Glaciated landscapes

OCR A-Level Geography

glaciated landscape as an open system

inputs - kinetic energy from wind and movement, thermal from sun and potential energy from material on slopes

Outputs - glacial and wind erosion from rock surfaces; evaporation, sublimation and meltwater

Throughputs - stores including ice, water and debris accumulations and flows such as movements of ice, water and debris downslope by gravity

Accumulation

inputs of snowfall, blown snow and avalanches

ablation

inputs transferred by gravity and mass is loss from the system by melting and evaporation

glacier mass balance

difference between the amount of snow and ice accumulation and amount of ablation occurring in a glacier over a one year period

wind influence on glaciated landscapes

picks up material and uses it in the processes of erosion, deposition and transportation (aeolian process)

precipitation on glaciated landscapes

provide input of snow, sleet and rain

temperature influence on glaciated landscapes

affects input and outputs to system

Temperature rises, snow melts and becomes output

In high altitude may be be summer snowmelt and in areas of high latitude temperatures may never rise above zero

lithology influence on glaciated landscapes

chemical and physical composition of rocks

Rocks like clay have weak lithology with little resistance to erosion, weathering and mass movements as bonds are quite weak

Others like basalt are made of dense interlocking crystals are highly resistant and likely to form prominent glacial landforms such as pyramidal peaks

Limestone made of calcium carbonate is soluble in weak acids and so vulnerable to decay by chemical weathering

geology structure on glaciated landscape

properties of individual rock types such as jointing, bedding and faulting

Includes permeability of rocks

Porous rocks like chalk, have pores separating minerals particles which can absorb and store water

Latitude influence on glaciated landscapes

high latitudes like artic and Antarctic circles at 66 degrees N and S have cold and dry climates with little seasonal variation in precipitation

High latitudes = more present

Large stable ice sheets that are different to those of dynamic valley glaciers

Low latitudes by high Altitude influence on glaciated landscapes

higher precipitation but more variable temperatures

Decrease in temperature with altitude that glaciers found near equator

Temp decreases with altitude at 0.6 degrees per 100m

relief influence on glaciated landscapes

steeper relief, greater resultant force of gravity and more energy a glacier will move downslope

aspect influence on glaciated landscapes

air temps close to zero, aspect of slope faces away from general direction of sun, temperatures remain below 0 for longer as less solar energy is received so less melting occurs

Formation of glacier ice

When temperatures low enough for snow that falls in one year to remain frozen throughout

So next year, fresh snow falls on previous snow

Each new fall compresses and compacts layers beneath, causing air to be expelled and converting low density snow to high density ice (Diagnesis)

Valley glaciers

contained within valleys

May be outlets from ice sheets or fed from corries

Follow course of existing valley as move downhill

Ice sheets

large accumulation of ice extending more than 50,000km squared

Currently 2 - Antarctica and Greenland

warm based (temperate) glaciers

high altitude

Steep relief

Basal temperatures at pressure melting point

Rapid movement

High accumulation in winter and ablation in summer so very active and large volumes being transferred across equilibrium line

cold based glaciers

high latitude locations

Low relief

Basal temperatures below pressure melting point and so frozen to bedrock

Very slow rates of movement

Influences on glacier movement

gradient - steeper = more movement

Thickness of ice

Glacial budget

two zones in a glacier

upper zone with brittle ice that breaks

Lower zone with under pressure deforming ice

basal sliding

warm based glaciers

Consist of slippage, creep and bed deformation

3 parts of basal sliding

slippage - circular motion that can cause ice to move away from the back wall of a hollow

Creep - slow downward movement of loose rock and soil down a gentle slope

Bed deformation - movement of soft sediment or weak rock beneath a glacier

2 parts of internal deformation

Inter granular flow - where individual ice crystals move relative to each other

Laminar flow - where individual ice crystals move along layers within glacier

extending flow

when ice moves quickly over a steep slope so unable to deform quickly enough and fractures, forming crevasses

Leading ice pulls away from ice behind

compressing flow

when gradient is reduced, ice thickens and following ice pushes over the slower moving leading ice

Planes of movement called slip banes at different angles

weathering

ubiquitous process of wearing down using energy to produce physically or chemically altered materials from surface or near surface rock

physical or mechanical weathering

breakdown of rock that produce smaller fragments of same rock

freeze thaw

water enters cracks / joints and expands by 10% when it freezes

In confined spaces this exerts pressure on rock causing it to split or break

More frequent and regular the fluctuations of temperature around zero, more effective

frost shattering

extremely low temperatures, water trapped in rock pores freezes and expands creating stress which disintegrates rock to small particles

pressure release

when weight of overlying ice in glacier is lost due to melting, underlying rock expands and fractures parallel to surface

chemical weathering

decay of rock involving chemical reaction between elements of weather and some minerals within rock

oxidation

some minerals in rocks react with oxygen in air or water

Iron is especially susceptible

Becomes soluble under acidic conditions and original structure is destroyed

carbonation

rainwater combines with dissolved carbon dioxide from the atmosphere to produce weak carbonic acid Which reacts with calcium carbonate in rocks such as limestone to produce calcium carbonate B

biological weathering

physical actions such as plant growth of roots or chemical processes such as chelation by organic acids

mass movement

forces acting on slope material exceed forces trying to keep material on slope

plucking

when meltwater seeps into joints in the rocks of the valley floor sides

This then freezes and becomes attached to the glacier

As glacier advances it pulls pieces of rock away

Abrasion

glacier moves across surface and debris embedded in its bases scours the surfaces of rocks, wearing them away

nivation

glacial process that isn’t easily classified as erosion or weathering

Include combination of freeze - thaw action, solifluction and chemical weathering

