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freeze-thaw (physical weathering)
water enters rock cracks -> expands when refreezes -> exerts pressure on rock -> rock splits/breaks off
frost shattering (weathering)
water trapped in rock pores -> freezes -> expands -> repeating freezing and thawing -> rock joints weaken and widen -> rock breaks into small particles away from main body of rock
oxidation
oxygen combines with another substance to create oxides which breaks rocks apart
oxidation - rock
sandstone (iron rich material)
carbonation
water mixes with CO2 to make carbonic acid which reacts with rocks making them easily crumble
carbonation - rock
limestone or chalk
solution
minerals soluble in water, dissolve, wreaking structure of rock
solution - rock
limestone
hydrolysis
chemical reaction between rock minerals and acidic water to create other materials
hydrolysis - rock
granite -> clay
hydration
water reacts with minerals, rock absorbs water making it suffer
hydration - rock
anhydride -> gypsum
factors influencing rates of weathering
rock type
climate
vegetation
climate change
aspect
location
altitude
mass movement examples
-rock fall -sliding -slumping
rock fall
rocks become detached by physical weathering processes and fall to create scree slopes
sliding
movement downhill (blocks of rock) along a straight-line slip plane
slumping
slides may occur due to steepening under-cutting of valley sides by erosion at the base of the slope
plucking (erosion)
meltwater in joints of rocks -> freezes -> attach to glacier -> glacier advance -> pluck rock
abrasion (erosion)
debris embedded in base/side of glacier -> rock moves in ice under force of gravity -> scrapes/indents valley floor/sides in glacier as it moves
example of a corrie
The Walcott Corrie, Antartica, 3km high back wall
example of an arete
Striding Edge, Lake District, 200-300km high
example of a pyramidal peak
Matterhorn, Swiss Alps, over 1200m high
example of a roche moutonnee
Norfolk Island, Lake District
example of a glacial trough
Glen ridding Valley, Lake District
example of a ribbon lake
Ullswater, Lake District
example of a hanging valley
Helvellyn Gill, Lake District
example of a truncated spur
Walls Crag, Lake District
lodgement till
material deposited by moving ice when its weight becomes too heavy to move
ablation till
material which is deposited directly at the end of the glacier by water melting when the ice is stagnant
moraines
deposits of glacial till
ground moraine
unsorted material left all over ground as glacier retreats up valley in warmer times (lodgement till)
terminal moraine
rocks deposited (ablation till) in a ridge at max advance of ice
lateral moraine
ridges from valley sides and run parallel to them
medial moraine
ridge of rocks running down the middle of a valley formed by 2 lateral moraines from 2 glaciers coming together
recessional moraine
ridges parallel to terminal moraines marking the retreat of a glacier (ablation till) - the less time the glacier was stagnant the less material there will be
push moraine
mounds of material found where a drop in temp or increase in precipitation allows glacial re-advance and the glacier pushes previously deposited moraines forward
till plains
large expanse of gently rolling hills of till - forms when a large mass of unstratified drift is deposited at the end of an ice sheet when it detaches from the main body of a claire and melts
erratics
large rocks or boulder that have been picked up (plucked) by a glacier or ice sheet, transported and deposited in a new area
drumlins
half-egg shaped hills of till
example of an erratic
Norber erratics, Yorkshire Dales
example of a drumlin
Vale of Eden, Lake District
transportation
rockfall
avalanches
debris flow
aeolian deposits
volcanic eruptions
plucking
abrasion
subglacial debris
embedded in the base of the glacier
supraglacial debris
carried on the surface of a glacier
englacial debris
debris within the ice
erosional landforms
-corries -arêtes -pyramidal peaks -troughs -roche moutonnee -striations
depositional landforms
-terminal moraine -lateral moraine -recessional moraine -erratic -drumlin -till plain
folding
the bending of rock layers due to stress
faulting
process of cracking that occurs when the folded land cannot be bent any further
geomorphic processes
-erosion -weathering (physical, biological and chemical weathering) -mass movement -transportation -deposition
conditions for physical weathering
high altitude/low latitude for variation in temperatures to allow for melting and freezing
pressure release (physical weathering)
weight of overlying ice in a glacier is lost due to melting -> underlying rock expands -> rock fractures parallel to the surface -> significant exposure of sub-surface rocks -> these rocks are more susceptible to other forms of weathering e.g. freeze thaw
where in a glacial system will pressure release most likely occur
areas where ice has retreated
biological weathering
weathering of rocks caused by tree roots or the decomposition of plant and animal matter
chelation
the organic acid produced by decomposition that reacts with rocks
significance of biological weathering
not significant in glacial regions - more in tundra/periglacial regions and only in summer
chemical weathering makes rocks more prone to...
