Every one of the twenty-eight most populous cities in the US is sinking. Not only coastal cities, but inland ones as well. Researchers tracked millimeter-level vertical land motion across the country’s biggest urban areas and uncovered trends in ground subsidence and how it could put stress on critical infrastructure.
“This is the first high-resolution, satellite-based measurement of land subsidence across the 28 most populous U.S. cities,” said Leonard Ohenhen, a postdoctoral researcher at Columbia University’s Lamont-Doherty Earth Observatory. “As cities continue to grow, we will see more cities expand into suburban regions. Over time, this subsidence can produce stresses on infrastructure that will go past their safety limit.”
In a study by Columbia Climate School’s Lamont-Doherty Earth Observatory, 25 of 28 cities had two-thirds or more of urban land that is subsiding, meaning land sinking into the ground. The city hit the hardest is Houston, where over 40% of the city is sinking at least 5 millimeters per year, and 12% of the city is sinking twice as fast. Other cities in Texas that are affected are Fort Worth, Dallas, and San Antonio.
Inland centers such as Denver, Indianapolis, and Chicago are sinking due to natural geological processes and human activities, such as the extraction of fossil fuels. Some land movement is natural. For example, land that moved upwards during the last Ice Age is still in the process of settling, such as New York, Philadelphia, and Portland. However, researchers found that 80% of the sinking is caused by groundwater extraction. Aquifers that are made from fine-grained sediments compact when water is removed, which results in surface subsidence. Oil and gas extraction further exacerbates this problem by destabilizing the ground. In New York, Researchers have found that the weight of over a million buildings has contributed to the city’s sinking as well.
“Unlike flood-related subsidence hazards, where risks manifest only when high rates of subsidence lower the land elevation below a critical threshold, subsidence-induced infrastructure damage can occur even with minor changes in land motion,” Ohenhen warns.