I had a frost heave appear on/in/under my driveway last March. It mostly settled itself – the driveway shrunk back down nearly to its normal height once spring settled in. And I swear I’ll actually seal the crack(s) once and for all during the upcoming (now weather-pending) Crack Weekend.
One of my favorite bloggers, National Review’s John Derbyshire, apparently has a similar problem, though the timing suggests something other than a frost heave. His inquiry for ideas lead to a bevy of possibilities, including subterranean mushrooms, an old well, dandelions (a problem I’ve had – they do push through asphalt!), a volcano, a baby driveway (i.e., sidewalk) and more. Possible solutions range from fungicide to shotguns. All of which are far more interesting than my problem and (lack of) solution.