THE CAROLINA BAYS

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                                                    IMPACT MECHANICS





If the Carolina Bays are the result of impact of a fragmenting comet or asteroid, aspects of impact mechanics may lead to further conclusions concerning the likelihood of such an event. The basis for these impact studies are found in the energy relationships for terrestrial craters, both from impact and from nuclear explosion, and are well documented by Baldwin (1963). The results of these experiments can be stated as a simple cube scaling law where crater diameters are proportional to the cube root of the energy of the explosion. (*) For one such explosion (Teapot-Ess) a 300 foot crater was produced by a 1.2 kiloton nuclear device. The relationship for this blast is:

     
D = kWl/3               (equation 1)                                                   


where:

D = diameter of the crater in feet
k = proportionality constant                     
W = energy of blast in ergs (1 ton TNT = 4.16 X 1016  )

Solving for the proportionality constant:


          3______________________                             
300' = k \/(1.2 X 103)(4.16 X 1016)

           
k = 8.1 X 10-5

(*) More exact relationships can be found using exponents other than 3.00 (Baldwin, 1963). The authors feel, however, that simple cube scaling will suffice for a first approximation.





This relationship (D = 8.1 X 10 5 X W 1/3) has been used for impact craters and for craters produced by other nuclear devices and appears to be legitimate. This expression, then, can be applied to the Carolina Bays to determine the size of object necessary to produce one average bay and the size of object required to produce all bays, assuming fragmentation. The energy, W, can be calculated by assuming all the kinetic energy to be available for the blast. The cube scaling law then becomes:

           
D = k(l/2MV2)1/3          (equation 2)



where:

     
1/2MV2  = kinetic energy.



If assumptions are made concerning the velocity of impact (V) needed to form a particular size crater (D), then the mass can be determined from equation 2 or rewriting as 3:

     
    2D3/
M =   /           (equation 3)
     / k3v2



Further assumptions can be made as to the density of the material, and the size of the object represented as a sphere can be determined from equation 4 shown below:

           
      1.5D3/
R =       /                 
         / p(3.141..)k3v2



where:

D = diameter of crater in feet     
   
p = density of impacting material g/cm3

k = proportionality constant of cube scaling

F = velocity of impacting body in cm/sec.





This model was used to determine the size of a single fragment necessary to create a Carolina Bay one-half mile in diameter and the original dimensions of the body needed to create 500,000 bays of the same size. This was done as a small computer program (Appendix A) in which different velocities, densities, exponents and proportionality constants for cube scaling could be changed. The results for impacting asteroids and comets are shown in (Table 4). Only the values from the computer output for the upper and lower limits of the impact velocity are included. The resulting size range appears to fit the range of expected diameters for either comets or asteroids.

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        TABLE 4: IMPACT MECHANICS (1) FOR HIGH AND LOW VELOCITY ASTEROIDS AND COMETS





Impacting Body Impact mps Velocity (km/sec) Density g/cm3 Single Mass lbs (kgm) Fragment Diameter (2) ft (m) Entire Mass T (MT) Body Diameter (3) mile (km)



Asteroid 7 (11) 3.00 .118X106 (.536X108) 106.4 (32.43) .608X1010 (.268X1010) 1.6 (2.57)

Asteroid 10 (16) 3.00 .579X105 (.263X108) 83.89 (25.57) .298X1010 (.131X1011) 1.26 (2.03)

Comet 7 (11) 1.30 .118X106 (.536X108) 140.6 (42.86) .608X1010 (.649X109) 2.1 (3.4)

Comet 45 (72) 1.30 .286X104 (.130X107) 40.67 (12.40) .147X109 (.268X1011) .61 (.98)



(1) Cube scaling = 3.00, energy available for impact = 100%

(2) Mean diameter of crater - 2640.0 ft (1/2 mile)

(3) Total number craters - 500,000


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Other constraints on the fall and impact process can restrict the model. A limit can be set on the mass of an object which will pass through the Earth's atmosphere without retardation of velocity. Objects with masses of one ton or less will be decelerated until the original impact velocity has reached zero and the object will continue to fall at terminal velocity in the atmosphere. Objects greater than 1000 tons will not significantly decrease in velocity (Hawkins, 1964, p. 90-91).

