Pyramidal Peak
Arêtes
An arête, coming from the French for ‘edge’, is a very thin ridge of rock, which is typically formed when two glaciers erode parallel U-shaped valleys. As each glacier erodes either side of the ridge, the edge becomes steeper and the ridge becomes narrower. The knife-like edge of the rock is then sharpened by freeze-thaw weathering.
eg. Striding Edge found on Helvellyn in the Lake District. |
Corrie or Cirque
Corries/Cirques are often the starting point of an alpine glacier. Snow collects in a hollow and overtime turns to glacial ice. Erosion and weathering by abrasion, plucking and freeze-thaw action will gradually make the hollow bigger.
The ice is trapped in the hollow, but gravity still acts to move the glacier down, creating a circular motion movement - this is rotational slip. The ice may be able to pull away from the back wall; rock debris can then be plucked from the back wall and cause further erosion with a steep side. Some of this debris is deposited at the edge of the corrie, building up the lip. A cirque is often more visible once the glacier has melted and left the bowl-shaped landform behind. This looks much like a titled bowl. |
Corrie Lochan or Tarn
Ribbon Lake
As a glacier flows over the land, it flows over hard rock and softer rock. Softer rock is less resistant, so a glacier will carve a deeper trough. When the glacier has retreated, water will collect in the deeper area and create a long, thin lake called a ribbon lake. The areas of harder rock left behind are called rock steps.
eg. many of the lakes in the English Lake District are ribbon lakes, eg Windermere. |