Glacial-Landforms-A.pdf

1 Glacial Environment The cryosphere: Consist of total Earth’s frozen waters, that includes ice and snow present in the atmosphere, in lakes and rivers, in oceans, on the land, and under the Earth’s surface. A glacier is a thick ice mass that forms above the snowline over hundreds or th...

1 Glacial Environment The cryosphere: Consist of total Earth’s frozen waters, that includes ice and snow present in the atmosphere, in lakes and rivers, in oceans, on the land, and under the Earth’s surface. A glacier is a thick ice mass that forms above the snowline over hundreds or thousands of years. 2 Last Glacial Maxima - LGM Glaciers presently cover ~10% of Earth’s land surface. Most are confined to Polar Latitudes, with 99% in Antarctica, Greenland and Artic… During Last Ice Age (Last Glacial Maxima – LGM), that occurred during 19-20 Ka it covered ~32% of the Earth’s land surface. 3 Type of Glaciers… Two types of Glaciers: Continental glaciers cover vast areas of land in extreme polar regions, including Antarctica and Greenland. Alpine glaciers (or valley glaciers) originate on mountains, mostly in temperate and polar regions, but even in tropical regions if the mountains are high enough. 4 Type of Glaciers… Two great continental glaciers on the Earth are, at Antarctica and Greenland, comprise about 99% of all of the world’s glacial ice, and ~ 68% of all of Earth’s fresh water. The Himalaya means the ‘abode of snow’. True to its name, the Himalaya encompasses the world’s third largest glacier systems after Antarctica and Greenland. The Himalaya feed rivers, such as the Indus, Ganges and Brahmaputra Continental Glaciers do not flow “downhill” because the large areas that they cover are generally flat. Whereas the flow of Alpine Glaciers is primarily controlled by the slope of the land beneath the ice… 5 Quaternary Glaciation 6  Quaternary glacial–interglacial cycles Quaternary glacial–interglacial cycles have caused distinctive changes in middle- and high- latitude landscapes. The extremes, cold and dry climates with warm and moist phases would have affected weathering, erosion, transport, and deposition, causing shifts in the type and rate of operating geomorphic processes. During warm and wet interglacial, strong chemical weathering processes (such as leaching and piping) would have led to formation of deep soil and regolith. During cold and dry glacial period, permafrost, ice sheets, and cold deserts developed. 7  Landscape during a glacial–interglacial cycle Leslek Starkel (1987) summarized the changes in a temperate soil landscape during a glacial–interglacial cycle. During a cold stage, erosion is dominant on the upper part of valley-side slopes, while in the lower reaches of valleys abundant sediment supply leads to overloading of the river, to deposition, and to braiding. During a warm stage, erosion thresholds are not normally exceeded, most of the slopes are stable, and soil formation proceeds. Meandering channels tend to aggrade, and erosion is appreciable only in the lowest parts of undercut valley-side slopes and in headwater areas. All these changes create distinct sequences of sediments in different parts of the fluvial system. In arid and semi-arid climatic zone – the pluvial and interpluvial phases causes erosion at different scale. [Pluvial – a period marked by increased rainfall] 8 Ice: The Water Mineral ❖ Ice is a solid water (H2O) ❖ Forms when water cools below the freezing point. ❖ Natural ice is a mineral; it grows in hexagonal forms.  Formation of Glacial Ice Snow is transformed into ice… ❖ Delicate flakes accumulate. ❖ Snow is buried by later falls. ❖ Compression expels air. ❖ Burial pressure causes melting and recrystallization. ❖ Snow turns into granular firn (a crystalline snow, which not yet been compressed into ice). ❖ Over time, firn is converted into interlocking crystals of ice. Ice may form… ❖ Quickly (10s of years). ❖ Slowly (1,000s of years).