Further complications exist if the body breaks into fragments as required for bay formation. The mass of the objects (Table 4) are appreciably greater than 1000 tons and will, on entering the atmosphere, maintain their original approach velocity. After fragmenting, the individual particles range in size from approximately one ton for a fast moving comet to fifty tons for a slow moving asteroid. If fragmentation occurs at a fairly high altitude, then considerable deceleration and loss of mass through ablation will probably occur. Fragmentation at lower altitudes would reduce ablation and deceleration considerably. Both instantaneous and continual fragmentation has been observed in meteor falls. It is expected that the higher velocity objects impinging on the Earth's atmosphere are more apt to break up (Hartmann, 1973, p. 180).

Although the characteristics of fragmentation favors a cometary impact, the general impact model appears to satisfy the requirements for either a comet or an asteroid collision. Examination of the morphometric characteristics of the Carolina Bays may permit further differentiation as to the possible source of the impacting body.

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                                 CRATER MORPHOMETRY AND THE CAROLINA BAYS





The majority of lunar craters and known terrestrial cryptoexplosion features such as Gosses Bluff, Australia (Milton and others, 1972), and the Arizona Meteorite Crater are commonly recognized as impact structures. Such features, similar in form to craters produced by chemical or nuclear devices, result from the release of energy at or below ground level caused by impact of a rapidly moving mass. These energies override the chemical bonds in the rock, causing severe deformation and brecciation plus formation of high-density Si02 polymorphs and shattercones (Baldwin, 1965). If the velocity of the mass is sufficient (over 6 miles per second), the impact results in a violent explosion, vaporizing some or all of the impacting particles.

Because impact craters are analogous to chemical and nuclear explosions, much crater research has concentrated on these more readily available, if smaller sized forms (see Baldwin, 1963; 1965). Various morphometric crater characteristics have a fundamental relationship--expected logarithmic relationships between crater depth (D) and crater diameter (d), between rim height (RH) and diameter, and between crater rim width (RW) and diameter. Impact craters ranging from several inches to hundreds of miles in diameter are plotted in Figure 3a. While Baldwin plotted both cubic and linear solutions, the shallow cubic relationship deviated only slightly from the linear solution (Baldwin, 1965, p. 68-72). Therefore, only the straight line approximations are included in Figure 3a.

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For a Carolina Bay with a major axis of one mile to be regarded as an impact crater, the expected depth should be approximately 1,000 feet, the rim height 150 feet and the rim width 1,000 feet. There are few field data available on the depths of Carolina Bays. However, from descriptions of bays with a major axis of approximately one mile, the depth is less than 1,000 feet by several orders of magnitude.

Actual measured data on any aspect or Carolina Bay morphometry are scarce. Measurements are confined to rim heights and rim widths for nine bays (Prouty, 1952, p. 179-183) with bay length determined either from Prouty's text of U.S.G.S. topographic maps (Table 5). Those bays such as Junkyard and St. Luke's Church, which are close to one mile in length along the major axis, have rim heights of less than ten feet, whereas the expected rim heights derived from Baldwin approximate 150 feet. The rim widths, on the other hand, are somewhat closer to the expected values. Baldwin's model predicted widths of almost 1,000 feet whereas Junkyard has a mean rim width of 575 feet and St. Luke's Church has a mean rim width of 300 feet.

According to Prouty (1952, p. 183), the maximum rim width for Junkyard Bay is 1,200 feet, whereas the maximum cited rim width for St. Luke's Church Bay is only 350 feet. In both cases the maximum rim widths occur at the southeast end of the bays where rims tend to be best developed. Observed rim width maxima sometimes exceed and sometimes do not approach the predicted rim widths from Baldwin's model. Part of this variation may represent field measurement error: the rim heights are low, the rim width slopes are quite gentle, and the outside perimeter of the rim is irregular, almost scalloped, causing wide fluctuations in rim widths over short distances.

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                                               TABLE 5: BAY MORPHOMETRY





Bay Name Location x RH (feet) x RW (feet) Major Axis (feet)

Lake Waccamaw Columbus Co., N.C. 23.0 2000 32,366

Junkyard Clarendon Co., S.C. 7.4 575 6,660
 
Polk Swamp Orangeburg Co., S.C. 7.4 378 13,590 

St. Luke's Church S.C. (county unknown) 5.25 300 6,300

Grassy Allendale Co., S.C. 5.25 272 7,286

Big Horsepen S.C. (county unknown) 7.25 525 7,804

Bowman (location unknown) 6.0 750 10,230

Little Sister Marion Co., S.C. 4.5 350 10,560

Swallow Savanna Allendale Co., S.C. 7.8 523 3,150





after Prouty, 1952, pp. 179-183

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Carolina Bays do not even closely approximate impact crater morphometric characteristics.

