the East Coast of the United States and New England


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 09, 2007, 12:34:01 am
Caribbean Islands - Earthquakes and Volcanic Eruptions

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-10.jpg)

The Caribbean is home to some of the most geologically active areas outside of the Pacific Ocean. Similar to the Indonesian islands, this area has a subduction zone that is located just north of the island of Puerto Rico, where the North American plate is being subducted beneath the Caribbean Plate at the Puerto Rico Trench. This area includes other troughs and active areas of plate tectonics that have produced numerous earthquakes, submarine landslides, volcanic eruptions, and resulting tsunami activity. A detailed 3-D shaded interpolated image of the Caribbean seafloor (Figure 10), and specifically the Puerto Rico Trench and vicinity (Figure 6), show this tectonically and volcanically active area.

Many of the islands of the Lesser Antilles are volcanically active. Of these, Montserrat has been one of the most active. The Soufriere Hills volcano, located in the southern portion of the island, erupted recently in 1997, 1999, and 2003 - all of these eruptions resulted in the formation of tsunamis due to failures of the volcano's flanks. The tsunamis caused only localized destruction. See the Dr. George Pararas-Carayannis website for more information on volcanically active islands in the Caribbean that have caused tsunamis.

Although this is the most seismically and volcanically active area in the Atlantic Ocean, future events would probably result in localized impacts within the Caribbean Sea, similar to recorded past events (1867, 1918 earthquakes and tsunamis) and it is unlikely that any volcanic eruptions or earthquakes would trigger a tsunami that would have a major impact on the New England area.

North Carolina/Virginia Continental Shelf - Submarine Landslide

Although the east coast of the United States is generally much less likely to be affected by a tsunami than the west coast, tsunami threats do exist. Closer to home, Driscoll and others (2000) found evidence of a large submarine landslide off of the coasts of Virginia and North Carolina. This slide, called the Albemarle-Currituck Slide, occurred approximately 18,000 years ago, in which over 33 cubic miles of material slid seaward from the edge of the continental shelf, most likely causing a tsunami (Figure 11). A three-dimensional image of the slide is shown in Figure 12. Investigation of the outer continental shelf just north of the slide and the slide's structure found that cracks in the continental shelf exist (marked as a, b and c in Figures 11 and 12, from Driscoll and others, (2000). These cracks may indicate a progression towards slope failure and the potential for another submarine landslide to occur that could trigger a tsunami on the order of a few to several meters in height, similar to a storm surge resulting from a Category 3 or 4 hurricane.

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-11.jpg)

Figure 11. Images showing the location of the Albemarle-Currituck slide (bottom right inset) off of the NC/VA coastlines. The larger figure (left-hand side) shows the bathymetry in the vicinity of the slide site and surrounding submarine canyons. The upper right inset shows a close-up of the en-echelon cracks (faults) that have developed at the top of the continental shelf marked a, b, and c (south to north). These cracks could lead to future slope failure and the formation of a slide (images from Driscoll and others, 2000).

--------------------------------------------------------------------------------

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-12.jpg)

Figure 12. Side-scan sonar imagery of the Albemarle-Currituck slide site and submarine canyons to the north. The faults (cracks) in the upper slope marked a, b, and c correspond with those from Figure 9 (from Driscoll and others, 2000).



Volcanic Eruption and Landslide - La Palma, Canary Islands

The Canary Islands are a volcanic island-arc chain located in the eastern Atlantic Ocean just west of the Moroccan coastline (Figure 13). La Palma is the western-most and the youngest of the Canary Islands, and is volcanically active with 3 large volcanoes (Figure 14). It is home to the most active volcano of the Canaries, Cumbre Vieja, which last erupted in 1949 and 1971. It is here that some researchers point to as a possible ticking time bomb for large tsunami creation in the Atlantic Ocean.

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-13.jpg)  (http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-13.jpg)

Figure 13. The Canary Islands are located approximately 60 miles west of the coast of Morocco. The island of La Palma, home of the Cumbre Vieja volcano, is one of the westernmost islands (image from GraphicMaps.com).

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-14.jpg)

Figure 14. Space shuttle image of La Palma and the Cumbre Vieja volcano (Space shuttle photo STS074-085-092).

(http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05-15.jpg)

Figure 15. Evolution of the La Palma landslide tsunami from 2 minutes (A, upper left) to 9 hours (I, lower right). Red and blue contours cover elevated and depressed regions of the ocean respectively and the yellow dots and numbers sample the wave height, positive or negative, in meters. Note the strong influence of dispersion in spreading out an original impulse into a long series of waves of decreasing wavelength. See also that the peak amplitudes generally do not coincide with the first wave. Even after crossing the Atlantic, a lateral collapse of Cumbre Vieja volcano could impose a great sequence of waves of 10-25 m height on the shores of the Americas (from Ward and Day, 2001).

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During the 1949 eruption, an extremely large block of the volcano's western flank abruptly dropped 4 meters due to the development of a fault along the crest of the volcano. Scientists have deemed this western flank to be indeed unstable. Based on a study of past landslide deposits and existing geology of the volcano, Ward and Day (2001) determined that the west flank of the Cumbre Vieja volcano may experience catastrophic failure during a future eruption, resulting in a landslide of a block of 15-20 km in width and 15-25 km long into the depths of the Atlantic Ocean. Computer modeling suggests that such an event could trigger a massive mega-tsunami hundreds of meter in height that would propagate to the north, south, and west. Within 9 hours, an estimated 10-25 meter wave could reach the US east coast (Figure 15, from Ward and Day (2001).

Various modeling simulations of the Cumbre Vieja tsunami event are available for viewing via the University of California Santa Cruz (download required Apple QuickTime)

Although the flank instability of Cumbre Vieja is noted, many scientists tend to disagree with massive failure of the western flank of the volcano; rather, they think it would happen in smaller separate events that would not be capable of triggering a mega-tsunami (Wynn and Masson, 2003). There is much scientific debate over the timing of an eruption that would trigger such events (considered to be decades to thousands of years), whether or not a massive failure of Cumbre Vieja's flank would occur during an eruption, or even if a mega-tsunami could possibly result (and reach the United States with such projected wave sizes). Mader (2001) used different wave modeling and determined that the resulting tsunami waves that reached the U.S. east coast and Caribbean would be on the order of 3 meters. The International Tsunami Information Center provided the following information in regards to the creation of a mega-tsunami by massive flank failure:

While the active volcano of Cumbre Vieja on Las Palma is expected to erupt again, it will not send a large part of the island into the ocean, though small landslides may occur.
No such event - a mega tsunami - has occurred in either the Atlantic or Pacific oceans in recorded history.
The colossal collapses of Krakatau or Santorin (the two most similar known happenings) generated catastrophic waves in the immediate area but hazardous waves did not propagate to distant shores. Carefully performed numerical and experimental model experiments on such events and of the postulated Las Palma event verify that the relatively short waves from these small, though intense, occurrences do not travel as do tsunami waves from a major earthquake.
To view more information on the scientific debate of Cumbre Vieja and a mega-tsunami, see the following links:

International Tsunami Information Center
Dr. George Pararas-Carayannis - Evaluation of Mega-Tsunami
Mader (2001)
Benfield Hazard Research Center


http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05.htm


Title: Re: Can a Continent Sink?
Post by: Blackstone on April 11, 2007, 09:06:56 pm
Adam,

This is a fabulous collection of information.  Thanks for posting it.  I read about a subduction zone in the Atlantic in Science News and thought "hey!  That's how Atlantis could have vanished!"  But, I have an addition: what if there was a land mass near a subduction zone that was also hit by a large meteor?  I wonder if such an impact could/would accelerate subduction of a large land mass?  Or even precipitate subduction?


Title: Re: Can a Continent Sink?
Post by: Mark of Australia on April 12, 2007, 07:48:10 pm
Hi Adam ,Blackstone

Well I don't know about an entire continent sinking but maybe a 'microplate' or a 'block' of continental crust will rise suddenly or sink suddenly. You might be interested in the ideas of the late Christian O'brien who found evidence that the Azores Islands used to be merely the mountain tops of a large island about the size of Spain!!.

http://www.goldenageproject.org.uk/survey.html

As for Tsunami ,A great book on the subject that also has a section on the evidence for mega-tsunami is 'Tsunami-the underrated hazard' by Edward Bryant. I think it covers all you need to know about Tsunami.

An example of the mega tsunami evidence would be how there is evidence in North Western Australia (My backyard  :D)  for a tsunami that was powerful enough to overwash sand dunes that are 5km inland and 60m high !!!  Bryant thought the magnitude was so big that he could only see meteor impacts as the likely cause !!

My idea is that maybe it could be a completely terrestrial phenomenon causing these mega-tsunami.And that this phenomenon also  accounts for the sinking of Atlantis .


Title: Re: Can a Continent Sink?
Post by: Blackstone on April 14, 2007, 01:23:12 pm
What did 'continent' mean to island-hoppers of the Mediterranean thousands of years ago?  And that's beyond language misinterpretations.  I like the idea of micro plates/blocks.  Why not?


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 14, 2007, 04:35:30 pm
Adam,

This is a fabulous collection of information.  Thanks for posting it.  I read about a subduction zone in the Atlantic in Science News and thought "hey!  That's how Atlantis could have vanished!"  But, I have an addition: what if there was a land mass near a subduction zone that was also hit by a large meteor?  I wonder if such an impact could/would accelerate subduction of a large land mass?  Or even precipitate subduction?

Hello Blackstone, and thank you for the compliments considering this research.  If an object from space struck a subduction zone, it would bring about the process of subduction. How big of a landmass would be immersed?  That, I cannot say.  I do know that there are many undersea volcanoes in the Atlantic Ocean and they have erupted many times before.  Geologists frequently claim that these areas are currently dormant, but they have barely researched any of them (to the point of not even bothering to name most of the undersea volcanoes in the Atlantic), so who are they to say?

