A ‘sinkhole’ swallowed a car in Salt Lake City. How did it happen, and how common are they?

“It was crazy,” said a man who lives on the street where it happened.

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

A portion of roadway collapsed in Salt Lake City on Tuesday, swallowing a car into a pit of deep, murky water in what officials referred to as a “sinkhole.”

The car-eating crater was caused by a water main break, which in turn caused flooding early Tuesday near 1300 South between 700 and 900 West, leading to the “sinkhole.”

Fire officials responded at about 4 a.m. Tuesday, and although the event caused no injuries, some homes experienced significant flooding. All homeowners were able to get in and out of their residences with assistance from Salt Lake City fire crews, Capt. Shaun Mumedy said, though some cars also got stuck in debris.

How do sinkholes happen?

The hole that swallowed a silver SUV on Tuesday was probably not a technical sinkhole, William Johnson, a University of Utah professor with expertise in geologic hazards, said. Instead, the roadbed likely collapsed when the broken water main eroded sediment from underneath it.

Sinkholes by geologic definition typically occur when a layer of rock — like limestone — is dissolved and removed by water that percolates in, Johnson said. In this case, the sediment was likely just washed away, because limestone in the Salt Lake Valley doesn’t lie directly under the roads, Johnson said.

Colton Clark, who lives three doors down from where the roadway caved in, said his wife woke him up to the sound of sirens and water rushing down the street early Tuesday.

“We looked out the window and saw the water in the street and couldn’t figure it out how could it have possibly rained that much,” Clark said. “We ran downstairs and saw water coming in our basement.”

The couple thought it was coming in through the windows, and they worked to try and divert it.

“That’s when I looked over and saw that car just spinning in the sinkhole,” he said.

Clark spent about an hour shoveling, searching for the source of the flooding. The fire department ultimately explained that it was flowing in from underground due to the water main break, surging up through his home’s main water line and in from the fireplace.

“My basement’s cinderblock, and so it’s very porous — it’s an older house and so some of the grout lines are extra porous,” Clark said. “So it was just finding its way in.”

(Francisco Kjolseth | The Salt Lake Tribune) Homes with extensive water damage begin the cleanup process as crews work to repair a water main break that created a large sinkhole that swallowed a parked car near 765 W. 1300 South in Salt Lake City on Tuesday, May 3, 2022.

‘It was crazy’

The Clarks have floor drains in their basement, and with a lot of effort, they were able to divert some of the water. The most they had in their home was about 4 inches.

Some of their neighbors were not as lucky, he said. At least two families who experienced severe basement flooding were put up in a motel by Salt Lake City Public Utilities.

“It was crazy,” Clark said. “I’m still worried about settling issues and what it could cause foundationally for my house in the future.”

But mostly, he is thinking about seeing that car disappear into the ground, he said. “That’s enough to make me believe that the corner of my house could probably go if if the conditions were right.”

Salt Lake City Public Utilities arrived shortly after fire crews, according to communications manager Holly Mullen. The department contracts with disaster cleanup services, and had a truck in the area Tuesday to help suck out water.

The department is still investigating the cause of the water main break, Mullen said, but sometimes, they “just break.”

An all-day repair

The water main that broke was made from 1940s-era cast iron, but the city has even older pipes, so the cause was not necessarily age. Public Utilities employees located the break early Tuesday and replaced a 10-foot piece of the water line’s pipe along with about 60 feet of a damaged sewer line.

Mullen said the department “really, really rallied yesterday — they were there from 4 a.m. until early [Wednesday] morning.” Water was restored to area homes by about 8 p.m. Tuesday.

Now that the water main is repaired, Public Utilities is working on refilling the hole in the roadway and repairing the street, which should reopen in a few days to traffic.

As for damage to homes on the street, the incident was referred to the city attorney’s risk management division, Mullen said. She wasn’t sure if other water lines in the area would also need to be repaired or replaced.

“The department is always under a constant process of evaluating, testing ... and just constantly looking at aging, and any kinds of issues that that might necessitate immediate repair or replacement,” Mullen said.