susceptible to subsidence — East Coast land continues to collapse at a worrying rate It’s steadily sinking or subsiding, which is destabilizing levees, roads, and airports.
Matt Simon, WIRED.com – Jan 6, 2024 12:17 pm UTC Enlarge / Lower Manhattan and One World Trade Center in New York City are reflected on a monument as the sun rises on December 22, 2023, as seen from Jersey City, New Jersey. Gary Hershorn / Getty Images reader comments 163
Unless youre sinking into quicksand, you might assume that the land beneath your feet is solid and unmoving. In actual fact, your part of the world may well be undergoing subsidence, which is where the ground collapses as sediments settle or when people over-extract groundwater. New York City is sinking, too, due to the weight of all those buildings pushing on the ground. In extreme cases, like in Californias agriculturally intensive San Joaquin Valley, elevations have plummeted not by inches, but by dozens of feet.
Last year, scientists reported that the US Atlantic Coast is dropping by several millimeters annually, with some areas, like Delaware, notching figures several times that rate. So just as the seas are rising, the land along the eastern seaboard is sinking, greatly compounding the hazard for coastal communities.
In a follow-up study just published in the journal PNAS Nexus, the researchers tally up the mounting costs of subsidencedue to settling, groundwater extraction, and other factorsfor those communities and their infrastructure. Using satellite measurements, they have found that up to 74,000?square kilometers (29,000 square miles) of the Atlantic Coast are exposed to subsidence of up to 2 millimeters (0.079 inches) a year, affecting up to 14 million people and 6 million properties. And over 3,700 square kilometers along the Atlantic Coast are sinking more than 5 millimeters annually. Thats an even faster change than sea-level rise, currently at 4 millimeters a year. (In the map below, warmer colors represent more subsidence, up to 6 millimeters.) EnlargeCourtesy of Leonard Ohenhen
With each millimeter of subsidence, it gets easier for storm surgesessentially a wall of seawater, which hurricanes are particularly good at pushing onshoreto creep farther inland, destroying more and more infrastructure. And its not just about sea levels, says the studys lead author, Leonard Ohenhen, an environmental security expert at Virginia Tech. You also have potential to disrupt the topography of the land, for example, so you have areas that can get full of flooding when it rains. Advertisement
A few millimeters of annual subsidence may not sound like much, but these forces are relentless: Unless coastal areas stop extracting groundwater, the land will keep sinking deeper and deeper. The social forces are relentless, too, as more people around the world move to coastal cities, creating even more demand for groundwater. There are processes that are sometimes even cyclic, for example in summers you pump a lot more water so land subsides rapidly in a short period of time, says Manoochehr Shirzaei, an environmental security expert at Virginia Tech and coauthor of the paper. That causes large areas to subside below a threshold that leads the water to flood a large area. When it comes to flooding, falling elevation of land is a tipping element that has been largely ignored by research so far, Shirzaei says.
In Jakarta, Indonesia, for example, the land is sinking nearly a foot a year because of collapsing aquifers. Accordingly, within the next three decades, 95 percent of North Jakarta could be underwater. The city is planning a giant seawall to hold back the ocean, but itll be useless unless subsidence is stopped.
This new study warns that levees and other critical infrastructure along the Atlantic Coast are in similar danger. If the land were to sink uniformly, you might just need to keep raising the elevation of a levee to compensate. But the bigger problem is differential subsidence, in which different areas of land sink at different rates. If you have a building or a runway or something thats settling uniformly, its probably not that big a deal, says Tom Parsons, a geophysicist with the United States Geological Survey who studies subsidence but wasnt involved in the new paper. But if you have one end thats sinking faster than the other, then you start to distort things. Page: 1 2 Next → reader comments 163 WIRED Wired.com is your essential daily guide to what’s next, delivering the most original and complete take you’ll find anywhere on innovation’s impact on technology, science, business and culture. Advertisement Channel Ars Technica ← Previous story Next story → Related Stories Today on Ars
