NASA Images Show Where US East Coast Is Sinking

The U.S. East Coast faces a future threatened not only by rising sea levels but also by sinking of the land itself, researchers told Newsweek.

NASA images reveal the extent to which the coast is collapsing, with some areas dropping by several millimeters per year. Using satellite data and ground-based GPS sensors, a NASA-funded team of scientists at Virginia Tech's Earth Observation and Innovation (EOI) Lab found that the land that major cities such as New York, Baltimore, and Norfolk, Virginia, are built on sank by 1 to 2 millimeters each year between 2007 and 2020.

Some counties in Delaware, Maryland, South Carolina and Georgia sank at double or triple that rate, according to a paper in the journal PNAS Nexus.

Leonard Ohenhen, a Ph.D. student at Virginia Tech and one of the paper's authors, told Newsweek, "In this research, we analyzed satellite radar data to assess how land subsidence increases the vulnerability of communities, properties and infrastructure to coastal hazards. Our major findings show that between 2,000 to 74,000 square kilometers of land area, which is home to 1.2 to 14 million people and 476,000 to 6.3 million properties, are sinking at a rate of 1 to 2 millimeters per year.

"This sinking land affects more than half of the infrastructure in several major cities, putting them at an increased risk of flooding and other coastal hazards," he said.

This could exacerbate the effects of rising sea levels, estimated to exceed one foot across most U.S. coasts by 2050 and lead to increased levels of tidal flooding and damage to homes and infrastructure.

"Subsidence is a pernicious, highly localized, and often overlooked problem in comparison to global sea level rise, but it's a major factor that explains why water levels are rising in many parts of the eastern U.S.," Ohenhen said in a NASA Earth Observatory post sharing the maps.

The map above highlights the variability in the rising and falling of land—or vertical land motion—across much of the East Coast. Areas shown in blue subsided between 2007 and 2020, with the darker blue areas sinking the fastest. The areas shown in dark red rose the fastest. The satellite data in the map has an average spatial resolution of 50 meters per pixel, which is better than previous maps based only on ground-based sensors.

"The good news is that subsidence is a problem that we can slow at local scales to some degree," Manoochehr Shirzaei, a co-author of the paper and director of the EOI Lab, said in the NASA Earth Observatory post.

The mid-Atlantic coast is sinking more significantly than the northeastern coast, as a result of ancient ice sheet movements. The Laurentide ice sheet coated most of North America thousands of years ago, ending south of New Jersey, and pushed down the northern lands under its immense weight. When the sheet began melting 12,000 years ago, the northern land began to rise back up and the mid-Atlantic coast started to sink.

This process of land shifting like two sides of a scale is known as glacial isostatic adjustment and is likely responsible for much of the sinking seen along the coast. Other factors driving the sinking in parts of Maryland and Virginia may be due to the withdrawal of groundwater. Subsistence in coastal Georgia, South Carolina and North Carolina may also be driven by the presence of dams that are blocking sediment that would usually accumulate in coastal lands.

Charleston, South Carolina, is one of the fasting sinking cities, subsiding at a rate of about 4 mm every year. This sinking, compounded by rising sea levels, could be catastrophic for the city, much of which is less than 10 feet above sea level already.

"It definitely will exacerbate the vulnerability of sea level rise in most coastal communities. Most communities will face the impacts of sea level rise sooner, due to the compounding effects of the sinking land and the sea level rise," Ohenhen said in the NASA Earth Observatory post.

Charleston has seen an increased frequency of tidal flooding in recent decades, leading the city to now consider building an 8-mile seawall to protect it from storm surges.

The researchers hope to map even more of the U.S. coast and how much it's sinking, with the Gulf Coast next on their list.

"Our long-range goal is to map all of the world's coastlines using this technique," Shirzaei said. "We know that planners in several U.S. cities are already using our data to make our coastlines more resilient, and we want cities all over the world to be able to do be able to do the same."

Update 2/21/24, 2:25 p.m. ET: This story was updated with comments from Viriginia Tech's Leonard Ohenhen.

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