Cold 2- Glacial/Fluvioglacial landforms Flashcards
Weathering
The breakdown of rocks in situ
Finer particles are then moved away by the wind or running water
Frost shattering
During the day water enters cracks and then freezes at nighttime, expanding by 9% and exerting pressure on the crack
This process repeats on bare rocky outcrops and the crack widens until pieces of rock break off (scree)
Processes of glacial erosion
Abrasion- angular material wears away at the valley floor and sides
Plucking- the ice freezes onto rocky outcrops and as the glacier moves, pieces of rock stuck to the ice are pulled away
Nivation
Snow collects in depressions and beneath it frost shattering occurs and also carbonation (carbonic acid corrodes rock like limestone)
Corries
An enlarged armchair-shaped hollow with a steep back wall and an over-deepened basin
Formation of corries
Hollow initially deepened by nivation
Accumulation of snow causes rotational flow, plucking occurs and then frost shattering provides debris for abrasion
Water trickles down Bergshcrund and more frost shattering occurs
Arête
When two or more corries erode back to back towards each other from opposing sides, they produce a knife-edged ridge (e.g. Striding Edge)
Pyramidal peak
When three or more corries erode back towards each other, a sharp point is formed (e.g. Matterhorn)
Glacial troughs
Steep-sided, flat-floored (U-shaped) valleys
Ribbon lakes
Compressing flow over-deep ends parts of the valley floor (less resistant rock) forming long, narrow lakes
Truncated spurs
As glaciers move down a river valley, erosion along the valley sides may remove the tips of preglacial interlocking spurs
Hanging valleys
When smaller tributaries join a main glacier, the smaller glaciers have less power to erode so the valleys are raised above the main valley (waterfalls form)
Roches moutonnées
Small areas of more resistant rock on the valley floor which have a gentle upvalley side (stoss) polished by abrasion and a jagged downvalley side (lee) from plucking
Craig and tail
Larger masses of more resistant rock (crag) and a gently sloping tail of less resistant rock and/or sediment on the downvalley side
Types of debris
Supraglacial debris- on the surface of the glacier
Englacial debris- within the ice
Subglacial debris- beneath the ice
Deposition
Till is all material deposited directly by the ice (unsorted)
Fluvioglacial material is sediments deposited by meltwater streams (sorted)
Till
Individual stones remain angular
Lodgement till is from subglacial material (e.g. Drumlin)
Till produced at the snout is known as ablation till (end moraines)
Erratics
Fragments of glacial debris
‘Rocks in the wrong place’
Moraines
Lateral, medial, terminal and end moraine
Drumlins
Rounded, oval-shaped hills formed from unsorted till deposits by the glacier
They have a steep upvalley stoss and a sloping downvalley lee eroded into a streamlined shape by the glacier
Importance of meltwater
Enlarge nivation hollows, lubricate glaciers, frost shattering, transport fluvioglacial material
Subglacial streams
Flow under considerable hydrostatic pressure from the glacier, so have high velocities and high capacity to carry material
Outwash plains
An extensive, gently sloping area of sands and gravels that form in front of the glacier’s snout (stratified material)
Eskers
Long, sinuous winding ridges of sediment deposited by subglacial streams
Kames
Irregular, undulating mounds of sorted material, often steep sided and conical
Includes kame terraces, kame deltas and crevasse kames
Kettles
A series of small depressions formed by deposition occurring around a block of ice, which subsequently melts to leave a hollow
Varves
Layers of sediment deposited at the edge or in the bottom of meltwater lakes
Different bands from different seasons & years
