Washington, DC predicted to sink 6 inches or more by 2100

Washington DC is sinking
CC BY 2.0 Library of Congress

A detailed geological-drilling study warns of threats to the region's monuments, roads, wildlife refuges, and military installations.

For more than half a century tide gauges have indicated that the Chesapeake Bay’s sea level has been rising twice as much as the global average and faster than anywhere else on the East Coast. Geologists have hypothesized that the land in this part of the country was once pushed up by a prehistoric ice sheet to the north and is now settling back down since the ice melted.

Now a new study by a group of geologists from the University of Vermont and the U.S. Geological Survey have confirmed that hypothesis through research using extensive drilling in the coastal plain of Maryland. The study concludes that, indeed, the land under the Chesapeake Bay is sinking quickly and the researchers project that Washington, D.C. could drop by six or more inches in the next century.

"This falling land will exacerbate the flooding that the nation's capital faces from rising ocean waters due to a warming climate and melting ice sheets," notes a press statement for the study, "accelerating the threat to the region's monuments, roads, wildlife refuges, and military installations."

Washington's worries come courtesy of what’s known as a "forebulge collapse." During the last ice age, a massive North American ice sheet placed so much weight on the surface of the planet that the mantle rock began to flow slowly out and away from underneath the ice, causing a bulge under the Chesapeake Bay region. When the ice sheet began melting 20,000 years ago, the bulge began to sink back down.

"It's a bit like sitting on one side of a water bed filled with very thick honey," says Ben DeJong, the lead author on the new study, "then the other side goes up. But when you stand, the bulge comes down again."

For the study DeJong and his team drilled seventy boreholes up to a hundred feet deep on the Chesapeake's eastern shore. THey then studied the layers of sediment deep from the earth using high-tech techniques to figure out the age of various media in each layer. By feeding this data through high-resolution LiDAR and GPS map data, the team was able to create a detailed 3D portrait of both the current and previous post-glacial geological periods in the Chesapeake, winding back to several million years ago. This longer view gives the geologists confidence that they have a "bullet-proof" model, DeJong says, showing that the region today is early in a period of land subsidence that will last for millennia.

"Right now is the time to start making preparations," said DeJong. "Six extra inches of water really matters in this part of the world." Not to mention how much more the land might subside in the upcoming 1,000 years.

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