Why Parts of New York City Are Slowly Sinking

by Sofia Zapata, age 15

New York City and other coastal cities are experiencing vertical land motion, with some areas sinking while others are rising. The regions that are sinking are facing a faster rate of subsidence compared to those that are rising. In New York City, specific areas such as lower Manhattan, southern Brooklyn, and Queens are slowly subsiding. Scientists have identified two primary factors contributing to this sinking. One potential cause is the alterations to the Earth’s surface due to construction and land modification, which make the ground less compact beneath buildings. Another cause traces back to the most recent ice age and the natural processes that followed. Around 24,000 years ago, a large ice sheet covered most of New England and upstate New York. After this ice sheet melted, the Earth's mantle has been slowly readjusting, leading to the gradual subsidence observed today. The land where New York City stands was once uplifted by the ice sheet, and as the ice melted, the land began to sink back down.

On average, the metropolitan area is subsiding by about 0.06 inches per year. However, in places like Queens and LaGuardia Airport, subsidence rates are higher, around 0.15 inches per year, and at Arthur Ashe Stadium, about 0.18 inches per year. Although these figures may seem small every year, they can compound over time and significantly increase the risk of local flooding, particularly in conjunction with rising sea levels due to climate change.

Some areas within New York City are rising. For example, East Williamsburg is rising by about 0.06 inches per year, and Woodside experienced a rise of about 0.27 inches per year between 2016 and 2019, though this area has since stabilized.

Different researchers have utilized various techniques to understand this vertical land motion. Since 2016, NASA has been using a remote sensing technique called “interferometric synthetic aperture radar” (InSAR), which combines 3D observations from the same region to monitor surface land movement. Scientists have also used radar from the European Space Agency’s satellites, which helped map subsidence in areas like LaGuardia Airport and Arthur Ashe Stadium. NASA's Jet Propulsion Laboratory has led efforts, such as the “Observational Products for End Users from Remote Sensing Analysis,” to better monitor vertical land motion along with other changes associated with natural hazards.

The implications of this rising and sinking are not yet fully understood. Although the authors of the Earth’s Future study have not called for an emergency evacuation of New York City, it is important to remain vigilant about this issue. As oceans continue to rise due to climate change, every additional building could exacerbate the risk of future flooding, potentially creating significant challenges.

[Sources: NASA; Forbes]