Uploaded on Jul 13, 2014 to YouTube: https://youtu.be/prW_mfQIyHk
This presentation discusses how the Carolina Bays could have formed from a cosmic impact.
The Carolina Bays are marshy, shallow depressions with sandy rims found along the Eastern seaboard of the United States, primarily in North Carolina, South Carolina and Georgia.
Aerial photography in the 1930s brought attention to their characteristic elliptical shape and their northwest-to-southeast orientation.
It is estimated that there are at least half a million Carolina Bays along the coast. Some Carolina Bays are very large.
On the East Coast of the United States, the Carolina Bays can occur at elevations as high as 200 meters, or 650 feet above sea level.
The land surface near Tatum, South Carolina is densely covered with Carolina Bays. These are some basic questions that are often asked:
Carolina Bays occur in sandy, unconsolidated ground along the Atlantic seaboard, but similar bays are also found in Nebraska and Kansas, where they are called "rainwater basins". The bays in these Midwestern states differ from the ones in the East Coast in that their major axes are aligned from the northeast to the southwest.
The Carolina Bays have a wide range of sizes.
This graph displays the frequency of the various sizes of bays from a survey of approximately 500 bays. The graph was produced by Michael Davias, who has a web site featuring LiDAR images of the Carolina Bays. In this graph we can see that bays with major axes of 220 meters and minor axes of 160 meters are the most common.
One of the most striking features of the Carolina Bays is their perfect elliptical shape.
One of the first proposals for the formation of the Carolina Bays was made by Melton and Schriever from the University of Oklahoma in 1933. They suggested that a meteorite shower or a colliding comet coming from the northwest could have created the bays.
In 2007, Richard Firestone and several coauthors proposed that an extraterrestrial impact 12,900 years ago caused the late Pleistocene megafaunal extinctions and the Younger Dryas cooling event, which was a cold period that lasted approximately 1000 years. Firestone proposed that a comet airburst could have killed the mastodons and saber-toothed tigers that lived in North America toward the end of the last ice age and triggered a cold event. A few Carolina Bays were examined to obtain impact spherules and nanodiamonds that were supposed to prove that a comet airburst had occurred.
Firestone extended his argument in another publication in 2009 by pointing out the radial orientation of the Carolina Bays.
Firestone's hypothesis, which was dubbed the "Younger Dryas Impact Hypothesis" was soundly rejected by the scientific community for not providing the type of impact evidence established by hypervelocity impact science.
Geologists have proposed theories like substrate dissolution, marine waves and modification by wind or ice-push processes. The bays have also been characterized as thermokarst or thaw lakes that are circular or elliptical in shape aligned with the prevailing wind. None of the proposed ideas for terrestrial processes has been accompanied by a physical or a computational model to explain why the bays have elliptical shapes with eccentricities that are in a very narrow range.
This slide illustrates thermokarst lakes in Alaska and Russia. These lakes form when underground ice melts in a region that has permafrost and the ground collapses like a sinkhole. The cavities fill with water forming lakes, and the shape and alignment of the thaw lakes is determined by the contours of the land.
The salt lakes in western Australia share some visual similarity to the Carolina Bays. The Australian salt lakes formed when marshy ground dried up leaving oval pools along the landscape. However, the drying process does not create the raised rims or overlapping ellipses which are characteristic of the Carolina Bays.
The most popular explanation of the origin of the Carolina Bays involves a combination of wind and water processes. According to Mark J. Brooks and his co-authors, The Carolina bays formed during the Pleistocene epoch starting as shallow lakes along the Atlantic Coastal Plain from New Jersey to Florida. The distinctive shape and NW to SE orientation of the bays developed through stronger-than-present southwesterly winds blowing over water ponded in shallow depressions. The depressions were expanded and oriented by wave erosion, resulting in bay elongation perpendicular to wind direction and the formation of peripheral, downwind sand rims and shorelines on the eastern and southeastern margins.
The dates of formation of the Carolina Bays have been measured using Optically Stimulated Luminescence, or OSL, which estimates the time since last exposure to sunlight for quartz sand and similar materials.
