Week 11 Glacial.docx

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Geographical Biogeosciences
GEOB 103
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Week 11 Alpine Glaciers What is a glacierA glacier is a mass of ice that has its genesis on land and that represents a multiyear surplus of snowfall over snowmelt Glacial ice accumulates in mountains alpine glaciers or over continents ice sheets ice caps Glaciers are found in mountainous areas throughout the world from the tropics to the poles Perennial ice covers about 11 of the land areas of the Earth Within the past 2 million years glaciers and ice sheets expanded to cover about 29 of the total land area of the EarthGlaciers form in any area in which annual snow accumulationsnow melt Successive layers of snow are slowly compacted until the loose snowflakes gradually become more and more dense with increasing depth and age As gravity slowly deforms this mass of ice and it begins to flow a glacier is formedWhy study glaciersFluctuations of the volume of glacier ice are related to climatic variations in temperature and precipitation Glaciers are very effective agents of erosion and deposition significantly modifying the landscape Glaciers hold over 75 of the worlds fresh waterthey act as frozen freshwater reservoirs that release water during the summerGlaciers in Mountainous Regions Alpine GlaciersFranz Joseph Glacier NZGlaciers in Bhutan HimalayaDiagrams of an alpine glacier from Strahler and ArchiboldGlaciers can only form at or above the lower limit of perennial snow or the snowlineoThe snowline is the elevation above which snow persists year round It is a function of latitude The atmosphere cools at a rate of64 C per kilometer as air masses expand Therefore the snowline rises at lower latitudes where temperatures at sea level are warmerGlacier ice is formed from snow that does not melt in the summer The snow recrystallizes to form LARGE crystals of ice Rough and granular called firn Its much like packed snowballsLower layers then turn to solid ice under the weight of overlying firn and snowWhen ice accumulates on sloping ground it will flow downhill away from theaccumulation zone snowfallmelt and into the ablation zone meltsnowfallThe point on the glacier where annual accumulation is exactly equal to annualablation is referred to at the equilibrium line altitude ELAoAt the coast of BC ELA is about 2000 m but in the Rocky Mountains theELA rises to 3000 m Q WhyThe end of the glacier is referred to as the glacier terminus the glacier snout or sometimes the toe of the glacier
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