Glacial erosion landforms

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A-Levels Glaciation Mindmap am Glacial erosion landforms, erstellt von EmmaSmile am 06/05/2013.
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Glacial erosion landforms
  1. Glacial trough
    1. Nant Ffrancon Valley, Snowdonia
      1. Steep sided, in places may have truncated spurs. Usually fairly straight, U shaped. Stepped long profile, deep valley. Floor consists of post-glacial alluvium and may contain misfit stream, ribbon lack or Roche moutonnee. May stop abruptly in a steep wall, trough end.
        1. Length 1-50km and width 0.5-3km. Length greater than width.
        2. As glacial ice moves through pre-existing river valley due to gravity, erodes sides and floor of valley by abrasion and plucking.
          1. Glacial ice straightens, widens and deepens valley as ice has more power than original river that cut valley.
            1. Glacial trough parabolic in nature due to accumulation of scree at base of slope, lessens slope angle. Scree formed due to weathering of the upper valley sides.
              1. Stepped long profile of many glacial troughs is due to over-deepening of parts due to compressing flow causing enhanced abrasion
                1. Rock-basins and steps created, clear where bands of less and more resistant rock are present.
        3. Roche Moutonee
          1. Found on flat valley floor of Nant Ffrancon Valley, Snowdonia
            1. Lump of resistant rock found on floor of glacial valley. Gentler lee end (upstream side) which may be polished and striated while steep stoss end (downstream) is jagged. Feature orientated in direction of ice flow.
              1. Where resistant rock projections stick out on floor of trough, localised pressure melting on up valley side as ice passes over due to increase in pressure and meeting of PMP.
                1. On up glacier (stoss) side ice streamlines rock due to abrasion. Polishes as well as creating scratches due to embedded moraine.
                  1. Meltwater trickles into joints of rock and as ice passes over rock pressure reduced, ice refreezes resulting in plucking and steepening of lee (down glacier side)
                2. Crag and tail
                  1. Edinburgh Castle (Crag) and Royal Mile (Tail)
                    1. Large feature with steep bare upstream side consisting of resistant rock and gentle downstream side made of glacial till deposits; angular and unsorted.
                      1. Formed when glacier ice flows around large and resistant rock obstacle. Pieces of resistant ock protect less resistant material on lee side from being eroded. Results in tapering in down-glacier direction.
                      2. Ribbon Lake
                        1. Long, linear, finger shaped lake occupying base of glacial trough
                          1. Windemere, Lake District
                            1. Formed when glacial abrasion causes overdeepening of valley floor as glacier passes over alternative bands of hard and soft rock. Hollow created in softer rock, called rock basin. The areas either side of rock basin consist of more resistant rock.
                              1. More resistant rock eroded less, acting as dams enabling areas to fill with water after glacial retreat - ribbon lake.
                                1. Lakes may also form behind terminal or recessional moraine, acting as dam.
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