Dr. Eugene M.
U.S. Geological Survey
2255 North Gemini Drive
Flagstaff, Arizona 86001
Dear Dr. Shoemaker:
Enclosed is another barrage of Carolina Bay information. "A Re-evaluation of the Extraterrestrial Origin of the Carolina Bays" (1975) is a research paper I learned of only recently; the authors make several valid points. Unfortunately, they evoked "Tunguska craters" (following W.K. Hartman's "Moons and Planets" 1973) to illustrate the geomorphic results of low altitude shock waves which they believe sculpted the Carolina Bays. Though more recent investigators attribute the Tunguska depressions to permafrost melt, this does not negate the premise of Eyton and Parkhurst that the Bays were formed by fragments of Tunguska like stuff coupling energy to the ground in a blast wave fashion.
Disregarding dynamics, the energy to bring a volume of permafrost through the transition to a liquid state sufficient to cause slump or compaction is about 1/7 of what it would take to bring an equal volume of wet sandy soil to a steamy explosive state. I suspect, however, that wet soil would absorb radiant and mechanical heat from a blast more efficiently than could frozen ground, and so would respond more violently to a given blast type energy input.
The physical common denominator of areas where bays are found seems
to be wet plastic soil. I believe it was the abrupt phase change
of water to steam that excavated these shallow features. This would
occur in three steps with intervals determined by the impactor's terminal
flare height. Step one is the arrival of radiant energy from the
phase change which produced the terminal volatilization of the impactor.
This would elevate the wet soil temperature to a degree dependent upon
radiant energy yield, the pulse width or duration of liberation, and radial
distance from the
source. Step two is the arrival of a blast or over-pressure wave (the interval between S1 and S2 increasing with terminal flare height). Step 3 is the arrival of the ballistic wave which, if steps 1 and 2 were within limits (the terminal flare was low enough to produce an explosive phase change in wet soil) would disperse soil elevated in the steam explosion.
Assuming this three step process would yield a bay like structure the remaining problem is getting the terminal flare of the impactor to occur close enough to the ground. I believe this trick could be accomplished by a comet like mass density object of sufficiently large mass and low impact velocity. The paper by Levin and Bronshten ("The Tunguska Event and Meteors with Terminal Flares," included) seems to allow such arrivals.
I am curious to know if you think the above a feasible scenario. In the midst of preparing this packet I received correspondence from Leroy Ellenberger indicating that he had written to you of Gault's idea that the Bays could be formed by ejecta from a glacial impact. This would seem a needless complication if large terminal flares can occur within a few kilometers of Earth's surface.
Robert E. Kobres