Why do pipes crack when the water in them turns to ice?

Most substances shrink when they change from liquid to solid state. But water is one exception. When water becomes solid or ice, it expands by around one ninth of its volume. So 9 litres of water will freeze into 10 litres of ice. As pipes can’t stretch to accommodate the increased volume they will crack. In Finland, this freezing power of water is used to break big blocks of rock by filling cracks in the rock with water and then freezing it.