The most common type of sinkhole occurs when rainwater has dissolved a limerock substrate. The limerock is pretty strong, and it can hold up quite a bit of weight. When enough of the limerock has been eaten away, the top of the dome collapses without warning, swallowing anything that was on there at the time.

The second most common type of sinkhole occurs when a high-pressure waterline or high-volume drainline breaks. As water shoots out of the pipe underground, it eats a hole in the dirt. Because the pipe is hidden (and usually many decades old), nobody suspects until a large section above the pipe collapses. I recall a major pipebreak in San Diego, CA, which ate a large section of an onramp to highway I-8. Because it happened at night, a lady drove into it and was seriously injured. The folks behind her stopped and flagged down all the oncoming traffic. They ended up digging a 700ft ditch to get at the pipe.