Research Says Washington, D.C. Is Slowly Sinking Into the Ocean

July 30, 2015

New research says the land under the Chesapeake Bay region is sinking and projects that Washington, D.C., could drop by six or more inches in the next century — adding to the problems of sea-level rise.

The research says the falling land in the Chesapeake Bay region, including Washington, D.C., would exacerbate the flooding that the nation’s capital faces from rising ocean waters — accelerating the threat to the region’s monuments, roads, wildlife refuges, and military installations. The research was conducted by geologists at the University of Vermont and the U.S. Geological Survey. Its results were presented online July 27 in the journal GSA Today.

The researchers note that for 60 years, tide gauges have shown that sea level in the Chesapeake is rising at twice the global average rate and faster than elsewhere on the East Coast. Geologists have been hypothesizing that land in this area, pushed up by the weight of a pre-historic ice sheet to the north, has been settling back down since the ice melted.

The new study — which uses data gathered from extensive drilling in the coastal plain of Maryland — confirms this hypothesis, and provides an estimated rate of the sinking.

Researchers also say their detailed field data make clear that the land sinking around Washington, D.C., is not primarily driven by human influence, such as groundwater withdrawals. Rather, the sinking is a long-term geological process that will continue for tens of thousands of years, independent from human land use or climate change.

‘Forebulge Collapse’

The land sinking comes from what geologists call “forebulge collapse.” During the last ice age, a mile-high North American ice sheet that stretched as far south as Long Island, New York, piled so much weight on the Earth that underlying mantle rock flowed slowly outward, away from the ice. In response, the land surface to the south, under the Chesapeake Bay region, bulged up. About 20,000 years ago, the ice sheet began melting, allowing the forebulge to sink again.

“It’s a bit like sitting on one side of a water bed filled with very thick honey,” said Ben DeJong, the lead author on the new study, who conducted the research as a doctoral student at University of Vermont’s Rubenstein School of Environment and Natural Resources with support from the U.S. Geological Survey, “then the other side goes up. But when you stand, the bulge comes down again.”

The new research provides the first high-resolution data from the same latitude as Washington, D.C., DeJong said, of how this forebulge has subsided, and will continue to. “Until recently, the age of the thing was really poorly constrained,” he said.

“Right now is the time to start making preparations,” said DeJong. “Six extra inches of water really matters in this part of the world.”

Source: University of Vermont

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