Ever wonder why rocks seem to forever be working their way to the surface?
Here's your answer...
We had a little impromptu science lesson this morning, in the yard.
Observe the humble mole hill...
On the small scale it's called needle ice. On the large scale it's frost heave.
Basically, there is water in the soil. The air above drops below freezing.
Ice crystals begin to form, and they grow in the direction of heat loss. Up.
And they push the soil and stones up above them.
Pretty amazing :D