Holy Cow Sink Hole?!

I'm watching the news, and there appears to be what can only be referred to as a big *ss sink hole outside of Houston. 900 feet wide and 250 feet deep. Thing is freaking huge. I tried to look it up online to see if there are any good explanations for how that happens, but I have to say there is nothing clear offered up. They pull out the oil and replace it with salt water? but what is the deal? What suddenly causes it to collapse. There are only about 1,000 people in the town, but they must be freaking.