3.1.4.4 Glaciated Erosion Landforms Flashcards
10 landforms produced by glacial erosion
- Nivation hollows
- Corrie
- Pyramidal peaks
- Arêtes
- Glacial trough
- Truncated Spurs
- Hanging valleys
- Rock steps
- Ribbon lake
- Roche Moutonnee
What do nivation hollows turn into
Corrie
How is a nivation hollow formed
- Snow falls into small depressions/hollows (survives summer melt)
- Snow is compacted by further snow falls + melting into a névé and in long term a firn
- Weathering (freeze-thaw) weakens soil+ rocks under snow patch to create slope failure at back of snow patch
- Erosion from meltwater washes sediments out of snow patch base
- Weather particles are moved downslope by soil creep, solifluction + rill wash
What does freeze thaw weathering cause to occur at the back of the snow patch when forming a nivation hollow
Slope failure (soil creep + moved downhill)
3 processes that moves weathered particles downslope in nivation
Soil creep
Solifluction
Rill wash (water)
How big are nivation hollows compared to corries
Smaller
3 typical features of a landscape of glacial erosion
Steep ridges
Bare rocky outcrops
Wide valleys
What is a Corrie/cirque/cwm
Semi-circular hollow high up at the head of a glacial valley on a glacial mountain
4 parts to a Corrie
Steep back head wall
Bowl-shaped centre rock basin
Sometimes filled with a Corrie lake/tarn
Rock lip at lower end
How are corries formed (beginning of ice age) - 3
Snow accumulates in hollow + survives summer melt
Downhill ice movement pivots deepening Corrie floor
Underlying rocks disintegrate, but summer meltwater removes debris
What is it that causes the Corrie floor to deepen when ice pivots in it (beginning of ice age)
Increasing pressure
How are corries formed (during ice age) - 3
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
How are corries formed (after ice age) - 3
In warmer climate the ice melts to leave a deep, rounded lake/tarn
What in a Corrie helps to retain the tarn
Moraine at the rock lip
When are pyramidal peaks formed
E.g
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
What’s an arête
A narrow knife-edged ridge with steep sides in upland glaciated areas
How do both arêtes and pyramidal peaks begin to form (3)
- Backwards erosion of Corrie by erosion on head wall, getting steeper by plucking of loose fragments
- Also water causes frost shattering (freeze-thaw) and releases pressure in rocks
- Land in between gets narrower +steeper as the Corrie walls erode back
How do an arête + pyramid peak remain rocky + steep
Due to frost shattering
Describe a glacial trough
Steep-sided
broadly flat-bottomed
often 100 metres in depth
1km->1000km
3 main landforms in a glacial trough
Truncated spurs
Hanging valley
Misfit stream
Why do truncated spurs tend to be straight
Due to the power and inflexibility of the glaciers that gourge them out
What shape do glaciers turn valleys into
V shaped -> U shaped
How do truncated spurs form
What does the top of them mark
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
What are hanging valleys
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
How were hanging valleys formed
By smaller glaciers joining a main glacier, but the smaller glaciers had less erosive power so couldn’t erode deeply
What are rock steps
Small scale irregularities on the valley floor consisting of alternating rock bars and rock basins which form steps in the trough floor
Why is the depth of glacial ice (rock steps) greater in depressions in the valley floor
What does this mean
As compressive flow occurs here
They’ll be further eroded
What causes more resistant, less eroded rock steps to be left
Extending flow
What’s a ribbon lake
An elongated lake occupying a rock basin produced by overdeepening on the floor of a glacial trough
Theories of over deepening valley floors (3)
Extra erosion following confluence of 2 glaciers
Presence of weaker rocks
Zones of well jointed rocks
What erosion may deepen trough floor
Extending + compressing flow
What’s a Roche moutonnee
A protruding knob of bedrock found along the floor of a glaciated valley - more resistant rock
What does Roche moutonnee look like
Why
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
What are striations
How are they formed
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
