When ice melts, its volume increases. This is because the water molecules in ice are arranged in a very regular, crystalline structure. When ice melts, these molecules break free from this structure and move more randomly. This causes the water to expand and take up more space.

The amount of expansion that occurs when ice melts is about 9%. This means that if you have a glass of water that is filled with ice, the water level will rise by about 9% when the ice melts.

The expansion of water when it melts is important for a number of reasons. One reason is that it can cause damage to objects that are exposed to freezing and thawing conditions. For example, water that seeps into cracks in concrete can freeze and expand, causing the concrete to crack. Another reason is that the expansion of water when it melts can be used to generate power. This is done by using a hydroelectric dam to harness the energy of flowing water.