Alarming Nasa images show US east coast cities sinking at rapid pace

Major cities along the US East Coast are sinking at an alarming rate, with some areas sinking over 2 inches per year, according to new Nasa satellite data and analysis. This sinking, known as subsidence, has already made certain areas more vulnerable to flooding from storms and sea level rise caused by climate changes.
Nasa’s satellite imagery and data, interpreted by scientists at Virginia Tech’s Earth Observation and Innovation Lab, demonstrate that various East Coast regions, including major cities like New York, Baltimore, and Norfolk, are subsiding annually by 1 to 2 millimeters from 2007 to 2020.
Leonard Ohenhen, a Virginia Tech PhD student and one of the authors of the study, explained, “Our major findings show that between 2,000 to 74,000 square kilometers of land area, home to 1.2 to 14 million people and 476,000 to 6.3 million properties, are sinking at a rate of 1 to 2 millimeters per year.” This land subsidence poses a heightened risk of flooding and other coastal hazards, particularly when combined with the effects of global sea level rise.
The subsidence map from Nasa illustrates areas of the East Coast that have been sinking or rising between 2007 and 2020, showcasing the widespread nature of the issue. The study also suggests that the mid-Atlantic coast is experiencing more significant subsidence than the northeastern coast, largely due to the historical weight of the Laurentide ice sheet.
In South Carolina, Charleston is identified as one of the fastest sinking cities, with a rate of approximately 4 millimeters per year, exacerbating the city’s vulnerability to rising sea levels and leading to considerations for an 8-mile seawall to mitigate flooding and storm surges.
The phenomenon known as glacial isostatic adjustment, where the land shifts similar to the movements of a seesaw, is believed to be a primary cause for the coastal sinking observed. In areas of Maryland and Virginia, the extraction of groundwater is also contributing to this downward trend. Furthermore, in coastal regions of Georgia, South Carolina, and North Carolina, the construction of dams, which prevent the natural accumulation of sediment, is another factor causing the land to sink.
Charleston, South Carolina stands out as one of the cities most affected by subsidence, descending approximately 4 mm annually. This issue, in conjunction with escalating sea levels, poses a significant threat to the city, which is predominantly situated less than 10 feet above the current sea level.
“It definitely will exacerbate the vulnerability of sea level rise in most coastal communities. Most communities will face the impacts of sea level rise sooner, due to the compounding effects of the sinking land and the sea level rise,” Ohenhen said.
The research, aiming to extend to the Gulf Coast and eventually global coastlines, hopes to inform and assist urban planning to counteract these subsidence effects.