A friend of mine lives by a river that always freezes over in winter. The ice gets so thick you could drive a truck over it. As the spring sun gradually warms the earth, the ice is being affected, but it doesn't seem that anything is changing. Yet if you look carefully, you notice that the ice is beginning to honeycomb with cracks.
One year, as winter was on its way out, my friend was standing on the banks of the river when he heard loud sounds like explosions. It was the ice suddenly cracking. Within minutes the whole foot-thick surface of ice on the broad river was heaving and moving with tremendous force. Huge floes started pushing downstream, crashing against one another and in some places gouging deeply into the banks. My friend had to move to higher ground to get out of the way. Amazingly, in an hour and a half, the river was just about clear. The impenetrable ice was gone, except for a few big, scattered chunks marooned on the banks. And the river, although high, was running quite smoothly.
The spring thaw isn't always as rapid and dramatic as that, but it is inevitable. Eventually the ice melts and disappears.
