Cold Environments: Glacial Landforms

Cold Environments: Glacial Landforms

1. Erosional Landforms

   • Corries/Cwm/Cirque
     • Corrie is also known as a Cwm (Wales) or a Cirque (France) and is an enlarged hollow on a mountainside.
     • Steep back wall and sides, generally hollow and very deep and may contain a small lake called a tarn.
     • The front of a corrie often has a raised rock lip, which helps explain the presence of the tarn.
   • Arêtes
     • Two neighbouring glaciers cut back into a mountainside-each one eroding a corrie-the ridge between the two corries becomes narrower.
     • This is a knifed-edged ridge called an arête that are common in both present-day glacial landscapes, and post-glacial landscapes.
   • Pyramidal Peak
     • When three or more corries erode back-to-back, the ridge then becomes an isolated peak called a pyramidal peak.
   • Glacial Trough
     • This is, in effect, a U-shaped valley. They tend to be steep-sided and flat-bottomed. They are also generally straight, because of their immense power and inflexibility of the large glaciers that gouge them out
     • A valley glacier will just cut through any previously existing interlocking spurs to form truncated spurs up the valley side.
     • If a glacier encounters weaker bedrock, or if a tributary joins the main valley which increases volume of ice, there might be enhanced erosion in parts of the trough (overdeepening). Localised enhanced erosion can form a narrow, but deep, ribbon lake
     • When main glacier melts, tributary glaciers are left hanging, and when they melt a hanging valley is formed
     • Resistant bands of rock on valley floor can lead to formation of roche moutonnee
   • Roche Moutonnee
     • Formed when a glacier flows over a band of resistant rock
     • Approximately 20 meters in height, and 10 meters in length
     • Strations on upstream side dues to abrasion, and polishing due to rock flour
     • Plucking on downstream side

2. Depositional Landforms

   • Moraines
     • Lateral Moraine consists largely of frost shattered rocks that have fallen onto the glacier from the valley sides
     • Medial Moraine is when a tributary glacier joins the main glacier, and two lateral moraines join up.
     • Englacial Moraine is moraine that has been trapped inside the glacier for many years
     • Ground Moraine is the rock material that grinds along at the base of the glacier.
     • Terminal Moraine is the moraine that marks the furthest the glacier has travelled.
     • Recessional Moraine is formed when a glacier retreats, then after a long time starts to move again, gathering moraine as it travels. This moraine is then deposited here and this is known as recessional moraine. It marks a temporary halt in the retreat of the glacier.
   • Outwash plain
     • Lies beyond the terminal moraine
     • A vast expanse of sand and gravel-deposited by braided meltwater rivers from the glacier.
   • Till
     • The material deposited/dumped on the ground when a glacier retreats.
   • Drumlins
     • Upstream side (stoss) is the steep sided
     • The downstream side (lee) is the gentle sloping side.
     • Egg-shaped hillocks that usually occur in clusters (swarms) in low-lying valley bottoms.
     • Consisting of a mixture of boulders and clay (ground moraine)
     • Thought to have been a result from the moulding of rock debris on the valley floor by ice moving over it.
     • Approximately 10 meters in height, and 40-50 meters in length
     • Steep upstream, and long slope downstream

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