The Glacial SystemThe Glacial System

What is the glacier system?What is the glacier system?

The glacier system consists of inputs, transfers (flows), stores and outputs in the same way as a river.

Inputs come from avalanches along the sides of the glacier but mainly from precipitation as snow.

Over time snow accumulates and is compressed into ice. The water held in storage is the glacier.

Under the force of gravity, the glacier flows downhill.

Meltwater is the main output from the glacier, along with some evaporation.

Glaciers are systems in that they involve recognisable inputs, stores and outputs

How does the glacier operate as a system?

Growth of GlaciersGrowth of Glaciers

Glaciers grow or recede as a function of the balance Glaciers grow or recede as a function of the balance between accumulation and ablation of snow and ice. between accumulation and ablation of snow and ice.

The The accumulation zone accumulation zone is a region where snowpack is a region where snowpack or superimposed ice accumulation persists.or superimposed ice accumulation persists.

The The ablation zoneablation zone is the region where all of the snow is the region where all of the snow has melted away and bare glacier ice is exposed.has melted away and bare glacier ice is exposed.

The Glacial BudgetThe Glacial Budget

The The glacial budget glacial budget is the total of accumulation and ablation for a is the total of accumulation and ablation for a glacier.glacier.

In winter the budget is equal or can exceed melt causing the glacier to In winter the budget is equal or can exceed melt causing the glacier to grow, but in summer snow and ice melt exceed deposition.grow, but in summer snow and ice melt exceed deposition.

The glacial budget or net balance

Describe the shape of the two curves in the graph. Give reasons for the differences between them

AccumulationAccumulationThe 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.

Measuring the previous year’s snow accumulation on Colle Gnifetti on Monte Rosa, Switzerland.

Accumulation areaThat 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.

Accumulation area of Glärnischgletscher, a small mountain glacier in NE Switzerland.

AblationAblationThe process of wastage of snow or ice by melting, sublimation and calving.

[Sublimation = change of ice to vapour]

Ablation on Glacier de Tsanfleuron, Switzerland causing water to run off the glacier margin. Photo J. Alean.

Ablation area/zoneThat part of a glacier’s surface, usually at lower elevations, over which ablation exceeds accumulation.

Ablation area of Glärnischgletscher, a small mountain glacier in northeastern Switzerland.

Glacier tableA 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.

Glacier table on Vadret Pers, Grisons, Switzerland.

Equilibrium line/zoneEquilibrium line/zone The line or zone on a glacier’s surface where a year’s ablation balances a year’s accumulation. It is determined at the end of the ablation season, and commonly occurs at the boundary between superimposed ice and glacier 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.

Calving event at Hubbard Glacier, Alaska.

Glacier advance The forward movement of the snout of a glacier following successive years of positive mass balance

Crusoe Glacier, Axel Heiberg Island, has a steep front, typical of advancing glaciers.

Glacier recession The shrinking of the snout of a glacier following successive years of negative mass balance. Also referred to by the term glacier retreat.

Extremely rapid recession of Triftgletscher, Bernese Alps, Switzerland. Left: 2002, right 2003. 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.

Snout of Bergsetbreen, Jostedalen, Norway

The Glacier system