- grooves on rock created by abrasion due to debris embedded in base of glacier - Sharp, pointed hilltop between three or more corries (e.g. Snowdon, N Wales) - large armchair shaped hollow enlarged as ice moves in a rotational movement under gravity (e.g. Cwm Idwal, Glaslyn, North Wales) - Knife shaped ridge between two corries (e.g. Grib Goch, N Wales) Striations Corrie (Cirque) Arête Pyramidal Peak Ribbon Lake - long narrow lake occupying an area of the trough floor which has been overdeepened (e.g. Llyn Ogwen, Snowdonia)
small tributary valley above the floor of the main valley (due to differential erosion) (e.g. Cwm Dyli, N Wales)
- steep-sided valley with flat-floor (e.g. Nant Ffrancon, N Wales) - steep, rocky section of the side of a trough where the tips of pre-glacial interlocking spurs have been removed by glacial erosion (nr trough end in Nant Ffrancon Valley) - resistant rock outcrop with gentle sloping smooth up-valley side and jagged lee-ward side. (e.g. in Nant Ffrancon Valley, N Wales) Hanging Valley U-shaped valley (trough) Truncated spur Roche Moutonnée
Ribbon Lakes Many glacial troughs contain long, anwrro ribbon lakes. They may be the result of: (i) sreioon when a reicalg over-deepens part of its alylev in an area of softer okcr . (ii) a glacier over deepening its valley due to increased erosive power after being joined by a ibuttarry glacier (iii) deposition of aeimnor across the main valley forming a dam. When the glacier retreats, the deepened sections fill with melt water and become lakes. These lakes remain after glaciation, supplied by rainfall, streams and rivers. There are a number of examples of ribbon lakes to be found in the Lake District.
Can you identify a corrie, pyramid peak, hanging valley, terminal moraine, corrie lip, arete, glacial trough? In summary….
1 is a Pyramidal Peak because it has steep, triangular faces divided by sharp ridges or arêtes.
2 is an Arête , because it is a sharp ridge between corries.
3 is a Corrie or Cirque , because it is an armchair shaped hollow with steep back and sides.
4 is a Corrie Lochan or Tarn , because water has gathered in the hollow in the floor of the corrie.
5 is an Alluvial Fan , because it is a fan shaped pile of rock remains (alluvium) washed down by the stream and piled up where the steep valley side meets the valley floor.
6 is a Ribbon Lake , because it is a long narrow lake in a part of the valley cut deeper by the glacier.
7 is a Truncated Spur , because the ridge has been cut off sharply by the ice that flowed down the main valley.
8 is a Misfit Stream , because it is far too small to have cut the valley.
9 is a Hanging Valley , because the valley floor is much higher than the floor of the main valley.
10 is a 'U' Shaped Valley , because it has steep sides and a nearly flat floor. (The other side of the valley is missing in this cut-away diagram.