Glaciation Flashcards
(56 cards)
Describe plucking
As ice moves over the rock surface below, meltwater freezes around loose sections, pulling them away as the glacier moves forward
Describe abrasion
Rocks and boulders embedded in the base of the glacier act like sandpaper, scratching and scraping the rocks below. Large boulders can cause striations.
Describe freeze-thaw weathering
Water seeps into cracks in a rock face
Temp falls at night, cauisng water to freeze
Water expands as it turns to ice, putting pressure on rock either side of crack, causing it to tear open
Ice melts, sinks deeper into crack and freezes again
What are the erosion processes of glaciers?
Plucking and abrasion
Is freeze-thaw weathering an erosion process?
No, it isn’t caused by a moving force, it takes place in a particular place and remains of rock don’t move.
Evidence for freeze-thaw weathering
Scree slopes and blockfields
What is meltwater?
Ice at the base of glacier that has melted due to the pressure or water that has travelled from surface of glacier to base
How do glaciers move?
Rotational slip and basal slip
Describe rotational slip
At the top of glaciers, circular motion of ice can erode out hollows, which get deeper over time. This is how corries form
Describe basal slip
Meltwater beneath a glacier enables it to slide forward as a mass by a few metres each year.
How does a glacier transport material?
Bulldozing
Describe bulldozing
Rocks at the snout of a glacier are shoved forwards by the sheer force of the moving ice. Material is also carried on surface of glacier and inside.
Why would material be carried on the surface of the glacier?
Surface - Freeze-thaw weathering occurs on mountain-sides above glacier, causing rocks to become detached and fall onto the ice
Why would material be carried inside a glacier?
Plucking has torn away rock below the moving ice which is now embedded in the base of the glacier
Some rocks fall into crevasses at the surface of the glacier which reach deep into the glacier
Where on the mountain does glacial deposition take place and why?
Lowland areas, warmer climatic zones, causing more meltwater to flow.
Describe the two types of glacial sediment deposited
Till - range of sizes, angular shape, deposited by ice
Glacial outwash - Rounded rocks, sorted by size, deposited by meltwater
Describe how till is deposited
Melting takes place at front of glacier and is dumped on the ground. Because it is transported by solid mass of ice, it is unsorted
Describe how glacial outwash is deposited
In summer months, meltwater rivers flow from snout of glacier and carry outwash material . It is carried by water so it smaller (attrition) and sorted by size.
Suggest why material deposited by a glacier is mixed in size
Transported by ice which picks up all sizes of debris. Glacier bulldozes everything in its path.
Till has a wider range as it consists of materials moved by solid ice so everything is picked up
Explain the formation of a glacial trough
V-shaped is filled with ice.
Glacier moves through the valley eroding the valley floor and sides by abrasion and plucking.
Truncated spurs are formed as glaciers cut through interlocking spurs.
Glacier melts/retreats, leaving behind glacial trough.
Explain the formation of a corrie
Snow forms in a hollow and gets compressed, forming a dense mass of ice. Glacier moves downhill by rotational slip
As the ice pulls away from walls of the hollow, rocks are plucked.
Freeze-thaw weathering occurs on back wall of hollow, above the ice, causing rocks to fall on surface of ice. Retreating steep back wall is formed.
These rocks become embedded in the ice and abrade the hollow, making it deeper and wider.
Describe how an arrête occurs
When two corries are eroded back to back, the ridge in between them becomes narrower.
(Use explanation of formation of corrie)
Describe how a pyramidal peak forms
When three or more corries form on all sides of the mountain. Corries erode the mountain behind them, the remaining rock is freeze-thaw weathered into a sharp point
(Use explanation of formation of corrie)
Describe how a hanging valley forms
As a glacier moves through a V-shaped valleys, abrasion and plucking cut off the valley sides. Tributaries that used to flow down river valley sides exit abruptly through a gap in the valley wall. Water cascades from a high altitude, creating a waterfall.