Professors Rule!

So you may remember this post in which I asked why doesn't the land settle where oil has been pumped out and create gaping caverns, and why doesn't Texas just sink into one giant sinkhole. I emailed a professor and asked... and she answered!

Mining of ores, excess pumping of ground water and extraction of oil give rise to settlement of the ground. Usually these settlements are pretty localized - that is why you don't see huge gaping holes in the ground like what you describe - however the land level itself has dropped because materials have collpased into the cavern left by the removal of the water/gas.
For example, in California excess pumping of groundwater has resulted in severe settlement problems in certain areas. This is also true in tunneling work. When they constructed the Mount Baker I-90 tunnel the residents above were concerned about settlement of their land - In fact after coal mining, the mines are supported by columns or non-hazardous materials such as fly ash is pumped into these caverns to prevent collapse and future land settlement. In Florida there are chemicals that can dissolve easily in the presence of water - that is why they have the problem with sinkholes.
If you are interested in reading more, you may want to visit the USGS site on land subsidence due to liquid extraction….
Also, if you go into google and type in "pumping of oil subsidence" you get some interesting information/pictures on how oil extraction has affected different regions.

Kind of cool, eh?