Indianapolis is sinking — very, very slowly. Here’s why and what it could mean for city

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Indianapolis is sinking — very, very slowly. Here’s why and what it could mean for city

If you live in

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, there is a good chance the ground underneath your feet is sinking — just very slowly.

About 98 percent of the city is experiencing this phenomenon, called

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, according to

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published in the journal Nature. And Indianapolis isn’t alone.

Twenty-five of the 28

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are slipping deeper into the earth. Many of these metropolises can attribute their condition to

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, but Indianapolis is a different case.

Indianapolis’s sinking, which the study found occurred at a rate of about 2 millimeters a year from 2015 to 2021, is probably a side effect of the last

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, according to the study. It’s likely the phenomenon has been ongoing since.

Due to the sheer amount of sink, researchers warn it could alter drainage patterns and change how cities like Indianapolis construct effective stormwater management systems.

How can a city start to sink?

Imagine you’ve just laid down on a plush memory foam mattress.

Beneath your body, the foam compresses. And just to the side of your arms and legs, the foam puffs upward, buoyed by your weight.

This, essentially, is what happened to

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.

A glacier — over half a mile thick — used to sit atop much of the state.

“Think about the weight of that,” said David Lampe, the associate director of the United States Geological Survey’s

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. “It actually pushed the bedrock and the land down in elevation.”

While some areas were smushed down, other regions experienced uplift, just like the raised foam next to the imprint of your body.

When you rise from the mattress, eventually the foam will resettle. And now that the glacier has retreated, the earth is trying to recalibrate. Compressed areas rise back up, and uplifted regions experience sinking.

“That’s what Indiana is doing now. Now that the glaciers have melted, it’s balancing out,” said Lampe.

The future of flooding

The study highlighted how some cities across the US are facing an increased risk to infrastructure — like buildings, roads and bridges — as sinking progresses.

But infrastructure damage is often due to elevation change that isn’t uniform. For example, if one block of downtown San Francisco is sinking faster than its neighboring block, it could create an uneven mosaic of subsidence across the city, jeopardizing roads, dams and buildings.

Sinking “is a big issue if it’s very variable,” said Bryan Catlin, a surveyor with the Marion County Surveyor’s office. But “if it’s happening over a larger area, then everything moves with it, and it’s not necessarily a crisis.”

Indianapolis, luckily, is sinking mostly all at once. And because of the uniformity, the risk for infrastructure damage is low.

Flood risk remains, however, said

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, a geophysicist at Columbia University who authored the study.

Sinking is usually associated with an increased flood risk for coastal cities, but it can pose a threat for inland areas, too, according to the study.

“Indianapolis is a city that faces the periodic flooding,” said Ohenhen. “Even such a minute rate [of sinking], though small, can change rain patterns or can cause flooding.”

By pinging signals at the earth and measuring how long it takes them to return, satellites could track how far cities sank from 2015 to 2021. Indianapolis’s rate — two millimeters — is equivalent to the thickness of a mere nickel. But every 12 to 13 years, the city will sink about an inch, which could significantly change the drainage pattern over a decade, said Ohenhen.

“You are moving from a moderate risk of flooding to high rates of risk of flooding,” said Ohenhen. “Accounting for subsidence or having subsidence driven policy changes in a city could be helpful to adapt.”

The DPW declined to make anyone available for comment, but

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. It is unclear if the city’s elevation change is a factor in the stormwater management plan.

IndyStar’s environmental reporting project is made possible through the generous support of the nonprofit Nina Mason Pulliam Charitable Trust.

Sophie Hartley is an IndyStar environment reporter. You can reach her at *****@*****.tld or on X at @sophienhartley.

This article originally appeared on Indianapolis Star:

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#Indianapolis #sinking #slowly #Heres #city

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