This image shows Big Bay in South Carolina. According to Brooks, Big Bay formed from wind-driven sand sheets from the Wateree River, which is 10 kilometers to the west. The sand moved across Big Bay about 74,000 years ago and was resurfaced subsequently 33,000 to 29,000 years ago. The innermost sand rim at Big Bay was remodeled as recently as 2,200 years before the present.
Geometrical conic sections can be used to model the Carolina Bays. The elliptical bays are produced when oblique conical cavities intersect with the level surface of the earth.
These images show an experiment conducted by Peter H. Schultz from Brown University using NASA’s Ames Vertical Gun. A high-speed impact shatters the ice and ice chunks are ejected at high velocity radiating from the point of impact. Professor Schultz's experiment demonstrates that a hyperspeed impact on ice could have produced an ejecta curtain of ice fragments.
The Carolina Bays and the Nebraska bays appear to radiate from the Great Lakes region around central Michigan. It is possible to estimate the distances that the ejected ice fragments would have traveled. We can calculate the launch speed, the time of flight and the maximum height for various launch angles.
Knowing the launch velocities of the ejected ice and the size of the Carolina Bays, it is possible to estimate the size of the glacier ice chunks that created the bays. The size of any crater depends on the projectile's size, speed, and the angle at which it strikes. Other factors are important, such as the projectile's composition and the material and the structure of the target surface.
The application of Newton's laws of motion and the scaling laws relating crater size to kinetic energy allow us to make some educated guesses about the proposed extraterrestrial impact.
Sandy soil becomes like quicksand in response to soil vibrations. Liquefaction has been responsible for extensive damage to buildings and vehicles during earthquakes. These pictures show some buildings that toppled in Japan and some cars that submerged in New Zealand.
This image from the U.S. Geological Survey shows the estimated Depth to water in North Carolina. The light blue color along the coastline indicates a water table within 5 feet, or 1 1/2 meters, from the surface. This coincides with the areas that have bays.
In Nebraska, the bays also are found in soil that is close to the water table. This image from the University of Nebraska at Lincoln shows the depth to water in several shades of blue. Many bays can be found in the area with the light blue color in the flood plain of the Platte River, particularly in Phelps and Kearney counties.
A high-speed impact starts with a contact and compression stage in which the projectile is destroyed and transfers its kinetic energy almost instantaneously to the target surface in an expanding hemispherical shock wave that eventually forms a bowl-shaped cavity.
A projectile traveling through a viscous medium can create a conical cavity.
For conical cavities, the eccentricity of the ellipse depends on the angle of impact, and the size of the ellipse is determined by the energy of the projectile. A large projectile will create a large cavity and a small projectile at the same speed will create a small cavity, but the aspect ratios of the ellipses will be the same as long as the projectiles hit at the same angle.
Relating the elliptical shapes of the bays to conic sections makes it possible to use mathematical formulas to determine the angle at which the ice boulders impacted the surface.
Here is a short video of an experimental impact. Do not blink or you will miss it!
Video of experimental impact. [a mockingbird sings in the background]
These images show the conical cavities with overturned flaps created by impacts of ice projectiles. The target surface retains the conical shape of the shock wave created by the projectile.
Raised rims are a common feature of all the Carolina Bays.
Overlapping bays can be created by adjacent impacts.
Viscous relaxation is a deformation by gravity that decreases the vertical dimension of the features of a landscape.
This image illustrates the reconstitution of the ground by the flow of the viscous medium. The deeper layers of the cavity, which are under the greatest pressure from the force of gravity, flow faster. The depth of the cavity is reduced and converts a conical cavity into a shallow depression.
Viscous relaxation reconstitutes the terrain and transforms the overturned flaps into raised rims.
The onset of the Younger Dryas cooling event and the extinction of the North American megafauna may have been caused by the heavy bombardment of ice ejected by an impact.
The bibliographic references for the background material about the Carolina Bays are contained in the book:
Killer Comet: What the Carolina Bays tell us. — available from Amazon