Ice sheets, ice caps and valley glaciers compose the main elements of glacial environments. Many different processes deriving from their movement, as well as marine aeolian and fluvial influences, affect these environments putting them amongst the most complex present on Earth today.
Vital to the health of a glacier is its mass balance. Mass balance comprises of accumulation; all processes that add mass to a glacier, minus ablation; all processes that subtract mass from a glacier in a given year.
Determining the health of a glacial system is dependent on mass balance. A glacier with a positive mass balance is out of equilibrium with processes of accumulation being larger than that of ...view middle of the document...
These changes are propagated down the glacier by kinematic waves; ice flows moving down-slope by internal deformation and sometimes causing a protuberance in the ice surface as it spreads out the ice. Kinematic waves have a faster velocity than the ice and may initiate advancement at the snout when reached, which can take years. The rate at which this occurs is restricted principally by the slope, basal thermal and physical conditions. The distance a glacier will advance is determined solely by the amount of available ice, however, not by the kinematic wave itself (Paterson 1981) .
Variation in ice-thickness in the upper and middle sections of a glacier may be diminutive as it is the snout which is particularly susceptible to changes in mass balance.
Response times to mass balance changes also vary significantly from place to place and are dependent on the length and thickness of the glacier and the ablation at the snout. In general, small, high gradient, high-velocity, thin, temperate glaciers have a quick response time, reacting within a few years. For example, cirque glaciers may take as little as one to two years to respond, valley glaciers from 5 to 100 years. On the other hand, large, low-gradient, low velocity, thick, cold glaciers, ice sheet may take thousands of years to respond, such as the Antarctic ice sheet which takes up to 5,000 years.
Many different techniques are used to measure mass balance. Methods within the accumulation zone include snow pits, a fairly simple method involving digging through the previous winters residual snow pack to determine its depth. Probing is used in conjunction with temperate glaciers and comprises of inserting a probe into the ice until resistance increases suddenly indicating that the tip has reached the ice formed the previous year. Crevasse stratigraphy is used to measure accumulation in vertically walled crevasses making use of the distinguishable annual layer dirt bands which reflect summer dirt deposition and other seasonal effects. This method has its advantages as it can be used in cold regions where probing is not feasible.
To measure mass balance in an ablation zone, stakes are driven into the glacier at the beginning of the melt season. Surface melt on the glacier runs-off to reveal a certain amount of the stake, which is then measured. Numerous stakes placed in the ablation zone enable measurement of net ablation. The mass balance for an individual body of ice is usually expressed as the rate of change of the equivalent volume of liquid water, in m3/yr; the mass balance is zero for a steady state .
There is some controversy surrounding the relationship between mass balance and climate. Recent media attention has focused upon global warming, suggesting that as we increase the burning of fossil fuels we add carbon dioxide into the atmosphere and increase the temperature of the Earths atmosphere through the greenhouse effect. Subsequently, it is proposed that these processes will...