a period of ice advance associated with falling temperatures.
a period of ice retreat associated with rising temperatures.
FTW - Freeze-thaw weathering
if you visit a glacial area you will notice huge piles of jagged rocks lining the sides of the valleys. These are piles of scree and they result from freeze-thaw weathering.
Abrasion- this has a sandpaper effect caused by the weight of the ice scouring the valley floor and sides using the angular rock material trapped underneath. In the same way that sandpaper smoothes wood, abrasion results in a smooth and often shiny rock surface. Scratches caused by large rocks beneath the ice can often be seen. These are called STRIATIONS.
Plucking- when melt water beneath a glacier freezes, it-bods the glacier base to th rocky surface below rather like glue. As the glacier moves, any loose fragments of rock are plucked away, like extracting loose teeth. This process leaves behind a jagged rocky surface as opposed to the smooth surface resulting from abrasion.
explaining the formation of a corrie
- beginning of ice age, snow accumulates in hollow;compressed into ice.
- during the ice age, Freeze-thaw above glacier
: plucking steepens the back wall
: abrasion deepens the hollow
: rate of erosion decreases
: moraine left at end of glacier
- after the ice age, jagged summit
: steep back wall ( still freeze-thaw in winter )
:leaving corrie lake (tarn)
how aretes are formed
aretes are formed when two corries back to back wear away rock on their back wall through plucking and Freeze-thaw weathering. This results in a steep ridge.