The rim widths appear to be the only measure which even falls within the range predicted by the impact model. In an attempt to examine this phenomenon, a curve relating rim height and rim width was derived from Baldwin's curves and the values for the bays in Table 5 were plotted (Figure 3b).

For an impact crater to have a rim height of 7.5 feet, it should have a rim width of 100 feet.

Junkyard Bay has a mean rim width of 575 feet with a mean rim height of only 7.4 feet. In all nine bays, rim width is considerably greater with respect to rim height than the model predicts.

As impact structures, the Carolina Bays exhibit crater depths that are much too shallow for their diameter, rim heights that are too low for their diameter, and rim widths that are too narrow for their diameter. The rim widths are considerably wider than is expected with respect to the actual rim heights.

Clearly, the bays are not impact phenomena of the type that created the lunar and terrestrial craters.

Additional terrestrial Carolina Bay characteristics such as the absence of coesite and stishovite
(Si02 polymorphs), the lack of any meteorites genetically related to bays, and the elliptical, rather
than circular form of the bays, also do not support any traditional type of extraterrestrial impact bay formation model.

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                                    A COMET AS THE BAY FORMING MECHANISM *





One other aspect peculiar to comets may be important to the genesis of the Carolina Bays. Because of the volatile content in a comet nucleus, a collision trajectory may not result in actual impact. Observations of meteors and fireballs indicate that some of these objects break up as they enter the Earth's atmosphere and sometimes explode in the air.

The 1908 Tunguska fall in Siberia is commonly regarded as the explosion of a very small comet nucleus. Hartmann (1973, p. 146) said that the explosion, estimated to be 1021 to 1023 ergs, knocked a man off his porch 38 miles away. Trees as much as nine miles from the impact site were felled radially outward by the shock wave, whereas trees at ground zero were merely denuded of their branches and left in growth position. Baldwin (1963, p. 37) added that trees in protected locations such as deep valleys remained standing and in some cases were still alive. According to Hartmann ( p. 146), by 1928 when trained observers first visited the site, they found the impact site to be pockmarked with a series of shallow, funnel-shaped depressions of variable width but not more than four or five meters in depth. No meteorites were discovered. Baldwin (1963, p. 37) noted that in 1928 the original forest vegetation was replaced with tundra except in the craters where swampy vegetation was already well established Hartmann (1973, pp. 146-147) summarized the evidence supporting a cometary origin for the 1908 fall:

1. The object evidently exploded in the air, since trees at "ground zero" stood upright but were stripped of branches. A loosely consolidated ice comet nucleus would be expected to volatilize and explode before it hit the ground.

2. The lack of meteorite fragments is consistent with our picture of a predominantly icy nucleus.

3. A 1961 expedition recovered soil samples that contained small spherules believed to be part of the object. The spherules would be consistent with the idea of an admixture of small grains of non-icy "dirt" in the dirty iceberg and their spherical shape could be the result of sudden melting during the explosion.

4. Observations of the motion of the object across the sky indicated that it was traveling toward the earth probably in retrograde motion at a very high velocity, perhaps 50 km/sec, which would be typical of a comet but not of ordinary meteorites. .

5. For weeks afterward, the night sky in Europe and Russia was anomalously bright. This may have been due in part to atmospheric interaction with tail and coma material (although the comet was too small to have been noticed prior to the collision, being on the order 101g to 1011g in mass instead of about 1018g, typical of observed comets).

Multiple shallow craters of variable widths, a climax vegetation destroyed except where topographically protected, the absence of meteoritic finds, a high velocity but low angle trajectory, plus a shock wave felt at least 38 miles and heard 620 miles from the impact site suggest a cometary explosion before actual impact. Hartmann stated that the Tunguska fall was a small comet nucleus. If such a singular event happened once, it could happen at least once more.

*While a heading in the article concerning the original extraterrestrial hypothesis mentions the possibility of a cometary impact (Melton and Schriever, 1933, p. 63), the article never explores such a mechanism as an alternative to meteoritic showers.

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                                           AVAILABLE COMETARY ENERGY





In a discussion of the energies needed to produce craters by nuclear explosions, Baldwin (1963, pp. 41-42) indicated that:

As the transition is made from an air burst to a surface burst to a subsurface burst, the energies which go to produce the crater become an increasing percentage of the total energy and the attenuation of the shock waves in the air becomes marked. The maximum blast effect of a 20 KT bomb are greatest for a height of air-burst of about 1,850 feet. Baldwin reports that calculations of the energy in the Tunguska air blast could be the equivalent of a 23.9 KT bomb.

