sum up New York City has about a million buildings, weighing about 1.7 trillion pounds against the Earth. This does not include all other infrastructure such as roads and sidewalks. All that weight deforms the ground like a bowling ball on a memory foam mattress, causing a type of subsidence known as subsidence as the land slowly compresses.
A new study found that New York City’s subsidence rate averages 1 to 2 millimeters per year, but can reach up to 4 millimeters in some places. This may not sound like a worrying number, but it is a significant subsidence that is worsening each year and effectively doubling the relative sea-level rise in large cities. “Sea levels will rise about one to two millimeters, but on average they will fall one to two millimeters,” said U.S. Geological Survey geophysicist Tom Parsons, co-author of a new paper describing the study. I’m here. “This is a common problem in cities around the world. There seems to be a clear relationship between urbanization and land subsidence.”
For example, parts of Jakarta, Indonesia are sinking by almost one foot per year. The San Francisco Bay Area could lose up to 165 square miles of coastline from rising sea levels combined with subsidence. And just last month, another team of researchers reported that they found parts of Delaware sinking up to 10 millimeters per year up and down the East Coast.
The main way to cause dramatic subsidence is over-pumping of groundwater, as is the case in Jakarta. A drained aquifer collapses like an empty water bottle. But in New York City, land subsidence depends on the composition of the underlying soil. A long time ago, glaciers carved through the area, depositing sediments. A lake also formed and deposited more sediment. For this reason, the metropolis is constructed using a complex combination of materials such as clay, silt, and artificial embankments that are prone to subsidence, as well as sand and gravel that are difficult to subside.
“The softer the soil, the more likely it is to compress under load,” Parsons says. “Even if you don’t stack it, it will sink under its own weight. But with that as a base, it definitely sinks pretty well.”
Parsons and his colleagues calculated New York City’s subsidence rate by first summing all of the city’s weights and then combining that with geological data on the composition of various sediments. They also collected satellite data that measured minute changes in altitude, showing which areas were sinking and which were relatively stable.
Manhattan skyscrapers may be the heaviest buildings in the city, but they’re anchored to the bedrock below, so they don’t suffer as much from subsidence. The problem is more along the coast, where spongy materials such as clay and artificial fill are particularly susceptible to compaction, and where sea levels are rising.
Land subsidence is a hidden vulnerability for coastal cities and is not yet taken into account in models that predict how much sea level will rise in a particular region. By 2050, mean sea level in the United States will rise one foot, by which time 70 percent of the world’s population will be urban dwellers, up from 56 percent today. The boom will exacerbate the problem in coastal cities, as more people will have to pump more groundwater, requiring more buildings and roads, which will put more pressure on sediments. deaf.
