13-year-old Exeter sinkhole creates large crater

Wednesday, February 21, 2018
Shown is an aerial photo of a large, water-filled sinkhole west of Exeter, taken by Richard Walker of Southwest City, with his drone. The sinkhole opened in approximately 2005. Since that time, the dirt road it is located on was closed off, and the area is inaccessible by vehicle. Contributed photo

Sinkholes common in Barry County

A large, water-filled sinkhole near Exeter is just one of many reported to be in Barry County, and is the result of a natural phenomenon.

After it opened in approximately 2005, the road was closed off, making it inaccessible.

“The only way to see it is to walk across a field overgrown with brush or by drone,” said Southwest City resident Richard Walker, who remembers when it occurred.

“People came from all around to see it when it first opened up,” he said.

Sinkholes are craters that open up in the ground and are caused by water erosion. They occur when water seeps into solid bedrock, especially limestone.

According to the U.S. Geological Survey, they

form in areas where water gathers without external drainage, and as it drains below ground, it can dissolve subterranean caverns, especially in areas where water-soluble bedrock is made up of salt, gypsum or carbonate rocks such as dolomite or limestone — the latter of which is common in Barry County.

Most of the time, they form gradually, but some have been known to collapse suddenly, swallowing Corvettes in Kentucky, condos in Florida and homes in Texas.

In a January 2014 article in the Cassville Democrat, Kimberly Scritchfield, an environmental public health specialist, provided information on the geological characteristics of Barry County, stating that sinkholes are very common, citing 89 recorded sinkholes, and 169 caves. She also shared that the typography of Missouri can easily lend itself to contaminated water due in large part to the karst cartography of the region, which describes the landscape created by water erosion through soluble bedrock such as limestone.

In May 2013, Walmart officials closed off a portion of its parking lot to make repairs to the pavement. A company spokesperson indicated there was a problem with the pavement, but denied sinkholes as the cause.

Sinkholes can also appear when leaking water or sewer pipes undermine roadways. An investigation by the Science News site www.phys.org in May 2017 found that urban sinkholes are a growing problem as cash-strapped cities neglect aging infrastructure.

For example, in January 2017, a 55,000-pound Hydro-Vac truck sunk into a sinkhole in the parking lot of an auto shop in Oakwood, Ga., due to a crumbling storm drain.

In September 2009, firefighters dispatched to investigate a flooding in the Valley Village neighborhood of Los Angeles, Calif., became trapped when their truck fell into what was a water-filled pit, which reportedly resulted after a 6-inch cast iron pipe broke.

David Brock, Cassville public works director said that in his line of work, he has observed a lot of utility excavations settle over time, which usually only results in surface depressions versus sinkholes.

“I’ve never had to deal with the large-scale cave-ins that are usually associated with much larger pipes and facilities than found in towns of 20,000 population or less,” he said.

In any case, the department follows up any reports of suspected sinkholes.

“We investigate any reports of sinkholes to see if it might be related to any buried utilities and provide general technical advice,” he said.

According to the U.S. Geological Survey (USGS), the most dangerous sinkholes have been found in Missouri (known as ‘the cave state’), Florida, Texas, Tennessee, Pennsylvania, Alabama and Kentucky.

According to information posted on the website of Live Science, geologists divide sinkholes into three types:

Dissolution sinkhole

In this type of sinkhole, there is little soil or vegetation over the bedrock. Water from rain trickles through crevices in the bedrock, dissolving it, gradually forming a depression. These sinkholes sometimes become ponds if the depression gets lined with debris, trapping water inside. They are generally not dangerous, but one that becomes a pond can drain suddenly if water makes it through the protective bottom layer. The Exeter sinkhole fits this description.

Cover-subsidence sinkhole

These sinkholes happen in areas where sand covers the bedrock.The sand filters down into openings in the rock, gradually causing the land surface to sink. Continued erosion increases the size of the depression. Like dissolution sinkholes, cover-subsidence sinkholes happen slowly.

Cover-collapse sinkhole

These are the most dangerous types. Bedrock is covered by a layer of clay. Beneath this ground cover, however, water dissolves an underground cavern. Gradually, ground sediments begin to erode, or spall, into the cavern from the bottom. The ground continues to crumble from beneath until only a thin layer remains between the surface and the underground opening. When that layer collapses, the sinkhole opens up suddenly, swallowing any structures on top.

Warning signs

Areas with underlying dissolvable rock are most susceptible to sinkholes. The ground may slump noticeably, causing fence poles or trees to lean. Soil might also expose buried surfaces of trees or foundations.

A structure threatened by a sinkhole may show small cracks, and doors and windows may stick or refuse to shut as the structure subtly settles. Circular patches of wilting vegetation or water gathering in small ponds where it never gathered before can also hint that the ground is failing.

One important warning sign is a ‘chimney hole’ or ‘chimney sinkhole,’ which are deep vertical holes of varying sizes with steep sides.

If residents notice any such signs, they should report them to the proper city or county officials.

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