As Harmon Maher walked along the Keystone Trail in central Omaha one morning in February, he spotted something odd: The creek next to the path, normally a gray-green color, ran bright orange.

It was full of sediment, probably from some construction upstream, the retired geology professor reasoned. Maher didn’t think much of it until hours later when his son alerted him to a mishap that was quickly becoming the talk of the town.

A patch of Pacific Street the size of a sand volleyball court had collapsed into the earth, swallowing a silver Ram pickup truck and a maroon Jeep Cherokee. The sediment Maher noticed in the creek had washed out from under the road, creating a massive void that the cars fell into.

“I was sorry I wasn’t still teaching,” Maher said. “I would’ve probably spent (time) in class saying, ‘Look, here’s the relevance. Here’s geology in action. Here’s a sinkhole.’”

Videos of the moment the road gave way quickly racked up millions of views from all over the world. But most Omaha sinkholes don’t go viral.

Over the last five years, city work crews reported more than 2,100 “cave-ins,” ranging from small dips in the pavement to gaping chasms like the Pacific Street sinkhole. Though most are minor, Omaha sees more cave-ins than several other Midwestern cities, according to a Flatwater Free Press analysis.

The city’s susceptibility to sinkholes comes from its soil, geologists say. Much of Omaha sits atop a fine-grained sediment called loess (pronounced “luss”) that can be easily carried away by water, leaving behind gaps underground.

“It’s great for growing corn, but terrible for building roads,” said City Engineer Austin Rowser.

More or ‘loess’

The sinkholes that typically attract online virality and dominate the pages of geology textbooks don’t happen in Nebraska.

That’s because the state is one of only a few that doesn’t appear to have much karst topography. Dissolvable bedrock makes places such as the Missouri Ozarks and Florida’s “Sinkhole Alley” more susceptible to massive sinkholes, said Matt Joeckel, Nebraska’s state geologist and a professor at the University of Nebraska-Lincoln.

By contrast, Omaha’s sinkholes are generally shallower and often result from human-made infrastructure interacting with the fine-grained sediment that blankets eastern Nebraska, geologists said.

“We’re not going to have a situation in which a giant sinkhole suddenly appears … and continues to grow and eat up a neighborhood,” Joeckel said.

When a pipe breaks or a sewer leaks, water can carry away loess or fill dirt underground. Omaha’s hilly topography aids that movement, said Maher, who taught at University of Nebraska at Omaha for four decades.

Rowser, the city engineer, theorized that the Pacific Street sinkhole started months before as a small leak in a Metropolitan Utilities District water main that found its way into the storm sewer, creating a small void that went undetected. Eventually, the water pushed enough dirt into the sewer to create the huge cavity that collapsed under the weight of two vehicles on Feb. 24, Rowser said.

MUD has challenged the city’s explanation, contending that the city’s damaged storm sewer was responsible for the sinkhole and that the water main broke after the road collapse.

Locked in a chicken-and-egg dispute, the city and MUD have filed claims against each other for the cost of repairs.

Omaha has averaged more than 400 cave-ins annually since 2021, according to a Flatwater analysis of Public Works data.

Many appeared only as slight dips in a road or sidewalk. The city ordered barricades for about 40% of cave-ins indicating some kind of hazard at the surface, Rowser said.

Omaha sees far more sinkholes in warmer months than colder ones — frozen soil doesn’t erode as easily, Rowser noted. That differentiates them from potholes, which typically form as moisture seeps into cracks in pavement during freeze-thaw cycles in late winter and early spring.

After the collapse, construction crews worked rapidly to repair pipes and fill in the square of missing road.