University of Mary Washington students investigate loss of Shark Tooth Island • Virginia Mercury
Think back to your childhood and imagine how cool it would have been to find a shark tooth in the sand.
An island in Virginia containing a collection of these fossils of the ocean’s largest predator could be gone in a matter of decades, preventing future generations from making such discoveries.
“I’ve been going to Shark Tooth Island to look for shark teeth since I was 12,” says John P. Tippett, an associate professor at the University of Mary Washington. “I’ve seen the island disappear over the course of my life. It’s a dramatic change from what was here when I was younger.”
Tippett and Kate Stoneman, a rising junior and research associate at UMW, are trying to predict when the island in the Potomac River — officially Hollis Island but colloquially known as Shark Tooth Island — will disappear and why. They say climate change is a key factor.
“This is a landmark that people love to visit,” Stoneman said. “I want to show them that climate change affects them on this personal level, whether they want it or not, because it does.”
Barrier islands
About an hour east of Fredericksburg near Westmoreland State Park, private Shark Tooth Island is a barrier island similar to the Outer Banks and northeastern parts of Virginia’s Eastern Shores.
Barrier islands are formed by tides and wind patterns that displace sand in certain areas, which builds up to form a sandbar that eventually becomes large enough to form an island.
The sand that forms the island supports the teeth of smaller sharks, which in the Potomac River may include spiny dogfish and bull sharks. Sharkshence the nickname of the island.
Because of the drifting nature with which barrier islands are formed, they can disappear quickly. When the island disappears, a natural resource is also lost that serves as a recreational site and can also maintain water quality and shorelines by absorbing wave energy, thus preventing tides from causing erosion.
“Unfortunately, barrier islands are disappearing at an alarming rate,” the National Oceanic and Atmospheric Administration in 2021.
The causes
Tippett and Stonemen look at the loss of the island from two perspectives: sea level rise and land subsidence.
By burning fossil fuels and releasing heat-trapping greenhouse gases, humans are increasing global temperatures and contributing to sea level rise.
“That will melt our land ice, melt our glaciers,” Stoneman said. “And the warming of our atmosphere will also warm our oceans. When water warms, it starts to expand. That will also increase the volume of the ocean.”
Humans are also involved in subsidence: they extract water from the Potomac Aquifer, the groundwater reservoir beneath the earth’s surface in the region.
“Sediment is now compacting in the space where water used to be,” Stoneman said. “That’s coming from industry, agriculture and coastal wells, all of which are sucking water out of our aquifers faster than the recharge rate allows.”
And last but not least, the island’s demise was a phenomenon of glacial isostatic adjustment, “a rather complicated term,” says Stoneman.
“During the last ice age, there was a huge ice sheet that covered northern North America from Canada to the Pennsylvania area, but not the island itself,” Stoneman said. He explained that the heavy ice sheet pushed the land in the north down, which in turn forced the land on the coast up.
“When the ice sheet finally melted, the land to the north wanted to move back to where it was before,” Stoneman continued. “The land on whose coast the island lies will now sink again.”
The research
Tippet and Stoneman’s research included summarizing previous findings, determining the area of land already lost, and conducting their own fieldwork, walking across the island in waders.
In 2013The United States Geological Survey found that Shark Tooth Island is being lost to sea level rise at a rate of about 1.8 millimeters per year.
Additional data from this USGS study, which examined the water level of the Potomac Aquifer, found that the land on which Shark Tooth Island sits is subsiding at a rate of 2.1 millimeters per year.
Combining those two numbers gives a total water level rise of about 3.9 millimeters per year, or “1.5 inches every 10 years,” Stoneman said.
To confirm the land loss, Stoneman added that she reviewed images of the island from 1994 to 2024 and calculated how much vegetation was present in each image, finding that the island lost about 32.4 acres in those 30 years.
“That was kind of the big launch of our project to really show that the island is getting a lot smaller,” Stoneman said.
To then calculate the year in which the island would be completely submerged, Stoneman and a classmate went to the island for three hours in October and then for an hour in May with another classmate. They were equipped with a theodolite – the surveying device you usually see along roads – and a long pole to find the highest point on the island.
But unlike surveying flat, paved roads, the two students had to walk through vegetation consisting of the invasive reed species, which they had to knock down with the collapsible pole, then contend with pollen, avoid an old hunting blind and an old building, and leave the tree line before reaching a clearing where they could take the measurements.
“I asked for a machete. Mr. Tippet didn’t give me one,” Stoneman said. “It was a lot, but it was important. It was important to what we were doing, so it would get done.
So what is the answer?
“We’re crunching the numbers,” Tippet said, adding that the highest points they found were “a few inches” above mean tide, the highest point to which water rises before flowing back out to sea.
“And… we see a relative sea level rise of 3.8 cm every 10 years,” he continued. “That gives us a rough idea.”
The dynamic nature of barrier islands makes matters worse. Increasingly intense rainfall could wash more debris into the sea, which “maybe” flattens the island again, but sea level rise could happen faster and engulf the island.
“But when you look at the current data, it’s clear that the island is losing,” Tippett said.
State officials are aware of the loss of barrier islands, marshes and dunes. Before appointing a chief resilience officer to better coordinate flood issues in the last legislative session, the state created the Virginia Coastal Resilience Master Plan, which is scheduled to be updated later this year.
By 2080, the loss of beach and dune landscape, including that in the Eastern Shore region, “is expected to reach 3,800 acres, representing a loss of 38% of existing habitat,” according to the plan.
However, the research is currently not aimed at influencing policy, Tippet said.
“There’s a lot of misinformation, a lot of people who think climate change isn’t real or isn’t that bad,” Tippet said. “We’re trying to address that part here. We can’t make change at the policy level until the people who vote actually get behind it.”
