2.a glacial processes + land forms

freeze-thaw (physical weathering)

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

1. snow (input) falls and accumulates and nivation deepens the hollow it collects in

2. over time the hollow enlarges and contains more snow which is eventually compressed into glacier ice

3. 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

4. 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

5. once the hollow has deepened, the thinner ice at the front is unable to erode so rapidly and so a higher lip is left

6. post-glacial landscape the corrie may become filled with water forming a small lake or tarn

role of energy in corrie formation?

• gravitational potential energy → rotational movement

• kinetic energy → less of it so forms a higher lip as hollow deepens

• heat/solar energy → small circular lake or tarn

arête characteristics

-narrow, steep-sided ridge found between two corries -knife-edged

arête formation

1. corrie formation

2. 2 corries form side by side and erode backwards into the mountain, narrowing the peak

role of geomorphic processes in the formation of aretes

corrie

• weathering

• erosion: plucking and abrasion

• deposition

arête

• erosion: two corries retreat + slopes steepen to form a sharp ridge

pyramidal peak characteristics

-sharp-edged mountain peak

pyramidal peak formation

1. three or more arêtes/corries form back to back around a mountain top and their back walls retreat to create a peak

2. nivation and weathering of the peak may further sharpen its shape

roche moutonnee characteristics

-smooth -streamlined by abrasions -straitions -rock hill shaped

roche moutonnee formation

1. resistant rock found on valley floor which advancing ice passes over

2. localised pressure melting occurs and abrasion on the up-valley side (stoss) -> smooth rock with striations

3. on the down-valley side (lee) pressure is reduced and meltwater re-freezes, resulting in plucking and the steeping of the rock

glacial trough formation

1. glaciers flow down pre-existing V-shaped river valleys under gravity - the mass of the ice has far more erosive power than a river and so erodes the sides and floor of the valley

2. as it moves (gravitational potential energy) it plucks the rock from beneath and those rocks rub against (abrasion) the bed of valley, eroding it further making the shape become deeper, wider and straighter

its long profile is a realist of compressing flows making the valley over-deepened to form rock basins and rocks steps, particularly evident where there are alternating bands of rock of different resistances on the valley floor (the weaker rocks being eroded more rapidly to form the basins)

glacial trough characteristics

-U-shaped valley -deep -wide -straight

hanging valley formation

smaller/tributary valleys feed into the main valley as they have been eroded slower and shallower - sit between truncated spurs

truncated spur characteristics

-steep-sided -wide -relatively flat-bottomed

truncated spur formation

1. a river flows through the landscape, creating interlocking spurs.

2. interlocking spurs are truncated as the glacier cuts straight through the landscape by the processes of abrasion, plucking freeze-thaw.

3. the truncated spurs can then be identified by the exposed rock found on valley sides. They will continue to steepen after glaciation due to freeze-thaw

ribbon lake characteristics

• long, narrow lake

• found in the bottom of a glacial trough

ribbon lake formation

1. extending and compressing flows causes the valley floor to over deepen at a variety of erosional rates due to thicker ice or areas of softer rock

2. this means that some parts of the valley floor are over deepened creating ribbon lakes

striations formation

scratches or grooves made by debris embedded in the base of the glacier - abrasion is the key process