Glacial erosional landforms

Question 1

Fluvio-glacial erosion

Answer 1

Basal ice melting beneath temperate glacier can produce large volumes of meltwater which causes fluvial erosion.
Subglacial meltwater very fast and under high pressure (hydrostatic pressure) because its confined under glacier. Force of water may dislodge rock debris through hydraulic action

Question 2

Glacial crushing

Answer 2

Direct fracturing of weak rock beneath glacier due to ice weight. Must be weakened first either by intensity of FT weathering or repeated glacier/retreat/advance called dilation.
Dilation-rock fracture due to removal of overlying glacial weight
Glacial stress- ice density x acceleration due to gravity x glacier thickness

Question 3

Abrasion

Answer 3

Follows plucking. Material plucked from glacier is frozen and dragged as glacier moves downslope. Rubs against valley sides and floor-sandpapering effect
Striations-more likely in temperate glacier
Rock flour-fine rock debris that smooths surfaces and polishes rock. Proof-milky water (mixed with rock flour)
Tarn-remnant meltwater after glacier has departed

Question 4

Plucking

Answer 4

Rocks well jointed and weakened and where meltwater is present at glacier base due to PMP.
MW penetrates joints and around blocks, then freezes into rocks
As ice moves, immense pulling force into attached rock is exerted which may fracture and be ‘plucked’ from position.
Leaves jagged landscapes

Question 5

U-shaped valley

Answer 5

Valley glacier moves around landscape
FT weakens rock, plucking widens valley
Plucking and abrasion deepen the valley
U shape valley left behind after glacier leaves

Question 6

Ribbon lake

Answer 6

Glacier runs through glacial trough
Plucking and abrasion deepen v-shape trough
Can form behind terminal moraine after glaciation

Question 7

Crag and tail

Answer 7

Large mass of hard rock forms steep stoss w/ gently sloping tail of deposited material.
Large mass of hard rock resistant to ice scoring-steep stoss. Reduced glacier velocity which protects softer rock and allows deposition.
Sheltering effect diminishes w/ distance, creating sloping tail

Question 8

Knock and lochan

Answer 8

As glacier moves, abrasion occurs.
Softer rock erodes faster leaving lochans
Harder rock is smoothed and forms knocks
Scouring at glacier base excavates areas of weak rock, forming hollows that fill with meltwater and precipitation following ice retreat

Question 9

Roche moutonee

Answer 9

Mass of bare rock on valley floor with smooth stoss. More resistant rock causes creep and regelation around it. As ice strides over rock, it scours and smooths stoss while refreezing on ice causes plucking on the lee side (steep)

Question 10

Corrie

Answer 10

Armchair shaped hollow in mountain side.
Snow accumulates, compacts into glacier.
Meltwater produced under pressure, triggering rotational slip
Cracks and joints from FT penetrated by FT.
Back wall steepened by plucking. Plucked material transported sub-glacially, causing abrasion and deepening corrie

Question 11

Pyramidal peak

Answer 11

Pointed mountain peak with 3 or more corries
The corries erode backwards through plucking and abrasion into each other, creating a sharp pointed mountain summit

Question 12

Hanging valley

Answer 12

U or V shaped valley that sits high above trough, usually with waterfall.
Thicker glacial ice faster than thinner ice due to high pressure, increasing vertical erosion
PMP reached causes more meltwater, glacier ablates
Leaves valley high above glacier

Question 13

Arete

Answer 13

Narrow knife edge between 2 corries
They form when back walls of 2 corries erode backwards towards each other due to plucking and abrasion.

Question 14

Truncated spurs

Answer 14

Valley with V sides that used to interlock pre-glaciation
Glacier less flexible than river
Plucking widens, abrasion deepens