Edexcel A-level Geography - Glaciers

variations in solar output

low sunspot activity causes cooler temperatures, e.g. maunder minimum(1650-1750)

volcanic emissions(short term causes of climate change)

volcanoes inject large amounts of sulphur dioxide(ghg) into the atmosphere, which consequently trap heat in the atmosphere

eccentricity

changed to the earth’s orbit over a 100,000 year cycle(circular to oval)

axial tilt(milankovitch)

changed to the earth’s tilt over a 41,000 yr cycle - changes how much solar energy is received at the earth’s poles

precession

‘wobbles’ in the earth’s axis over a 21,000 yr cycle

periglacial environments

surround glacial environments, feature permafrost(permanently frozen ground) e.g. siberia

cryosphere

regions on earth where water turns into snow or ice

relict glacial landscape

no longer contains an active glacier, will still have distinct features left behind by its glacial past e.g. lake district, cumbria

freeze-thaw weathering

water enters cracks in the rock. when temperatures drop, the water freezes and expands causing the crack to widen

solifluction

mass movement of soil due to waterlogged conditions, causing it to flow downhill because of gravity

frost heave

the uplift of soil due to the expansion of groundwater when freezing

high winds(transportation)

due to limited vegetation cover, the wind is able to pick up and transport sediment

ice wedges

active layer freezes in winter(causes cracks), summer meltwater enters the cracks, widening them, meltwater freezes in winter to form ice wedges

patterned ground

develops through repeated freezing and thawing of moist, frost-susceptible soil, typically forming circles, polygons, irregular nets and stripes

loess(depositional)

silt that’s picked up and transported by wind, can form extensive deposits of loess

pingos

water filters down into the upper layers of the ground and freezes, the expansion of the ice causes the overlying sediments to heave upwards into a dome(pingo)

greenland case study:

• avg rate of ice loss has gone up from 34gt a year in 92-01 to 215gt a year between 02-11

• loss of ice cover is making the surface darker, accelerating melting(negative feedback loop)

• melting of the ice sheet has contributed 0.33mm a yr to global sea rise between 02-11

how do warm based glaciers move

basal slippage(sliding) - glacier sliding over the bed due to the ice acting as a lubricant

movement of cold based glaciers

internal deformation - the weight of glacier ice and gravity causes ice crystals to deform, so the glacier very slowly moves down

factors controlling the rate of glacial movement

• ice thickness - greater thickness creates more pressure in the ice, causing faster movement

• slope

• ice temperature

• variations in mass balance - more ablation = more meltwater causing more basal slippage

• altitude - high altitude = more snowfall so faster movement due to accumulation, low altitude = warmer so more meltwater, more basal slippage

how do glaciers alter landscapes

erosion

removal of weakened material by glacial ice

abrasion

glacier drags rocks, sediment and debris in its basal ice, grinding the bedrock beneath

plucking

rocks become frozen to the glacier and are plucked from the ground as the glacier moves forward

crushing(erosion)

as the glacier moves it causes erosion along the soil and rock it sits on, the weight may cause physical stress to the ground whilst picking up boulders

transport

rock debris is transported on the ice surface(supraglacial), within the ice(englacial) and at the base of the ice(sub-glacial)

deposition

till is sediment deposition directly by glacier ice, fluvio-glacial(erosion from meltwater) debris is deposited by glacial meltwater

glacial landforms

valley glacier landforms

arete

develops through plucking and abrasion on the back wall of two cirques, this means they erode backwards towards each other, creating a narrow ridge

pyramidal peak

erosional processes within nearby cirques mean they erode backwards towards each other, creating a pointed mountain summit

glacial trough(u-shaped valley)

v-shaped valley is widened and deepened as a result of plucking and abrasion by a valley glacier

truncated spur

when a valley fills with a glacier, any land which is in the way of the moving glacier will be eroded away, causing a truncated spur

hanging valley

tributary glaciers entering a glacial trough

ribbon lake

areas of increasing plucking and abrasion by the valley glacier deepen part of the valley floor, usually because of weaker rocks, meltwater then fills this as the glacier retreats

cirque

snow accumulates in a sheltered location on a mountainside, nivation enlarges the hollow and more snow accumulates, a cirque glacier develops, plucking forms the back wall, abrasion scoops out the cirque hollow

roche moutonee

a more resistant rock causes ice movement, as the ice slides over the rock, it smooths the stoss(up-valley side) while refreezing on the lee(down-valley side) causes plucking resulting in jagged rock

dispositional features

moraine

the material carried by a valley glacier and is deposited as till

terminal moraine

debris being deposited at the limit(end) of a glacier

drumlins

theory: formed by deposition when glacier ice becomes overloaded with debris when exiting an upland area, the deposits are streamlined and shaped by moving ice

lowland depositions features

till plain

when a large ice sheet becomes detached from a glacier and melts, material is deposited over a sizeable area

lodgement till

when debris that was being transported gets lodged or pressed into the glacier bed

ablation till

ablation is the melting of the ice and the till is deposited as the glacier melts, includes supraglacial and englacial material

formation of fluvio-glacial landforms

kame

as meltwater streams emerge onto the outwash plain at the glacial snout, their velocity falls and the sediment is deposited

kame terrace

during summer, the valley sides radiate heat, melting the edge of the glacier, forming meltwater streams, which deposit sediment, the sediment forms a kame terrace as the glacier retreats

eskers