Glaciers are an important element of the Earth system. Glaciers provide numerous, though poorly appreciated, ecological and economic benefits. However, glacial processes can also be hazards. Local glacial hazards include catastrophic floods from lakes impounded by glaciers and their moraines, landslides and debris flows induced by glacier thinning and retreat and permafrost thaw, and enhanced seismicity and volcanism due to large-scale deglaciation. Regionally, rivers can be affected by changes in sediment supply from glacier forefields. Perhaps the greatest hazard that glaciers pose on a global scale of coastal erosion and flooding caused by sea-level rise. If Earth's climate continues to warm, as scientists forecast, the rate of sea-level rise will increase and some low-lying coastal areas will be flooded by the end of this century.