15th Cape sinkhole opens up

A new sinkhole has appeared on Cape Girardeau's south side. Discovered Wednesday, sinkhole No. 15 is a relatively small opening next to the concrete-reinforced bank of Cape LaCroix Creek near South Sprigg Street.

Last week's historic amount of rain is partly to blame. The downpour weakened ground surfaces while filling rivers, creeks and underground streams. The underground water dissolves limestone, creating voids. When the hidden stream disappears, the earth above can collapse.

Sinkholes have appeared sporadically on the city's southside for years.

But a rash of them began appearing in July. That's when the ground fell away, rupturing an AmerenUE gas line. Ameren officials chose to move that line and an electric utility line.

Since then, the city has been working with state and federal agencies as well as area businesses, such as Burlington Northern Santa Fe Railway, SEMO Stone and Buzzi Unicem, to figure out what's causing the spontaneous holes and how to stop them.

By Friday, Ken Eftink was able to stand on the dried cement cap over the refilled hole No. 15. Eftink said every sinkhole is overfilled to allow for settling.

A few inches away, a series of concrete panels are angled along the creek bank, installed to limit erosion. The seam between the two panels closest to No. 15 is hidden by a pile of rocks; the ground below them also fell away. He took photos of the area, images to be shared with the Missouri Department of Natural Resources geologists and specialists from the U.S. Army Corps of Engineers.

AARON EISENHAUER ~ aeisenhauer@semissourian.com Ken Efftink watches as crews move rock to build a temporary levee around sinkholes three and ten as waters in LaCroix Creek rise with the river on Friday, March 21, 2008.

At least once a week, Annie Anand, the city's geographical information systems coordinator, visits the site to evaluate changes in the various holes. She maps the holes, reports changes to the city and posts new images online.

Become depressions

Many sinkholes refill themselves as the soil walls slough off and over time become depressions in the land. But many of Cape Girardeau's southside sinkholes are large, ranging from a few feet across to more than 100 feet in diameter and as much as 80 feet deep. Sinkholes No. 3 and 10, near the south bank of Cape LaCroix Creek, just east of South Sprigg Street, have begun to merge, as have two more, No. 4 and 7, just south of that site.

Water, whether rising from underground or falling from the sky, caused new depressions in some repaired sinkholes. In No. 14, nearly 25 feet of rainwater has collected. The reopened sinkholes cannot be filled by construction workers until the water abates or is pumped out, Eftink said.

In advance of today's predicted crest of the Mississippi River, construction crews worked around the clock for days to move stone and dirt into levee formations along Cape LaCroix Creek's bank. The mound of rock covering sinkhole No. 3 was removed and added to the creek levee.

An earthen levee was constructed farther south, across the railroad tracks. The levees are intended to protect the Buzzi Unicem plant should Cape LaCroix Creek rise as expected.

"They're buying time taking the rock here and moving it into a levee. The river's backing up into LaCroix Creek," Eftink said Friday. "It's part of the river now."

Once the Mississippi River crests and begins to fall, more sinkhole problems are expected. As the underground water falls back toward the river, it will carry along sediment — dirt and small rocks — and create more underground caves. The more rain from above, the more likely weak earth will fall into underground caves.

The Department of Natural Resources' division of geology and land resources offers an illustrated description showing eight stages of sinkhole formation at <a href="http://www.dnr.mo.gov/geology/geosrv/geores/sinkhole_formation.htm" target="_self" title="www.dnr.mo.gov/geology/geosrv/geores/sinkhole_formation.htm">www.dnr.mo.gov/geology/geosrv/geores/sinkhole_formation.htm.

pmcnichol@semissourian.com

335-6611, extension 127

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