Geography - Glaciers

Pearson Edexcel A-Level Glaciation Notes

4 types of cold environment

1. tundra/periglacial

2. polar (land) e.g. large masses of ice

3. polar (marine) e.g. icebergs

4. alpine (mountains)

cryosphere

all locations on Earth where water is in its solid state (can be permanent or temporary)

Largest ice mass

Antarctica (85%) and Greenland

The Quaternary period

covers the most recent period of geological time (2 million years ago → now so including the Pleistocene and the Holocene)

last glacial stage

Devensian period

pleistocene

the last ice age

holocene

warm period since 12000 years ago

the Milankovitch cycle causing climate change

the theory states the amount of solar energy reaching the earth’s surface varies with the shape of the Earth’s orbit around the sun, the angle of the tilt of the earth’s rotation and the direction of the axis of rotation

how does shape of orbit affect climate change

every 100,000 years the shape changes from circular (glacial phase) and elliptical (interglacial phases as closer proximity to the sun in summer months)

how does obliquity (tilt of Earth on its axis) affect climate change

varies from 21.8 degrees to 24.4 degrees over a 41000 timescale - when the tilt is greater, the seasons are longer so increased melting so interglacial period

how does procession (the earths ‘wobble’) affect climate change

change in direction of rotation every 19000 - 23000 years and can be used to explain the smaller increases and decreases

tectonic movement causing climate change

caused the Pleistocene (2.5 million yrs ago) - when N.America and S.America joined which pushed warm water northwards → more moisture from evaporation → more snow in N. hemisphere

albedo causing climate change

once ice sheets begin to develop, the Earth’s albedo (reflectivity) increases as ice is very reflective of solar energy → leads to a further decrease in temp

thermohaline circulation causing climate change

a slow, pattern of flow involving surface and deep ocean currents which is driven by differences in the density of sea water (which is controlled by temperature and salinity) → warm currents may keep some areas warmer e.g. UK

volcanic eruptions causing climate change

when a volcano erupts it releases ash into the atmosphere and when this ash reaches the stratosphere it stays suspended and reflects incoming solar radiation, causing average temps to drop e.g. Mount Tambora caused ‘the year without summer’

sunspot cycles causing climate change

every 11 years the sun changes its magnetic poles causing sun spots which make the earth warmer. They are bursts of energy where the sun emits a high amount of radiation

maunder minimum

name for when there is a lower number of sun spots

carbon dioxide levels causing climate change

greenhouse gas which is increased due to industrial revolution and population increase (increase energy reliance so increase burning of fossil fuels) prevents solar energy from leaving the atmosphere

food production causing climate change

produces large amounts of greenhouse gases from the clearing of land to make way for crops and agriculture, growing of food, processing, packaging and transporting it

(1/4 of global greenhouse gases from agriculture and food production)

deforestation causing climate change

trees capture CO2 and remove it from the atmosphere and so this is reduced when trees are removed but they also store the CO2 in trunks so when deforested, they release this extra CO2

burning of fossil fuels causing climate change

release of greenhouse gases like CO2 and sulfur dioxide which has a cooling effect on the planet as they reflect incoming solar radiation (key to slowing down climate change)

tree trunks being evidence for climate change

cross-sections where each ring represent a year of growth - this growth is effected by climate as thicker = warmer and wetter (up to 10,000 yrs ago)

ice cores being evidence for climate change

ice sheets build up over approx. 1 million years and we can drill down and collect ice cores which contain tiny bubbles with samples of the environment at that time e.g. CO2 levels

micro-fossils being evidence for climate change

skeletons of tiny, single celled creatures called foraminifera which live in oceans - they build up in layers and can by dug up - different species prefer different climates

weather stations being evidence for climate change

contain:

1. thermometers - indoor and outdoor temp

2. lux metre - solar energy

3. anenometer - wind speed and direction

4. barometer - air pressure

5. rainfall gauge

Loch Mond Stadial (stadial = short-term cooler phase within a generally warmer climate)

caused the reemergence of ice over Scotland - caused by sunspot cycles or volcanic eruptions

Little Ice Age

Thames froze and had frost fairs on top - caused due to the Maunder Minimum - virtually no sunspot activity

glacier

an accumulation or large mass of ice moving down due to gravity as well as its own weight

unconstrained glaciers

glaciers that have a morphology (form, shape and structure) and flow pattern that is independent of underlying topography (land beneath)

constrained glaciers

glaciers that have a morphology and flow pattern which is strongly dependent on underlying topography

alpine glaciers

high altitude so cold conditions and air of a lower pressure (every 100m increase = temp drops by 0.6 degrees) so increased glacier growth and causes valley glaciers e.g. Himalayas

polar terrestrial

very high latitude (colder as the angle or insolation means weaker sunlight is used to heat a larger area so less concentrated), forms ice sheets e.g. Antarctica, Greenland

polar marine

high altitude (sea will freeze) forming sea ice which is NOT a glacier (sea ice = dense ice that floats on the sea)

tundra

high latitude but not always ice covered due to low precipitation. Ground is frozen without ice = permafrost e.g. North Canada, Alaska

cirque (‘corrie’) glaciers

form as mountain side hollows and are found in nearly all alpine landscapes that support ice accumulation

