The top block of Napes Needle has a big crack underneath it. I was wondering if freeze-thaw might eventually make this too dangerous. Although the covalent bonds inside the water molecule are strong, there are weak hydrogen bonds holding the molecules together. At room temperature, the thermal agitation keeps breaking these bonds. Below 4 degrees and into the solid state, the thermal agitation is not enough and the molecules are able to stay together. These intermolecular bonds take up angles that push the molecules apart so ice has a bigger volume than liquid water. Water penetrates cracks with ease but the expansion on freezing pushes against the rock.
