2a. Glacial landform development due to climatic & geomorphic processes

Question 1

What are geomorphic processes?

Answer 1

Weathering
- physical/mechanical
- chemical
- biological

Question 2

What is physical/mechanical weathering?

Answer 2

causes majority of breakdown of rocks into smaller rock fragments

Question 3

State some processes of physical weathering?

Answer 3

• freeze-thaw
• frost shattering
• pressure release

Question 4

Physical weathering: what is freeze-thaw?

Answer 4

• water enters cracks, freezes, expands by 9%
• exerts pressure, causing rock fragments to break off
• more effective with regular fluctuations in temp

Question 5

Physical weathering: frost shattering

Answer 5

Breaks rock into small particles when trapped water freezes, expands and causes pressure

Question 6

Physical weathering: pressure release

Answer 6

• when glacier melts, weight of the ice on the rock is released causing it too expand and fracture parallel to surface

Question 7

What is chemical weathering?

Answer 7

• decay of rock as a result of chemical reactions between rock and weather elements
• rate is faster in higher temps

Question 8

State some processes of chemical weathering?

Answer 8

• oxidation
• carbonation
• solution

Question 9

Chemical weathering: oxidation

Answer 9

Minerals in rocks react with oxygen (eg. iron) and becomes soluble under acidic conditions

Question 10

Chemical weathering: carbonation

Answer 10

Rain combines with CO2 forming weak acid, reacts with some rocks such as limestone, makes it soluble

Question 11

Chemical weathering: solution

Answer 11

Rock minerals may dissolve in water

Question 12

What is biological weathering? State some processes of biological weathering?

Answer 12

• physical actions (have very little significance as plant/animal activity is limited in glacial systems)
• tree roots
• organic acids

Question 13

Biological weathering: tree roots

Answer 13

• tree roots grow into cracks, exerting a pressure (similar to freeze-thaw)
• if tree topples, roots exert leverage

Question 14

Biological weathering: organic acids

Answer 14

• organic acids produced by decomposition of plant/animal material causes oil eater to become acidic, reaction with minerals in rocks

Question 15

What is mass movement and what impact does it have on the glacier?

Answer 15

• Occurs when forces acting on slope material (gravity) exceed forces holding it back (friction)
• adds material to glacier beneath, giving it abrasive power

Question 16

Mass movement: rock fall?

Answer 16

• Rocks on slope become detached by physical weathering
• material can from scree slope or be removed by transportation

Question 17

Mass movement: slides?

Answer 17

• 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

Question 18

What are glacial processes?

Answer 18

• erosion
• nivation
• transportation
• deposition

Question 19

Erosion: plucking (or quarrying)

Answer 19

• meltwater seeps into joint on valley floor, freezes, attaching it to glacier’s base
• as glacier advances, it pulls rock fragments away

Question 20

Erosion: abrasion

Answer 20

• 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

Question 21

Erosion: factors that increase rates of abrasion

Answer 21

• 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

Question 22

Nivation: what does it involve? What is it responsible for?

Answer 22

• responsible for initial enlargement on hillside hollows/corries
• involves a combination of freeze-thaw, solifluction, transport by water, chemical weathering

Question 23

Transportation: where does the material being transported come from (sources)?

Answer 23

• rockfall
• avalanches
• aeolian depostis
• plucking
• abrasion
  etc.

Question 24

Transportation: what are the 3 methods of transportation?

Answer 24

• 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

Question 25

Deposition: reasons a glacier may deposit material?

Answer 25

• result of ablation
• when glacier becomes overloaded with debris

Question 26

Deposition: names/types of material that can be deposited?

Answer 26

ALL deposited material is called drift, but is subdivide into:
- till = deposited directly by ice
- outwash/glacio-fluvial = deposited by meltwater

Question 27

Till: what are the two types?

Answer 27

• 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)

Question 28

Till: characteristics of till?

Answer 28

• 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)

Question 29

Erosional glacial landforms?

Answer 29

• corries
• Aretes & pyramidal peaks
• Troughs
• Roche moutonnees & striations
• Ellipsoidal basins

Question 30

Erosional landforms: What is a corrie? Shape?

Answer 30

• armchair-shaped hollow found in mountainsides
• steep back wall with lip at front (deposits)

Question 31

Erosional landforms: How is a corrie formed?

Answer 31

• 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

Question 32

Erosional landforms: what is an arete? example?

Answer 32

a narrow, steep sided ridge found between two corries (knife-edged) where the back walls have retreated
eg. Striding Edge, Lake District

Question 33

Erosional landforms: what is a pyramidal peak?

Answer 33

where 3 or more corries develop around a hill and heir back walls retreat

Question 34

Erosional landforms: what is a trough? what other feature are found here?

Answer 34

• a u-shaped valley, with steep sides and a flat bottom
• hanging valleys, truncated spurs, misfit streams

Question 35

Erosional landforms: how is a trough formed?

Answer 35

• 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

Question 36

Erosional landforms: what is a roche moutonnee? What is a striation?

Answer 36

• 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

Question 37

Erosional landforms: how are roche moutonnees & striations formed?

Answer 37

• 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

Question 38

Erosional landforms: what can a roche moutonnee tell us about glacial movement?

Answer 38

the direction of movement of the glacier

Question 39

Erosional landforms: What are ellipsoidal basins?

Answer 39

large, deep lakes formed from the impact of ice sheets eg. Laurentide ice sheet created Great Lakes

Question 40

Depositional glacial landforms?

Answer 40

• Moraines
• Erratics
• Drumlins
• Till sheets

Question 41

Depositional landforms: What is a terminal moraine?

Answer 41

ridge of till (crescent shape) across the trough marking the maximum advance of the ice - deposited through the glacier snout

Question 42

Depositional landforms: What is a lateral moraine?

Answer 42

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

Question 43

Depositional landforms: What is a recessional moraine?

Answer 43

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)

Question 44

Depositional landforms: what is an erratic?

Answer 44

• 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

Question 45

Depositional landforms: what is a drumlin?

Answer 45

• 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

Question 46

Depositional landforms: how are drumlins formed?

Answer 46

• 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

Question 47

Depositional landforms: till sheets?

Answer 47

• formed when large mass of unstratified material is deposited when an ice sheet retreats - till depends on where material has been transported from