• localised to all arm-chair shaped bedrock on a mountain side

valley glaciers

exist within bedrock valleys and are overlooked by ice-free slopes (found in many alpine environments). They have high erosive power and are fed in the upper parts by ice and snow from tributary glaciers

ice sheets + ice caps

confined to Antarctica and Greenland as both are broad and have slowly moving ice domes at their centre. They almost completely submerge the landscape with only the tips of mountain peaks piercing the service

ice caps are smaller

snow

90% air

coarse-grained snow

50% air

firn

20-30% air

glacial ice

20% air as bubbles (10-20 years)

accumulation

the amount of mass/snow added to a glacier e.g. through snowfall, avalanche, tributary glaciers, wind blown snow and rain

ablation

the total amount of ice that a glacier loses each year e.g. through melting (above 0 degrees celcius), calving (a section of a glacier breaks off) and sublimation (ice → gas)

snow line

the lowest edge of permanent snow cover in a mountainous area (warm summers = higher snow line)

glacial budget

the difference between accumulation and ablation in one year (positive or negative)

examples of disappearing glaciers

1. Columbia Glacier, Alaska - retreated over 12 miles since 1980 (max 5km in 1 year) as tide-water causes huge icebergs to carve away daily

2. Kalis Glacier, Peru

temperate glaciers

warm based

move far more quickly as ice isn’t frozen to the bed (through basal sliding as -1 degrees at base)

high accumulation and ablation

mobile glacier and therefore = erosion

moves 2-3m/day (100x polar glacier)

e.g. Himalayas

polar glaciers

cold based

move very slowly (1-2cm/day) as frozen to the bed (-30 degrees at base(

ice moves by inter-granular movement

ablation and accumulation limited

little erosion or deposition as little debris carried

pressure melting point not reached = no basal sliding

brittle zone

crevasses form as the ice fractures due to there not being enough pressure for the ice to be flexible

plastic zone

ice is flexible as higher pressure

basal sliding

responsible for 80% of glacial movement but only found in temperate glaciers

as pressure increases, the pressure melting point of ice lowers meaning ice melts at the -1 degree temperature at the base of most temperate glaciers

produces meltwater which lubricates the ice, meaning it slides over the rock below

(crevasses can also fill with water which can drip down and increase meltwater)

intergranular movement/laminar flow

occurs in every glacier but specifically polar glaciers as the bottom layer is frozen to the ice which cannot move

the higher the layer, the further the ice will move over the top of the layers below

can form crevasses due to tensions of layers of ice moving at different speeds

extending flow

when ice goes down a steeper gradient, it accelerates causing crevasses to form as the ice begins to thin

compressing flow

ice goes over a flatter gradient causing it to slow down which causes the ice to thicken and increase in depth

forms concentric ridges at the snout called compressional ridges as ice bunches as it slows down

rotational flow

only occurs in corrie/cirque glaciers

ice rotates around a pivot point which increases the pressure at the bottom of the bowl

this causes erosion and in turn the glacier to deepen

regelation slip

when a glacier approaches an obstacle, there is an increased pressure on the stoss side as the ice hits it

this causes the pressure melting point to lower which increases melting and meltwater produced

this causes the velocity of movement over the obstacle to increase but as it starts to move away over the leeward side, the pressure decreases and refreezing occurs

as the ice freezes onto the rock on the leeward side, when it breaks free it may pluck some rock off with it

glacial surge

occurs when

1. a sudden release of meltwater occurs

2. the gradient suddenely becomes very steeo and ice mass is high

3. the loss of a snout which acted like a blocker

velocities reach 10-100x faster than normal

very rare

how does gradient affect rate of movement

1. higher gradient = higher momentum so faster

2. if going uphill = much slower as going against gravity

3. glacial surge = more likely to occur if gradient suddenly becomes very steep

how does temperature affect rate of movement

high temperatures = high melting = more meltwater = faster basal sliding

how does precipitation affect rate of movement

1. increases accumulation = lowers PMP = increased melting = faster basal sliding

2. fills crevasses and drips down = increased lubrication = more basal sliding

how does rock type affect rate of movement

impermeable rock e.g. granite = water cannot pass through = rock is more lubricated = faster basal sliding (opposite for permeable rock)

how does mass of ice affect rate of movement

1. higher mass = heavier = more momentum = quicker

2. decreases PMP = more melting = more meltwater = better lubricated = moves quicker by basal sliding

entrainment

small rock fragments are trapped by basal ice freezing around them and applying sufficient drag to pull them along

subglacial

environment beneath the glacier ice

proglacial

environment located at the front of a glacier

periglacial

environments near glaciers

supraglacial

on top of the ice

englacial

within the ice

abrasions

when entrained rocks slide along the bedrock, eroding the bottom and side through scratches

striations

large scar

factors affecting abrasion

1. speed of glacier movement (slower = more abrasion)

