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Straits Times
16-05-2025
- Science
- Straits Times
How big cities across the US are slowly sinking
The skyline of Dallas, Texas. Urban centres in Texas are among US cities sinking the most due to subsidence. PHOTO: BLOOMBERG How big cities across the US are slowly sinking A new analysis of America's 28 largest population centres found that all but three are sinking overall, and in many cases significantly. Several of the most affected areas are in Texas, particularly around Fort Worth and Houston. But the problem is nationwide, affecting cities as scattered as Seattle, Detroit and Charlotte, North Carolina. Sinking land, also called subsidence, can worsen the effects of sea-level rise, intensify flooding and strain the very foundations of urban infrastructure. The new research, published in the scientific journal Nature Cities, built on previous work using satellite measurements to paint a detailed picture of rising and falling land. It also closely examined the connection between changes in land elevation and changes in groundwater, using data from individual monitoring wells. Water pumped from wells isn't something that people think about often. 'You just turn on your tap, do what you need to do, and you go on your way,' said Mr Leonard Ohenhen, a researcher at Columbia University's Lamont-Doherty Earth Observatory and lead author of the study. But extracting more water than can be replenished 'can have a direct relationship with what happens on the surface,' he said. 'You can cause the ground to sink significantly.' A 2023 New York Times investigation found that unsustainable pumping of water from underground aquifers can be a major cause of sinking land. Other factors also influence land elevation. For example, a vast expanse of bedrock beneath parts of the country, pressed downward by enormous glaciers during the last ice age, is slowly rebounding back into place. But over time it creates a sort of seesaw effect that today is adding 1mm to 2mm per year to subsidence rates in much of the northern United States. Texas draws immense amounts of groundwater for agriculture, industry and the public water supply. The extraction of oil and gas, including the growing use of 'monster fracks,' can also cause the land surface to slump. Climate change can worsen the issue. Hotter temperatures and more extreme droughts, particularly in the West, dry out soil, streams and reservoirs, leading people to pump larger quantities of freshwater from underground. Americans have also been moving in droves to some of the hottest and driest parts of the country. In the past few decades, metro areas in Texas have ballooned in population and sprawl. Groundwater depletion was the main cause of subsidence in Houston between the 1950s and '70s, when nearly all water usage came from the ground, said Dr Bob Wang, a professor of geophysics at the University of Houston. Cracked roads and buildings were a common sight. Several subsidence-management districts were established in the area to address the issue. Among other things, groundwater use was reduced and instead more water was taken from surface-water sources such as rivers. Subsidence has since slowed in the city centre. However, when new neighbourhoods developed to support growing populations, the most affordable source of water was often what people could pump from below. Subsidence is in itself a hazard. But when adjacent land sinks at different rates, or when sinking occurs next to land that's rising, it can cause roads and buildings to crack. Though this process happens slowly, in millimeters per year, over time it can create added stress to infrastructure in areas where flooding, earthquakes or sea level rise are already a problem. Extreme weather adds to the risk. When surface soils expand during extreme rainfall, then compact during prolonged droughts, it can lead to structural damage. 'In the Houston area, foundation repair is a very good business,' Prof Wang said. Cities along the coast, which are often built on soft soil or marshland like Houston, can be particularly vulnerable. But the research paper also looked at inland cities facing similar sinking challenges. Phoenix, a desert city, has a long history of groundwater depletion but has managed to turn things around. After the state of Arizona implemented its 1980 Groundwater Management Act, management districts were established and many conservation rules were put in place. Still, the legacy of overpumping still affects the area. One reason is that, once groundwater is pumped out, it can be difficult if not impossible for some aquifers to recharge and refill to their earlier levels. In other words, it's very hard to reverse land that has already settled. Subsidence can still occur 'even as groundwater levels recover, because the pore spaces in the subsurface that were once being held open by groundwater are now just filled with air,' said Mr Brian Conway, a principal hydrogeologist at the Arizona Department of Water Resources. Those spaces sometimes can be refilled with water, but sometimes they compress and can't be recharged. In Phoenix, managed recharge has helped to fill those pore spaces, replenishing underground reservoirs. While subsidence still occurs, it's a far cry from the rates that caused a record 18 feet of elevation drop in Phoenix between the 1950s and 1990s. Outside the city, however, land is still sinking as fast as ever. Methodology: Vertical land movement data with higher uncertainty, including areas around dense vegetation and water bodies, were not included in the maps. Researchers analysed the most populated areas in the United States, and included all cities with more than 600,000 residents. They used 2020 US census data for the population estimates. NYTIMES Find out more about climate change and how it could affect you on the ST microsite here.
