72919
Glacial erosion landforms
- Glacial trough
- Nant Ffrancon Valley, Snowdonia
- 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.
- Length 1-50km and width 0.5-3km.
Length greater than width.
- Length 1-50km and width 0.5-3km.
Length greater than width.
- As glacial ice moves through pre-existing river
valley due to gravity, erodes sides and floor of
valley by abrasion and plucking.
- Glacial ice straightens, widens
and deepens valley as ice has
more power than original river that
cut valley.
- 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.
- Stepped long profile of many
glacial troughs is due to
over-deepening of parts due to
compressing flow causing
enhanced abrasion
- Rock-basins and steps created, clear
where bands of less and more resistant
rock are present.
- Rock-basins and steps created, clear
where bands of less and more resistant
rock are present.
- Stepped long profile of many
glacial troughs is due to
over-deepening of parts due to
compressing flow causing
enhanced abrasion
- 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.
- Glacial ice straightens, widens
and deepens valley as ice has
more power than original river that
cut valley.
- Nant Ffrancon Valley, Snowdonia
- Roche Moutonee
- Found on
flat valley
floor of Nant
Ffrancon
Valley,
Snowdonia
- 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.
- 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.
- On up glacier (stoss) side ice streamlines rock due to
abrasion. Polishes as well as creating scratches due to embedded moraine.
- 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)
- 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)
- Found on
flat valley
floor of Nant
Ffrancon
Valley,
Snowdonia
- Crag and tail
- Edinburgh Castle (Crag) and Royal Mile (Tail)
- Large feature with steep bare upstream
side consisting of resistant rock and
gentle downstream side made of glacial
till deposits; angular and unsorted.
- 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.
- Edinburgh Castle (Crag) and Royal Mile (Tail)
- Ribbon Lake
- Long, linear, finger shaped lake occupying base of glacial trough
- Windemere, Lake District
- 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.
- More resistant rock eroded less, acting as dams enabling areas to fill with water after glacial retreat - ribbon lake.
- Lakes may also form behind terminal or recessional moraine, acting as dam.
- Lakes may also form behind terminal or recessional moraine, acting as dam.
- More resistant rock eroded less, acting as dams enabling areas to fill with water after glacial retreat - ribbon lake.
- Long, linear, finger shaped lake occupying base of glacial trough
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