"The slow and gradual sinking of Earth’s surface — land subsidence — is a present and growing hazard with costly environmental, social and economic impacts on urban centers," according to the study. "Even modest rates of urban subsidence can profoundly impact the structural integrity of buildings, roads, bridges and dams."
The study relied on data from radar and satellite images captured between 2015 and 2021 to measure gradual sinking in the 28 most populated cities in the country as of 2020. Researchers measured the upward and downward motion of land within each city's boundaries — and found that, in most places, at least half of the land was slowly pressing downward because of human activity and lingering effects of ancient glaciers.
For Denver, dropping two millimeters a year is too little to have to worry about dropping under the 5,280-foot elevation mark and losing the Mile High City moniker. However, the study warns that sinking land can slowly and silently weaken tall buildings, highway overpasses and dams in a way that won't be noticed until it's "potentially catastrophic."
For Denver, dropping two millimeters a year is too little to have to worry about dropping under the 5,280-foot elevation mark and losing the Mile High City moniker. However, the study warns that sinking land can slowly and silently weaken tall buildings, highway overpasses and dams in a way that won't be noticed until it's "potentially catastrophic."
Nearly 250 Denver Buildings at High Risk
According to researchers, about 98 percent of the land within Denver boundaries is sinking, and Denver was one of ten cities where sinking was that widespread; in most cities, at least 65 percent of the land is sinking. All 28 cities studied are seeing at least 20 percent of their land sink because of groundwater extraction, or pulling water out from under the land, which is often from aquifers that aren't being replenished quickly enough, researchers warn.Nearly 250 Denver Buildings at High Risk
While the study didn't suggest when buildings and bridges might start to fall, it warned that more than 3,000 properties in the U.S. are at a "very high risk" of collapse over the next 25 years, and cited incidents like the Surfside condo collapse in Miami in 2021, which killed nearly 100 people, as a recent example.
Human activities like oil, gas and groundwater extraction, as well as mining and damming, are speeding up and exacerbating a geological phenomenon in the U.S. known as glacial isostatic adjustment, the study authors note. Glaciers covered the northern hemisphere during the last ice age 16,000 years ago, and the land is still sinking or elevating in response to the massive amounts of ice that melted away.
Denver has more than 240 properties that the study considers at "high risk" and thirteen at "very high risk" of collapsing due to continued sinking. However, that's a relatively small amount of high-risk properties compared to the other cities studied. In Texas, oil drilling has put more big cities at risk: Austin and Fort Worth are home to hundreds of "very high risk" buildings, while San Antonio has more than 1,500 such buildings, making the state responsible for more than half of the"very high risk" properties found in the study.
The way to get ahead of the risk of sinking cities, according to Virginia Tech researchers, is for cities to collect more data of their own on what areas and neighborhoods are at risk. Researchers also recommend that cities pass laws to limit new buildings in high-risk areas; reinforcing buildings and compacting soil could also help, the study adds.
As parts of Colorado sink, others shrink. Colorado's famous Fourteener peaks were remeasured in April 2024 by the National Oceanic and Atmospheric Administration, which found that several of them were as much as two feet shorter than previously thought. Because NOAA remeasured all of Colorado, a re-ordering of the tallest Fourteener list was in order, and new places in Denver could join the Mile High Club.
Governor Jared Polis's office has said it will consider moving the brass "5,280 feet above sea level" marker on the State Capitol Building's west steps up a few steps in 2026, the state's 150th anniversary.
Governor Jared Polis's office has said it will consider moving the brass "5,280 feet above sea level" marker on the State Capitol Building's west steps up a few steps in 2026, the state's 150th anniversary.
