The processes of cave formation in glaciers are analogous to cave formation in limestone and form from the preferential enlargement of high permeability pathways that connect discrete recharge and discharge points. Cave enlargement in glaciers is driven by small amounts of heat produced by friction as water flows through these high permeability pathways. Because rates of ice melting are many orders of magnitude faster than rates of the dissolution of limestone, glacier caves can grow to humanly traversable diameters within time scales of days to weeks whereas limestone caves of equivalent dimensions require 105–106 years. Because glacier ice is deformable, ice caves are squeezed shut at rates that increase with ice thickness, with deep caves squeezing closed in a matter of days. Glacier cave formation is therefore a dynamic process reflecting competition between enlargement and creep closure. While some glacier caves are reused and continue to evolve from year to year, many glacier caves must form each melt season. The processes of cave formation in glaciers exert important control on subglacial water pressure and affect how fast glaciers flow from higher, colder elevations, to lower warmer elevations. Ice flow directly into the ocean and glacial melt generally are important contributions to sea-level rise. Glacier caves are common in all glaciers that experience significant surface melting.