[bombcar]

Yep, water gets under the stone in the dirt, not enough for it to sink, and then the water/ground freezes, and pushes the stone up.

It's why foundations are build below the frost line, to prevent heaving.

[felipemnoa]

The explanation actually makes sense. Although, why wouldn't the stone just sink back down when the water melts? It is not like the space made by the expanding ice gets filled in by dirt.