In an attempt to see how a reduction of energy because of an air blast would affect the impact model, we re-ran the model using decreasing amounts of energy available for impact (Figure 4). The diameter for the comet nucleus is within an acceptable range of sizes of available cometary material.

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Impact of a shock wave caused by an air blast has considerable portent for structure of the bays. The shock wave would be extended for the duration of time each particle volatized and exploded. This could account for the elliptical structure of the bays. The elliptical structure would also be more pronounced if the trajectory of the comet as it approached the earth's surface was low. We have not been able to ascertain what the specific shape of the Tunguska craters were. Presumably , since descriptions refer to diameters, the depressions are probably rounded or sub-rounded rather than elliptical. However, the Campo del Cielo meteorite which fragmented in the atmosphere over Chile and Argentina produced individual craters which are elliptical to sub-rounded (Cassidy and others, 1965, p. 1058), so ellipticity, per se, cannot rule out an extraterrestrial origin as was suggested by Price (1968, p. 104).

A shallow trajectory and air blast could also account for the apparent piling up of material on the southeast rims of the bays. Although a fairly speculative model at present, there is the precedence of the Tunguska fall. Further support can be found in the orientation of the bays.

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                                                      BAY ORIENTATION





Many scholars (Melton and Schriever, 1933; Johnson, 1942; Prouty, 1952; Price, 1968; and Thom, 1970) have variously interpreted the northwest-southeast orientation of the major axes of the bays. Melton and Schriever (p. 63) said that the alignment is and should be parallel, because bays formed by a meteoritic shower of particles were on a common trajectory. Johnson, using mean orientation of 75 bays scattered from North Carolina to Georgia, said that the azimuthal standard deviation was too large for alignment to be a significant bay attribute. Later, when Prouty measured the orientation of Carolina Bays, he recognized a radial alignment with southern locations having orientations slightly west of north and northerly bays oriented almost due west.

We measured the azimuths of a 358 bay sample including fourteen counties from Georgia north to Virginia (Table 6). The mean azimuths vary from 344.2o in southern South Carolina and 342.6o in southern Georgia to a mean azimuth of 294.9o in Virginia. In general these results appear to verify those of Prouty who stated that there was a systematic latitudinal variation in orientation. Systematic locational variation may have led Johnson to conclude that the overall standard deviation was too large to be meaningful.

While our mean azimuth (342.6o) for Atkinson County, Georgia, is similar to Prouty's 345o for the same county, measurement error is a very real possibility. Measuring the precise orientation of an ellipse where overlap occurs is difficult. Although we omitted bays where we thought the orientation was too indistinct, some subjectivity in the actual alignment certainly occurred. Relatively small sample sizes, particularly in counties with wide azimuthal fluctuations, also affects the results. Nonetheless, a wide scatter in bay orientations in a localized area has a possible significance.

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                                        TABLE 6: CAROLINA BAY ORIENTATION





State County Number Measured Bays x Azimuth S/x +/-1 S/x in Degrees



Ga. Atkinson 27 342.6o 16.5 359.1 - 326.1

S.C. Allendale 10 341.4o 7.8 349.2 - 333.6

S.C. Barnwell 30 344.2o 5.1 349.3 - 339.1

S.C. Florence 2* 322.0o --- -------------

S.C. Georgetown 9 328.4o 6.5 334.9 - 321.9

S.C. Horry 38 312.3o 6.1 318.4 - 306.2

S.C. Lee 2* 319.5o --- -------------

S.C. Marion 8 316.5o 6.7 323.2 - 309.8

S.C. Sumter 3* 342.0o --- -------------

N.C. Bladen 98 311.4o 4.7 316.1 - 306.7

N.C. Carteret 9 300.4o 6.3 306.7 - 294.1

N.C. Cumberland 15 311.6o 8.5 320.1 - 303.1

N.C. Robeson 90 311.2o 5.8 317.0 - 305.4

Va. Powhatan 17 294.9o 20.3 315.2 - 274.6

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*Sample size too small

The mean azimuths for the fourteen sample counties are plotted on Figure 5. They display radial alignment, but more significantly, they have an apparent focus in either southern Ohio or Indiana which indicates the possibility of a point source. Other than measurement errors, variations in mean orientation per county may indicate localized effects or not quite simultaneous explosions and the resulting shock waves. The azimuths tend to support the possibility of a cometary bay forming mechanism.