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Lecture 4

GEG3107 Lecture 4: Lecture 4

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Antoni Lewkowicz

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Lecture 4: Geomorphology of Polar Regions Landforms produced by ground ice formation: - Palsas  True palsas are only found in peat, but mineral-cored and lithalsas also exist  Can be up to 10 m high, and 50 cm in diameter  Mainly found in discontinues permafrost zone, but may be found in continuous too  Found in areas of poor drainage (bogs and fens), caused by segregated ice  Natural cycle of growth and degradation [flow chart], independent of climate change (but climate change does have an effect) - However as air temperatures rise, the degradation increases (and growth has slowed/stopped) - Degrading palsas may release methane or CO as th2 organic material breaks down - As mounds grow larger they begin to break apart (wind erosion…)  Very fast, as geologic process go - Water is a major cause of palsa degradation  Norway: Air temperature rise from -3 to -2, resulting in substantial degradation  Wolf Creek: Rapid change, but caused by animal activity, not climate change - Beavers came back and (re)built dams, which flooded the area - ERT (Electrical Resistivity Tomography)  Lots of water in the active layer, water is a good conductor = low resistivity - Pingos  Much larger than palsas (up to 60m high)  Can be open-system or closed-system  Open-system (Greenland type): - Found in areas of discontinuous permafrost - Caused by hydraulic pressure due to groundwater flow (under the permafrost) and high/mountainous topography  In valleys and at the base of mountains  Closed-system (Makenzie type) - Found in continuous permafrost zones, esp. Mackenzie delta & Siberia - Form when a talik (unfrozen ground) that was beneath a lake or river is exposed when the water is drained or moves - Talik begins to freeze inwards, putting pressure on the sediments and water within, which leads to lifting of the ground (to release the pressure)  If the water pressure can escape in other ways, pingos will not form - Pingo continues to grow as long as the talik remains unfrozen - Can be round (from beneath lakes) or longitudinal (beneath rivers) - Seasonal frost mounds  Develop in one winter and degrade in the next summer (usually)  Similar to open-system pingos, they are caused by high groundwater pressures  Found in discontinuous zone and in high relief areas  3 types: - Icing Mounds: form where groundwater escapes from the ground and freezes in layers, building up a broad mound - Icing Blisters: Develop by icing as a result of groundwater beneath it. The pressure is relieved by heaving. Are recognized by dilation cracks - Frost Blisters: Groundwater that reaches the surface during the summer gets pinched off by freezing. Pressure builds up between active layer and permafrost is relieved by up-heaving of frozen s
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