Alien Meteors, or Just Plain Wind and Water?
A Story of the Formation of Carolina Bays by Paige Brown, Museum Blogger-in-Residence.
An aerial view of the Atlantic seaboard from Florida to New Jersey, especially if you are privy to super-human infrared vision, reveals a series of rather extraterrestrial-looking oblong depressions in the landscape. What look like crater holes in the landscape are filled with water, sand and/or vegetation. These natural, elliptical depressions in the land, bordered by rims of sand, are known as Carolina Bays, thanks to the bay trees (as in the bay leaves you might use in your beef stew) and other rich wetland vegetation that often grow inside them. Carolina bays vary significantly in size, while as oblong circular structures they are typically aligned in a particular direction depending on their location. The egg-shaped Carolina bays on the Atlantic Coastal Plain typically have one end pointing northwest and the other southeast. Some of the more familiar Carolina bays in North Carolina include Lake Waccamaw, the largest of the Carolina bay lakes, and Jones Lake. While these bays are filled with water, other Carolina bays have been drained, by either human or natural forces, and are now filled with vegetation and wildlife.
While many of the natural Carolina bays are familiar state park attractions, the origins of these “pocks” on the land surface are rather mysterious. Some might say they bear a resemblance to lunar craters, the cup-like depressions on the surface of the moon caused by impact events. The Carolina bays themselves have been called “otherworldly,” with claims that the wetland depressions might have been created once upon a time by a great meteor shower.
However, says Dr. Lee Phillips, associate professor of geology at the University of North Carolina at Pembroke, while fantastic and otherworldly stories of science might gain lots of attention, especially in the news, real science often provides much simpler explanations. Phillips gave a talk about Carolina bays at the North Carolina Museum of Natural Sciences on Saturday, June 1, in the Windows on the World classroom on the 3rd floor of the Museum’s main building. Phillips talked about the climate conditions that have helped form and shape Carolina bays throughout the centuries.
The Carolina bays were first recognized in the 1800’s. With the advent of aviation and human flight, scientists were able to get a better view of the extent of Carolina bays along the coast of North Carolina from the air. Since that time, scientists have suggested many different hypotheses as to what caused the formation of these natural depressions rimed with sand. These hypotheses range from the work of extraterrestrial meteors, to the action of wind on sand structures, to the work of both wind and wave action on the loose sediments of the coastal plain.
“There is a lot of evidence that these things have no causal links to impact craters,” said Phillips during his Saturday talk. “We don’t find any meteor fragments whatsoever. There is no evidence of extraterrestrial material within a Carolina bay. It would have to be a HUGE meteor shower coming in and spraying many landscapes simultaneously to produce the observed similarity in orientation of these bays across the range of their occurrence. So that doesn’t make any sense.”
So what does make sense, according to scientific data collected by Phillips and others, for the origin and formation of Carolina bays? Phillips and other researchers who study the Carolina bays have used core sampling techniques, radioactive carbon dating and other dating techniques to find out how old the Carolina bays are. They have also constructed small-scale physical models of the bays in the laboratory to see how water and wind forces might have formed these bays in landscapes dominated by loose sediments and sand.
What Phillips and other researchers have found can officially lay to rest outlandish hypotheses of Carolina bay formation involving meteor showers and large whales. The Carolina bays vary rather significantly in their ages, ranging from 130,000 years old to 8,000 years old or less. They do not date from a single specific time period, meteor shower or other discrete event. The dates of Carolina bay growth also correspond to times when the earth was relatively warm and free of ice, when wind and lapping Atlantic water could deposit and shape sand on the North Carolina coastal plain. The Carolina bays seem to have formed predominantly in flat landscapes composed of sand, sandstone, limestone and other sedimentary materials.
From his research on Carolina bays, Phillips has found evidence that Carolina bays were formed as wind swept over sandy landscapes and lakes on the coastal plain. Late Pleistocene winds sweeping up and around the Atlantic coast from the south shaped lakes sitting in sandy landscapes into ovals. These elliptical structures ended up being oriented differently depending on the direction that the wind was coming from.
Phillips has also found that the times when Carolina bays formed and grew seem to correspond to climate transitions in Earth’s history, or times when the climate was changing. For example, Phillips and his group dated one sand pit at Jones Lake to 8,500 years ago, or a time when a cold snap reduced vegetation on the coastal plain of North Carolina, and wind blew and deposited sand easily across the landscape. On the other hand, Carolina bays seem to stop growing when sand is held down by rich vegetation, such as when the bays are drained of water and filled with vegetation. Available sands on the Atlantic coastal plain appear to be critical for the formation of Carolina bays.
“It is amazing to think about this landscape without all the pine trees,” Phillips said. “The evidence that we have from the research that I’ve done and what many others have done supports a mechanism of formation of Carolina bays dominated by the movement of sand by wind and water.”
So much for meteors from outer space. The Carolina bays, with their associated rich wetland ecosystems, were formed by the simple action of wind and water on the sedimentary landscape of our continent’s coast. Now that we understand how they were formed, it is equally important to preserve these natural land structures in the future. Unfortunately, largely due to farming activities, fewer than half of North Carolina’s natural Carolina bays still remain. Some bays have been drained, while others have gradually eroded away. Carolina bays act as natural reservoirs for water, which in turn promote boggy vegetation and rich wetland ecosystems. And these structures are not only important as wildlife refuges; the rim sands that border the bays are important sources of climate history for geologists and other scientists.
Who knew Saturday science could be so fun, and so environmentally important?