3.1.4.4 Glaciated Erosion Landforms

Question 1

10 landforms produced by glacial erosion

Answer 1

1. Nivation hollows
2. Corrie
3. Pyramidal peaks
4. Arêtes
5. Glacial trough
6. Truncated Spurs
7. Hanging valleys
8. Rock steps
9. Ribbon lake
10. Roche Moutonnee

Question 2

What do nivation hollows turn into

Answer 2

Corrie

Question 3

How is a nivation hollow formed

Answer 3

1. Snow falls into small depressions/hollows (survives summer melt)
2. Snow is compacted by further snow falls + melting into a névé and in long term a firn
3. Weathering (freeze-thaw) weakens soil+ rocks under snow patch to create slope failure at back of snow patch
4. Erosion from meltwater washes sediments out of snow patch base
5. Weather particles are moved downslope by soil creep, solifluction + rill wash

Question 4

What does freeze thaw weathering cause to occur at the back of the snow patch when forming a nivation hollow

Answer 4

Slope failure (soil creep + moved downhill)

Question 5

3 processes that moves weathered particles downslope in nivation

Answer 5

Soil creep
Solifluction
Rill wash (water)

Question 6

How big are nivation hollows compared to corries

Answer 6

Smaller

Question 7

3 typical features of a landscape of glacial erosion

Answer 7

Steep ridges
Bare rocky outcrops
Wide valleys

Question 8

What is a Corrie/cirque/cwm

Answer 8

Semi-circular hollow high up at the head of a glacial valley on a glacial mountain

Question 9

4 parts to a Corrie

Answer 9

Steep back head wall
Bowl-shaped centre rock basin
Sometimes filled with a Corrie lake/tarn
Rock lip at lower end

Question 10

How are corries formed (beginning of ice age) - 3

Answer 10

Snow accumulates in hollow + survives summer melt
Downhill ice movement pivots deepening Corrie floor
Underlying rocks disintegrate, but summer meltwater removes debris

Question 11

What is it that causes the Corrie floor to deepen when ice pivots in it (beginning of ice age)

Answer 11

Increasing pressure

Question 12

How are corries formed (during ice age) - 3

Answer 12

Water down bergschrund causes more freeze-thaw
Ice accumulates + rotates due to pressure. Abrasion + plucking deepen how further + form steep back wall
Rock lip forms at end as pressure+ erosion is reduced

Question 13

How are corries formed (after ice age) - 3

Answer 13

In warmer climate the ice melts to leave a deep, rounded lake/tarn

Question 14

What in a Corrie helps to retain the tarn

Answer 14

Moraine at the rock lip

Question 15

When are pyramidal peaks formed

E.g

Answer 15

When 3/more adjacent corries develop on the side of a mountain leaving a very sharp peak with steep sides and arêtes from the central peak

E.g the Matterhorn in the alps

Question 16

What’s an arête

Answer 16

A narrow knife-edged ridge with steep sides in upland glaciated areas

Question 17

How do both arêtes and pyramidal peaks begin to form (3)

Answer 17

1. Backwards erosion of Corrie by erosion on head wall, getting steeper by plucking of loose fragments
2. Also water causes frost shattering (freeze-thaw) and releases pressure in rocks
3. Land in between gets narrower +steeper as the Corrie walls erode back

Question 18

How do an arête + pyramid peak remain rocky + steep

Answer 18

Due to frost shattering

Question 19

Describe a glacial trough

Answer 19

Steep-sided
broadly flat-bottomed
often 100 metres in depth
1km->1000km

Question 20

3 main landforms in a glacial trough

Answer 20

Truncated spurs
Hanging valley
Misfit stream

Question 21

Why do truncated spurs tend to be straight

Answer 21

Due to the power and inflexibility of the glaciers that gourge them out

Question 22

What shape do glaciers turn valleys into

Answer 22

V shaped -> U shaped

Question 23

How do truncated spurs form

What does the top of them mark

Answer 23

As the glacier bulldozes interlocking spurs of the formed valley out of the way to create steep glacial trough sides
Top marks depths of ice

Question 24

What are hanging valleys

Answer 24

A tributary glaciated valley perched above the main glaciated valley floor. Streams flowing down these tributary valleys often descend to the main valley by waterfalls

Question 25

How were hanging valleys formed

Answer 25

By smaller glaciers joining a main glacier, but the smaller glaciers had less erosive power so couldn’t erode deeply

Question 26

What are rock steps

Answer 26

Small scale irregularities on the valley floor consisting of alternating rock bars and rock basins which form steps in the trough floor

Question 27

Why is the depth of glacial ice (rock steps) greater in depressions in the valley floor
What does this mean

Answer 27

As compressive flow occurs here

They’ll be further eroded

Question 28

What causes more resistant, less eroded rock steps to be left

Answer 28

Extending flow

Question 29

What’s a ribbon lake

Answer 29

An elongated lake occupying a rock basin produced by overdeepening on the floor of a glacial trough

Question 30

Theories of over deepening valley floors (3)

Answer 30

Extra erosion following confluence of 2 glaciers
Presence of weaker rocks
Zones of well jointed rocks

Question 31

What erosion may deepen trough floor

Answer 31

Extending + compressing flow

Question 32

What’s a Roche moutonnee

Answer 32

A protruding knob of bedrock found along the floor of a glaciated valley - more resistant rock

Question 33

What does Roche moutonnee look like

Why

Answer 33

gentle + smooth upvalley slope
steep + uneven down valley slope

On upvalley slope (stoss side) the PMP decreases (pressure increases) so ice melts + basal sliding occurs + abrasion
On down valley slope (lee side) PMP increases (pressure falls) causing refreezing + plucking of loosened material

Question 34

What are striations

How are they formed

Answer 34

Series of scratches + grooves left behind in rock

Caused when a glacier moves across exposed rock and angular subglacial moraine being transported creates scratched as they’re dragged across the rock surface