Subsidence risk on the U.S. East Coast
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VERTICAL LAND MOTION ON THE US EAST COAST (LEFT); PRIMARY, SECONDARY, AND INTERSTATE ROADS IN HAMPTON ROADS, VA (TOP RIGHT), AND JFK AIRPORT (BOTTOM RIGHT). NOTE THAT THE YELLOW ORANGE AND RED AREAS ON THESE MAPS INDICATE SINKING.
view moreCREDIT: OHENHEN ET AL.
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.
JOURNAL
PNAS Nexus
ARTICLE TITLE
Slowly but surely: Exposure of communities and infrastructure to subsidence on the US east coast
ARTICLE PUBLICATION DATE
2-Jan-2024
Study: From NYC to DC and beyond, cities on the East Coast are sinking
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THE ABOVE GRAPHIC FEATURES: A SPATIAL MAP OF VERTICAL LAND MOTION ON THE EAST COAST (LEFT PANEL); PRIMARY, SECONDARY, AND INTERSTATE ROADS ON HAMPTON ROADS, NORFOLK, AND VIRGINIA BEACH, VIRGINIA (TOP RIGHT PANEL); AND JOHN F. KENNEDY INTERNATIONAL AIRPORT, NEW YORK (BOTTOM RIGHT PANEL). THE YELLOW, ORANGE AND RED AREAS ON THESE MAPS DENOTE AREAS OF SINKING.
view moreCREDIT: IMAGES BY LEONARD OHENHEN.
Major cities on the U.S. Atlantic coast are sinking, in some cases as much as 5 millimeters per year – a decline at the ocean’s edge that well outpaces global sea level rise, confirms new research from Virginia Tech and the U.S. Geological Survey.
Particularly hard hit population centers such as New York City and Long Island, Baltimore, and Virginia Beach and Norfolk are seeing areas of rapid “subsidence,” or sinking land, alongside more slowly sinking or relatively stable ground, increasing the risk to roadways, runways, building foundations, rail lines, and pipelines, according to a study published today in the Proceedings of the National Academies of Sciences.
“Continuous unmitigated subsidence on the U.S. East Coast should cause concern,” said lead author Leonard Ohenhen, a graduate student working with Associate Professor Manoochehr Shirzaei at Virginia Tech’s Earth Observation and Innovation Lab. “This is particularly in areas with a high population and property density and a historical complacency toward infrastructure maintenance.”
Shirzaei and his research team pulled together a vast collection of data points measured by space-based radar satellites and used this highly accurate information to build digital terrain maps that show exactly where sinking landscapes present risks to the health of vital infrastructure. Using the publicly available satellite imagery, Shirzaei and Ohenhen measured millions of occurrences of land subsidence spanning multiple years. They then created some of the world's first high resolution depictions of the land subsidence.
These groundbreaking new maps show that a large area of the East Coast is sinking at least 2 mm per year, with several areas along the mid-Atlantic coast of up to 3,700 square kilometers, or more than 1,400 square miles, sinking more than 5 mm per year, more than the current 4 mm per year global rate of sea level rise.
“We measured subsidence rates of 2 mm per year affecting more than 2 million people and 800,000 properties on the East Coast,” Shirzaei said. “We know to some extent that the land is sinking. Through this study, we highlight that sinking of the land is not an intangible threat. It affects you and I and everyone, it may be gradual, but the impacts are real.”
In several cities along the East Coast, multiple critical infrastructures such as roads, railways, airports, and levees are affected by differing subsidence rates.
“Here, the problem is not just that the land is sinking. The problem is that the hotspots of sinking land intersect directly with population and infrastructure hubs,” said Ohenhen. “For example, significant areas of critical infrastructure in New York, including JFK and LaGuardia airports and its runways, along with the railway systems, are affected by subsidence rates exceeding 2 mm per year. The effects of these right now and into the future are potential damage to infrastructure and increased flood risks."
The new findings appear in the open access journal PNAS Nexus. In the work “Slowly but surely: Exposure of communities and infrastructure to subsidence on the US east coast,” Virginia Tech and U.S. Geological Survey (USGS) scientists measured how much the land along the East Coast has sunk and which areas, populations, and critical infrastructure within 100 km of the coast are at risk of land subsidence. 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 caused by climate change.
“This information is needed. No one else is providing it,” said Patrick Barnard, a research geologist with the USGS and co-author of the study. “Shirzaei and his Virginia Tech team stepped into that niche with his technical expertise and is providing something extremely valuable.”
JOURNAL
PNAS Nexus
ARTICLE TITLE
Slowly but surely: Exposure of communities and infrastructure to subsidence on the US east coast
ARTICLE PUBLICATION DATE
2-Jan-2024
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