Richmonder Kirk Millikan has visited state parks all around Virginia, including Bear Lake and Twin Lakes. He recently noticed something interesting about these lakes: They’re manmade.
Virginia has built plenty of man-made dams (also known as reservoirs) to generate electricity, and help with flood control and water storage over the years — but only has two natural lakes.
“And I’m curious, why does Virginia only have two natural lakes?” Millikan asked.
Curious Commonwealth went searching for answers and got to the bottom of this mysterious query — by heading southwest to one of the two lakes: Mountain Lake in Giles County.
Mountain Lake may be familiar to film buffs for its central role in the 1987 film Dirty Dancing: It was one of the movie’s primary filming locations. The naturally-formed lake is surrounded by a rolling Allegheny Mountain landscape and hardwood forests.
A lot of the movie lore is still alive there today: Visitors can rent cabins, dine at the lodge and even partake in Dirty Dancing-themed weekends complete with dance lessons.
Chester “Skip” Watts, an engineering geologist and Radford University professor emeritus, knows a lot about how this picturesque lake outside Blacksburg was formed. He first became interested in Mountain Lake when he was a student at Virginia Tech. One of his professors outlined a list of theories because, in the 1970s, it was a mystery.
“And when I heard that it was starting to experience very low water levels, my students and I just became interested in what might be causing that?” he said.
Watts and a team of other researchers — including students from Virginia Tech, Radford and Kent State — have been studying this lake for decades.
“We did just about every kind of geologic study you can imagine,” Watts said. “This is probably one of the most studied sites in all of this part of Virginia.”
Watts and his team have uncovered evidence showing a landslide on the north end of Mountain Lake several thousand years ago formed a natural dam that created the lake.
There used to be a gorge here, too, with steep sides surrounding what used to be a meadow with a stream running through it instead of a lake. During the landslide, boulders, rocks and sediment all slid downhill to fill the gorge.
“The walls collapsed down into that gorge some roughly 6,000 years ago, and that landslide created a natural landslide dam that backed the water up,” Watts said.
There are still multiple streams feeding Mountain Lake today, though some are just a trickle of water at this point. Watts said research has determined that some of the water is escaping through the dam.
“A landslide dam tends to be a leaky dam,” Watts said. “Whereas a man-made dam is going to usually be concrete or it could be compacted Earth, very carefully built and tends to leak very, very little.”
Hiking along to another area at Mountain Lake, Watts points to other important evidence of the landslide. Trudging through a forest, piles of large white quartz sandstone boulders come into view.
“We're about to go through a crack in the wall and emerge in a different world,” Watts said.
This area is known as the Garden of the Gods: a labyrinth of sandstone blocks strewn with bright ferns and moss. The rocks form a sort of maze — and Watts said students have even named its streets and alleys.
“One of the geomorphic terms for a landscape like this is a rock city,” Watts said. “And you can imagine these rock blocks are like buildings, and these gaps between them are streets and alleys.”
Newer technology has allowed Watts’ team to make what’s called a bare earth model, stripping away vegetation to show just the rocks and soil. Watts said it's obvious the rock layers are all connected, and that rocks higher up had broken off and slid downhill.
“That was kind of like the final definitive piece of evidence,” he said.
Mountain Lake is also situated in one of the few seismically active areas in Virginia, so Watts said it’s possible that an earthquake triggered the landslide. Until 2011, the area was the site of Virginia’s largest earthquake.
“It takes a very unique set of circumstances to form a natural lake, and we just right here happen to have sort of the perfect conditions, geologically, on top of each other,” he said.
Watts said the natural landscape, the landslide and other factors like the natural bowl shape of the valley where the lake is now have all contributed to the formation of the lake here.
An efficient network of streams and rivers
Christopher “Chuck” Bailey, a structural geologist and department chair at William & Mary, said Virginia’s geography helps explain why the state has only two natural lakes.
“Virginia is a landscape that has been sitting here being eroded for millions and millions and millions of years,” Bailey said. “And when you do that, what happens is stream networks slowly erode away things, and then things that are depressions or enclosures are oftentimes then connected to the stream network and drained.”
There are just under 50,000 miles of rivers running through the commonwealth, according to theNational Wild and Scenic Rivers System, which Matt Heller, Virginia’s state geologist, agrees is one of the key reasons why Virginia has so few naturally-formed lakes.
“We've developed this really nice network of river valleys and a network of streams and rivers that are pretty efficient at carrying water out to their ultimate destinations,” Heller said. “So it's hard for a river to get clogged up because they're constantly carrying water and sediment away, and they seem to do a very good job at that.”
Bailey adds at the end of the last Ice Age about 12,000 years ago, there were no glaciers in Virginia. That means no glacial lakes – in contrast to states like Maine or Minnesota, which is known as “the land of 10,000 lakes.”
“Those regions were glaciated 20,000 years ago … and glaciers have a way of sculpting the landscape that creates little bowls and depressions and knobs and hills,” Bailey said. “And then when the glaciers melt, these are low spots, and voila: you make lakes.”
Heller said other states with more natural lakes than Virginia, like Utah and Nevada, exist in areas where the Earth’s crust has pulled apart, creating low-lying areas called basins. In Florida, underlying limestone rock has dissolved to create natural lakes there.
He added that there are sinkholes in southwest Virginia formed by dissolved limestone, but they’re not large enough to be considered lakes — though he added there’s not a clear, consistent distinction between a lake and a pond.
“Our limestone layers in the western part of Virginia are folded, so we don't have these big, sort of flat limestone layers like they do in Florida,” Heller said.
The possibility of sinkholes playing a role in Mountain Lake’s formation has been studied somewhat, but so far hasn’t been proven or ruled out.
A great dismal lake
The other natural lake in Virginia is Lake Drummond. Dramatically different from Mountain Lake, Drummond sits in the middle of a low-lying area called the Great Dismal Swamp, where the water table intersects the ground’s surface.
The swamp encompasses a large area of southern Hampton Roads and parts of northeastern North Carolina. It’s about 20 miles from north to south, and 13 miles from east to west.
Bailey said it was not an area early settlers liked. In the 19th century, it was home to marginalized groups — including enslaved people who ran away in search of freedom.
“In fact, it was viewed to be kind of the place where there was miasma and bad air and bad water, and a place you couldn't do much of anything with. Why? Because it was wet all the time,” Bailey said. “So there was a lot of energy spent from the early days of the US Republic to try to drain the swamp.”
Bailey said the lake is about two-and-a-half miles across and about six feet deep.
“Your feet would sink quite a ways into the sediment, because it’s very porous. It's a mixture of the peat and other things, and there's a lot of water in it,” Bailey said. “So it's not like you would hit a hard bottom. You just basically slip — really, subside — into the mud or the ooze, the ick.”
While Bailey said more research is needed to say for sure what led to the creation of Lake Drummond several thousand years ago, the most plausible theory is a peat fire, slowly burning over a number of years.
“That potentially could create a shallow depression that would then slowly fill with the groundwater seeping back in,” Bailey said.
He pointed to research published in 2023 by the US Geological Survey that showed much higher levels of charcoal in layers of the natural swamp that are 4,000 to 7,000 years old. The high level of charcoal in these layers indicates there were likely a lot of fires in the area during this time.
“In some ways, I think we have a much better history of the Great Dismal Swamp as a feature than we do of actually the lake itself,” Bailey said.
What led to the formation of Lake Drummond is an ongoing curiosity left for researchers of Virginia’s lakes to dive into.
This story was produced as part of the VPM News series Curious Commonwealth.
