Thanks for contributing. I also think that fracking has something to do with some of the sinkholes, but I also believe that my Dangerous Gas theory may have something to do with others as well. And, they actually tie into together because one of the main causes of the methane increase in the past five years could be fracking. There is a lot of information in the Dangerous Gas thread in my signature below, but there has been a recent study that shows much more methane gas is being released from fracking than originally thought. Fracking got its kickstart in about 2005-06, and methane release which had slightly risen for the past 150 years leveled off in the late 90's, but started increasing again and much more rapidly about the same time fracking started. The other way I believe that methane gas is contributing to the sinkholes is the permafrost melt. I've talked about how I think earthquakes and volcanoes are increasing in the quote below but sinkholes fall into the same category.
I do believe that an increase in earthquakes and volcanoes is part of a chain reaction causing more gas leaks. Volcanoes are a major cause of an increase in methane gas releases. The rapid increase of methane gas is helping to heat up the atmosphere as long-wave infrared comes in from the sun, heats up objects on earth and would normally safely escape the atmosphere as short-wave infrared, is being trapped due to the build up of methane. A dangerous cycle. The heating of the atmosphere is in turn melting more Arctic permafrost (which also releases more methane) which then causes earthquakes by the theory proposed here
The argument goes like this: when the climate changed naturally in the past, and the planet emerged from an ice age, large ice sheets covering much of the planet retreated. They were so heavy that the resulting release of pressure on the earth's crust caused it to 'bounce back', triggering earthquakes, tremors, and even volcanic activity along pre-existing fault lines.
Right now the ice is retreating so if this theory is correct it could be relieving pressure which would cause earthquakes, volcanoes and sinkholes.