2. Geomorphic processes Flashcards

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1
Q

What is weathering?

A

A ubiquitous process that uses heat energy to produce chemically altered materials from surface or near surface rock

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2
Q

Name the five processes of chemical weathering and explain:

A

Oxidation
rock reacts with oxygen in air or water and is destroyed eg. Iron

Carbonation
rainwater + carbon dioxide ——> weak carbonic acid which breaks down rock
carbonic acid reacts with calcium carbonate ——> calcium bicarbonate (soluble)

Solution - process where minerals dissolve, occurs because many minerals are soluble and are removed when they come into contact with water

Hydration - occurs when water is absorbed by minerals in the rock, creating crystals which exert pressure on the surrounding rock, eventually causing it to crumble eg anhydrite forms gypsum

Hydrolysis - occurs when water reacts with minerals in the rock causing the chemical composition of the rock to change and become more unstable. This reaction makes the rock more susceptible to decomposition eg feldspar reacts with water to produce china clay

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3
Q

When is rate of chemical weathering the quickest?

A

Fastest when temperatures are high

Van’t-Hoff’s Law states that a 10 degree rise in temp leads to a 2.5 times increase in rate of chemical reaction

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4
Q

What is physical weathering?

A

The breakdown of rock to produce smaller fragments without chemical alteration
The surface area of the rock is increased so further weathering ie chemical can occur

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5
Q

Name the three processes of physical weathering:

A

Freeze-thaw - water enters cracks and freezes causing it to expand by 10%,exerting a pressure on the rock causing it to split, occurs mainly when temp. fluctuates around 0 degrees

Frost shatter - water enters rock pores, freezes and expands causing rock to disintegrate into small particles

Pressure release - when weight of glacier decreases due to melting the underlying rock expands and fractures parallel to surface

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6
Q

Explain biological weathering:

A

The breakdown of rock by plants, animals and micro-organisms.

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7
Q

What types of biological weathering are there?

A

Plant roots can enlarge cracks in a rock as they grow and expand
Organic acids produced during decomposition cause soil water to become acidic and react with minerals = chelation

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8
Q

Name the three types of erosion:

A

Abrasion - debris carried in glacier base/sides erodes valley wall and floor eg. striations
Glacial debris is also worn down to produce rock flour

Plucking - meltwater seeps into rocks in the valley and freezes - as the glacier advances pieces of rock are pulled away
Particularly effective at base of glacier where there is lots of meltwater due to exceeding pmp

Crushing - creates chattermarks as downward pressure jolts debris along bed

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9
Q

Factors affecting rate of abrasion:

A

Removal of fine debris eg. Rock flour

Ice thickness

Basal water pressure

Sliding of basal ice

Movement of debris to base

Presence of basal debris

Debris size and shape

Relative hardness of particles and bedrock

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10
Q

What are the estimates for erosion by a valley glacier?

A

Embleton and King suggest that mean annual erosion for active valley glaciers is between 1000 and 5000m3

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11
Q

What is nivation?

A

A complex process thought to be a combination of freeze-thaw, solifluction, transport by running water and chemical weathering
Responsible for the creation of corries

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12
Q

Where does the debris carried by glaciers originate from?

A
Rockfall
Avalanches containing rocks
Debris flows: during summer when meltwater combines with soil and mud
Aeolian deposits 
Volcanic eruptions 
Plucking 
Abrasion
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13
Q

How can glacial transportation be classified?

A

Supra-glacial - on the top - debris from rockfall and weathering

Englacial - inside - previously supra-glacial debris that has since been covered by ice

Subglacial - underneath - debris from plucking and abrasion

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14
Q

When does deposition occur?

A

When their capacity to transport material is reduced

Usually occurs during ablation in seasonal periods or during de-glaciation

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15
Q

What is drift?

A

All the material deposited by a glacier

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16
Q

Name the two types of drift:

A

Till - dropped directly from glacier, tends to be angular and sharp

Outwash - dropped by meltwater, tends to be smoothed and rounded

17
Q

What are the characteristics of till?

A
  • Angular in shape: embedded in the ice so hasn’t been subject to erosion by meltwater
  • Unsorted as glacier deposits material of all sizes together
  • Unstratified: dropped in mounds rather than in layers
18
Q

What are the two types of glacial till?

A

Lodgement till - material deposited by advancing ice when subglacial debris is forced into valley floor and left behind as ice moves

Ablation till - material deposited by retreating ice

19
Q

What are the characteristics of outwash?

A

Smooth and round: subjected to erosion by meltwater
Sorted: water deposits material based on size as the water loses energy
Stratified: water sorts the outwash into layers