What Caused the Mysterious Carolina Bays?

North Carolina Bay — The image above was taken from a NASA Earth Observatory post and shows several Carolina Bays near Bladen Lakes State Forest in North Carolina. Many here are still ponds, though some are dried up and used for agriculture. S.C. Department of Natural Resources

When the Wright Brothers gave us the engine-powered airplane in the early 20th century, they didn't just give us a new way to get around. Flight also gave us an entirely different perspective on the things around us (or the things below us). From above, people became tiny specs and fields looked like brown and green squares tilled together like a quilt. And before long, on the East Coast of the U.S., pilots began noticing something even more interesting.

What we once thought were just simple isolated ponds and wetlands along the Atlantic coast, began to be seen as a pattern of thousands of egg-shaped depressions that were oriented exactly the same way. From above, it almost looks like a giant from outer space sneezed all the way from Florida to New Jersey leaving shallow depressions in his wake.

The origins of these depressions is still a scientific mystery today, but these ponds are as important to the landscape now as they were millions of years ago.

The native Algonquins called these shallow depressions pocosins, but they are more commonly referred to as Carolina Bays because of the large number of these water pockets along the coast of North and South Carolina.

"Carolina Bay is the name given to most any wetland along the eastern Coastal Plain that has an elliptical shape and is often isolated from other bodies of water, such as small streams or rivers," says Kyle Barrett, associate professor of wildlife conservation at Clemson University in South Carolina. "Carolina Bays occur in low spots in the landscape, and because they typically only fill up from precipitation, they may dry out during the hot and dry portions of the year."

Pocosin Lakes National Wildlife Refuge is located in North Carolina's Inner Banks and is named for the pocosin peat wetlands that make up the majority of the protected habitat. It's home to animals like the black bear, alligator, two species of fox, bobcat, raccoon, coyote, opossum, beaver, river otter, mink and red wolf.
Wikimedia/(CC BY-SA 3.0)

An Ancient Answer

"Because the elliptical Carolina Bays are almost always oriented along a northwest to a southeast axis, and because they can be really concentrated on the landscape, it was suggested in the 1950s that a meteor shower formed all the Carolina Bays," Barrett says. To discover the true origins of the unusual formations, scientists took to carbon dating.

"There have been studies that use radiocarbon dating of buried organic sediments or other techniques to estimate their age," says Barrett. Turns out, Carolina Bays were not all formed at the same time. Some were formed tens of thousands of years apart. "Some wetlands are estimated to be over 100,000 years old, whereas others may 'only' be 15,000 years old or less."

This age difference led scientists to believe the bays were not caused by a meteor shower since they would be around the same age.

"There isn't any support for this [meteor shower] idea, since they don't have the same origin date, and no material has been found in the soil to suggest extraterrestrial formation," Barrett explains. So no, the Carolina Bays don't outline an otherworldly message, and scientists have not found remnants of space matter, to the chagrin of UFO theorists.

The next best hypothesis, while less cryptic, is the most likely answer: wind.

It's suggested that during the late Pleistocene period (2.5 million years ago), very strong southwesterly winds on ponds caused currents. Those currents washed against the southwest and northwest sides of ponds and resulted in sediment deposits on the northeast and southeast sides. Over time, they formed what we now know as the Carolina Bays.

Carolina bay wind formation — The most likely hypothesis for how the Carolina Bays were formed is from wind that created currents millions of years ago. (The bay is in blue.)
S.C. Department of Natural Resources

A Disappearing Pillar of the North American Ecosystem

At one point, there may have been as many as 200,000 Carolina Bays, but researchers say that nearly 97 percent of Carolina Bays have been impacted by agriculture and logging. Human impact hasn't just erased a piece of our geological past, it's also disrupted a delicate ecosystem of marshes that are important to many wetland species like salamanders and frogs in North America.

"Carolina Bays, along with other types of isolated wetlands, offer a wide range of environmental benefits. Many insects and amphibians are particularly abundant in these wetlands since Carolina Bays are without fish most of the time," Barrett explains. "Even 'terrestrial' species, such as birds and bats, are more abundant in patches of forest containing a Carolina Bay than equal-sized forested areas without one."

Wetlands, like the Carolina Bays, are also essential in preventing flooding and improving water quality, too. "Water quality is particularly important since many bays occur in agricultural areas where fertilizers and herbicides may be common," Barrett points out.

Unfortunately, many bays have been repurposed for human use like farmlands, the development of homes or businesses, or expanded into ponds. Any wetlands that aren't near a permanent stream or river, Barrett says, aren't protected by the Clean Water Act (CWA). This is because protecting thousands of small wetlands is a burden to landowners.

"For this reason, if you look at aerial imagery (on Google Maps, for example), you'll see loads of elliptical shapes along the coast of the Carolinas that used to be wetlands, but are now filled in for agriculture," says Barrett. The result is that wildlife takes on the burden of wetland loss.

However, Barrett suggests an expanded interpretation of the CWA could protect important wetland locations. "I don't know that every isolated wetland needs to be federally protected — that seems like it could create an unreasonable burden for many landowners. But I do think a broader interpretation of the CWA would help save many important isolated wetlands. States could also enact protections that better address local issues related to wetland loss."

Lake Waccamaw State Park — Lake Waccamaw is a 2,400-acre (971-hectare) Carolina Bay in North Carolina that's home to species of aquatic life found nowhere else.
North Carolina Division of Water Resources

Gems of the Eastern United States

Carolina Bays are just one example of Earth's natural mysteries that are important elements of our North American ecosystem. When land is filled in for pasture or crops, it doesn't just take away important habitat's wetland species; it also disrupts a balance of water flux and natural flooding protections, which is bad for our homes and livelihoods, too.

Furthermore, Barrett reminds us that without these wetland habitats, we miss out on some of the most biologically varied ecosystems in North America. "Many people don't have an opportunity to see the incredible amphibian and reptile diversity we have in the Southeast," he says. "But these wetlands, along with others in the region, are an incredibly important home to these species. Visiting these wetlands can open your eyes (and ears when the frogs are calling) to some of the underappreciated gems of the eastern U.S."