2a. Glacial landform development due to climatic & geomorphic processes Flashcards
What are geomorphic processes?
Weathering
- physical/mechanical
- chemical
- biological
What is physical/mechanical weathering?
causes majority of breakdown of rocks into smaller rock fragments
State some processes of physical weathering?
- freeze-thaw
- frost shattering
- pressure release
Physical weathering: what is freeze-thaw?
- water enters cracks, freezes, expands by 9%
- exerts pressure, causing rock fragments to break off
- more effective with regular fluctuations in temp
Physical weathering: frost shattering
Breaks rock into small particles when trapped water freezes, expands and causes pressure
Physical weathering: pressure release
- when glacier melts, weight of the ice on the rock is released causing it too expand and fracture parallel to surface
What is chemical weathering?
- decay of rock as a result of chemical reactions between rock and weather elements
- rate is faster in higher temps
State some processes of chemical weathering?
- oxidation
- carbonation
- solution
Chemical weathering: oxidation
Minerals in rocks react with oxygen (eg. iron) and becomes soluble under acidic conditions
Chemical weathering: carbonation
Rain combines with CO2 forming weak acid, reacts with some rocks such as limestone, makes it soluble
Chemical weathering: solution
Rock minerals may dissolve in water
What is biological weathering? State some processes of biological weathering?
- physical actions (have very little significance as plant/animal activity is limited in glacial systems)
- tree roots
- organic acids
Biological weathering: tree roots
- tree roots grow into cracks, exerting a pressure (similar to freeze-thaw)
- if tree topples, roots exert leverage
Biological weathering: organic acids
- organic acids produced by decomposition of plant/animal material causes oil eater to become acidic, reaction with minerals in rocks
What is mass movement and what impact does it have on the glacier?
- Occurs when forces acting on slope material (gravity) exceed forces holding it back (friction)
- adds material to glacier beneath, giving it abrasive power
Mass movement: rock fall?
- Rocks on slope become detached by physical weathering
- material can from scree slope or be removed by transportation
Mass movement: slides?
- linear slides = movement along a straight slip plane
- rotational slides (slumps) = movement along a curved slip plane
- occur due to steepening of valley side by erosion, adds to downward force
What are glacial processes?
- erosion
- nivation
- transportation
- deposition
Erosion: plucking (or quarrying)
- meltwater seeps into joint on valley floor, freezes, attaching it to glacier’s base
- as glacier advances, it pulls rock fragments away
Erosion: abrasion
- debris embedded in base/side of glacier scrapes surface rocks when glacier moves, wearing them away
- course material scratches, fine material smooths
- debris itself gets worn down, forming rock flour - makes water milky white
Erosion: factors that increase rates of abrasion
- more larger, angular basal debris
- hardiness od debris & bedrock
- ice thickness (up to a certain point of 100-200m - too much pressure causes friction)
- basal water pressure & sliding (up to a point - too much meltwater causes buoyancy of glacier)
- removal of fine debris by meltwater
Nivation: what does it involve? What is it responsible for?
- responsible for initial enlargement on hillside hollows/corries
- involves a combination of freeze-thaw, solifluction, transport by water, chemical weathering
Transportation: where does the material being transported come from (sources)?
- rockfall
- avalanches
- aeolian depostis
- plucking
- abrasion
etc.
Transportation: what are the 3 methods of transportation?
- supraglacial = material carried on glacier surface
- englacial = debris carried within glacier, may have been covered by snow/sunk into ice
- subglacial = debris embedded in base of glacier
Deposition: reasons a glacier may deposit material?
- result of ablation
- when glacier becomes overloaded with debris
Deposition: names/types of material that can be deposited?
ALL deposited material is called drift, but is subdivide into:
- till = deposited directly by ice
- outwash/glacio-fluvial = deposited by meltwater
Till: what are the two types?