Yahoo
15-05-2025
- Science
- Yahoo
28 American Cities Are Literally Sinking Into the Earth
"Hearst Magazines and Yahoo may earn commission or revenue on some items through these links." Major U.S. cities are experiencing some degree of subsidence, a.k.a. sinking. It's not just major coastal cities like New York, Los Angeles, and Houston; landlocked cities like Las Vegas, Denver, Nashville, and more are showing signs of sinking. Causes range from groundwater extraction to plate tectonics. It's a well-known fact that sea levels around the world are slowly rising. According to the U.S. National Oceanic and Atmospheric Administration (NOAA), sea levels have risen some eight to nine inches around the world since 1880, and show no sign of stopping. That's concerning enough on its own, considering that 40 percent of the U.S.'s population lives near coastlines. But American cities—along with cities around the world—are facing yet another problem that's only exacerbating this concerning side effect of climate change: They're sinking. In a new study led by scientists at Virginia Tech, a research team tracked the subsidence (a.k.a. sinking) rate of 28 major U.S. cities across the country and found that at least 20 percent of the urban area of all of the cities was sinking to some degree. In 25 of those 28 cities, more than 65 percent of the land area was sinking to varying degrees. The most extreme example is Houston, Texas, where scientists discovered that some areas of the city were sinking as much as 10 millimeters per year. The results of the study were published in the journal Nature Cities. Obviously, the image of cities slowly sinking paints a picture of places like Houston, New York, and L.A. simply slipping into the sea. But the implications of this higher-than-expected subsidence rate comes with a much more complex list of nearer-term practical problems for both city planners and average homeowners. 'Even slight downward shifts in land can significantly compromise the structural integrity of buildings, roads, bridges, and railways over time,' Leonard Ohenhen, a former Virginia Tech graduate student and the lead author of the study, said in a press statement. The cause of the sinking varies from city to city. The leading cause of subsidence is groundwater extraction, which eventually leads to compaction of soil and sediments and—you guessed it—the net result of slowly sinking land. However, other causes can also be pretty impactful. Some parts of the country, for example, are still experiencing the extraordinary see-sawing of bedrock caused by the retreat of glaciers during the tail of the Pleistocene epoch. Meanwhile, out West in cities like Portland, Seattle, and San Francisco, plate tectonics can claim some of the blame. 'Sustained groundwater extraction lowers pore pressure in aquifer systems, leading to compaction of fine-grained sediments, which results in land subsidence that can be detected from satellites,' Susanna Werth, a co-author of the study from Virginia Tech, said in a press statement. 'Such land subsidence has been observed across the U.S. for many decades, but its increasing relevance in urban areas is especially hazardous.' Ohenhen and his team are part of that observational history. Just last year, they published a study in the journal Proceedings of the National Academies of Sciences about the rapid subsidence of cities along the East Coast. However, this new study shows that not only is the phenomenon more widespread than originally understood, it's also not contained to coastal cities. Las Vegas, Denver, Oklahoma City, Nashville, Indianapolis, and many landlocked metropolitan areas also show signs of sinking. While this study only focused on the contiguous United States, the country's two most far-flung states—Alaska and Hawai'i—are also struggling with increased subsidence. For Alaska, the main culprit is permafrost degradation. And regarding Hawai'i, a study published earlier this year showed that some areas of O'ahu are sinking as much as 25 millimeters per year due to some industrial sectors having been built atop artificial fill. None of this means that the U.S. is about to become some legendary, water-filled Atlantis. But understanding the rate at which cities are sinking—and the rate at which sea levels are rising—can help city planners, water resource managers, and average homeowners prepare for the slowly sinking future ahead of us. You Might Also Like The Do's and Don'ts of Using Painter's Tape The Best Portable BBQ Grills for Cooking Anywhere Can a Smart Watch Prolong Your Life?
