Glaciation and Glacial Processes Flashcards
What factors move glaciers?
Their own weight and gravity
Give an Irish example of truncated spurs
Glenmalure Valley, Co. Wicklow
Define moraines
Ridges of till left at different parts of the glacier
Give an example of a corrie in Ireland
Coomingshaun, Comeragh Mountains, Co. Waterford
Explain the different forms of glacial movement
Internal deformation (plastic flow): Ice crystals within the glacier change shape and slide over each other
Basal slippage (sliding): Meltwater at the base of the glacier acts as a lubricant, allowing the glacier to slide over the bedrock
Rotational movement: Ice moves in circular movement due to gravity
When does basal slippage occur?
Temperate glaciers
Define boulder clay/glacier till
The load the glacier deposits when it loses its energy
Explain how hanging valleys are formed
The main glacier erodes more deeply than the smaller tributary glacier
What processes form truncated spurs?
Abrasion and plucking
Define arête
A sharp ridge that forms between two cirques or glacial valleys.
Name some features of glacial deposition
- Drumlin
- Outwash plain
- Eskers
- Kettle holes/kames
- Moraines
- Erratics
Define kettle holes/lakes
Depressions formed when blocks of ice become buried in outwash and then melt, leaving holes that may fill with water.
Explain freeze thaw weathering in the context of glaciation
- Water enters cracks in rocks during the day, freezes at night, expands and causes the rock to break apart.
- This creates loose debris for the glacier to use in abrasion
Give an example of an esker
Esker Riada, Co Meath and Co Galway
Define erratics
Large rocks transported and deposited far from their origin
Define u-shaped valley
A valley with a flat floor and steep sides, carved by a moving glacier
Give an Irish example of a hanging valley
Glenealo Valley, above Glendalough, Co. Wicklow
Give an Irish example of a pyramidal peak
Lugnaquilla, Wicklow Mountains, Co. Wicklow
Define truncated spurs
Steep cliff faces where a glacier has cut through river valley spurs
Define paternoster lakes
A series of small lakes linked by a stream in a glacial valley.
Where does rotational movement occur?
Cirques and corries
What erosional processes form pyramidal peaks?
Plucking, abrasion and freeze-thaw action
Define outwash plains
Flat areas of sorted material eg. sand and gravel deposited by meltwater streams beyond the snout of the glacier
Define glacier
A large mass of ice that forms on land from the accumulation and compaction of snow over time and moves slowly under its own weight
Draw a diagram to show the anatomy of a glacier
See notes
How does a pyramidal peak form?
Three or more cirques erode into a mountain from different sides. The back walls are worn away by plucking and abrasion. Freeze-thaw action sharpens the peak to a point
Draw a diagram to show how glaciers move
See notes
How are arêtes formed?
They are formed between two cirques or glacial valleys when glaciers erode both sides by plucking and abrasion, narrowing the ridge. Freeze-thaw weathering sharpens the edge further
What erosional processes form arêtes?
Plucking, abrasion and freeze-thaw action
Define zone of accumulation
The area where snow and ice build up
Define eskers
Long, winding ridges of sand and gravel deposited by rivers flowing under or within a glacier.
Explain how a coom lake forms
It forms in a cirque after the glacier melts and meltwater fills the hollow. A rock lip often holds the water in place.
Where are lateral moraines found?
Along the sides
Define kames
Mounds of sand and gravel deposited in hollows on the glacier surface, left behind when the glacier melts
What erosional processes form cirques?
Plucking and abrasion
Define cirque/corrie
A bowl shaped hollow found on mountain sides where snow and ice gather. Birthplace of glacier.
Define pressure release in the context of glaciation
When overlying ice is removed, rocks expand and fracture, contributing to erosion
What erosional processes shape hanging valleys?
Plucking and abrasion
What erosional processes shape tarns?
Abrasion and plucking
Define plucking
A process of glacial erosion when a glacier moves over previously fractured/weakened bedrock - the glacial ice freezes around the rock and when it moves it “plucks” the rock and carries it away.
What is fluvioglacial deposition?
Deposition by meltwater from glaciers. Unlike glacial deposition, it is sorted and stratified
Give an Irish example of a u-shaped valley
Glendalough, Co. Wicklow
Name some features of glacial erosion
- Cirque/corrie
- Pyramidal Peak/Horn
- Arete
- Truncated spurs
- Hanging valley
- Tarn/coom lake -> glacial lake
- Ribbon lake/paternoster lake
What are the different types of morraines?
- Terminal
- Lateral
- Medial
- Ground
Where are terminal moraines found?
At the snout
Draw a diagram to show glacier and corrie formation
See notes
Define abrasion in the context of glaciation
When rock fragments at the base and sides of a glacier act like sandpaper. They smooth and polish the bedrock leaving striae
Give an Irish example of a coom lake
Lough Muskry, Galtee Mountains, Co. Tipperary
Give an Irish example of an arête
The Bone, MacGillycuddy’s Reeks, Co. Kerry
Define hanging valley
A smaller valley that joins a deeper U-shaped valley from above
Give an Irish example of paternoster lakes
Loughs of Cummenduff, MacGillycuddy’s Reeks, Co. Kerry
How are corries formed?
The glacier moves in a circular motion (rotational slip), eroding the hollow. Plucking steepens the back wall and abrasion deepens the base
How are truncated spurs formed?
The glacier erodes through the rock with abrasion and plucking, straightening the valley. The rounded interlocking spurs are left sharply cut off
Explain how glaciers form
- Snow falls and accumulates in a hollow or upland area
- Over time, repeated snowfall compresses lower layers of snow into firn/nevé, a granular form of snow
- Further compaction turns firn into solid glacial ice
- This process can take 30 to 100 years, depending on the climate
- When the glacier becomes heavy enough, it begins to move downhill under the force of gravity
Define drumlins
Oval shaped hills formed under moving ice, with a steep side facing up-ice and a gentle slope down-ice
Draw a diagram of glacial features
See notes
What erosional processes form u-shaped valleys?
Abrasion and plucking
How are paternoster lakes formed?
Abrasion over-deepens parts of the valley, often due to softer rock. When the glacier melts, water fills these depressions
What erosional processes form paternoster lakes?
Abrasion and plucking
Where are ground moraines found?
Beneath the glacier
Where does internal deformation occur?
Cold based glaciers