Two years ago, there was a large undersea expedition in the Atlantic.  Their findings?  From Europe, to North America, the ocean floor is covered with a large sheet of lava.  Obviously something dramatic happened in the Atlantic Ocean at one point.  Whether it fit Plato's description of Atlantis?  Who can say.


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on April 14, 2007, 04:47:07 pm
Hi Adam ,Blackstone

Well I don't know about an entire continent sinking but maybe a 'microplate' or a 'block' of continental crust will rise suddenly or sink suddenly. You might be interested in the ideas of the late Christian O'brien who found evidence that the Azores Islands used to be merely the mountain tops of a large island about the size of Spain!!.

http://www.goldenageproject.org.uk/survey.html

As for Tsunami ,A great book on the subject that also has a section on the evidence for mega-tsunami is 'Tsunami-the underrated hazard' by Edward Bryant. I think it covers all you need to know about Tsunami.

An example of the mega tsunami evidence would be how there is evidence in North Western Australia (My backyard  :D)  for a tsunami that was powerful enough to overwash sand dunes that are 5km inland and 60m high !!!  Bryant thought the magnitude was so big that he could only see meteor impacts as the likely cause !!

My idea is that maybe it could be a completely terrestrial phenomenon causing these mega-tsunami.And that this phenomenon also  accounts for the sinking of Atlantis .

Hello Mark,

I'm familiar with Christian O'Brien's work, I don't recall any specific criticsms that geologists have towards it, however, I do know that his ideas depart from mainstream thought.  They are interesting, but I don't believe that anything has been proven either way.  They do coincide neatly with Otto Muck's ideas about what could have brought about Atlantis' immersion, though.

While the Greeks came up with the idea of a continent, I don't believe that Plato actually ever refers to Atlantis as a continent.  We always assume that it was a continent because he described it as "larger than Libya and Asia combined," and he gives those gigantic measurements for the land. I believe the measurements are wrong and that he, perhaps meant "greater" as opposed to "larger."  I do see Atlantis as a sizebale landmass, but hardly a continent. Greenland is not even considered a continent and look at how big Greenland is.  Interesting that Greenland seems to fit the contours of the Kircher map and was also once considered to be Atlantis.


Title: Re: Can a Continent Sink?
Post by: Mark of Australia on April 26, 2007, 05:20:40 pm
Yeah ,I don't think Atlantis was a continent ,I think it was barely the size of Spain .


Title: Re: Can a Continent Sink?
Post by: rockessence on April 26, 2007, 07:32:24 pm
Adam,
Re your comment above of an object from space, etc.

Aparently the Gulf Stream began when "an object" struck the Caribbean area with enough force to scrape the mantle thin, thereby heating the ocean water enough to maintain the Stream's circuit for these millions of years.   This event may have been the catalyst to force such massive amounts of moisture into the air as to herald the beginning of precipitous ice at the poles.


Title: Re: Can a Continent Sink?
Post by: Mario Dantas on April 17, 2008, 06:33:59 am
Hi People,

Nice research Adam, a lot of the stuff you mentioned is in fact related with Atlantis Sink, as you stated:

"Two years ago, there was a large undersea expedition in the Atlantic.  Their findings?  From Europe, to North America, the ocean floor is covered with a large sheet of lava.  Obviously something dramatic happened in the Atlantic Ocean at one point.  Whether it fit Plato's description of Atlantis?  Who can say."

I think those lava sheets were completely molten and permitted a free Continental buoyancy allowing in so doing a large Island to float like any vessel would... but also the re approaching of the South American Continent, towards Africa.

There is in fact a strange pattern in this Geoid:

(http://www.gfz-potsdam.de/grace/results/grav/g005_eigen-gl04c_files/g005_diff_north_atl_CG03C.jpg)

http://www.gfz-potsdam.de/grace/results/grav/g005_eigen-gl04c.html

The Canary Islands have a wide circular range pattern, very close to Guelb er Richat, Mauritania, which has somehow a similar configuration too. Greenland has in itself the magnetic "shadow" of Iceland.

The Energy that took to only dislocate such a large landmass, might have caused real "Trumpets of the Lord" as Velikovsky thought Moses and the Israelites heard, on Mount Sinai. Echoing signs of a large Earth-Quake were imprinted upon the Crust in these strange frequency patterns.

M


Title: Re: Can a Continent Sink?
Post by: Mario Dantas on April 17, 2008, 06:53:29 am
And, of course it couldn't sink, because as Ice floats on water, likewise if the Crust (Tectonic Plates) is released from Continental "strains" would as well float on Magmatic media, simply because it is less dense. It is already floating, by the way, and only slightly micro restructuring its Plates boundaries. Today all our Crust is completely hardened but not long ago we had large portions of it in the molten state where you could see everywhere on the Planet, something like this:

(http://tbn0.google.com/images?q=tbn:6fvGnr33GTKKoM:http://starryskies.com/solar_system/venus/lava_domes2.jpg)       (http://tbn0.google.com/images?q=tbn:PXdfN-JGK6WqoM:http://www.windows.ucar.edu/earth/images/lava_channel.gif)      (http://tbn0.google.com/images?q=tbn:qmhkjcAaOYM2fM:http://www.wainscoat.com/lava/lava-steam.jpg)   (http://tbn0.google.com/images?q=tbn:r9KKf2BL_h66-M:http://www.letsgo-hawaii.com/volcano/lava0444_b8.jpg)


Title: Re: Can a Continent Sink?
Post by: HereForNow on May 08, 2008, 08:06:52 am
Another thing I would like to contribute to this thread. If a continent were to sink in one day and night, you can ony imagine the world wide effects that would be generated.

There would certainly be evidence of this everywhere.  :)
In which none to this point has surfaced so far.


Here is a great interactive globe for studying places.....

http://encarta.msn.com/encnet/features/mapcenter/map.aspx


Title: Re: Can a Continent Sink?
Post by: Qoais on May 13, 2008, 01:06:59 am
What "form" would this evidence take?

If it's true, that they had nuclear power and blew themselves to kingdom come, the place would have been vaporized -  atomized - as in being reduced to atoms.  Where does one find an atom with the inscription on it that says - I was once a part of Atlantis?

I've been thinking about land masses sinking.  I think if a land mass becomes de-anchored, un-anchored, whatever, from the crust, it will eventually sink.  Mainly because it would eventually be eroded by water, and little bits of it would be constantly falling to the ocean floor, until gradually it became so waterlogged, it would sink and just become another bit of the ocean floor.  Also, if it's base is rock, which is what seems to be under all land masses, the rock would be too heavy to float, unless of course, the weight is spread over a very large area, like a raft or has a bulge in the middle, like a cement sail boat.


Title: Re: Can a Continent Sink?
Post by: Mario Dantas on May 13, 2008, 10:34:40 pm
HFN,

Quote
There would certainly be evidence of this everywhere. 
In which none to this point has surfaced so far.

The Sahara Desert, all the Oceans Floor, the Himalayan post Orogeny, maybe even the moisturized Atmosphere is a sign of the veracity of the event. The water can make disappear any sign of it. The Ice and water at that moment might have acted more or less like in the Leidenfrost effect:

(http://upload.wikimedia.org/wikipedia/en/thumb/c/c6/Leidenfrost_droplet.svg/209px-Leidenfrost_droplet.svg.png)

Quote
The effect can be seen as drops of water are sprinkled into a pan at various times while it is heating up. Initially, as the temperature of the pan is below 100 °C, the water just flattens out and slowly evaporates. As the temperature of the pan goes above 100 °C, the water drops hiss on touching the pan and evaporate relatively quickly. Later, as the temperature goes past the Leidenfrost point, the Leidenfrost effect comes into play. On contact the droplets of water do not evaporate away so quickly. This time, they bunch up into small balls of water and skitter around, lasting much longer than when the temperature of the pan was much lower. This effect lasts until a much higher temperature causes any further drops of water to evaporate too quickly to cause this effect.

http://en.wikipedia.org/wiki/Leidenfrost_Effect





 Qoais,

Quote
the rock would be too heavy to float

The Crust is less dense than the "liquid" mantle underneath, therefore it should always float, like an Iceberg floating on the Ocean's water.







Title: Re: Can a Continent Sink?
Post by: HereForNow on May 15, 2008, 09:24:49 am
Interesting idea. I'll research it more.


Title: Re: Can a Continent Sink?
Post by: LoneStar77 on March 10, 2009, 03:34:56 am
Adam, you've given us an impressive wealth of data. And all your sources seem solid references to this discussion. I've learned a few things, here. I especially liked the data on mega-tsunamis. Thanks!

On the subject of "continents," though, I think there has been much misinformation published in the past. Plato never states that Atlantis was a continent, as Adam pointed out. However, Plato's description of size is a bit vague and likely misunderstood. First of all, "Libya" was their word for "Africa," but only that portion of Africa known to those ancient Greeks -- namely the northern coast and a small distance inland. Likely, this did not include Egypt. This did not include most of the Sahara and none of sub-Saharan Africa. "Asia" to them was "Asia Minor," or most of what is modern Turkey. Add these two together and we get a landmass somewhere between 1 and 2 times the size of Texas (USA).

In 2002, while working on a novel project, I made several dozen discoveries in the scientific literature that may support the story of Atlantis. The three most startling are detailed at,

http://www.ancientsuns.com/ancient-earth/atlantis.php

All three of these events coincide with Plato's date for the destruction of Atlantis. Briefly, they are,
  • An abrupt and worldwide change in climate at the end of the Younger Dryas.
  • A moderately large trace of volcanic debris in the Greenland ice cores.
  • A 2-meter drop in sea level worldwide.