Yahoo
15-05-2025
- Science
- Yahoo
Scientists say Nashville is sinking. Here's why
NASHVILLE, Tenn. (WKRN) — A new scientific study shows that some of the largest cities in the United States are slowly sinking. In fact, Nashville appears to be sinking about one millimeter each year. News 2 spoke with Leonard Ohenhen, one of the researchers in the study, who said the sinking across the country is caused by both natural and human-caused processes. According to Ohenhen, water use, drilling of natural gas/oil, and the weight of infrastructure is causing sinking in some of the cities in the study. He added that sinking in Music City is caused naturally by a process called 'Glacial Isostatic Adjustment.' Where are Tennessee's earthquake hot spots? Glacial Isostatic Adjustment is the land's reaction to the melting of the glaciers thousands of years ago. Ohenhen said this causes some locations to rise and others to sink. 'Think of it like a memory foam, if you put a large weight on it, where the weight is after the weight is removed starts to rising, and places that were adjusting to where the weight was would rise due to that weight, but when the weight is removed it starts going down to sort of have equilibrium,' Ohenhen told News 2. Nashville's sinking could reportedly lead to worse flooding during heavy rain events, but Ohenhen said there shouldn't be many infrastructure issues because the whole city is sinking at the same speed. | READ MORE | 'Roads, railways, buildings, and other infrastructure themselves can over time be compromised due to land subsidence, but in Nashville, the good thing is all the land is sinking almost at an even rate,' he explained. Ohenhen said this isn't the same for other cities in the study, adding many of the cities in Texas have a high or very high risk of infrastructure issues. According to the study, not every city is sinking. In fact, Memphis was one of the cities that were slowly rising. Ohenhen said the entire city isn't rising, but parts of Memphis are rising due to the natural recharge of the groundwater. ⏩ The biggest concern with the sinking is coastal flooding, but Ohenhen said obviously that is not a problem for Nashville. To read the entire study, click here. Copyright 2025 Nexstar Media, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
Newsweek
14-05-2025
- Science
- Newsweek
Scientists Warn That These Popular American Cities Are Sinking Under Residents' Feet
Based on facts, either observed and verified firsthand by the reporter, or reported and verified from knowledgeable sources. Newsweek AI is in beta. Translations may contain inaccuracies—please refer to the original content. If you live in a major American city, the ground might be sinking beneath you. Ground beneath major U.S. cities—including New York, Dallas and Seattle—is slowly but steadily sinking, with more than 20% of urban land in all 28 of the country's largest cities affected, according to new research published in Nature Cities. The study, led by researchers at Virginia Tech, found that land in these areas is dropping by two to 10 millimeters a year, mostly due to the overuse of groundwater. That slow drop may seem minor, but researchers say it can cause significant damage to buildings, roads, bridges and other infrastructure over time—especially in places with uneven land movement. Stock image: Houston, Texas. Stock image: Houston, Texas. Photo by Nantiya Rattanatum / Getty Images "One of the most impactful findings was just how widespread and significant subsidence already is," study author Leonard Ohenhen told Newsweek. "We found that at least 20% of the urban area in every city we studied is subsiding, affecting more than 34 million people, which is 1 in every 10 Americans, just from the analyses of 28 cities." Why It Matters Sinking land, also known as subsidence, is typically hidden from view. However, it poses real dangers to public safety and infrastructure. Even slight downward shifts can cause cracks in foundations and roadways or destabilize large structures. As demand for water grows in expanding cities, pulling too much from underground aquifers causes the soil to compact, leading the land above to sink. Climate change, which increases the stress on water supplies, is expected to make this problem worse. "In drought-prone regions, reduced surface water availability may increase dependence on groundwater, accelerating aquifer depletion and land compaction," Ohenhen told Newsweek. "Additionally, in coastal cities, the combination of subsidence and rising seas leads to increased relative sea-level rise—meaning the land is sinking while the water is rising, compounding the hazard. "This shortens the timeline for when cities reach critical thresholds for chronic flooding." What To Know The Virginia Tech team used satellite radar data to create high-resolution maps of land movement from 2015 to 2021. All 28 cities studied—including places like Los Angeles, Chicago, San Antonio, Phoenix and Las Vegas—had areas of significant sinking. In 25 cities, at least 65% of the urban area was affected. Houston showed the highest levels, with some neighborhoods sinking more than 20 millimeters (about 0.8 inches) per year. Even New York, which averages slower sinking, has notable hotspots such as around LaGuardia Airport. Uneven land movement was also seen in cities like Las Vegas, New York and Washington, D.C., where differences in how much the ground sinks can put extra stress on infrastructure. What Other Cities Are Sinking The study found that New York, Dallas, Chicago, Seattle, Denver and others are sinking at rates around 2 millimeters a year. Texas cities were particularly at risk—parts of Houston, Fort Worth and others are dropping by 5 millimeters, or more. According to Ohenhen, Texas cities are struggling "primarily due to a long history of intensive resource extraction." "When fluid is removed from the ground, particularly those composed of clay-rich or compressible sediments, the pore spaces collapse, leading to land compaction and surface subsidence," he told Newsweek. "Houston, in particular, has experienced decades of aquifer drawdown." What's Next The researchers urge local governments to integrate land subsidence monitoring into their planning and building policies. They recommend tighter groundwater management, improved infrastructure design and long-term monitoring systems to detect issues before they become critical. "Subsidence is a silent but powerful force reshaping our cities," Ohenhen told Newsweek. "It's a slow, often invisible process that undermines infrastructure, increases flood risk, and quietly erodes urban resilience. "What makes it especially dangerous is that it frequently goes unmonitored and unregulated, even in places where it is actively worsening. "The good news is that we can respond through adaptive planning practices."
