Glacier

A glacier is a persistent body of natural ice, classified geologically as a form of rock, that moves slowly under its own weight, forming wherever snow accumulation exceeds melting and evaporation over many years or centuries. As glacial ice flows and deforms under gravity it develops crevasses and seracs and carves the surrounding landscape into features such as cirques, moraines and fjords. Roughly ninety nine percent of the world's glacial ice sits in the great polar ice sheets, and mountain glaciers occur on every continent except mainland Australia, with Pakistan alone holding more than 7,000 known glaciers, more non-polar glacial ice than any other country. Glaciers and ice sheets together hold about sixty nine percent of the world's fresh water, the planet's largest reservoir, and because glacial mass responds closely to long term precipitation, temperature and cloud cover, changes in glacier mass are considered among the most sensitive indicators of climate change.