Glacial Budgets

The glacial budget or net balance

Humid & cold Inputs The glacial system showing inputs, stores, transfers & outputs

Ablation The process of wastage of snow or ice by melting, sublimation and calvingcalving Ablation on Glacier de Tsanfleuron, Switzerland causing water to run off the glacier margin. Photo J. Alean.

Ablation area/zone That part of a glacier’s surface, usually at lower elevations, over which ablationexceeds accumulation.ablationaccumulation Ablation area of Glärnischgletscher, a small mountain glacier in northeastern Switzerland.

Glacier table A boulder perched on a pedestal of ice. The boulder protects the ice from ablation during sunny weather. Around the boulder the ice surface ablates and, therefore, is lowered, whereas the boulder remains at the original level. While the pedestal becomes higher and higher in relation to the glacier surface, the sun shines further under the boulder from the south (in the northern hemisphere). Consequently the pedestal gets ablated on its southern side, and the boulder will eventually fall off the pedestal, usually on its southern side (in the northern hemisphere). After this a new cycle of table growth and destruction may begin. ablation Glacier table on Vadret Pers, Grisons, Switzerland.

Accumulation The process of building-up of a pack of snow, refrozen slush, meltwater and firn. Net accumulation for one year is the material left over at the end of the melt- season.firn Measuring the previous year’s snow accumulation on Colle Gnifetti on Monte Rosa, Switzerland.

Accumulation area That part of a glacier’s surface, usually at higher elevations, on which there is net accumulation of snow, which subsequently turns into firn and then glacier ice.accumulationfirnglacier ice Accumulation area of Glärnischgletscher, a small mountain glacier in NE Switzerland.

Equilibrium line/zone The line or zone on a glacier’s surface where a year’s ablation balances a year’s accumulation (cf. Firn line). It is determined at the end of the ablation season, and commonly occurs at the boundary between superimposed ice (q.v.) and glacier ice.ablationaccumulationsuperimposed iceglacier ice The arrow in this photo actually points out the firn line. However, as the photo was taken near the end of the ablation season, the firn line more-or-less coincides with the equilibrium line.

Calving The process of detachment of icebergs and smaller blocks of ice from a glacier into water.icebergs Calving event at Hubbard Glacier, Alaska.

Mass balance (or mass budget) A year-by-year measure of the state of health of a glacier, reflecting the balance between accumulation and ablation. A glacier with a positive mass balance in a particular year gained more mass through accumulation than was lost through ablation; the reverse is true for negative mass balance.accumulationablation Mass balance investigations on White Glacier, Axel Heiberg Island. Photo J. Alean, 1976.

Glacier advance The forward movement of the snout (toe) of a glacier following successive years of positive mass balancesnoutmass balance Crusoe Glacier, Axel Heiberg Island, has a steep front, typical of advancing glaciers. Photo J. Aleaan, 1977.

Glacier recession The shrinking of the snout (toe) of a glacier following successive years of negative mass balance (q.v.). This is usually evident from the recession of the ice margin on land, or calving in the sea, but also from down-wasting. Also referred to by the term glacier retreat.snoutmass balancecalving Extremely rapid recession of Triftgletscher, Bernese Alps, Switzerland. Left: 2002, right Recession is accelerated by calving in the proglacial lake.

Glacier terminus Lowest end of a glacier Terminus of Bergsetbreen, western Norway

Snout The lower part of the ablation area of a valley glacier, commonly shaped like the snout of an animal. In North America, the term toe is more widely used.ablation areavalley glacier Snout of Bergsetbreen, Jostedalen, Norway