A Local Sinkhole

Near to where I live is a sinkhole. It's on private property, so access isn't allowed. Since it's in an old, still producing oilfield, oilfield workers still have access, which bring me to what crossed my mind this morning. 

I met a man that had the opportunity to work near the sinkhole. There was a boat accessible, so he, and a coworker, decided to see how deep the water was. After tying a heavy bolt to the end of a 1000' roll of nylon string, they let it out, until he was holding the very end of the roll. They never determined how deep the sinkhole was, but knew it was over 1000' deep. From what I've read, the sinkhole started about a century ago, and has steadily grown since that time.

The sinkhole, from what I know, is the result of the collapse of a salt dome that was structurally compromised after years of oil extraction. One of many in the area, the empty domes are used for storing brine, or ethylene. They usually hold, and no problems appear, but I'm glad I'm a long distance away from the area. I do know the sinkhole started to have a rising water level a few decades ago, which prompted the stoppage of a brine injection process. Otherwise, there was leakage between the salt domes, and what was being injected was coming back up. The same thing happened years ago in Mont Belview, Texas, except the leakage was from a propane storage dome. They evacuated much of the city, placed flares in yards, and a trip through the area on the highway allowed to stay open at night was a macabre experience. All the electricity was turned off, the darkened area was only lit by the pipes protruding from the ground with open flames burning off propane.

We had another sinkhole appear in another local community a few years ago. Due to the proximity to the highway running through the community, TxDot monitored the area closely, and would have closed the highway if the sinkhole had continued growing. 

We don't have the same type of sinkholes that are found in Florida. Those here are not caused by erosion of subterranean limestone deposits. They're caused by the removal of oil from salt domes, without injecting brine to continue the upward pressure. This leads to settlement, which may be gradual, and lead to a large area of land sinking over time, or a rapid settlement creating a sinkhole. It's sobering to think of where they might appear, and with directional drilling, there's no way to completely rule out an unsuspecting landowner finding a hole thousands of feet deep appearing in a short period of time.