G1:1.2 Glacial Processes and Landforms

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Weathering Processes

PHYSICAL

  • Freeze Thaw/Frost Disintegration: Water penetrates joints in the rock, undergoes melting and thawing over a relatively short time span (generally about a day). Ice is 9% larger than water at low temps, this increased pressure causes the rock to shatter.
  • Wind: Sediments exposed to the open can be blown by stong winds, creating Leoss deposits.

CHEMICAL

  • Acid Attack: Rocks degrade due to acid originating in animals and plants. LIMESTONE 
  • Acid Rain: Another strain of acid attack, due to Sulphur Dioxide in the clouds. Gnerally more of an issues in cities than the countryside, due to higher amounts of fossil fuels ending up in the localised atmosphere.
  • Rusting: Prone in rocks containing oxidising metails- e.g Iron

BIOLOGICAL

  • Fungi: Fungi extract minerals from rocks, rocks can then be decomposed this way.
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Erosion Processes

WEATHERING: Rocks being worn away and broken down insitue.

EROSION: Broken rocks being picked up and transported elsewhere.

  • Plucking: Ice adheres to the bedrock and as the glacier crawls, rock is pulled out and dragged along with the glacier.
  • Abrasion: Sediments at the foot of the glacier grates the rock, the movement is very similar to sandpaper, it leaves large gouges down to fine striations depending on the size of the sediment.
  • Glacial Deposition: Morraine Tills: The sediment dropped by the melted ice (ABLATION TILL) Lodgement Tills: Depostied by plastering of glacial debris from a sliding glacier bed.

Out of all of the WEATHERING PROCESSES, PHYSICAL is the most common as the temperature within glacial reigons is very low and fluctuating, slowing any CHEMICAL PROCESSES and redcing the likeliness of BIOLOGICAL methods living.

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Weathering Landforms

Very few landforms can ber atributed to weathering alone.

  • Scree: Collection of broken rocks, fragements at the base of valley shoulders. Largest rocks at the base, because they have the most momentum. E.g Lech di Dragon, Dolomites of South Tyrol, Italy. A glacier hidden under a thick layer of debris.
  • Soil Fluction: Soil creep (slow downwards movement of soil due to soil particales expanding and contracting due to absorbption of water) in areas of permafrost. E.g Swiss National Park, 
  • Moraine: accumulation of unconsolidated glacial debris that occurs in currently or formerly glaciated aread. Lateral Moraines: parallel ridges of debris- deposited ALONG the SIDES of the glacier., from freeze thaw of valley sides, don't experience post glacial erosion of the valley flow & lie in high ridges. E.g Gorner Glacier, Zermatt, Switzerland. Terminal Moraines: ridges depsotied at the snout of the glacier, they usually reflect the shape of the glacier's terminus, thr longer the glacier is staionary, th larger the deposit. Terminal advance=maximum advance of the glacier. E.g Wordie Glacier, North Eastern, Greenland
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Glacial Features

  • Mudflow: Debris partially or fully liquified by melt water. Occurs in 2 places in a glacier, firstly underneath the glacier, where meltwater acts as a lubricant, secondly at the advancing front of the glacier. E.g Jökulhlaup, Mount Katla, very liquidy meltwater erupts every 40-80 years.
  • Soil Creep: Slow downwards progression of rock due to filtration of water. Wet soil expands, dry soil contracts. This expansion and compression causes soil movement. E.g Less common in areas of permafrost.
  • Pingos: The active layer continually freezes and melts year on year above the permafrost and talik.  Over winter, as the active layer freezes down over water can become trapped between the descending freezing plane of the active layer and the permafrost that surrounds it.  This promotes the growth of an ice lens which pushes the land up above it as it expands. This water migrates to the ice lens and freezes, swelling the ground above further. E.g Ibyuk Pingo, Northern Territories, Canada.
  • Patterned Ground: DIstinct symmetrical shapesformed by ground material in peri-glacial reigons. They generally occur in areas, if not on, Pingos. Formation: Larger stones are rolled down onto even ground, leaving finer stones in the middle. As the ice lens grows, stones above it are shifted, but the finest sediment remains in situe. E.g Tamarack Larch, Canadian Boreal Forests.
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More Erosion Processes

  • Glacial Abrasion: Glaciers knock off and drag very hard boulders and gravel on their path to melting. The contact points act like sandpaper- either forging deep gauges or smoothing the surface, depending on the size of the sediment.
  • Glacial Plucking: Exploitation of preexisting cracks in the glacier. Rock is infiltrated by water (lubricant) and then it freezes, adhering the rock to the glacier.
  • Glacial Meltwater Erosion: Meltwater pools on the surface, then, rather than flowing it form meltwater ponds/pools. Meltwater can collect under the surface of the glacier (called subglacial lakes) can form due to geothermal heat and friction.

MICROSCALE < MESOSCALE < MACROSCALE

MICROSCALE FEATURES

  • Striations: a series of ridges, furrows or linear lines, as a result of a glacier moving; formed via abrasion. E.g Mount Rainier National Park.
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Glacial Features

MESOSCALE FEATURES

  • Roche Moutonnees: Steep jagged faces, formed by plucking and one longer smooth side, formed by abrasion. HARD ROCK ONLY E.g Dulnain Bridge, Cairngorms.
  • Subglacial Meltwater Channels: A channel beneath on ice mass, roughly parallel to main ice flow direction; they can range from metres to kilometres wide. E.g Postoruri, The Andes.

MACROSCALE FEATURES

  • Cirques: An amphitheatre-like valley head, formed at the head of a glacier by erosion. E.g Dana Glacier, Yosemite National Park.
  • Arêtes: A thin ridge of rock left seperating two valleys; they form when 2 glacial cirques erode headwards towards each other. E.g Striding Edge, Helvellyn, Lake District.
  • Pyramidal Peaks: Formed where three or more arêtes meet, glaciers have carved away at the top of the mountain. E.g Matterhorn, The Alps.
  • Glacial Troughs: A U-shaped valley formed through the process of glaciation. Steep sides, flat bottom. Formed when a glacier travels down a slope, carving it's way through, scouring the rock. E.g Glen Tilt, Perthshire, Scotland.
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More Glacial Features

  • Hanging Valleys: Smaller side valleys that contained a smaller mass of ice, and got cut off by a larger glacier, thus it is left hanging. E.g Bridalveil Fall, Utah.
  • Truncated Spurs: Rounded areas of land which have been cut off by a glacier moving through a valley. E.g Franz Josef Glacier, South Island, New Zealand.
  • Crag and Tail: A rocky outcrop with a tapering ridge of glacial deposits extending to one side. BOTH HARD and SOFT ROCK E.g Arthur's Seat, Edinburgh.
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