Recent research reveals that over two dozen of the largest cities in the United States are experiencing significant subsidence, raising concerns about the potential impact on infrastructure and populations. Utilizing satellite technology that measures ground movement through radar signals, scientists have identified that 25 out of the 28 biggest cities are sinking, with rates varying across different locations.
Fort Worth, Houston, and Dallas are noted for having the highest average subsidence rates, exceeding 4 millimeters per year. Other major cities, including New York, Chicago, and Seattle, are experiencing subsidence rates of more than 2 millimeters annually. Houston is particularly noteworthy, with 42% of its land area subsiding at rates faster than 5 millimeters per year.
The primary cause of subsidence varies by region. Groundwater extraction is highlighted as a significant factor in cities like Houston, whereas other areas such as New York and Washington, D.C., are affected by glacial isostatic adjustment. This phenomenon occurs when land that was once compressed under massive ice sheets rebounds unevenly after the ice melts, leading to varying rates of land movement.
In cities like Seattle, Portland, and San Francisco, tectonic activity is likely contributing to the observed subsidence. Researchers stress the importance of recognizing subsidence as a gradual but serious issue, as uneven ground movement can result in structural damage, including cracks in buildings and misalignment of doors and windows.
Geophysicists continue to study these trends, aiming to distinguish between human-induced and natural geological processes that contribute to subsidence in urban areas.