New York City’s skyline may start to look very different if the metropolis keeps sinking
Gary Hershorn/Getty Images
More than two dozen of the biggest cities in the US are sinking, which could affect thousands of buildings and millions of people.
The issue has been documented previously, particularly in coastal regions. However, through the utilization of satellite technology, which employs radar signals directed towards Earth’s surface to measure the time taken for them to return, researchers have discovered that 25 out of the 28 largest cities in the country are experiencing sinking.
“By analyzing multiple images captured over time from the same location, we are able to identify minute vertical movements of the ground, measuring as little as a few millimeters per year,” explained Manoochehr Shirzaei, a member of the team from Virginia Tech. “It’s akin to creating a detailed time-lapse of the Earth’s surface and observing how it either rises or falls over time.”
Cities such as Fort Worth, Houston, and Dallas exhibited the most significant subsidence rates among all large cities, surpassing an average of 4 millimeters per year. New York, Chicago, Houston, Columbus, Seattle, and Denver experienced average subsidence rates exceeding 2 millimeters per year.
Researchers noted that Houston, the city sinking at the fastest rate among the 28 most populous US cities, has 42% of its land area subsiding at a rate greater than 5 mm per year, with 12% sinking faster than 10 mm per year.
While most of the subsidence is attributed to groundwater extraction, certain cities like New York, Philadelphia, and Washington DC are primarily affected by “glacial isostatic adjustment.”
Shirzaei elaborated, “During the last ice age, these regions were covered by massive ice sheets. The immense weight of the ice compressed the Earth’s crust, analogous to sitting on a memory foam mattress. As the ice melted thousands of years ago, the pressure lifted, causing the ground to slowly rebound.”
“However, this rebound is not uniform,” Shirzaei continued. “In areas such as the US East Coast and Midwest, the land is sinking instead of rising due to their proximity to the forebulge, a region that was uplifted by the adjacent ice mass and is now subsiding.”
Plate tectonics are likely responsible for the subsidence observed in cities like Seattle, Portland, and San Francisco.
“It is imperative that we address subsidence as the gradual disaster it represents,” Shirzaei emphasized. The researchers also identified varying rates of sinking within certain cities, with some areas sinking while others are rising. This differential movement can lead to angular distortion and stress, potentially resulting in cracks in buildings, misaligned structures, or even structural collapse.
Jesse Kearse, a researcher at Kyoto University in Japan, utilized similar satellite data to demonstrate that various cities in New Zealand are also experiencing subsidence. Kearse highlighted the challenge faced by the geophysics community in attributing the observed trends to specific causes, whether they stem from human activities or natural geological processes.
Topics:
