Glacier Mass Balance

Glacial Mass Budget

• The difference between the amount of snow and ice accumulation and the amount of ablation occuring in a glacier over one year

Accumulation

• Gain of ice overtime

Ablation

• Loss of ice and snow through melting, evaporation and sublimation

Annual Glacial Budget = Total Accumulation - Total Ablation

+ve AGB -> Net Gain of Ice -> volume increase, glacial growth, equilibrium line moves down valley

-ve AGB -> Net Loss of Ice -> volume decreases, glacial retreat, equilibrium line moves up valley

0 AGB -> Stable amount of ice - > Maintains volume, no glacial growth or retreat, equilibrium line remains in same place

• Mass balance is measured by determining the amount of snow accumulated during winter and that is remaining at the end of the melt season and measuring the amount of snow and ice removed by melting in the summer. The difference between the two is the mass balance.

• Ablation is measured by emplacing stakes in glacier at the end of the previous melt season or the beginning of the melt season. As the glacier surface melts the amount of the stake emerging from the glacier is measured. Total melt at each stake at the end of the melt season is the net ablation
• Accumulation is measured by either probing or crevasse stratigraphy to determine the annual snowpack thickness at many locations. It is similar to reading tree ring width for climate analysis. These measurements are completed both in august and late september

• A glacier with a sustained negative balance is out of equilibrium and will retreat.
• A glacier with a sustained positive balance is out of equilibrium and will advance.

• In historic times, glaciers grew during the little ice age, a cool period from about 1550 to 1850.
• Sunsequently, until about 1940, glaciers around the world retreated as the climate warmed
• Glacier recession declined and reversed in many cases from 1950 to 1980 as slight global cooling occured
• Since 1980, glacier retreat has become increasingly rapid