U.S. East Coast Faces Subsidence Risk

A large area of the U.S. East Coast is sinking. Within that extent, a smaller area of up to 3,700 km2 is sinking more than 5 mm per year. Subsidence can undermine building foundations, damage roads, gas and water lines, cause building collapse, and exacerbate coastal flooding—especially when paired with sea level rise due to climate change. Leonard O. Ohenhen and colleagues used measurements of vertical land motion rates derived from radar satellite datasets to estimate which areas, populations, and infrastructure within 100 km of the U.S. East Coast are at risk of land subsidence. Subsidence rates of 2 mm per year affect up to 2.1 million people and 867,000 properties on the East Coast, with several communities having over 60% of their land area sinking, including Norfolk, VA; Virginia Beach, VA; Baltimore, MD; and Queens, the Bronx, and Long Island in New York City. In these communities, several critical infrastructures such as roads, railways, airports, and levees are also affected by differing subsidence rates. For example, the JFK and LaGuardia airports in New York show several areas sinking at more than 2 mm per year, including the runways. Subsidence is often caused by groundwater extraction or sediment compaction. Some cities are rising, however, as the North American continent continues its long slow rebound from the weight of the glaciers that pressed the land downwards during the last glacial period, around 10,000 years ago. Today, around the Chesapeake Bay, a patchy mix of rising and falling land creates medium–high risk of differential subsidence, in which angular distortion caused by strain changes between two adjacent points can tear structures apart over time. The authors note that while there is no universally agreed-upon threshold of subsidence that raises concern for policymakers and citizens, continuous unmitigated subsidence on the U.S. East Coast could cause concern particularly due to the high population and property density and the complacency towards infrastructure maintenance.