Glaciers

Glaciers Denali National Park and Preserve • Glaciers cover 17% of area (1,563 square miles) • Changes in temp. affect hydrologic regime, diversity/spatial distribution of communities, physical landscape • Majority of glaciers retreated, thinned or stagnated over observed time periods • Most notable on glaciers with accumulation zones below 8,200 ft. (2500m) • Average 66 ft. retreat per year. • LIDAR (laser altimetry on entire surface) used to measure volume change • Radar depth measurements used too. Cold Phase – Ended 10,000 years ago. Little Ice age- Began 900 years ago, peaked at 1850 Canadian Glaciers • Melted 25% and 75% since peak of little ice age. • Terminal moraine 100s of meters from present glacier margins. Peyto Glacier • Rocky Mountains. Alt. btwn. 2140m-31850m above sea level • Covers approx. 12km2 • Contributes flow to Mistaya and North Saskatchewan catchments Glaciers and Global Warming • Now glaciers are melting at rates that cannot be explained by historical trends o Arctic glaciers (other than some in Scandinavia and Iceland) generally shrinking • Results could be: o floods,  Formation of glacial meltwater lakes  1985 Lake in Nepal flood kills people, destroys arable land and infrastructure o water shortages o rise of sea level  destruction of coastal habitats  flooding, erosion, saltwater intrusion into aquifers  displacement of people living near water. • Harmful Chemicals trapped in ice will be released Measurement • Mass Balance  difference between accumulation (mass added as snow) and ablation (mass lost due to melting or calving off chunks)

Glaciers and Water Supply • Ecuador, Peru, Bolivia- glaciers supply water year round are sometimes sole source of water for major cities during dry seasons • Himalayas supply water to 1/3 of the world’s population o 10-20% of glacier ice in the Alps was lost in less than 2 decades • Increasing sea level allows salt water to get into groundwater reserves • Since 1960s mountain glaciers worldwide have net loss of over 4000 cubic km of water. Loss was twice as fast in 1990s than during previous decades. • 70% of freshwater in glaciers • Tropics- glaciers provide only source of year round freshwater • Himalayan glaciers feed ganga, Indus, Brahmaputra, Salween, Mekong, Yangtze, and huang he rivers. 7 great rivers of asia – supply year round water to 2 billion people. Glacier retreat on the ganga causes water shortages for 500 million people and 37% of India’s irrigated land. Other • Greenland contains 12% of the world’s ice • Glacier National Park (Montana, USA) has lost 75% of its glacier area since 1910. • Rockies (Banff, Jasper, Yoho National Park) glacier cover decreased by 25% in 20th century • Melting beneath Glaciers is now rapid and widespread in Antarctica Physical Geography.net Alpine Glacier Glacier on Mountain (lower/middle latitudes). Smaller Continental Glacier ice sheet covering ground (high latitudes), larger (ex. Canadian shield) - Now ice covers 10% of land surface - Pleistocene (ice age) 30% covered - Biggest continental glaciers in Antarctica and Greenland. - Cold Glacier Ice as cold as -30degrees Celsius. Melting on ground surface due to pressure - Temperate Glacier 10-20 degrees Celsius - Subpolar glacier as cold as -30degrees Celsius. Subject to Melting during warm seasons - Calving portions of glacier separate into water (forms icebergs) Glacier Movement - ice becomes heavy and flows by plastic deformation. - Middle of glacier moves with most speed due to friction. - Basal Sliding ice in contact with ground melts and water reduces friction with ground.

Glacial Erosion - melting and refreezing incorporates rock/sediment into moving glacial ice - Scouringabrasive action of held rock underneath glacier - Glacial milk scouring causes very fine sediments to be carried in glacial water - Plucking particle detachment by moving glacial ice. Basal ice freezes in rock surface cracks, as body moves, surrounding material pulled/plucked out. Greatest strength on lee (opposite to direction of flow) side of rock mounds Glacial Landscape Features Hanging Valley adjoining feeder valleys of glacial valley have elevated floor because glacial valley has been eroded by glacier Cirque glacially eroded rock basin on mountains Horn Pyramid-shaped peak that forms when several cirques erode a mountain from 3 or more sides (Matterhorn – swiss alps) Arête Sharp ridge that separates cirques on a mountain or that is/has been glaciated - Roche Moutonnee smooth on side of ice advancement and steep and jagged on opposite side. - Meltwater feeds glacialfluvial deposits - Moraine Deposit of glacial till o Lateral Moriane debris falls from valley side slopes concentrated into narrow belt o Recessional Moraine Morraine deposits formed in stopping of the retreat of a glacier o Medial Moraine Two glacier flow together and moraine fuses - Till Plain large, flat plain of till that forms when ice sheet detaches from main glacier and melts in place - Erratic Boulder deposited by glacier far from source - Kame water with lots of sediment flows into crevasse/depression in ice, Cone shaped pile of sand forms - Esker Sub surface glacial streams made of sand and gravel have surrounding ice melt, leaving band of sediment - Drumlin Looks like teaspoon laying bowl down. Tapered end points in direction of glacier movement. Form when saturated ground sediment oozes up into hollow at base of glacier.