The most telling, but sorely needing corroboration, is the 2-meter drop in sea level at the end of the Younger Dryas (9620 BCE). This drop is consistent with a Texas-sized plot of land dropping 3000 meters somewhere in the oceans of the world. None of these prove Atlantis, but they do prove that something very, very big happened the year Plato's Atlantis supposedly sank.

LoneStar77
(Carl Martin)
www.MissionAtlantis.Com (http://www.MissionAtlantis.Com)
www.AncientSuns.Com (http://www.AncientSuns.Com)
www.CarlMartin.Net (http://www.CarlMartin.Net)


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on May 03, 2009, 04:17:06 am
Thank you for the compliment, Carl.  Allow me to also wish you a Happy Birthday.

I try to look at Plato both literally and figuratively.  He could well have meant "greater" as opposed to "larger" as some have suggested, but if he is actually referring to a cataclysmic event in the Younger Dryas, we have to ask ourselves, how did he know about it?

This was before either the Greeks or the Egyptians existed as a people, before their languages were invented and before writing.

So, not only do we have to find an event that occurred back then, we haver to find a way to move writing and the first dates for Egyptian civilization as well.


Title: Re: Can a Continent Sink?
Post by: LoneStar77 on May 03, 2009, 05:19:43 am
Thank you for the compliment, Carl.  Allow me to also wish you a Happy Birthday.

I try to look at Plato both literally and figuratively.  He could well have meant "greater" as opposed to "larger" as some have suggested, but if he is actually referring to a cataclysmic event in the Younger Dryas, we have to ask ourselves, how did he know about it?

This was before either the Greeks or the Egyptians existed as a people, before their languages were invented and before writing.

So, not only do we have to find an event that occurred back then, we haver to find a way to move writing and the first dates for Egyptian civilization as well.

Adam, you're welcome, of course. And thanks for the birthday greeting.

I have to correct myself from time to time from speaking in absolutes. What we currently know about history and prehistory is not everything there is to know. Sometimes scientists seem to forget this. Just because we don't have proof of a thesis does not automatically disprove a thesis, yet some scientists and many skeptics tend to do this without thinking critically about what they're doing.

Could proto-Greeks have existed as a civilized people during the YD (Younger Dryas) as Plato seems to suggest? The recently dated site at Göbekli Tepe, Turkey shows the remains of a moderately advanced people from about the same time that Atlantis supposedly sank -- approximately 10,000 BCE. The putative civilization of the proto-Greeks was supposedly washed away by a great flood. The sinking of Atlantis would likely have created a mega-tsunami (great flood). Could the sinking of Atlantis have removed all evidence of the proto-Greek civilization?

New discoveries are still being made in Egypt. Will we some day find evidence that Egyptian civilization did indeed go back past 30,000 BCE? The most recent civilization of Egypt apparently started 8,600 BCE (according to Timaeus), but much of that "memory" has been lost (or never existed if Plato's tale was a complete fiction).

Perhaps we need to qualify what we know as "what is currently known." None of the boundaries of our knowledge are absolute. The mid-1990's discovery of Amazon warriors in the burial kurgans of Southern Russia showed that another myth had a basis in fact. But not all evidence we might require is necessarily so well-preserved. Nature has a habit of destroying evidence. For that matter, humans have a habit of destroying evidence, if only to reuse resources. The facing blocks of the Great Pyramids of Giza were reused, after the massive earthquake of 1301 CE, to build mosques and fortresses.

Skeptics are likely certain no high technology existed back then? That may perhaps be true, but how tempted would be the citizens of early civilization to melt down artifacts that no longer worked or which were not understood? The point is that we simply do not know. The point is to have an open mind, but demand proof. And, of course, that's why we're here and the skeptics are missing out on all the fun.

Carl Martin
http://www.MissionAtlantis.com (http://www.MissionAtlantis.com)


Title: Re: Can a Continent Sink?
Post by: BlueHue on May 16, 2009, 09:55:31 am
I just peeked in if 'Atlantis' was found yet !


Title: Re: Can a Continent Sink?
Post by: Horus on July 10, 2009, 08:04:39 pm
New Hypothesis Provides A Basis For The Reality Of The Legendary Continents Of Atlantis And Lemuria

The Demise of The Current Sea-Floor Spreading And Plate-Tectonics Theory

by William Hutton (aka Wyman Harrison, Ph.D. a tenured professor of geology)

To geologists it is no longer a hypothesis. It is now a theory. Every Earth scientist believes it is true. Right? And what is “it”? What I’m talking about is the theory of sea-floor-spreading and plate tectonics.

As a result of a comprehensive review published late last year, sea floor spreading and its plate tectonics corollary are shown not to explain correctly the origin of our planet’s ocean basins and continents. And what if the current “theory” is incorrect? If it proves to be wrong, a huge barrier is removed to the acceptance of the Cayce readings’ story on the lost continents of Atlantis and Lemuria.

No longer will it be delusional to consider vertical crustal movements to explain the origin of Earth’s ocean basins. “Elevator tectonics” will be in, and “shuffle-board” (plate) tectonics will be out, almost entirely. Although sea-floor spreading will still have a small place in geoscientists’ understanding of certain aspects of the origin and maintenance of continents and ocean basins, the really big picture, of elevation of ocean floors and - to a lesser degree - continents will rest upon a model that is driven by mantle surges.

Geologists know, for example, that a global surge of Earth’s mantle began in Mesozoic time. At its peak in the Cretaceous period, ocean floors in the Atlantic and Pacific were elevated above sea level. The resulting oceanic continents were full of volcanic terraces. The Mesozoic mantle-surge event was then followed by gradual cooling and collapse of the oceanic volcanic edifices.

To understand this radical departure in our understanding of mantle convective behavior, and its effects on Earth’s crustal structures, we need to review briefly the current model of sea-floor spreading and plate tectonics.

(http://www.bibliotecapleyades.net/imagenes_atlantidamu/lemuria7_01.jpg)
Fig 1. The conventional model of sea-floor spreading.


Current Sea-Floor Spreading Hypothesis

As shown in Figure 1, geologists currently believe that thermal plumes of hot magma are semi-continuously moving upward beneath ridges found in all of the world’s oceans. This semi-fluid basalt rock is exuded here and there along a ridge crest. The process forces sea-floor crustal plates on either side away from the ocean ridge and toward the continents. The continents may either be carried along by the adjacent sea floor, or the spreading sea floor may under-thrust a relatively immovable continent. See Figure 1 for examples of both hypothetical situations.

A given pulse of magma, over a relatively short distance along an ocean ridge, becomes magnetized when the semi-molten material cools below a specific temperature. Iron minerals in the basalt magma are then frozen in the rock and they point in the direction of the prevailing magnetic field. Geophysical survey methods can then used to detect whether the sea-floor rocks were magnetized in a normal geomagnetic field (like today’s) or in a reversed field. Because Earth’s magnetic field is moving and/or reversing through time, magnetic orientation directions of basalt exudations allow the sea-floor rock slabs be correlated with one another. This process results in a sort of “tape-recording” of the formation and movement of rock masses of the spreading sea floor - or so the hypothesis goes.

The crystallized rock of each new exudation then splits in two along an axis coinciding with the central valley of the ocean ridge. In Figure 2, two brown-colored slabs of newly crystallized, ocean-floor basalt are separated by a black line representing the central valley of a mid-ocean ridge.

(http://www.bibliotecapleyades.net/imagenes_atlantidamu/lemuria7_02.gif)
Fig. 2. Magnetic stripes and the current sea floor spreading model. Sea-floor stripes are formed by ocean-floor magma that cooled and crystallized in a specific magnetic-field orientation. These rock masses may be offset later along transform faults or large-scale fractures that run perpendicular to the ocean ridge.
(Fig. adopted from a page on the U.S. Geological Survey’s website.)

The presence of magnetic stripes on the ocean floor has been thought to be prima facie evidence for sea-floor spreading, and the basis for the plate tectonics (PT) model of crustal motion. Note in the diagram that segments of magnetic stripes of the same age are confined on either end by transform faults that run perpendicular to the ocean ridge. It was assumed early-on in the development of the PT theory that striped segments of the same age were offset from one another due to different amounts of subsequent effusions of magma at the ridge crest. Larger effusions would push the plates farther apart than would smaller ones.

Here then, is an abbreviated description of the sea-floor-spreading and plate tectonics model for the dynamic behavior of the crust and underlying mantle. Most geologists have assumed this model correct for the last 25 years or so. Its acceptance by geoscientists has, quite naturally, caused great difficulty for those who want to accept the Cayce readings’ story of Atlantis and Lemuria. How could there ever have been continents in the Atlantic or the Pacific oceans where there are now ocean floors? For doesn’t all the evidence point to stability of the submerged ocean floors and to the basically horizontal movement of crustal plates the world over?

Problems With The Conventional Model, According to Prof. MacKenzie Keith
(Now Deceased)

Now comes a convincing treatise on what may really be happening in the realm of global crust and upper-mantle dynamics. I will be basing the rest of this article on MacKenzie Keith’s comprehensive examination of sea floor spreading and plate tectonics, published last fall.1 His paper has about 300 references and is the product of Keith’s life of research and teaching in the field, laboratory, and classroom. Upon his death last year he was Emeritus Professor of Geochemistry at Pennsylvania State University.

Dr. Keith begins modestly by saying that although the essential features of the PT hypothesis are widely accepted, some aspects of the model are open to question. Quite simply, they conflict with known properties of Earth’s materials and the global crust/mantle dynamic system. Keith’s first objection is to the hypothesis that the plates are internally rigid. If a stress is applied to one side, it is transmitted to the opposite side with no deformation of the plate interior. But this is inconsistent with the results of experiments on rock strength and with the factors that govern the strength of large masses of rock over geologic time. Actually, large rock masses are weak, and they deform under the influence of heat.

