ablation: loss of ice from a glacier caused by melting or vaporization
accumulation: any process by which a glacier gains mass; usually by snowfall
but also by avalanching, wind-drifted snow, etc.
advance: when a mountain glacier's lowest end extends farther down-valley than
calving: process of ice breaking off and falling at a glacier's end
crevasse: an open fissure in the glacier surface
firn: rounded, well-packed snow that is older than one year
glacier: a large flowing ice mass
ice sheet: a dome-shaped mass of glacier ice that covers surrounding terrain and is greater
than 50,000 square kilometers
retreat: when the position of a mountain glacier's lowest end is farther up-valley than
snow: A collection of
loosely bonded ice crystals deposited from the atmosphere.