2. Geomorphic processes Flashcards
What is weathering?
A ubiquitous process that uses heat energy to produce chemically altered materials from surface or near surface rock
Name the five processes of chemical weathering and explain:
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
When is rate of chemical weathering the quickest?
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
What is physical weathering?
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
Name the three processes of physical weathering:
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
Explain biological weathering:
The breakdown of rock by plants, animals and micro-organisms.
What types of biological weathering are there?
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
Name the three types of erosion:
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
Factors affecting rate of abrasion:
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
What are the estimates for erosion by a valley glacier?
Embleton and King suggest that mean annual erosion for active valley glaciers is between 1000 and 5000m3
What is nivation?
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
Where does the debris carried by glaciers originate from?
Rockfall Avalanches containing rocks Debris flows: during summer when meltwater combines with soil and mud Aeolian deposits Volcanic eruptions Plucking Abrasion
How can glacial transportation be classified?
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
When does deposition occur?
When their capacity to transport material is reduced
Usually occurs during ablation in seasonal periods or during de-glaciation
What is drift?
All the material deposited by a glacier
