Saturday, August 3, 2013

Wallace County Sinkhole

WOW!  a new sinkhole just opened up in Wallace County Kansas - just a dozen miles or so south of our southern GMD border.  The picture here is of this new feature. It was a catastrophic collapse estimated at 200-250 feet wide and 80-90 feet deep.  There is no water in the bottom and the exposed dirt all appears dry and friable.

There are no oil and gas wells or high capacity water wells in the vicinity, so many are wondering what the heck happened.  I was in a meeting in Garden City, KS when the news broke, and just so happens the director of the Kansas Geological Survey, Rex Buchanan, was in attendance as well.  During the break, Rex showed me the pictures he had been emailed by the Kansas Secretary of Health and Environment, who was asking for some explanation of this not-so-common event.  Rex  explained that the most accepted explanation was the slow dissolution of carbonate minerals (mainly chalk) from the underlying Niobrara Formation.  Eventually the dissolution cavity collapses.  Rex continued by saying it's not the first time this has happened in Wallace County as there are at least two named sinks in the County that were formed in the early 1900's - Old Maid's Pool, and the Smoky Basin Cave-in which happened on March 9, 1926.

Anyway, this is an interesting development for sure.  What cracked me up is the TV news report I saw on the evening news when I returned home.  The reporter, on camera, was making the point that there were large, concentric fissures in the ground surrounding the sinkhole and that these chunks of ground could at any moment slough off into the sinkhole as it expands.  The thing was, he was standing INSIDE the first and largest fissure as he was making these points!  Not 15 feet from the current rim.  I hope there's not a new reporter on the beat tomorrow!

So, while groundwater is not a major player in this sinkhole, and isn't pooling into a lake inside it (at least not as yet) it was most likely the downward percolating groundwater (vadose water) that dissolved the chalk below it over many, many years.  Will more of these form?  Almost certainly.  But when and where is anyone's guess.

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