Keith next states that there is a need to re-examine the hypothesis of upwelling of magma beneath the axis of an ocean ridge. Computer models of heat flow beneath ocean ridges are based upon evidence of a wide plume of ascending molten basalt to produce the magma effusions along the ridge. But how, asks Keith, can broad plumes generate the narrow zone of axial ridge volcanism, the “knife-edge” separation of adjacent flow regimes on either side of a transform fault (see Fig. 2), and the unbelievable “overlapping spreading centers” advocated by some geologists?

Further questions are related to the concept of ocean floor spreading and the tape-recorder model for generating the oceanic magnetic stripes. Different rock chemical compositions are often found on opposite flanks of the ocean ridges. The rocks should be of the same composition if they come from the same magma effusion. And what of the failure to find the required narrow zone of crustal accretion, with the property of dividing neatly so that matching halves move to either side?

Keith now moves ahead with certainty to answer these questions. He asserts that no spreading is required to account for the observed sea-floor features. Instead, the oceanic magnetic stripes can be explained by narrowing of a formerly very wide mid-ocean volcanic zone and by consequent crestward migration of something he calls the “blocking temperature,” discussed below. He hypothesizes that a Mesozoic surge of mantle flow and volcanic-zone expansion that peaked in Cretaceous time (between 66 and 144 million years ago) produced a different “volcanic face” on Earth. Elevated ocean floors then began to collapse over millions of years, leading to the features we find today.

Finally, Keith postulates an alternative model of upper mantle flow to the current one. His conceptual model involves mantle upwelling beneath continents, flow of mantle from beneath continents to beneath oceans (for Atlantic Ocean type margins), and convergent sub-ocean mantle flow toward the axes of mid-ocean ridges. He asserts that the mid-ocean ridges are principal boundaries of convection cells in the mantle. He then summarizes a wide variety of information in the rest of his review paper to conclude that “the weight of evidence clearly supports the alternative model [his model] and is contrary to the [sea-floor] spreading model of plate tectonics.”

Alternative Model of Mantle/Crust Dynamics
How the Keith Model Works

We’ll begin by considering what happens relative to the mid-Atlantic ridge (MAR) of the Atlantic Ocean in the vicinity of the now submerged Reykjanes Ridge south of Iceland. Instead of hot, plastic upper mantle material having flowed away from the mid-ocean ridge, as shown in Figure 1, it has flowed toward it and elevated the entire ocean floor, as shown in Figure 3.

(http://www.bibliotecapleyades.net/imagenes_atlantidamu/lemuria7_03.gif)
Fig. 3. Simplified sequence of a series of cross-sections representing the cooling and sinking of Reykjanes Ridge, part of the MAR running southwest of Iceland (Fig. 4). This figure is modified from Keith, 2001, Fig. 11. The sections show Keith’s alternative model for generating oceanic magnetic stripes by ridge cooling following a Cretaceous-age peak in volcanic activity. The three early stages of cooling (and migration of blocking temperature isotherm B) represent conditions at magnetic anomaly ages 36, 24, and 16 million years ago (Ma). The blocking temperature isotherm is the temperature at which magnetic minerals acquire either normal or reverse remnant magnetism and thus record the Earth’s geomagnetic field orientation.

I have taken the liberty on Figure 3 of labeling the emerged part of the Reykjanes Ridge “Atlantis.” There is truly no better name to use for this formerly elevated, now- submerged oceanic continent. For actual physical evidence that parts of the mid-Atlantic ridge were above water during recent time, see below.

To continue now to elucidate Keith’s explanation of the origin of the magnetic stripes on the ocean floor, we quote from his p. 268, as follows.

“An essential feature of the proposed ocean ridge system is that all of the abnormal features that resulted from the Mesozoic surge of mantle flow:… uplift of the ridge, accelerated volcanism, broadening of the active volcanic zone, were subject to gradual Mesozoic to Recent relaxation and retreat, toward a steady-state system, a predictable effect of the slowing of convective overturn and volcanism, and the gradual diminishing, via return-flow gyres, of the accumulated large volume of sub-ridge subduction mixtures. The age-denominated sequence of magnetic anomalies, conventionally attributed to sea-floor spreading, is proposed to result, instead, from gradual narrowing of the active volcanic zone.”

Magnetic Banding According to Keith’s Cooling Model. Figure 4 may help to explain the above quote, as it applies specifically to magnetic banding. The basic idea is that a narrowing of the zone of mid-ocean ridge basalt volcanism (Fig. 4, reddish portions of bars) will be accompanied by crestward migration of the blocking temperature isotherm (Fig. 3). This is the temperature at which the magnetic minerals acquire remnant magnetism and thus record reversals of Earth’s magnetic field.

(http://www.bibliotecapleyades.net/imagenes_atlantidamu/lemuria7_04.gif)
Fig. 4. Idealized snapshots of one side of a mid-ocean ridge, to show the development of oceanic magnetic stripes, from the mid-Cretaceous period of Mesozoic time to the Present, as a result of gradual narrowing of the active mid-ocean volcanic zone. A is the ridge axis. This diagram, modified from Keith, Fig. 10, shows migration of the blocking temperature isotherm B. The reddish color to the right of B indicates the portion of the ridge for which the principal magnetic source remains above the blocking temperature.
[The geomagnetic polarity (normal or reverse) and the geologic time scale are from D. Kent and F. Gradstein,1986, “Jurassic to Recent chronology,” in The Western North Atlantic Region. Geol. Soc. America, Geology of North America, v. M, pp. 45-50, Plate 1.]

Keith proposes that fracture zones and transform faults (see Fig. 2) are ocean-floor surface expressions of the boundaries of “convective rolls” in the underlying mantle. Such rolls are judged to be,

“the principal form of secondary convection within the upper boundary layer of sub-ridge mantle, a low-viscosity region estimated at 75-125 km thick….”

(p. 240).

Translating Keith’s words for the non-geologist reader, imagine that the primary, heat-driven flow of the uppermost mantle is outward from beneath a continent like Africa, and toward the MAR. As the mantle moves there is subsequent heat loss in the oceanic region. In the downstream region of lateral flow and heat loss there is development of an upper mantle boundary layer that eventually becomes unstable and yields a regular pattern of upper mantle “rolls” aligned in the direction of principal flow. Boundaries that develop along each edge of a roll result in ocean floor fractures and transform faults. (A transform fault is merely a near-vertical surface over which one side slips past the other, but is unique in that the displacement suddenly stops or changes form).


To end his description of the formation of magnetic stripes on the sea-floor, Keith cites relevant laboratory, numerical modeling, and field measurements. He concludes by saying that the evidence is consistent with his proposed upper-mantle convergent flow and contrary to the plate tectonics model of mid-ocean upwelling and divergent flow.

To quote Keith on the implications of Figures 3 and 4,

“the proposed ridge-cooling model of magnetic stripe formation does not involve spreading or continental splitting, and there are no implications regarding continental drift, except that the continents are presumed to be floating in the mantle, each focusing one or more upwelling plumes, and free to move in response to changes in the global [mantle] convection pattern. The principal continental drift will be related to mantle surge episodes, and there will be a strong tendency for continents to re-establish their separate positions as part of a return to a steady-state flow regime.”

Keith’s Hypothetical Model of Proposed Mid-Ocean Ridge Dynamics and Structure 

Keith proposes a structure for a mid-ocean ridge to satisfy geophysical observations and his intuition about how, dynamically, the ocean-floor crust and underlying mantle behave. He calls this structure a “flexload syncline.” A syncline is simply a fold in Earth’s rocks, the core of which contains younger material and which is generally concave upward. The adjective flexload is used to emphasize the effects of gravity-produced flexure on the crustal stress regime. In his proposed ocean-ridge model, the structure of the crestal zone is attributed mainly to gravitational deformation that results from two types of loading: crestward-increasing volcanic loading and downward increasing densification. Keith cites evidence that major flexload sinking,

“is not restricted to the near-axial zone but is broadly effective beneath the ridge flanks and formerly extended over the full width of Mesozoic to Early Tertiary ocean ridges.”

What will a cross-section diagram of a mid-ocean ridge structure look like for Keith’s crustal-collapse-under-cooling model? Figure 5 gives us the picture.

(http://www.bibliotecapleyades.net/imagenes_atlantidamu/lemuria7_05.gif)
Fig. 5. M. Keith’s model of proposed mid-ocean-ridge dynamics and structure, including sub-ridge convergence and downflow, as adapted from Fig. 4 of his paper. The thickness of the crust is greatly exaggerated to show the structure.
This is a “flex load” syncline of former wide extent that reflects a crestward increase in volcanic loading and subsidence.
Red represents the region between the mantle and the sub-axial wedge of subducted crust, and is a zone of melting.
Blue lines represent crustal layering, dipping toward the axial valley. Solid lines are non-specific isotherms (lines of equal temperature). Green represents the low-velocity zone (for seismic wave propagation) that characterizes crust and mantle mixing. Brown indicates basalt-depleted residuum. “M” denotes the “Moho,” a boundary that separates the Earth’s crust from the underlying mantle.

Direct Evidence of An Emergent Atlantis

Incidental, almost, to Keith’s efforts to buttress one of his points about a former emergent continent in the Atlantic ocean is the material that he summarizes on former shallow water or emergent sites sampled by the Deep Sea Drilling Project (DSDP). The sampling sites are currently underwater in the region of the Mid-Atlantic Ridge (MAR). Locations for three of these sites (Keith, 2001, Table 1) are shown by large red dots on Figure 6, in a relief map of the Azores. The red dots are rather large because, while the sampling coordinates that are listed give degrees north latitude, they do not give degrees west longitude. It is understood, however, that the samples were taken in the vicinity of the MAR axial valley, clearly visible on Figure 6.
 

