DETROIT – Is Detroit sinking? According to a new study, yes.
The research looked at the 28 most populous U.S. cities to track the movement while observing the underlying cause.
What’s going on?
Leonard Ohenhen, a researcher at the Lamont-Doherty Earth Observatory at Columbia University, recently shared insights on a study examining land subsidence in major U.S. cities.
The research began around 2021, focusing on collecting and analyzing data from various urban areas.
“We wanted to explore a range of cities in the United States, particularly the most populous ones, where you have the highest exposure to subsidence,” said Ohenhen. “The study aims to understand how land sinking impacts both residents and infrastructure in these communities.”
To gather data, the researchers utilized radar satellite technology to observe land motion in different cities.
“Subsidence or sinking is often thought of as a coastal problem, and in some ways, that is true, because most coastlines have what we refer to as young sediment,” Ohenhen said.
The sediment, deposited thousands of years ago, naturally compacts over time, leading to subsidence.
However, human activities can accelerate this process.
“In those areas, such sediments have natural compaction, so they sink over time, but the added weight of humans causes an accelerated rate of subsidence,” Ohenhen said.
The unique case of Detroit
Interestingly, Detroit’s subsidence is largely due to natural processes rather than human activity.
“It’s sinking due to a natural process known as glacial isostatic adjustment, or GIA for short,” the researcher said.
This phenomenon refers to the land sinking after the melting of ice sheets from the last ice age, which occurred about 12,000 to 14,000 years ago.
“Areas that were uplifted by the large ice sheets are now experiencing subsidence as the weight of the ice is removed,” Ohenhen said.
To illustrate this, he likened the process to sitting on memory foam. “When you sit down, certain areas push up, and once you get up, the foam returns to its original form. That’s what happens in some of these areas.”
Mitigation and adaptation strategies
Ohenhen emphasized the importance of addressing subsidence through both mitigation and adaptation strategies.
Mitigation involves preventing subsidence, which can be challenging in areas where it is primarily driven by natural processes. However, in regions where groundwater extraction contributes to subsidence, managing aquifer recharge can help.
“You can limit how much water has been extracted or even manage aquifer recharge, which can cause the ground to naturally rise,” Ohenhen said.
In Detroit, adaptation is the more viable solution.
“Restricting buildings in the most high-risk areas will be some of the ways to respond,” he said. By integrating data on sinking areas into building codes, cities can ensure more resilient infrastructure.
Ohenhen also highlighted that maintaining existing infrastructure is crucial.
“Incorporating data sets for land subsidence into existing building or infrastructure codes can help build more resilient communities,” Ohenhen said.
The impact of subsidence in Detroit
According to the study, Detroit is sinking at an average rate of two millimeters per year, or about 0.1 inch annually.
“This translates to about an inch over a decade,” Ohenhen said.
While Detroit is better off than some other cities regarding subsidence rates, Ohenhen cautioned that there is no specific threshold for concern.
“Every little subsidence or sinking rate matters, particularly when it comes to other existing hazards,” Ohenhen said.
He noted that even minor changes in ground elevation can exacerbate flooding risks.
“If you reduce the elevation by this much, areas that were not previously flooded will start getting flooded,” Ohenhen warned.
The study has garnered positive feedback, particularly from geologists who recognize the significance of subsidence as an invisible threat.
“It’s hard for you to notice that the land you’re standing on is sinking slowly over time,” Ohenhen said.