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Can a Continent Sink?

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Adam Hawthorne
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« Reply #15 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).



 

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
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Adam Hawthorne
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« Reply #16 on: April 08, 2007, 11:58:55 pm »



Vertical distribution of potential temperature, salinity and potential density along a CTD transect across the Great Meteor Seamount (density scale inverted).
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Adam Hawthorne
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« Reply #17 on: April 08, 2007, 11:59:54 pm »



Horizontal distribution of potential temperature, salinity and potential density on the 250 dbar isobar (density scale inverted).
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« Reply #18 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 Wόst 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.


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http://www.agu.org/pubs/crossref/2005/2005GL023205.shtml
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Adam Hawthorne
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« Reply #19 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).





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.



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.





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



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
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« Reply #20 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.

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« Reply #21 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.


 
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).




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
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« Reply #22 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 Cool. 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.



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).



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).



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
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« Reply #23 on: April 09, 2007, 12:34:01 am »

Caribbean Islands - Earthquakes and Volcanic Eruptions



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.



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).

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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.

 

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).



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



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
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« Reply #24 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?
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« Reply #25 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  Cheesy)  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 .
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« Reply #26 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?
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« Reply #27 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.
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Adam Hawthorne
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« Reply #28 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  Cheesy)  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.
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Mark of Australia
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« Reply #29 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 .
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