There are three Carolina Bays aligned one after the other like a catena crater chain
near Myrtle Beach, South Carolina.
Three hits in a row.
Pow!
Boom!
Bang!
This presentation tries to determine their sequence of emplacement using the law of superposition
and a method of direct measurement of the LiDAR images compared to an indirect method
derived from a least squares fit of ellipses.
Welcome to another edition of the Carolina Bay of the Day where we study the secondary
impacts made by the glacier ice boulders that were ejected by one or more extraterrestrial
impacts on the Laurentide Ice Sheet by the Great Lakes.
The secondary impacts produced seismic vibrations that liquefied unconsolidated soil, and the
oblique impacts of glacier ice on viscous ground created inclined conical cavities that
became shallow elliptical basins by viscous relaxation.
The fact that well-preserved Carolina Bays have elliptical geometry is evidence that
these geological features originated as inclined conical cavities, as can be demonstrated by
experiments.
Today, we will examine three Carolina Bays known as the Carroll Road Bays.
These geological features are located about 84 km or 52 miles northwest of Myrtle Beach,
South Carolina.
The basin labeled A is at an elevation of 34 meters above sea level, and basins B and
C are at 33 meters above sea level.
The topography of this LiDAR image represents these elevations with different colors.
The rim of basin B over basin C is very faint, but from the law of superposition we can deduce
that basin C was emplaced before basin B. Basins A and B do not overlap, so their relative
time of emplacement cannot be determined from geological morphology.
This is a satellite image of the same area.
It is difficult to see the Carolina Bays.
LiDAR, which is a laser based ranging technology, is essential for the study of the Carolina
Bays.
The description of the video has a link to the LiDAR visualization tool for Google Earth
by Michael Davias.
When you measure the width or the length of a Carolina Bay with the ruler tool in Google
Earth, you don't really know if the end points that you are choosing are the best ones.
There is no way to know if the line that you have drawn is truly the major axis or the
minor axis of the ellipse.
An error of a few pixels on the image can represent a substantial distance in meters.
Using this manual method, the width and length of basin A measure 546 and 923 meters, respectively,
as illustrated in these images.
The northwest rim of basin C was completely covered by the emplacement of basin B.
This creates great uncertainty about the length of basin C. The left image illustrates a manual
measurement using the Google Earth ruler that shows a length of 598 meters for what appears
to be the inner dimension of the bay.
The image on the right shows a length of 667 meters using the templates provided by the
LiDAR visualization tool by Michael Davias.
In order to obtain the measurements based on the least squares fit, we need to identify
the points where the margins of the Carolina Bays are unambiguous.
The small circles represent the sample points.
Notice that no points are indicated where basin B touches basin A, and where basin B
intersects with basin C. Also, the northeast part of basin C has been destroyed by modern
construction, and no sample points were taken at that location.
Each sample point provides a set of coordinates.
The options in Google Earth are set to provide latitude and longitude of each point in decimal
notation for input into a Python program.
Processing the points with a least squares algorithm for fitting an ellipse provides
an image that shows how the points relate to the best fitting ellipse.
The program that displays the ellipse also provides the lengths of the major and minor
axes in meters.
Application of the least squares fit confirms the elliptical geometry of the three Carolina
Bays and provides the width and length of each ellipse.
These measurements are better than the single measurements obtained by using the ruler in
Google Earth because they are derived from the complete geometry of the bay from a multitude
of points.
This image shows the ellipses produced by the least squares method overlaid on the LiDAR
image of the three impact basins.
It is important to determine the reasons why single measurements using the ruler in Google
Earth can be wrong.
In the case of the basin labeled A, one of the points is significantly inside the elliptical
curve.
Although the point on the LiDAR image seems to be at the rim of the bay, the least squares
fitting of the ellipse indicates that the point is not where it should be.
A satellite image reveals the reason why the point is displaced from the elliptical curve.
A farm field along highway 917 has reclaimed some soil along the rim of the bay, and the
displacement of the rim makes the bay seem smaller on the LiDAR image.
Using the least squares method, it is not important that one point is out of place.
The overall geometry of the ellipse determines its width and its length, which correspond
to the minor and major axes of the ellipse.
Based on an experimental model, the glacier ice boulders that made these Carolina Bays
had diameters of one fifth of the bay length.
The width-to-length ratio of the ellipses corresponds to the trigonometric sine of the
angle of impact.
These bays are aligned toward Lake Michigan which is the convergence point of many Carolina
Bays.
The distance to Lake Michigan provides the flight distance and all this information is
sufficient to calculate the trajectory of the ice projectiles and their energy.
This table was calculated using the widths and lengths obtained by manual measurements
with the ruler tool from Google Earth.
The results reveal an inconsistency.
The time of flight for the creation of the basin labeled C is 35 seconds greater than
for basin B.
This means that basin C could have been created after basin B, which contradicts the geological
observation that basin B overlaps basin C and that basin C should have been emplaced
before B.
We can revise the calculations using the widths and lengths obtained by the least squares
method.
The most striking difference is the length of basin C, which is almost 100 meters more
than what was measured with the Google Earth ruler.
The times of flight calculated using the measurements from the least squares fitting procedure show
that the impact basin labeled C was made 12 seconds before basin B.
This is consistent with the sequence of emplacement that we can determine from the law of superposition.
Basins A and B were made almost contemporaneously, but they do not overlap.
The impacts that made these Carolina Bays were very powerful.
The kinetic energy for the formation of basin A was equivalent to 4.5 megatons of TNT.
Basin B and basin C were both in the two megaton range.
Each of these impacts created seismic vibrations of magnitude of 7.7 and above.
The strong tremors of these impacts liquefied unconsolidated soil and speeded up viscous
relaxation that transformed the inclined conical cavities into shallow depressions.
Application of the least squares method for fitting ellipses to Carolina Bays provides
a more objective method of determining the dimensions of the bays for forensic analysis.
The method is particularly suitable for dealing with overlapping Carolina Bays as demonstrated
in this example.
Thank you for joining me in the investigation of the Carolina Bays and the Younger Dryas
cataclysm.
I will continue to examine the Carolina Bays one bay at a time.
My book about the Carolina Bays is available at Amazon.
Please subscribe to my YouTube channel to be notified of future videos about the Carolina
Bays.