Here’s what was found:

  • at point A, at a depth of 12,802 ft: highly vesicular basalt, weathered and oxidized basalt, and a major gap in the basal sedimentary section that indicates subaerial erosion
  • at site B, at a depth of 12,440 ft, basaltic pebbles and weathered and oxidized basalt were found. 
  • at site C, in 12,313 ft of water, once again basaltic pebbles and weathered and oxidized basalt were found

All of the above findings are strong indicators of a formerly emerged MAR. And they suggest that this volcanic terrain has sunk a minimum of 12,300 ft since being exposed to the atmosphere. Note that Keith’s Table 1 lists six additional MAR sampling sites - to the south of those plotted on our Figure 6 and on down to the equator. Two of these sampling sites show ridge tops flattened by wave erosion, one revealed Tertiary-age shallow water sediment, and another revealed Cretaceous-age shallow water sediment. A final, rather startling finding consists of canyons and a trellis drainage system, quite possibly formed subaerially at a depth greater than 9800 ft. The MAR location is between 26º and 27ºN.

(http://www.bibliotecapleyades.net/imagenes_atlantidamu/lemuria7_06.gif)
Fig. 6. Physiographic diagram of the Azores region, based on a diagram by B. Heezen and M. Tharp. See text for an explanation of red dots A-C, sites of deep-water sampling of subaerial material representative of an emergent continent.
(Subaerial refers to conditions and processes that exist or operate in the open air on and immediately adjacent to a land surface).


As quoted from Keith (p. 266), additional evidence of former exposure of the MAR consists of,

“…extensive denudation of oceanic crust [and] development of deep canyons and trellis drainage patterns along fault scarps of the MAR (Tucholke et al., 1997). Tucholke et al. attributed the modified topography to sub-ocean mass wasting but erosional features … out to about 300 km [185 miles] from the axis, favor Recent subaerial exposure and erosion of the ridge crest. Former broader subaerial exposure, and progressive subsidence, is indicated by borehole intersections at off-axis sites….The stratigraphy of those borehole sections provides evidence of broad exposure of the ridge followed by ridge subsidence, [and] narrowing of the active volcanic zone….”
(Keith, p. 266).

Example of Cooling, Sinking, and Narrowing of the MAR Through Time

To illustrate the above process in map view, we have modified Keith’s Figure 9 and turned it into our Figure 7.

(http://www.bibliotecapleyades.net/imagenes_atlantidamu/lemuria7_07d.gif)
Fig. 7. Snapshots of a Cretaceous-to-Recent time sequence for a sector of the sinking Mid-Atlantic Ridge (MAR) between the Azores and the Charlie-Gibbs fracture zone, to show narrowing of the active volcanic zone, the proposed mechanism for generating oceanic magnetic stripes. The narrowing color pattern shows the extent of active volcanism at each selected stage of ridge sinking and cooling. The trailing of the crestward-retreating outer limit of volcanism is taken to be associated with progressive cooling of the ridge and with the migrating trace of the blocking temperature isotherm, at which remnant magnetism is frozen-in, thus recording the inclination and reversals of the Earth’s magnetic field. Approximate magnetic anomaly ages in the upper right of each panel are from Kent and Gradstein (1986).
See caption for Fig. 4, for complete citation. Ma = millions of years before the present.

Summary of Prof. Keith’s Proposed Global Model

This article would be too long if I were to go into any more of the aspects of the professor’s marvelous analytical piece of work. The evidence for emergence of Lemuria will be dealt with in a separate article. Keith’s application of the results of his literature review to continental rifts and their associations with oceanic rifts, to oceanic island-chain dynamics in the Pacific, and to a number of other important topics like hotspots must also be deferred.

Suffice it to say that Keith believed that the essence of his proposed global model “is that oceanic crust is a principal reservoir and that selective recycling of its components is a counter to weathering and riverine [sediment] transport from continent to ocean, and a key process in the self-regulating Earth system” (p. 282). He has little to say about the forces that drove the Mesozoic mantle surge, other than to say that there is a strong possibility that it may have been triggered by a cluster of meteorite impacts in the western equatorial Pacific. These impacts may have reactivated lower mantle, during a surge-promoted change from layered to whole-mantle convection. Deep “roll-margin” mantle recycling associated with the proposed impact-triggered change from layered to whole-mantle convection, and resultant mantle surge is deduced to have formed a range of mixtures that apparently constituted a source of Cretaceous basaltic magma and oceanic crust.

References:

Keith, M., 2001, "Evidence for a Plate Tectonics Debate," Earth-Science Reviews, 55 pp. 235-336.


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on August 31, 2009, 05:38:10 pm
Back in 1894, Professor Spencer Todd was convinced that the American continent was sinking:


THIS CONTINENT IS SINKING.; At Least that Is What Prof. Spencer Told the Geologists.


    *
      E-MAIL

August 16, 1894, Wednesday

Page 4, 859 words

The meetings of the scientific societies being held in Brooklyn are of a most instructive and entertaining nature, and marked attention is being paid to the able papers read by the learned specialists. One of the most interesting papers read so far was that by Prof. J. W. Spencer, before the Geological Society of America.

http://query.nytimes.com/mem/archive-free/pdf?res=950DE4DC1730E033A25755C1A96E9C94659ED7CF


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on August 31, 2009, 05:41:24 pm
Great work on getting the Hutton find, Horus.  If you don't mind, I will start a separate topic on it to garner it more attention.


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on August 31, 2009, 05:52:03 pm
Chapter V: Can Lands Sink and Rise?



I. Destructions

krakatao volcano eruption

We will deal here with cities, islands, civilizations lost because of calamities.

According to Roman history and tradition, Vesuvius had never erupted before August 79 AD. It only smoked a bit from time to time. The explosion was extremely violent; it covered the city of Pompeii  with ashes and killed 2000 people. Since that time, Vesuvius has had numerous minor eruptions and 18 major ones, the last one in 1944.

In the spring of 1902, Mont Pelee (Martinique)  in the Caribbean erupted and besides wiping out the biggest city of the country, Saint Pierre, it killed 30,000 people. The cone had been dormant for half a century. The only survivor was a prisoner in an underground dungeon.

In 1883, the violent explosion of Krakatao sent bits of pumice and dust up into the air 20 miles. Some of the dust was carried completely around the world by currents in the upper air. The entire mountain disappeared. The eruption cracked walls in Buitenzorg, Java, 100 miles away. The tidal wave that was created engulfed the neighboring shored and killed 36,000 people. The detonation was heard for 3,000 miles.

In the same area, in 1815, the volcano Tomboro on the island of Sumbawa took 12,000 lives.

In October 1822, another earthquake occurred on the island of Java. Lyell, in his Principles of Geology, says "the earth shook, and immense columns of hot water and boiling mud, mixed with burning brimstone, ashes, and lapilli, of the size of nuts, were projected from the mountain like a water-spout, with such prodigious violence that large quantities fell beyond the river Tandoi, which is forty miles distant." Four days later a second volcano eruption occurred accompanied by a violent earthquake and the summit of the mountain broke down. Over 4,000 people were killed and 114 villages destroyed. And this happened back then, when population wasn't as dense as it is now.

In 1912, in Alaska, Katmai erupted and blanketed Kodiak, 100 miles away, under a 10- to 12-inch fall of ash.

These are a couple of examples from modern times.

However, 6500 years ago Mount Mazama erupted and created the Crater Lake, in America. The volcano displaced about 17 cubic miles of rock. The mountain was swallowed  up in its own crater.

Helike and Bora are ancient Greek islands that sank during Plato's time. You will find more information on the legendary city of Helike later on.

According to Pliny, in 186 BC, in the gulf of Santorini, near Greece, the island of Old Kaimeni (the Sacred Island) emerged from the sea. In 19 AD, Thera (the Divine, Santorini), home of the Mynoan civilization appeared. However, parts of this island had sunk around  1,600 BC after a powerful eruption. The volcano sent the rocks swirling in the sky and to the island of Crete. Stones from Santorini are found on Crete. I will debate over this when I mention Santorini as a possible location for Atlantis. Also, in 1573 AD, another island was created and it was called "the small sunburnt island". In 1848, another volcanic convulsion that lasted three months created a great shoal. Since Santorini had emerged, the island went on sinking until, by the end of the 19th century, it had submerged 1200 feet.

 
II. Lands that Rise and Sink

Let's start with some easy examples. Within 5,000 years the shores of Sweden, Denmark, and Norway have risen from 200 to 600 feet. The coast or Peru continues to sink. Professor Winchell (The Preadamites) says that in 70 years the Andes sank 220 feet. Also, "the coast of South America lifted up bodily ten or fifteen feet and let down again in an hour".

Most of the information above uses as a source Ignatius Donnelly's book, Atlantis, the Antediluvian World. Other data was gathered from the net, from reliable sources.

In 1783, Iceland was touched by tremendous earthquakes. According to Donnelly, "about a month previous to the eruption on the main-land a submarine volcano burst forth in the sea at a distance of thirty miles from the shore. It ejected so much pumice that the sea was covered with it for a distance of 150 miles, and ships were considerably embedded in their course". An island emerged, and the Danish Majesty claimed it. It was called the "New Island". A year later, the island sank again, at about 30 fathom under water. The earthquake killed 9,000 people out of a population of 50,000.

The most interesting account is that of the Mexican volcano of Paricutin, west of Mexico City. It belongs to the Sierra Madre range. For 15 days before its appearance the earth trembled. In February 1943, a farmer who was plowing his cornfield saw a spiral of steam rising from the ground. Explosions rocked the night and by morning, the volcano had built up a cone of 50 feet. The puffs ejected every six seconds cinders, ash, and bombs of solid rock estimated at 2,700 tons a minute. Within six months the cone had reached 1,000 feet, and in one year it had reached 1,500 feet. For a radius of 20 miles all vegetation was killed and more than 8,000 people had to be evacuated. The volcano ceased to erupt in 1952. Its neighbor, El Jorullo, was born in 1759 and was active for 19 years.