2. supply of debris (more erosion as more friction)

3. subglacial meltwater (more = increases speed of movement due to basal sliding = less abrasion but plucking)

4. ice thickness (thicker = higher pressure at base so more abrasion)

5. rock type (hard bedrock erodes more slowly as requires a rock of similar density)

6. shape of debris (sharp/jagged may erode more + bigger = more erosion)

plucking

ice pulling rocks off of bedrock as it flows over (when meltwater refreezes and the ice moves, it pulls pieces of rocks off) causing bumpy and jagged rocks

freeze thaw weathering

when meltwater or rain gets into cracks in the bedrock, it freezes and expands causing the cracks to get larger causing the rock to break away

v-shaped valleys

• shallow, steep straight sides

• green from trees and vegetation

• often has interlocking spurs

• may have more rivers/lakes

u-shaped valleys

• deep and wide u-shaped valleys

• rockier and less green

• “misfit stream” within the valley

• truncated spurs

• ridges called aretes between valleys

corrie

a bowl shaped hollow in a mountain side which is scooped out by the process of abrasion from a glacier (rotational flow)

e.g. Red Tarn

corrie formation

1. snow compacts to ice and flows within a hollow in the mountain side

2. the rock above the glacier is weakened by freeze-thaw weathering, adding rocks to the glacier

3. hollow is made deeper by abrasion, plucking and rotational flow

4. the glacier melts so corrie is revealed (tarn if water fills the hole)

aretes

narrow ridges of rock formed where two glaciers erode a valley, side by side or back to back producing two steep sides on either side

e.g. Striding Edge

aretes formation

formed when two corries erode towards each other

pyramidal peak

the central mass of rock which is left on the mountain as 3 or more corries erode backwards into it (also forms aretes)

e.g. the Matterhorn

glacial troughs

u-shaped valleys with steep sides and a flat floor due to the high erosion power of ice

often contain a ‘misfit stream’ where a stream or river is much thinner than the valley floor

formed by weathering, erosion and transportation

ribbon lakes

elongated lakes which fill sections of the valley floor of a glacial trough and form due to the valley having a stepped profile

e.g. Ullswater

truncated spurs

where previous interlocking spurs are eroded back due to glaciers abrading the sides of the valley, creating jagged spurs as they no longer interlock

hanging valleys

where a smaller side valley is left ‘hanging; above the main U-shaped valleys as glaciers in the smaller valley are not as powerful so don’t erode as deeply

roches moutonees

where a protruding section of resistant bedrock is eroded creating an irregular shape

knock and lochan

large-scale feature covering extensive areas as a result of ice sheet scouring

formation of knock and lochan

created where ice sheets have weaker and stronger rock (weaker rock erodes faster) which forms the ‘lochan’ meaning lakes and the harder rock that is left over is known as ‘knocks’

found across Scotland

crag and tail

where a resistant area of bedrock forms an obstacle and plucking and abrasion erodes the stoss side and then sub-glacially transports this material to be deposited on the leeward side

the ‘crag’ is the bedrock and the ‘tail’ is the deposited material streamlined by subsequent ice flow

e.g. Edinburgh

striations

micro-scale feature formed when rock entrained in the ice is harder than the bedrock causing it to gauge out a groove/scratch parallel to ice flow

chattermarks

micro-scale feature which is horse-shoe shaped mark in bedrock formed by sub-glacial rocks jolting or juddering forwards in sudden movements

moraine

any material a glacier is carrying or has carried and deposited (unsorted and unconsolidated)

active/inactive depends on whether the material is currently being transported by the ice or not

erratic

a boulder transported and deposited by a glacier at a distance from its source which indicates patterns if former ice flow

how does material get deposited at the snout?

1. moves forward → pushes material proglacial further in front

2. retreats/melts → leaves material either entrained or supraglacial

till

racks deposited by ice/glaciers which is unconsolidated and unsorted

terminal moraine

a moraine ridge that marks the maximum limit of a glacier advance (at the end)

recessional moraine

found behind a terminal moraine limit and form during short-lived phases of a glacier advance or stand-still that interrupts the general pattern of glacier retreat (may be annually)

lateral moraines

forms along the glacier side and consists of debris that falls or slumps from the valley wall or flows supraglacially

medial moraines

debris ridges at the glacier surface running parallel to the direction of ice flow supraglacially

forms where lateral moraines meet at the confluence of two valley glaciers or where debris constrained in the ice is exposed at the surface due to melting

ground moraines

describes the uneven blanket of till deposited in the low-relief areas between more prominent moraine ridges

forms at the bottom of the glacier due to deformation and eventual deposition of sub-stratum (an underlying layer)

till plains

when an ice sheet retreats, large amounts of material are deposited over a sizeable area due to melting