Is it a hole in the ground? Or something else?

Last week, as Utah residents shed their winter coats and temperatures soared into the low 80s, creeks and rivers across the state surged with the first spring floods.

At Orchard Ridge, a Kaysville subdivision under construction, water poured down the street and half the street crumbled, creating a pit about 10 feet deep.

Brooke and Derek Schulthies live across from the newly constructed pit. As they stood next to the rushing water that tumbled down their neighborhood last Wednesday, they recalled the sounds of the previous night: running water and the crash of toppling dumpsters.

“The craziest part was when you were trying to sleep and you heard the rumble outside and your whole house was shaking — and then you went outside and another driveway fell off,” Derek Schulthies told the Tribune.

(Rick Egan | The Salt Lake Tribune) Flooding at Orchard Ridge Lane in Kaysville on Wednesday April 12, 2023.

While early reports referred to the chasm as a “sinkhole,” multiple sources told The Tribune the term was technically incorrect. “This damage is clearly caused by roadside erosion by surface currents in a construction area,” William P. Johnson, a professor in the University of Utah’s Department of Geology and Geophysics, replied in an email. “This is not a sinkhole being eroded from below by groundwater.”

While the asphalt-gulping void in Kaysville was technically not a sinkhole, The Tribune set out to determine what exactly might qualify as such and whether Utah might see more non-sinkholes in future flood events, or even as a result of super-saturated soil dated record-breaking snow of the winter.

What is a sinkhole?

True sinkholes occur in areas where the underlying rock (such as limestone, salt, or gypsum) is dissolving. When these soluble rock types come into contact with groundwater, caves can form beneath the land surface, explained Randall Orndorff, a research geologist specializing in sinkholes with the United States Geological Survey. This layer of rock usually dissolves over tens of thousands of years, forming underground caves that are difficult to see.

Whether a sinkhole collapses dramatically has to do with the type of ground above it. In some cases, the ground acts like an hourglass, and “the sand is slow to form this bowl shape as it penetrates the ground,” Orndorff said.

Clay soils are more cohesive and will hold up as the bedrock underneath disintegrates — but under certain conditions, this precarious land bridge can collapse.

Orndorff explained that drought could cause the clay soil to collapse. Conversely, heavy rains and flooding can add stress to the soil, causing the top layer to collapse into the cavern formed below. “That’s going to add a lot of weight and it just can’t support itself anymore,” he said.

Orndorff was working on a report that examined locations in the United States that have soluble rocks known as “karst” beneath them. “Almost every single state has some kind of dissolvable rock,” he said.

According to a report from the Utah Geological Survey, sinkholes formed in southern Utah that once swallowed La Verkin Creek for a week in 1996.

However, roads around Salt Lake City are not prone to natural sinkholes. “These soils aren’t typically found here in this part of Utah because we have very granitic rocky soil in and around our lands,” said Mark Stephens, Salt Lake City’s urban engineer. “What was reported as ‘sinkholes’ in Kaysville was actually washout caused by erosion from surface floodwaters,” Stephens said.

What do you call a non-sinkhole hole?

“I like to call these things infrastructure collapse,” Orndorff said.

Water pipes, culverts, and the various pipes that people put in the ground actually create holes. If a pipe breaks, the ground falls into the void. “It works the same way [as a natural sinkhole]”, said Orndorff, “but there are completely different causes.”

In May 2022, a water main burst in Salt Lake City’s Glendale neighborhood triggered a “car-eating crater,” the Tribune reported. It wasn’t technically a sinkhole either.

(Francisco Kjolseth | The Salt Lake Tribune) Crews are working to repair a burst water main that caused a large sinkhole that swallowed a parked car near 765 W. 1300 South on Tuesday, May 3, 2022 in Salt Lake City .

Just last January, flooding in California caused a void 50 feet wide and 30 feet deep that engulfed two cars, the New York Times reported. Numerous gaps appeared in the state. “They were actually infrastructure collapses,” Orndorff said, not natural sinkholes that created the California chasms.

Humans can cause sinkholes when they pump out groundwater and clear an area of ​​water-soaked substances. When it rains in a natural environment with trees and soil, the water seeps into the ground more or less evenly. Once that area is covered with pavement (what geologists like Orndorff call “impermeable surfaces”), “you’re concentrating all the water in one area and that’s going to trigger erosion, which will also include erosion of the underlying soil.”

More craters could come

But while Florida-style sinkholes may not open up around the Wasatch Front, flooding and runoff could result in more erosion.

“The damage will happen when we have to divert excess electricity across the streets to keep it away from buildings,” said Laura Briefer, director of the Salt Lake City Public Utilities Administration. When Wasatch Hollow, on the banks of Emigration Creek, began flooding last week, utility workers diverted the streams of water away from homes through the streets.

This eroded the ground under a small portion of the sidewalk at 1500 East, creating a miniature arch.

(Laura Briefer, Salt Lake City Government) Soil under a strip of sidewalk at 1500 E. eroded after the neighborhood was flooded last week.

“If we have to channel water over asphalt and concrete, there’s a risk that we’ll undermine the infrastructure,” explains Briefer.

To prevent leaching, urban engineer Stephens said proper erosion control measures are needed.

Home and business owners can do their part by watching where water flows on a normal rainy day, then making sure they have “grass or rocks or something that can keep the soil underneath from washing away,” Stephens said . And if they don’t have that, “they just have to be vigilant and have sandbags ready to direct water away from places they think might wash away.”

Water will always find its weakest point, Stephens explained.

“Water is very special, and it’s a very powerful thing in terms of where it’s going, how much of it there is, and what it can move.”

Justin Scaccy

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