In 1819, the fort and village of Sindree (east side of Indus), was submerged by an earthquake, together with a tract of country 2000 miles in extent.

In 1831, in Sicily, as a result of an earthquake, a whole new island emerged. It was called "Graham's Island". It reached a height of 200 feet and a circumference of three miles, in a month. Soon, however, it sank again.

In 1737, as a result of an earthquake and hurricane in Calcutta, India, 300 000 people died.

In November 1775, Lisbon (Portugal) an earthquake threw down the greater part of the city. In six minutes 60,000 people died. The area where the quay sank was at the end of the 19th century 600 feet deep.

In September 1730, in the Canaries, the earth opened near Year, in Lancerota Island. Several explosions created a hill of ejected matter. Eruptions continued and lava ran over villages and ten days later the lava had reached the sea. Putrid vapors condensed into drops killed the cattle around the country. The storms going on at that time were stronger than anything seen before by the people. The thing has lasted for five years, and the lava covered one-third of the island.

In 1963, a fishing boat off the south coast of Iceland radioed the base to report a cloud of smoke raising from the ocean. An explosion sent rocks flying out of the sea and a black land emerged from the depths. A weak later, the island was 200 feet above sea level and, since eruptions continued, by 1967 was 500 feet high and a mile long. The island was named Surtsey. Nowadays, the land is inhabited by birds and plants.

According to A. Tomas, Atlantis from Legend to Discovery, in 1780 a Spanish explorer, Maurelle found an island in South Pacific. The island was called Falcon. In 1892, the Government of Tonga planted 2000 coconut trees on the island, however, in 1894 the island was gone.

In 1135, in the Caspian Sea, the fortress of Caravan-Sarai rose from the waters, only to sink back again. In 1723, it rose again and it is still there nowadays.

In the Bay of Naples (Mediterranean), the sunk Temple of Jupiter-Serapis, built in 105 BC, rose again in 1742.

In Azores (has 12 volcanoes) a volcano rose suddenly in 1808 in San Jorge, at a height of 3500 feet. It burnt for 6 days and desolated the whole island. In 1811, near San Miguel, another volcano rose creating an island 300 feet high. The place was called Sambrina, but it soon sank again. Other similar eruptions took place in 1691 and 1720.

I will quote now from Donnelly's book, that uses Lyell's Principles of Geology:

"In the Nautical Magazine for 1835 [...], and in Compte Rendus, April, 1838, accounts are given of a series of volcanic phenomena, earthquakes, troubled water, floating scoria, and columns of smoke, which have been observed at intervals since the middle of the last century, in a space of open sea between longitudes 20 degrees and 22 mins W., about half a degree south of the equator. These facts, says Mr. Darwin, seem to show that an island or archipelago is in progress of formation in the middle of Atlantic."

The examples could go on and on, but I think I have made my point. It's not so hard to believe anymore that a continent can sink and rise in a single night, or, if you are still doubting that, in 1 matter of months.

http://atlantis.haktanir.org/ch5.html


Title: Re: Can a Continent Sink?
Post by: Mario Dantas on September 02, 2009, 06:16:29 pm
Dear Adam, and Horus,

An excellent work, thanks for sharing!

Quote
Suffice it to say that Keith believed that the essence of his proposed global model “is that oceanic crust is a principal reservoir and that selective recycling of its components is a counter to weathering and riverine [sediment] transport from continent to ocean, and a key process in the self-regulating Earth system” (p. 282). He has little to say about the forces that drove the Mesozoic mantle surge, other than to say that there is a strong possibility that it may have been triggered by a cluster of meteorite impacts in the western equatorial Pacific. These impacts may have reactivated lower mantle, during a surge-promoted change from layered to whole-mantle convection. Deep “roll-margin” mantle recycling associated with the proposed impact-triggered change from layered to whole-mantle convection, and resultant mantle surge is deduced to have formed a range of mixtures that apparently constituted a source of Cretaceous basaltic magma and oceanic crust.

Science is looking at things partially... there should be a reason for things in the Atlantic to happen the way they did. Since they got stuck with the mantle flow justification, no great advance was made because it was  not the flow of the mantle that sank Atlantis nor is it the reason for Plate Tectonics to occur.

Since there was life on Earth, there were no greater planetary revolution, than the Atlantis proposed sinking. Forget about Dinosaurs extinction or ancient meteors, the same event we search and cherish as the real cradle of Mankind was the most utterly transforming Tectonic procedure since Pangea breakup... it changed the face of the world and the only way to know this is to equate globally what happened. A change can be no longer a change but an entirely new entity, as in the case of Atlantis sink, which became a transfigured byproduct of the literal Tectonic chaos when such profound transformation ceased. It became invisible for too many reasons to be noticed...

Everywhere in the Planet witnessed these changes in Continental Geo-positioning and the hardening of the young Oceanic crust as Ice cooled things down. The 140m Sea level rise could have been a worse remedy than the disease, if the hole crust was to be completely submerged by water... The whole Planetary equilibrium was restored and not only Nature started imitating the previous equilibrium that existed with the previous animal and plants livestok that survived, adapting to new conditions and so on, but also completing or fulfilling the crust integrity, leaving the signals of the Pacific ring of fire as witness of a faulty wiped out crust? A clear Continental dislocation in the Atlantic MAR? or a Severe breach of the Black  and Aegean Seas? As someone once told me, like sugar in a tupperware...

http://en.wikipedia.org/wiki/File:Black_Sea_map.png

Quote
Strabo (7.3.6) thinks that the Black Sea was called "inhospitable" before Greek colonization because it was difficult to navigate, and because its shores were inhabited by savage tribes. The name was changed to "hospitable" after the Milesians had colonized southern shoreline, the Pontus, making it part of Greek civilization.
http://en.wikipedia.org/wiki/Black_Sea

As a matter of fact all Seas must have become inhospitable when Atlantis sank, the healing took time and certainly brought much misery to those living beings caught in the turmoil...


Can Lands Sink and Rise?


not with the size of Atlantis...

but was there, at the time, any larger island than the Island of Atlantis? Is there, at present, any sufficiently large Island in the Atlantic Ocean? Is there any other larger island in the world or even close to it? Is it presently sunk under water? not salt water... or are its neighbor islands (if any) also large? perhaps the largest in the world? Are they close enough?

regards,
Mario Dantas


Title: Re: Can a Continent Sink?
Post by: Adam Hawthorne on September 17, 2009, 12:04:02 am
Hi Mario,

I haven't seen any evidence that a large island, such as a continent, can sink and rise in the timeframe Plato suggests, however history provides many examples of volcanic islands doing such a thing.  Perhaps Plato was referring to the capital city?


Title: Re: Can a Continent Sink?
Post by: Mario Dantas on September 17, 2009, 12:06:55 pm

Dear Adam,

I hope you live to see it...

regards,
Mario Dantas


Title: Re: Can a Continent Sink?
Post by: Carolyn Silver on September 27, 2009, 04:45:17 am
Check this article out by Carl Martin (Lonestar):

Atlantis - Was it Geologically Possible?

http://www.eslteachersboard.com/cgi-bin/stories/index.pl?read=760


Title: Re: Can a Continent Sink?
Post by: vze39mpt on December 14, 2009, 08:39:24 pm
this object is 110 feet below the ocean in the Bahamas

(http://img442.imageshack.us/img442/8996/img0734p.jpg)

(http://img130.imageshack.us/img130/1360/img0740j.jpg)

(http://img46.imageshack.us/img46/6536/taggedphoto0720.jpg)


Title: Re: Can a Continent Sink?
Post by: vze39mpt on December 17, 2009, 01:50:38 pm
(http://img81.imageshack.us/img81/9272/img0720v.jpg)

Thanks for sharing with us. That is, indeed, fascinating. It appears to be a reverse chevron-style mustache. Very interesting.


Carry on.



The American Mustache Institute
(877) STACHE-1

Online: http://AmericanMustacheInstitute.org
Twitter: http://twitter.com/MustacheTalk
Facebook: http://www.facebook.com/AmericanMustacheInstitute

Reply from the AMI  ::)


Title: Re: Can a Continent Sink?
Post by: Geminden on January 02, 2010, 10:50:26 pm
vze39mpt, how does this have anything to do with a continent sinking?


Title: Re: Can a Continent Sink?
Post by: vze39mpt on January 04, 2010, 11:28:40 pm
I just thought that if this is what it look like and it is 110 feet below the sea. And it could be an indication that there was a large civilization stretching across, through or throughout the "Atlantic Ocean" area. Then either the "land" would have had to drop or "sink" or the water to have risen.
Sink holes, quakes, fault lines are they not in some ways showing us that the "ground" can fall?
when the earths inner core erupts isn't that moltent material replaced back in the core and if so where is it coming from? recycled? maybe?
isn't the cooler suface material heavier therefore "sinks"?
"I am but a humble student"
I am here to learn, share and ask




Title: Re: Can a Continent Sink?
Post by: Ostanes on September 09, 2010, 11:00:49 pm
Atlantis never sank and the Egyptian Neith priest identified by Plutarch as Sonchis of Sais never said it did.

What he actually said is that the Pelasgians of Athens "sank into the earth" whereas Atlantis "disappeared in the depths of the sea."

"But afterwards there occurred violent earthquakes and floods; and in a single day and night of misfortune all your warlike men in a body sank into the earth, and the island of Atlantis in like manner disappeared in the depths of the sea." -- Sonchis of Sais, priest, ~600 B.C.


