The Andean Glacier and Water Atlas

During periods of increased snow mass accumulation or ablation, the equilibrium is disrupted and the glacier will either advance or retreat more than normal (National Snow and Ice Data Center, 2018). Few glaciers ever remain at equilibrium. While glaciers are extremely sensitive to environmental and climatic changes, they also play a role in influencing the global climate. For example, the reflective capacity of ice and snow is important in regulating atmospheric temperature. The term ‘albedo’ describes the ability of surfaces to reflect solar radiation. Dark surfaces have a low albedo, which means they absorb more energy and warm up, while white surfaces have a high albedo, reflecting a large part of solar energy back into space. The high albedo of ice and snow keeps these surfaces cooler. The more atmospheric temperatures rise, glaciers shrink, and snow cover disappears, the more radiation is absorbed by the surrounding darker ground, which warms and reinforces the melting. This is an example of a positive feedback loop. Shrinking glaciers and reduced snow cover are not the only concern in regard to the earth’s changing albedo. Black carbon is emitted into the air as fine particles as a result of incomplete combustion, for example from wood fired stoves or from diesel burning engines. When the particles sink to the ground, they create a layer of soot. These fine particles can travel relative far in the air and, when covering glaciers or snow, they darken the surface and reduce the glaciers’ albedo. This causes the glaciers to absorb more sunlight and warm accordingly. Research shows that glaciers near population centres, where polluting activities are concentrated, are more affected by black carbon pollution than those further away (Schmitt et al., 2014).

glacier ice. When this ice gets thick enough the glacier begins to flow, due to the force of its own mass under gravity, either by sliding or internal deformation. A glacier can be divided into two zones; the upper accumulation zone, where the snow mass accumulates and the lower ablation zone, where more glacier mass is lost, or ablated, than gained through snowfall. Ablation can occur due to melting, wind erosion and calving (National Snow and Ice Data Center, 2018). The point between the two zones where accumulation equals ablation is termed the equilibrium line. The equilibrium line is visible on temperate glaciers, a glacier at melting point that contains liquid ice. The line marking the boundary between new snow and old snow (firn) exposed by melting. However, the line tends to be diffuse on polythermal glaciers, which have a complicated thermal structure (Hambrey & Alean, 2016).

Glacier mass balance

Snow precipitation

Avalanches

Lateral moraine

Accumulation zone

Snow and rn

Pressure and solution

Equilibrium line

Snow akes

Terminal moraine

Crevasses

Sublimation

Glacial Lake

Granular snow (50% air)

Ablation zone

Flood plain

Plucking

Melting front

Glacier movement

Firn (25% air)

Abrasion

GEO-GRAPHICS / GRID-Arendal 2018

18