New York City is experiencing a gradual Subsidence, Sinking at a pace of half a foot per century.

A recent study, released last Wednesday and led by NASA, employed high-resolution satellite imagery to examine the ground elevation across the approximately 300 square miles of New York City. This investigation served as a follow-up to a previous study published in May, which had theorized that the city’s land elevation drop, known as subsidence, was partly attributable to the weight of substantial concrete structures pressing down on the Earth’s surface.

However, the earlier conclusion, though widely covered in the media, turned out to be somewhat inaccurate.

The NASA team determined that the city’s massive 1.68 trillion pounds of steel and stone had a minimal impact on the sinking phenomenon, except when buildings were erected on landfill areas—a fairly common practice in NYC. Subsidence trouble spots were observed throughout the five boroughs.

Coney Island in Brooklyn, Arverne by the Sea in Queens, and the Rikers Island prison complex were all constructed on landfill. The southern portion of Governors Island is essentially a patch of land made on nearly 5 million cubic yards of rocks and soil excavated during subway construction in the early 1900s. Just beyond the metropolitan region, New Jersey’s highways, Route 440 and Interstate 78, are experiencing sinking in sections built on fill.

In non-landfill regions where researchers detected subsidence, the primary cause was the melting of glacial ice sheets that once covered the area approximately 20,000 years ago. During the last Ice Age, New York City was situated just beyond the periphery of a mile-high ice sheet that blanketed most of New England. The weight of the ice compressed the ground beneath it, while simultaneously creating elevated areas along its edges. Over time, those elevated regions are gradually subsiding.

Robert Kopp, the study’s co-author and co-director of the Rutgers University Office of Climate Action, explained the process by likening it to a mattress: when you apply pressure, you create a depression beneath the weight and a bulge at the edges. As the pressure is released, the bulges gradually subside.

Researchers expressed their primary concern, which is how sinking land will exacerbate coastal flooding as sea levels rise due to climate change. Kopp emphasized that understanding the rate at which the land is sinking, in conjunction with sea level rise, is crucial for future planning and design.

The research team used space satellites to measure annual changes in land height from 2016 to 2023. They discovered that while the average sinking rate is less than one-tenth of an inch per year, areas built on landfill are sinking approximately three times faster.

Prominent locations like the Arthur Ashe Tennis Stadium, home to the U.S. Open, and LaGuardia Airport, which handled 14.5 million passengers last year, are experiencing subsidence at rates of 0.15 and 0.18 inches per year, respectively.

Researchers believe that the upward movement of the land in these regions is primarily attributable to human interventions, such as environmental remediation efforts at Newtown Creek, which holds the status of a federally designated toxic Superfund site. According to Kopp, these activities encompass activities like groundwater extraction and the use of injection wells for treating water pollution. Another potential factor could be underground construction linked to New York City’s water system in Woodside. For the initial four years of the study, the land in that area was ascending at a rate of approximately 0.28 inches per year, but then experienced an abrupt halt in its upward movement.

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