Yahoo
12-05-2025
- Science
- Yahoo
Nashville among U.S. cities sinking due to this invisible threat, study says
Nashville is... sinking? That's what a new study from the British journal Nature Cities reported on May 8. Nashville, along with 27 other cities around the United States. In every city studied, at least 20% of the urban area is sinking. Plus, in 25 of the 28 cities studied, at least 65% is sinking. The reason behind the sinking ground is called subsidence, an often invisible threat that exists most often when water, oil, natural gas, or mineral resources are removed from the ground by pumping, fracking, or mining activities. Subsidence can also be caused by natural events like earthquakes, sinkholes, erosion, soil compaction and more, according to the National Ocean Association. Most often, extracting groundwater can be the most common reason for subsidence. The gradual subsidence may impact the structural integrity of buildings, roads, bridges and dams, according to the study. "One of the most harmful yet less visible effects of urban land subsidence is the potential damage to buildings, foundations and infrastructure, primarily caused by differential land motion," the study said. Generally, according to a statement from the Lamont-Doherty Earth Observatory — one of the study's authors, it happens as water is withdrawn from aquifers made up of fine-grained sediments; unless the aquifer is replenished, the pore spaces formerly occupied by water can eventually collapse, leading to compaction below, and sinkage at the surface. Nashville, along with New York, Indianapolis, Chicago, Philadelphia, Denver and Portland, is among the cities subsiding at a rate of 1 to 3 millimeters per year due to both human-derived and natural forces. "In particular, the weight of the towering ice sheet that occupied much of interior North America until about 20,000 years ago made the land along its edges bulge upward, somewhat like when one squeezes air from one part of a balloon to another," said the Lamont-Doherty Earth Observatory. The fastest sinking city is Houston, the study uncovered. Houston saw more than 40% of its area dropping more than 5 millimeters (about 1/5 inch) per year, and 12% sinking at twice that rate. No. In fact, Memphis is one of three cities identified in the study that appears to have a small uplift of around 0.1 millimeters. This doesn't mean that the city is rising per se, but more of an indication of its current stability, study lead author Leonard Ohenhen of the Lamont-Doherty Earth Observatory told USA TODAY. San Jose and Jacksonville are the other two U.S. cities that were uplifted, marked by light green dots on the map. Knoxville was not included in the study. Only the most populous 28 U.S. cities were included in the British journal Nature Cities' published study of land subsidence risk. Subsidence is not something that can be immediately reversed, however, the study does recommend ways to minimize the impacts on affected cities. The study highlighted the importance of monitoring land subsidence as a part of urban planning to prevent worsening infrastructure risks. "Regardless of the pathway a city chooses, any effective mitigation and adaptation effort must be targeted to the dominant subsidence driver in each city, proportional to local vulnerabilities, and incorporate a multifaceted approach," the study said. Techniques like groundwater management and long-term monitoring frameworks are a key way to combat land subsidence. USA TODAY reporter Doyle Rice contributed to this report. This article originally appeared on Nashville Tennessean: Nashville among U.S. cities sinking, according to new study