Title: Re: Can a Continent Sink?
Post by: LoneStar77 on September 10, 2010, 03:25:54 am
Atlantis never sank and the Egyptian Neith priest identified by Plutarch as Sonchis of Sais never said it did.

What he actually said is that the Pelasgians of Athens "sank into the earth" whereas Atlantis "disappeared in the depths of the sea."

"But afterwards there occurred violent earthquakes and floods; and in a single day and night of misfortune all your warlike men in a body sank into the earth, and the island of Atlantis in like manner disappeared in the depths of the sea." -- Sonchis of Sais, priest, ~600 B.C.

I don't understand your logic on this, Ostanes. If anything disappeared in the depths of the sea, I would consider it to have "sunk." That seems to be compatible with the definition of sinking.

Atlantis, if it existed, was not a continent, but uplifted oceanic plate (likely from convergent compression -- two tectonic plates colliding). Atlantis may have become weakened from plate rotation (Africa rotating around the Atlantis region with respect to the Eurasia plate), and was likely sucked down to compensate for the massive, post-Ice Age uplift (glacial isostatic rebound, or adjustment) of North America and Northern Europe.

Check out my short Mission: Atlantis video on the geology of Plato's lost island (http://www.ancientsuns.com/fwd/mia/atlantis.php). And then check out the articles on the geology of Atlantis (http://www.ancientsuns.com/fwd/mia/atlantis-articles/atlantis-geology.php), including diagrams, maps and source references. If Atlantis, existed, this may well be how it was formed and later destroyed.

Rod Martin, Jr.
Mission: Atlantis (http://www.ancientsuns.com/fwd/mia/)


Title: Re: Can a Continent Sink?
Post by: Ostanes on September 10, 2010, 11:16:14 am
I don't understand your logic on this, Ostanes.

If anything disappeared in the depths of the sea, I would consider it to have "sunk." That seems to be compatible with the definition of sinking.
Disappeared and sunk are two different words and have two different meanings.

If Plato had wanted to say sunk instead of disappeared surely he could have.

However, he did not do so.

Quote
Atlantis, if it existed, was not a continent, but uplifted oceanic plate (likely from convergent compression -- two tectonic plates colliding).
Tectonic plates are imaginary and do not exist in physical reality, and, if they did exist, it would be impossible for them to collide since there is no mechanism for them to do so.

In actual fact the mantle is cold and it's rigidity increases with depth, because otherwise seismic wave velocity wouldn't increase with depth.


Title: Re: Can a Continent Sink?
Post by: LoneStar77 on September 10, 2010, 11:07:06 pm
I don't understand your logic on this, Ostanes.

If anything disappeared in the depths of the sea, I would consider it to have "sunk." That seems to be compatible with the definition of sinking.

Disappeared and sunk are two different words and have two different meanings.

If Plato had wanted to say sunk instead of disappeared surely he could have.

However, he did not do so.

I can't believe I have to explain this. You may have a very valid point, but I don't see it. Your explanation is either missing some thought process which is completely obvious to you (but erroneously undisclosed), or else you are missing what seems perfectly obvious to me. I'll play nice and let you know my thoughts so they are no longer hidden. I hope you'll do the same.

Yes, Ostanes. "disappeared" and "sunk" mean two different things, but they also have meanings that can overlap. Anything which sinks does not necessarily disappear, but it might disappear if the substance into which the object sinks is opaque enough. A deep sea is effectively opaque because of that depth, so if you toss a bright, shiny coin overboard in the middle of the Atlantic, that coin effectively will have disappeared. The same thing with an island that subsides (read: sinks). Such an incredible, sinking island will have disappeared if the depth is greater than several hundred meters.

Now, let's be clear. The words you're quoting include more than merely "disappeared." What does "disappeared in the depths of the sea" mean? Let's take it apart, piece-by-piece.

"Disappeared" can mean several things. If something grows invisible (becomes completely transparent), like Harry Potter and the "cloak of invisibility," then it will have disappeared. It can also mean that something has moved out of the line of sight, or moved behind something else. In the case of something sinking into the ocean, the object will be "behind" or "underneath" many hundreds of meters of water and suspended particulates. Disappeared can also mean that something has achieved temporal discontinuity — ceased to have persistence in the time stream of physical reality. Can you think of any others?

"Depths" means a location which is down. That's funny. "Sinking" is also about the "down" direction — going to a location which is down, as in moving "down" into a liquid, or moving "down" into a solid when that solid becomes temporarily "liquid" (as in earthquake liquefaction) or has a temporary gap or chasm.

"Sea" means a large body of water, typically saline, as with the ocean, the Mediterranean, or Black Sea.

Okay, let's put these together: "disappearing" into the "depths" of the "sea" means to me, going down (sinking) into a liquid (water) to a point where the great depths effectively block one's ability to see that which has "disappeared."

Now, Ostanes, please tell me how something can disappear in the depths of the sea without sinking.

Quote
Atlantis, if it existed, was not a continent, but uplifted oceanic plate (likely from convergent compression -- two tectonic plates colliding).

Tectonic plates are imaginary and do not exist in physical reality, and, if they did exist, it would be impossible for them to collide since there is no mechanism for them to do so.

In actual fact the mantle is cold and it's rigidity increases with depth, because otherwise seismic wave velocity wouldn't increase with depth.

Very interesting point. Certainly the consensus amongst scientists is that tectonic plates exist. They measure their movements with GPS. There are movements along fault lines and along the putative plate boundaries which tend to imply semi-rigid body movement against those distinct boundaries. From this we get earthquakes (also a movement). We have the compression of Earth's crust forming mountains. I can't imagine how such mountains would suddenly spring up (defying gravity) without some movement of the Earth to force them upward. And we have so many volcanoes which spew hot (not "cold") magma.

Yet, scientists could be wrong. Your point about seismic wave velocity is interesting, and I'll look into it. Why do you say seismic wave velocity would increase? Would it increase with depth if it gets hotter with depth? Does sound travel faster in a hot solid than in a cold one? Is that what you're saying?

Somehow that seems counterintuitive to me. And some things in nature are counterintuitive. But it seems to me, with my limited understanding, that heat causes things to expand and I've always understood that sound (vibrational waves) travel faster in denser objects. Heat, because of expansion, makes objects less dense. Perhaps velocity is not directly related to density? What are your thoughts on these points?


Title: Re: Can a Continent Sink?
Post by: Tom Hebert on September 11, 2010, 01:51:13 pm
Hi Carl,

I can't believe you have to explain this, either.  Why can't we cut Plato some slack for literary license?  Why do we want to treat him like a German scientist instead of a philosopher and raconteur?  If we add a dose of context to Plato's tale, we are a lot more likely to arrive at the truth.


Title: Re: Can a Continent Sink?
Post by: Ostanes on September 11, 2010, 02:22:14 pm
Now, Ostanes, please tell me how something can disappear in the depths of the sea without sinking.
Very easily.

"Depths of the sea" is a Homeric expression from the Odyssey.

E.g. the island of Ogygia [Atlantis] "knows the depths of every sea."

Does that mean Ogygia sank?  Obviously not or else Odysseus wouldn't have been able to cry on the shore.

If I say the sentence "Odysseus disappeared in the depths of the sea" does that mean he sank to the bottom of the sea floor?  No.

It simply means he disappeared at sea.

Quote
Very interesting point. Certainly the consensus amongst scientists is that tectonic plates exist.
That proves they are wrong.  Whenever there is scientific consensus on something it is wrong.

Quote
They measure their movements with GPS.
And then they adjust the measurements to fit their models.  

In actual fact, the Earth is growing.

"The preliminary results from NASA indicate that the chord distance from Europe to North America is increasing by 1.5±0.5 cm per year, North America to Hawaii is increasing by 4±1 cm per year, Hawaii to South America by 5±3, and South America to Australia by 6±3 .... These results support Earth expansion, but not the plate tectonics theory, which is denied by the radius increase implicit in the data." -- S. Warren Carey, geologist, 1988

"The relative motion of Hawaii and Arequipa [Peru] is 80±3 mm/yr...." -- D.E. Smith, geophysicist, et al., 1990

Quote
There are movements along fault lines and along the putative plate boundaries which tend to imply semi-rigid body movement against those distinct boundaries. From this we get earthquakes (also a movement). We have the compression of Earth's crust forming mountains. I can't imagine how such mountains would suddenly spring up (defying gravity) without some movement of the Earth to force them upward.
Upward is the key word.  The Earth is growing.

Quote
And we have so many volcanoes which spew hot (not "cold") magma.
Wrong.  Magma never gets spewed out, lava does.  And hot lava comes from the crust not the mantle.

Quote
Yet, scientists could be wrong.
They almost always are.

Quote
Your point about seismic wave velocity is interesting, and I'll look into it. Why do you say seismic wave velocity would increase? Would it increase with depth if it gets hotter with depth? Does sound travel faster in a hot solid than in a cold one? Is that what you're saying?

Somehow that seems counterintuitive to me. And some things in nature are counterintuitive. But it seems to me, with my limited understanding, that heat causes things to expand and I've always understood that sound (vibrational waves) travel faster in denser objects. Heat, because of expansion, makes objects less dense. Perhaps velocity is not directly related to density? What are your thoughts on these points?
Waves travel faster through cold solids than they do through hot fluids.

"...no matter what the temperature of the outer core is, and most likely it is quite high, the mantle is cold, and its rigidity increases with depth, because otherwise seismic wave velocity cannot increase with depth, for example for P waves from 6-7 km/sec in the surface layers to about 14 km/sec at the mantle-core boundary." -- Stavros T. Tassos, seismologist, October 2008


Title: Re: Can a Continent Sink?
Post by: LoneStar77 on September 17, 2010, 12:16:48 am
Now, Ostanes, please tell me how something can disappear in the depths of the sea without sinking.
Very easily.

