Fire & Water

A Bob’s view on Carolina Bay formation...

In that there has been an increasing interest in the Carolina Bays as possible impact features I felt that the reader might like to know of my own opinion on how these features came to be. Simply put, I believe that these near flat, shallow, structures were formed by terminal flare induced steam explosions of wet exposed ground. The wet spots could have been beaver ponds, springs, marshes, wet weather ponds, slow flowing creeks, and so on. The principal requirement here is that the water on the ground be exposed sufficiently to the sky so as to receive enough radiant energy from the incoming bolide to produce a violent phase change or steam explosion. A geologist might think of these features as "top induced maars" as the structures of Carolina Bays have similarities to conventional maars, which are produced by Earth mantle heat induced steam explosions.

It is noteworthy that Prouty thought that steam explosion could be a factor in Carolina Bay formation, however conventional wisdom of the time insisted on a projectile of some fashion striking the surface and this is where Prouty expected to see energy liberated which could produce a steam explosion. In my scenario the intense radiation (much of it in the infrared) followed by the over-pressure pulse from the blast wave suffices to give the Bays their unusually regular shape.

An interesting thought here is that research on conventional or "bottom induced maars," which occur within a similar sandy substrate, might provide a benchmark of sorts for evaluating the likelihood of the Bays being formed this way. The key, I think, is getting researchers to look at the whole affected coastal area as potentially influenced by impact. In other words it is also important to look and take samples outside of the Bays.

To goad a bit, I will point out a few finds which tend to support this line of reasoning:

This image is not of a Carolina Bay. It is rather a photo of what Roy Gallant refers to as "one of the small, neat oval bogs that Kulik erroneously presumed to be secondary craters" that occur within the affected area of the Tunguska impact site. These features are apparently thermokarsts that have been modified by the impact event--possibly by steam explosion. I am told that thermokarst depressions outside of the affected area are not of such regular shape. Click on the image for a good overview of the Tunguska event but please come back.

This is a photo of Cerro Colorado volcano in the Pinacate Volcanic Field of northern Mexico. It is a maar volcano with a broad crater and low rims formed by hydrovolcanic processes. Prevailing winds blew toward the southwest at the time of eruption to form the high point of the rim. As above, you can click the image to find out some more about hydrovolcanic processes but if you have a slow link, you may want to turn off automatic loading of graphics before you do.

You guessed it--more maars. This field consists of over seventy-eight explosion craters and covers an area of around eighty square miles. The structures vary in size from a few hundred meters in diameter to over a kilometer. One of the Carolina Bay like aspects here is that the rims of these craters often overlap. Older circular pits scattered within the area are mostly filled with dust and ash, resulting in shallow floors often only a few tens of meters deep. The younger pits have much steeper rims and crater walls from one to two hundred meters deep. Some of these pits have thick forests within them. Seven of the craters have saltwater lakes.

The maars were produced by violent explosions of volcanic gases and steam at or near the surface. This activity occured over a very short period of time with some explosions being almost simultaneous. There are only three small lava flows in the whole field.

This image is also clickable and will take you to Volcano World, where you can fetch a larger image.

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