- lodgement till = deposited by advancing ice as pressure pushes debris into valley floor, left behind as glacier moves forward (eg. drumlins)
- ablation till = deposited by melting ice (forms most depositional landforms)
Till: characteristics of till?
- angular in shape - has been embedded in ice, not smothers by erosion
- unsorted - all sizes deposited en masse (unlike water deposits in size order)
- unstratified - dropped in mounds (unlike water deposits in layers)
Erosional glacial landforms?
- corries
- Aretes & pyramidal peaks
- Troughs
- Roche moutonnees & striations
- Ellipsoidal basins
Erosional landforms: What is a corrie? Shape?
- armchair-shaped hollow found in mountainsides
- steep back wall with lip at front (deposits)
Erosional landforms: How is a corrie formed?
- hollow accumulates snow, deepened by nivation
- more snow, compresses into glacial ice
- ice plucks back wall (by rotational movement) - steepens it
- debris from plucking & weathering of rock above abrades hollow, deepening it
- thinner ice at from has less erosional power - forms corrie lip of deposited material
- post-glaciation, corrie can fill with water forming a tarn
Erosional landforms: what is an arete? example?
a narrow, steep sided ridge found between two corries (knife-edged) where the back walls have retreated
eg. Striding Edge, Lake District
Erosional landforms: what is a pyramidal peak?
where 3 or more corries develop around a hill and heir back walls retreat
Erosional landforms: what is a trough? what other feature are found here?
- a u-shaped valley, with steep sides and a flat bottom
- hanging valleys, truncated spurs, misfit streams
Erosional landforms: how is a trough formed?
- glacier flows down existing river valley (v-shaped)
- erodes valley floor (abrasion) deepening it
- erodes valley walls (plucking) steepening it
- freeze-thaw above ice
- after glaciation - truncated spurs, misfit stream, hanging valley
Erosional landforms: what is a roche moutonnee? What is a striation?
- RM = a mass of more resistant rock with a gentle, smooth up-valley (stoss) slope and a steep, rough down-valley (lee) slope
- Striation = scratches from abrasion made by debris embedded in glacier
Erosional landforms: how are roche moutonnees & striations formed?
- on the up-valley side, the obstruction causes pressure melting (layer of meltwater produced
- surface is smoothed, often with striations
- on the down-valley side, reduced pressure causes meltwater to refreeze, causing plucking & steepens
Erosional landforms: what can a roche moutonnee tell us about glacial movement?
the direction of movement of the glacier
Erosional landforms: What are ellipsoidal basins?
large, deep lakes formed from the impact of ice sheets eg. Laurentide ice sheet created Great Lakes
Depositional glacial landforms?
- Moraines
- Erratics
- Drumlins
- Till sheets
Depositional landforms: What is a terminal moraine?
ridge of till (crescent shape) across the trough marking the maximum advance of the ice - deposited through the glacier snout
Depositional landforms: What is a lateral moraine?
ridge of till running along the edge of the valley - material that was on top of glacier from weathering of valley sides, has sunk through glacier to floor
Depositional landforms: What is a recessional moraine?
series of parallel ridges of till across trough - material that was deposited when the glacier stood still temporarily during the retreat (found behind terminal moraine)
Depositional landforms: what is an erratic?
- an individual piece or rock that is composed of a different geology to that of where it was deposited
- transported as supraglacial debris by weathering or rockfall
- varies in size from small pebble to large boulder
Depositional landforms: what is a drumlin?
- a mound of glacial debris that has been stream lined into an elongated hill, aligned in the direction of the glacier flow
- stoss (blunt end) faces ice flow & lee side is a more gentle slope
Depositional landforms: how are drumlins formed?
- formation is not actually known: on theory is ‘rock core’ obstruction
- glacial till accumulates around the rock core, especially when ice is over loaded and deposits material
Depositional landforms: till sheets?
- formed when large mass of unstratified material is deposited when an ice sheet retreats - till depends on where material has been transported from
