Previous Lecture Complete and continue

S.3 Geography Notes

Landforms Resulting from Glacial Erosion (Highland areas)

Both depositional and erosional landforms develop during glacial processes. In East Africa, the most impressive features result from glacial erosion and are both highly and lowland erosional features but the former are more dominant. The most common landforms produced by glacial erosion are:  

Glacial troughs (U-shaped valleys), Hanging valleys,  Arêtes, Cirques (Corries, CWM, Coire, Kar, Tarn), Pryamidal Peak or horns , Roche mountanne, Crag and Tail, Col/Pass, Rock Basins, Rock Steps.

A corrie/cirque/tarn is an arm chair like depression or a steep sided semi-circular rock basin. It is formed when ice occupies a small hollow on the side of the mountain. The hollow is enlarged and deepened by abrasion and steepened by plucking. Eventually the hollow becomes arm chair like in appearance. When a corrie is filled by melt water, it forms a glacial lake known as a tarn. When it is filled with water it became a cirque lake or tarn (corrie or cwm)  

                                              

Examples of the cirque lakes in:  

  • Uganda: Lac du Speke, Lac Noir, Lac Catherine, Lac Vert, Irene lakes, on Mount Rwenzori,
  • Kenya: Teleki Tarn, Hobley, Hidden on Mountain Kenya and  
  • Tanzania: - Mawenzi tarn on Mountain Kilimanjaro in Tanzania 

Arêtes: This is a steep sided knife edged ridge separating two corries. It is formed when two corries cut back to back in a process known as back wall recession/head ward recession by plucking.  Examples are Nelson, sharp ridges of Speke and Gessi 

                                               

Pyramidal peak: It is a sharp horn-like or jagged mountain peak. It is formed where three or more corries are eroded backwards in a process of back wall recession by plucking leaving a central pillar in the middle called a pyramidal peak.

Examples; point john, midget peak on mountain Kenya, Speke, Stanley, Alexandra Peak on mountain Rwenzori.

                                            

Glacial trough/U-shaped valley: It is a steep sided bottomed U-shaped valley. Before glaciation, it was V- shaped. The V-shaped valley was later widened by plucking and deepened by abrasion. Eventually the V- shaped was transformed into a U-shaped valley/Glacial trough.

Examples: Kamusoso, Mobuku, Bujuku, Kanywankoko, Lusilubi in Uganda; Karany on mountain Kilimanjaro and Teleki, Naro- movu valley in Kenya.

                                

Hanging valley: This is a tributary valley found high above the floor of the U-shaped valley. It is formed due to the presence of much more ice in the main valley (glacial trough) than in the tributary valley. Because of this, there is more erosion in the main valley than in the tributary valley through plucking and abrasion. Thus the tributary valley hangs above the main valley due to less erosion. 

                                         

Roche montonee: It is an outcrop of resistant rock in the path of a glacier. The upstream end is eroded by abrasion into a smooth gentle slope by the oncoming ice. The downstream end is plucked by the moving ice to give a steep jagged slope. 

Crag and Tail: It is a knob of resistant rock which obstructs the movement of the ice. The resistant rock is known as the crag; and protects the weaker rocks downstream. The eroded material is deposited on the downstream to form an elongated tail. 

Discussion

Get answers directory from your instructor
if you have any question about this topic.