Why Does Water Expand When It Freezes? The 4°C Secret, Why Ice Floats, and How Life Survives Winter
Water expands by about 9% when it freezes, and ice floats on water. We trace two distinct phenomena — the 4°C density maximum and the expansion on freezing — their hydrogen-bond and ice-Ih mechanisms, and how together they let a lake freeze from the top down so aquatic life can survive winter.