erosion later on
conditions for chemical weathering
high altitude/low latitude - variations in temperature as it needs water present to react with rocks
rotational movement (erosion)
occurs in a corrie -> downhill movement of ice pivoting around a point and overdeepening at that point -> enables abrasion and plucking to take place
solifluction (weathering)
base of the glacier where ice melt through friction occurs -> eroded material is carried along under the glacier -> debris is accumulated in glacier and alter deposited
rock conditions for effective plucking
when the rock is jointed or previously weathered and requires the presence of meltwater
abrasion requires...
meltwater for movement to occur and so is less effective in cold-based glaciers
difference between abrasion and plucking
abrasion is scratching while plucking is the removal of chunks of rock
abrasion in glaciers require rocks to erode the valley while plucking is the use of meltwater to carry rock fragments
3 factors influencing the rate of abrasion
amount of basal debris, speed of ice movement (steepness and meltwater), debris size and volume
how does steepness influence the rate of abrasion
increased steepness -> increased speed of ice movement -> friction is greater
the more basal debris in a glacier, the rate of abrasion will be...
...higher
the rate of abrasion by cold based glacier is...
...low as no meltwater means little movement
how does debris size and shape influence the rate of abrasion
larger and sharper rocks will abrade more
basal water pressure
in warm based glaciers there is presence of meltwater underneath and the pressure is increased by the height of the glacier and so the basal pressure will move the water quicker
nivation occurs...
...when snow starts to accumulate
nivation
weathering such as freeze thaw and erosion such as abrasion combined
nivation over time leads to...
...nivation hollows
nivation hollows
shallow pits as a result of nivation
how nivation hollows develop into corries
pits trap more snow -> more compression of snow -> increase pressure -> compacted snow and ice -> deepen further to form a corrie
how rock type influences rate of weathering
rock with a weak structure is more prone to physical weathering
chemical weathering can only occur in certain types of rocks
types of chemical weathering
oxidation, carbonation, solution, hydrolysis and hydration
how climate influences rate of weathering
glaciated regions -> colder, slightly drier locations will be more prone to physical weathering
non glaciated regions -> warmer, slightly wetter locations will be more prone to chemical weathering
how vegetation influences rate of weathering
more vegetation (in non glaciated regions) -> enhances biological weathering
how climate change influences rate of weathering
increase burning of fossil fuels -> more CO2 -> more carbonation
warmer temperatures -> more melting -> more chemical weathering
warmer temperatures -> more vegetation -> more biological weathering
how aspect influences rate of weathering
face away from sun -> colder -> more physical weathering
face toward the sun -> fluctuating temperatures around 0C -> more freeze-thaw weathering
how location influences rate of weathering
high latitudes -> less chemical weathering / some physical weathering / weathering will be slower
high altitudes, low latitudes -> more chemical weathering or freeze-thaw weathering will dominate
location determines the amount of precipitation
how altitude influences rate of weathering
higher the altitude -> colder it will be -> less chemical weathering
higher temperatures -> more chemical weathering
corrie characteristics
-armchair shaped hollow -steep back wall -over deepened basin with a lip at the front
corrie formation
snow (input) falls and accumulates and nivation deepens the hollow it collects in
over time the hollow enlarges and contains more snow which is eventually compressed into glacier ice
the ice acquires a rotational movement under its own weight which enlarges the hollow further - meanwhile the rotational movement causes plucking of the back wall, making it increasingly steep
the debris derived from plucking and weathering above the hollow falls into the Bergschrund crevasse which steepens the back wall and abrades the hollow deepening it
once the hollow has deepened, the thinner ice at the front is unable to erode so rapidly and so a higher lip is left
post-glacial landscape the corrie may become filled with water forming a small lake or tarn
