Glacier

A glacier is a large mass of snow and ice that forms on land where snowfall accumulates over many years and does not melt away completely. As layers build up, their weight compresses the snow into dense ice. When the ice becomes thick enough, gravity causes it to move slowly downhill or outward. This movement may be only a few meters per year or much faster in some glaciers.

Glaciers occur mainly in high mountains and polar regions, and their shape depends on climate, altitude, slope, and the landscape beneath them. Unlike sea ice, which floats on ocean water, a glacier is connected to the ground. Glaciers are active parts of Earth's water cycle and landscape.

They store a large amount of the planet's freshwater, and meltwater can feed rivers and lakes, especially during warmer seasons. As they move, glaciers can erode rock, carry sediment, and leave deposits behind, helping to create valleys, ridges, and other landforms. Scientists monitor glaciers because changes in their size and movement provide important information about climate conditions.

A glacier can grow when snowfall and accumulation exceed ice loss, while it retreats when melting, ice loss, or other forms of ablation exceed the supply of new snow. A retreating glacier is therefore not simply “moving backward”; its front is losing ice faster than new ice is added.