Glaciers Flashcards
What is plucking?
- as the ice moves over the rock surface below, meltwater freezes around loose sections, pulling them away
- this includes rocks being plucked away by the ice
- increase in plucking increases abrasion
What is abrasion in ice erosion?
- rocks and boulders embedded in the base of the glacier scratch and scrape the surface below
- large boulders can scare the landscape with features called striations
What are striations?
-scratches of gouges cut into the base rock by abrasion
What is freeze-thaw weathering?
- water (from rainfall or snowmelt) seeps into cracks in a rockface
- temp falls at night causing water to freeze
- water expands by 10% when it turns to ice therefore pressure increases causing the crack to widen
- repetition of this process results in large boulders of rock shattered apart
Where is evidence of freeze-thaw found?
-scree slopes and blockfields
What are scree slopes and blockfields?
-piles of rock or debris that blanket large upland areas
How do glaciers move?
- accumulation of snow in hollows is compressed into granules of ice
- as the weight of ice accumulates, gravity causes it to flow over the lip and down the mountainside
- surface of glacier cracks as the glacier moves over the uneven valley floor=crevasses
What is basal flow?
-when the glacier ice slides over the underlying rock on a film of meltwater
What is internal deformation?
-the ice at the base of the glacier moves, speeding up and slowing down in response to changes in gradient
What is ground moraine?
-large amounts of eroded rock fragments on the valley floor due to plucking and abrasion
What is the snout and what happens there?
- end point of the glacier
- large amounts of meltwater pour off the snout and carry debris beyond
How does a glacier transport material?
-as the ice from upland areas descends into lowland areas, the snout bulldozes material
-soils, rocks and boulders are shoved forwards due to the huge force of the ice
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Why is material carried inside the glacier?
- plucking results in rocks being embedded in the glacier
- some rocks fall in crevasses at the surface of the glacier. These crevasses can reach deep into the glacier resulting in the build up of material
What is glacial outwash?
- sediment from the glacier carried in the meltwater river
- outwash becomes rounded due to attrition
What is a corrie?
- large circular depressions in the rock
- Glaciers start in them high up in the mountainside
- typically filled with a lake called a tarn
How are corries formed?
- -snow accumulates in a slight hollow, is compressed then turns to ice
- ice mass slides downhill due to it’s weight
- the back wall is made steeper by plucking, abrasion deepens the hollow
- freeze-thaw happens at back wall of hollow resulting in it retreating
- material deposited as moraine on the rock lip
- after the ice age, ice has melted leaving it to be filled with a tarn
What is an arete?
-two-sided, knife-edged peak found at the back of a corrie of separating 2 glaciated valleys
How are aretes formed?
-due to freeze-thaw and the erosion of back to back corries by plucking
What is a pyramidal peak?
-an angular sharply pointed mountain peak
How is a pyramidal peak formed?
- when 3 or more aretes meet back to back
- corries erode backwards towards each other and freeze thaw creates a sharply pointed summit
What is a u-shaped valley or glacial trough?
-the once v-shaped valley is torn away by abrasion and plucking due to the glacier
What is a hanging valley?
-a tributary valley with a floor at a higher relief than the main channel
How is a hanging valley formed?
- after glaciation, small rivers and u-shaped valley is left behind
- tributary streams are left cascading down into the main valley and create waterfall
What are truncated spurs?
-a former river valley spur which has been sliced off due to the moving valley glacier
How are truncated spurs formed?
-Glacier slices off the spur due to the sheer force, leaving a flat-faced ridge called a truncated spur
What is lateral moraine?
-material at the edges of the glacial trough
What is ground moraine?
-material underneath the glacier
What is medial moraine?
-when glaciers meet, 2 lateral moraines form together to become medial moraine
What is terminal moraine?
-enormous ridge of material that gets bulldozed by the snout of the glacier