"Depths of the sea" is a Homeric expression from the Odyssey.

E.g. the island of Ogygia [Atlantis] "knows the depths of every sea."

Does that mean Ogygia sank?  Obviously not or else Odysseus wouldn't have been able to cry on the shore.

If I say the sentence "Odysseus disappeared in the depths of the sea" does that mean he sank to the bottom of the sea floor?  No.

It simply means he disappeared at sea.

Ostanes, you seem to be making some interesting points, but also you're not being very logical on others. Okay, I grant that one definition of the English "depth" might refer to horizontal distance. That could support your argument if the original text was in English. The fact remains, however, that the English is a translation. The translator likely chose the best words (as commonly understood) for the language they were translating. "Depth" as horizontal distance is not the most common usage. I would bet that if you were to take a survey, you'd find most people think of depth in terms of vertical distance when referring to the sea. I think translators would choose this language accordingly.

Now for the illogical. Frequently, you seem to compare apples to oranges. "Disappear in the depths of the sea" has a far different context than "knows the depths of every sea." Both, to me, seem to use "depth" as a vertical distance — not horizontal.

Knowing the depth of a sea, to me means that one knows how deep (depth) the sea is at a particular location (like at its deepest part). Knowing the depths of all seas, to me means having a good nautical chart to navigate around shallows and dangerous reefs.

Just because someone on an island (Ogygia) knew the depths of all seas does not change the idea that disappearing in the depths of a sea means "sinking" or "submersion." You can't ignore the words "disappear in" and "knows" and "of every" which differ between the two phrases. The two phrases are not equivalent, so to treat them as such is entirely illogical.

If I were translating from another language and wanted to mean "disappeared at sea," I might use "disappeared across the sea," but never "disappeared in the depths of the sea." Such a translation would be entirely misleading in meaning. If we were not talking about the sea, but say "the wilderness," then "disappeared in the depths of the wilderness" would be perfectly okay in meaning horizontal distance, but this is a more poetic treatment than literal. Horizontal depth of the wilderness is more acceptable only because one does not typically think of vertical depth in the wilderness in this context.

Quote
Very interesting point. Certainly the consensus amongst scientists is that tectonic plates exist.
That proves they are wrong.  Whenever there is scientific consensus on something it is wrong.

Now, this reaches a new level of illogicalness.

If your statement were true, then if everyone suddenly agreed with Ostanes, Ostanes would be suddenly wrong. My dear Ostanes, if your logic can't do better than that, I will likely not be replying to any more of your postings. I don't have time to educate those unwilling to learn. Yet, perhaps someone can benefit from the discussion.

Quote
They measure their movements with GPS.
And then they adjust the measurements to fit their models. 

In actual fact, the Earth is growing.

"Adjust the measurements?" You're talking of scientific misconduct. That's unethical. Do all scientists do this? If we believe you, they must. But somehow I sincerely doubt it.

"The preliminary results from NASA indicate that the chord distance from Europe to North America is increasing by 1.5±0.5 cm per year, North America to Hawaii is increasing by 4±1 cm per year, Hawaii to South America by 5±3, and South America to Australia by 6±3 .... These results support Earth expansion, but not the plate tectonics theory, which is denied by the radius increase implicit in the data." -- S. Warren Carey, geologist, 1988

"The relative motion of Hawaii and Arequipa [Peru] is 80±3 mm/yr...." -- D.E. Smith, geophysicist, et al., 1990

I don't know about D.E. Smith, but S. Warren Carey seems to have fallen into disfavor amongst fellow geologists. But what if all geologists suddenly believed as Carey did? By your logic, above, Carey would suddenly be wrong. That would be, after all, a consensus.

What Carey seems to leave out are the areas (across subduction zones and convergent boundaries) where the distances are decreasing. Duh! Earth is not growing, at least by every set of data I've ever seen.

And I think your quote of D.E. Smith is interesting. If I'm not mistaken, the 80±3 mm/yr is in approach! In other words, shrinking. Why? There is a subduction zone between the Pacific plate and the South America plate all along the Andes. In fact, that's why the Andes are there. Subduction tends to produce volcanoes, as in the subduction of the Philippine Sea plate underneath the Sunda plate, creating the Philippines archipelago, where I currently live.

Quote
And we have so many volcanoes which spew hot (not "cold") magma.
Wrong.  Magma never gets spewed out, lava does.  And hot lava comes from the crust not the mantle.

Definition "magma":
2. Geology The molten rock material under the earth's crust, from which igneous rock is formed by cooling.
[from the American Heritage dictionary]

The igneous rock which is on the surface of Earth was at one time "lava," or "molten rock."

Quote
Yet, scientists could be wrong.
They almost always are.

Really? If that were true, then most of the technology of our wonderful civilization would never have worked. I think technology does work, otherwise we would not be having this conversation over the internet, using electricity, TCP/IP data packets, and computers.

Good luck, Ostanes.
 ;)


Title: Re: Can a Continent Sink?
Post by: Essan on September 17, 2010, 02:02:12 am
Atlantis never sank and the Egyptian Neith priest identified by Plutarch as Sonchis of Sais never said it did.

What he actually said is that the Pelasgians of Athens "sank into the earth" whereas Atlantis "disappeared in the depths of the sea."

"But afterwards there occurred violent earthquakes and floods; and in a single day and night of misfortune all your warlike men in a body sank into the earth, and the island of Atlantis in like manner disappeared in the depths of the sea." -- Sonchis of Sais, priest, ~600 B.C.

Don't forget the rest of the quote

Quote
. For which reason the sea in those parts is impassable and impenetrable, because there is a shoal of mud in the way; and this was caused by the subsidence of the island.

 ;)


Title: Re: Can a Continent Sink?
Post by: Ostanes on October 01, 2010, 11:24:28 pm
Atlantis never sank and the Egyptian Neith priest identified by Plutarch as Sonchis of Sais never said it did.

What he actually said is that the Pelasgians of Athens "sank into the earth" whereas Atlantis "disappeared in the depths of the sea."

"But afterwards there occurred violent earthquakes and floods; and in a single day and night of misfortune all your warlike men in a body sank into the earth, and the island of Atlantis in like manner disappeared in the depths of the sea." -- Sonchis of Sais, priest, ~600 B.C.

Don't forget the rest of the quote

Quote
. For which reason the sea in those parts is impassable and impenetrable, because there is a shoal of mud in the way; and this was caused by the subsidence of the island.

 ;)
Antarctica subsided under ice... ;)


Title: Re: Can a Continent Sink?
Post by: LoneStar77 on October 03, 2010, 08:49:05 pm
Antarctica subsided under ice... ;)

Cute, Ostanes. That's a perversion of the word "subsided."  :-[ I don't know of any definition of the word that would fit your usage. And where is there a shoal of mud in or around Antartica, covered by ice? I doubt anyone would know there was frozen mud underneath all that ice. I sincerely doubt any ancient Egyptian or Greek travelers would've made it that far south.

And Antarctica does not face Gadira (Cadiz, Spain). Plato drew a pretty clear picture of the location of Atlantis. If the large island (NOT continent, please!) existed, this would've been the perfect place for it -- right along a tectonic plate boundary. Over 90% of all mountains are formed near tectonic plate boundaries, as are numerous islands, like the Philippines, where I currently live. You might want to check out my video on "Why the Philippines will Not be the Next Atlantis (http://www.ancientsuns.com/fwd/mia/atlantis.php)." And if you want sources and more details, check out the article on "Geology of Atlantis," on the same website.

Rod Martin, Jr.
Atlantis Tours (http://hubpages.com/hub/Atlantis-Tours)
Mission: Atlantis (http://www.ancientsuns.com/fwd/mia/)


Title: Re: Can a Continent Sink?
Post by: BlueHue2 on May 09, 2014, 09:07:58 am
Dear Mrs CAROLYN  SILVER,

Thank you
for this Link to this Book," Atlantis found "
It does however feature the original
false location theories around Spain.

I think that the former Nickname of this
Writer, Carl Martin, was " WIND "( who had the same Theory.)
(Now Lone-Star 77.)

About Subsidence or Subduction of an Island Atlantis,
Whoever can corroberate that a if any Mega-Tsunami could EVER
sink a City or Continent 150 m lower ?!

Didn't PLATO mention that Atlantis sunk beneath the( Elevated !)
waves of a raised SpringFlood? And Thus not beneath Mean-Sealevel?
I myself cannot read Greek. but I can understand THAT much ! aBalooney.

B.T.W.  Could you please find out, pretty please,
what is the present Nick Name of Mr. Cedric Leonnard ?
I cannot seem to locatre HIM on this Website-Index
and neither could Mr.'Atalante' earlier.

That is strange because Mr Leonnard has commented
several times, yet sparsely,  in the past unfortunately, I always forgot
to check his Pseudonym.  I am Thanking you in advance !

PS.
To tease you, have you checked on the earliest occurence
of the name Atlantic-Ocean in America ?
It crops-up earlier than 1649 but only became official in That year.
Hence on a 1625 - 1645 MAP of Pensylvania it is Non-existant.

instead the Name containing the word 'Ocean' reads rather,
'MARE-Oceanum' ( Britannicum.)and NOT ( Mare-)Oceanum-Atlanticum.
With all your fervent,  relevant Articles seeking,
 you may have overlooked this simple Poëtic, thus, un-important--detaill ???

No offences meant !
Sincerely, yours,
Mr. ' Blue-Hue  'dd. May-9 2014


Title: Re: Can a Continent Sink?
Post by: knakker on March 06, 2019, 03:34:43 am
a continent cannot sink but Atlantis on the western horizon was the underworld. In the east, Endtimes Babylon will sink in the Euphrates.

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