The Hole Truth -- Are Sinkholes man-made?
Sinkholes form when groundwater slowly eats away calcium carbonate rocks, like limestone, forming holes in the rock. The holes grow together, so that larger chambers form, underneath the ground. Caves, but not caves, as many of them are filled with groundwater, and have no openings to the surface to allow human exploration.
Eventually, the rocks on the top of the sinkhole are unable to support the 'roof' of the cave, and crack and break, falling down into the cave, and forming a large sinkhole. This is called Karst topography, and many areas look as if they have been cratered with bowl-shaped indentations in the rock.
CBS news discusses the nightmare of sinkholes in a really good article on their news site. The article not only discusses natural sinkholes, like those near Mammoth Cave, KY-- but those that are created by man's activities, like the giant sinkhole of Louisiana, caused by salt mining activities, and oil and gas activities.
The video below illustrates the formation of sinkholes in the earth, both by natural and man-made reasons.
All states in the US, but Hawaii have karst areas, because all states have deposits of limestone and other calcium carbonate rocks at the surface, somewhere. There may be a sinkhole near you!
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Most sinkholes are naturally made, but are drastically affected by lowering the water table by pumping high volumes of water. However, other sinkholes are created by man-- and are a specific question within mine subsidence. Both of these are considered to be geologic hazards!
Is there limestone near where you live?
Here is a karst map of the US-- could there be a sinkhole under your house?
No. I live on a huge glacial deposit of clay and shale. And when I say huge, I mean huge!
My house is on top of this hill
Historic photo of the "hills" that flank the village of Roslyn. I live on the one to the right.
Really beautiful area!
Welllll, there is glacial till all over karst. It's the bedrock that determines whether or not karst topography forms. I doubt that you do-- I seem to remember that bedrock is REALLY deep there, and there should be plenty of water down there, still, to keep the top of the sinkhole "floating".
We have karst around us, and very likely under us, as well. No one knows, nor do I believe there is a way, how to find out if there is a sinkhole directly under our house. Hope not!
I think FL's problem is due more to over pumping existing aquifers, with sinkholes that are close to the surface. Without the buoyancy of the water, they fall apart!
I need to go up to Indiana in the Mitchell Till Plain and take pictures of the sinkholes-- the area has no surface streams, because the water all sinks down into the ground... Hard to farm-- no flat spots. It looks like greened-up craters of the moon up there.
We have aquifers throughout Long Island.
Yes, you do!!! All the way down to bedrock! I don't know if bedrock is a good aquifer or not, but the glacial stuff is wonderful!
Much of the McGoffy aquifer is contaminated from septic systems, but the Lloyd aquifer is great! That's the one that Great Neck used!
This sink hole was a bout a 40 minute drive, yeah, we might be in the zone. Just one more thing to worry about, thanks. *wink*
I always though they formed in places that were backfilled over time and the water undercut them. Interesting article. Especially, the part about rapid water removal.
It surely does to me! Unstable areas where the bedrock is weaker, so let's go and put a bunch of buildings on it... Makes a LOT of sense!
Much love to you!
It doesn't 'seem' possible, but the water has a certain amount of buoyancy that helps to support the roof of them. So, when the water is removed by over-pumping, splash!
Our house was built directly on top of the bedrock, (in the basement), so it kind of worries me, too... We're on the Louisville Limestone. The worst area are those where the St. Genevieve limestone is at the surface. That's some porous stuff!
Much love to you!