Follow slow rivers of ice as they shape peaks and supply water.
Glaciers form where snow survives summer, compacts into ice, and begins flowing downhill under its own weight.
Layers of snow compress into dense ice.
Learn MoreGravity makes glaciers deform and slide.
Learn MoreCrevasses and moraines reveal movement.
Learn MoreIce widens valleys and transports rock.
Learn MoreSeasonal melting feeds rivers downstream.
Learn MoreClimate controls long-term gains and losses.
Learn MoreWhere more snow accumulates than melts, buried layers are squeezed into rounded grains and then solid glacial ice. The process takes years or decades. A glacier begins when the mass becomes thick enough to move under gravity.
Glacial ice behaves like a brittle solid near the surface and a slowly deforming material deeper down. It may also slide over wet rock at its base. Flow is usually fastest near the center and surface, where friction from valley walls and bedrock is lower.
Crevasses open where the surface stretches over changing terrain. Dark stripes of debris called moraines collect along edges or where glaciers join. The terminus marks the glacier's lower end and can advance or retreat even while ice continues flowing forward.
Rock frozen into a glacier scrapes bedrock, while moving ice plucks loose blocks. Over time glaciers carve broad U-shaped valleys, sharp ridges, bowls, and deep lakes. Deposited sediment records where ice once extended.
Glaciers release meltwater during warm seasons, helping sustain streams when rain is limited. Communities use this water for ecosystems, farming, and hydropower. Rapid melting can also enlarge unstable lakes and increase flood hazards.
A glacier's size reflects snowfall and melting over many years. Most mountain glaciers worldwide are losing mass as temperatures rise. Scientists use field measurements, aerial images, and satellites to track changes and improve forecasts of water supply and sea-level rise.