Big Apple slowly sinking under its own weight
If rising oceans aren’t worrying enough, New York is slowly sinking under the weight of its skyscrapers, homes, asphalt and humanity itself.
New research estimates the city’s landmass is sinking at an average rate of 1mm to 2mm per year, something referred to as “subsidence”.
That natural process happens everywhere as ground is compressed, but the study published this month in the journal Earth’s Future sought to estimate how the massive weight of the city itself is hurrying things along.
More than one million buildings are spread across the city’s five boroughs. The research team calculated that all those structures add up to about 1.5 trillion tonnes of concrete, metal and glass — about the mass of 4700 Empire State buildings — pressing down on the Earth.
The rate of compression varies throughout the city. Midtown Manhattan’s skyscrapers are largely built on rock, which compresses very little, while some parts of Brooklyn, Queens and downtown Manhattan are on looser soil and sinking faster, the study revealed.
While the process is slow, lead researcher Tom Parsons of the United States Geological Survey said parts of the city will eventually be under water.
“It’s inevitable. The ground is going down, and the water’s coming up. At some point, those two levels will meet,” said Parsons, whose job is to forecast hazardous events.
But there’s no need to invest in lifejackets just yet, Parsons assured.
The study merely notes that buildings themselves are contributing, albeit incrementally, to the shifting landscape, he said.
Parsons and his team of researchers reached their conclusions using satellite imaging, data modelling and a lot of mathematical assumptions.
It will take hundreds of years — precisely when is unclear — before New York becomes America’s Venice, which is famously sinking into the Adriatic Sea.
But parts of the city are more at risk.
“There’s a lot of weight there, a lot of people there,” Parsons said, referring specifically to Manhattan.
“The average elevation in the southern part of the island is only 1 or 2m above sea level — it is very close to the waterline, and so it is a deep concern.”
Because the ocean is rising at a similar rate as the land is sinking, the Earth’s changing climate could accelerate the timeline for parts of the city to disappear under water.
Already, New York City is at risk of flooding because massive storms can cause the ocean to swell inland or inundate neighbourhoods with torrential rain. The resulting flooding could have destructive and deadly consequences, as demonstrated by Superstorm Sandy a decade ago and the still-potent remnants of Hurricane Ida two years ago.