Factors that influence glacial abrasion

• Debris size and shape

• Relative hardness of particles

• Ice thickness

• Basal water pressure

Transportation

• rockfall

• Avalanches

• Debris flow

• Aeolian deposit

• Volcanic eruptions

• Plucking

• Abrasion

Deposition

deposit loads when capacity to transport is reduced usually occurring as a result of ablation during seasonal periods of retreat

Known as drift and divided into till and out wash

lodgement till

material deposited by advancing ice

Due to downward pressure exerted by thick ice, subglacial debris may be pressed and pushed into existing valley floor material and left behind as ice moves

Drumlins

ablation till

material deposited by melting ice from glaciers that are stagnant or in retreat, during a warm period of end of event

3 characteristics of till

angular or sub angular - been embedded in ice and not be subjected to further erosion which would be it smoother and more rounded

Unsorted - glaciers deposit material, all sizes are deposited en mass

Unstratified - glacial till dropped in mounds and ridges rather than in layers

5 types of erosional landforms

• corries

• Arêtes and pyramidal peaks

• Troughs

• Roche moutonnées and striations

• Ellipsoidal basin

Corrie formation

armchair shaped hollows found on upland hills or mountainsides

Steep back wall and over-deepended basin often with a lip at. The front

Vary is size and shape

1. Nivation of a small hollow on hillside in which snow collects and accumulates year on year

2. Over time hollows enlarge and contain more snow, eventually compressing into glacier ice

3. At critical depth, ice acquires a rotational movement under own weight which enlarged hollow further

4. Meanwhile rotational movement causes plucking on back wall, making it increasingly steep

5. Debris derived from plucking and weathering above hollow falls in crevasse

6. This debris helps to abrade hollow and make it deeper

7. Once hollow has deepened, thinner ice at front is unable to erode so rapidly, leaving higher lip

8. May be filled with water forming a tarn post glacial

Arête

narrow knife-edged steep sided ridge found between 2 corries

Form from glacial erosion, steepening slopes and retreat of carries that are back to back

Pyramidal peaks

when 3 or more corries develop around a mountain top and back walls retreat

Weathering may further sharpen shape

troughs

glaciers flow down pre- existing river valleys under gravity

As move erode sides and flow of valley, causing a deep, wider shape

Mass of ice has more erosive power than previous river

Often parabolic shape

Resultant scree slope that accumulated at base of valley sides lesson slope angle

Roche moutonnées and striations

resistant rock on floor of glacial troughs

As ice passes over, localised pressure melting on valley side

This is smoothed and streamlined by abrasion leaving scratches and grooves by debris embedded in base

Roche indicate direction of ice movement

ellipsoidal basin

created by ice sheets

E.g. Laurentide ice sheet covering North America 12,000 years go

4 depositional landforms

• morraines

• Erratics

• Drumlins

• Till sheets

Terminal moraine

ridge of till extending across a glacial trough

Usually steep on upper valley sides lesson slope and be crescent shaped

Mark position of maximum advance of ice and were deposited at glacier snout

Lateral moraine

ridge of till running along edge of valley glacier

recessional moraine

series of ridges running transversely across glacial troughs and which are broadly parallel to each other and to terminal moraine

Form during temporary still-stand in retreat

Erratics

individual piece of rock, varying in size composed of different geology from area in which they have deposited

They were eroded by plucking, in area of one type of geology and then transported into a different area

drumlins

mound of glacial debris that has been streamlined into an elongated hill

Aligned in direction of ice floor

Higher and wider stoss with gently tapered lee

Formed maybe through

• lodgement of subglacial debris as it melts out of basal ice layers

• Reshaping of previously deposited material during re-advance

• Accumulation of material around a bedrock obstruction

• Thinning of ice as it spreads out over a lowland area reducing its ability to carry debris

Till sheets

formed when large mass of unstratified drift is deposited at end of a period of ice sheet advance, smoothing underlying surface

Significant landforms because of extent

Variable composition

glacial trough in Snowdonia

Nant Ffrancon

Corrie in Snowdonia

Cym Idwal

Pyramidal peak in Snowdonia

Mount Snowdonia (1085m)

geology impact on formation of Snowdonia landscape

1. Cambrian period (500 million years ago) flooded with sea water forming a marine basin and with large volume of marine sediments, formed sedimentary rocks

2. Ordovician period (460 million years ago) oceanic plate subjected to north west of Snowdonia causing eruptions of lava and ash from underwater volcanoes. Craggier areas made of igneous rock harder than sedimentary rock like granite and rhyolite

3. Devonian period (400 million years ago) North America, Scotland and Ireland joined and tectonic activity led to folding of rocks in North Wales e.g. Cwym. Idwal and led to recrystallisation of mineral grains forming slate

4. Quaternary period (2.6 million to present) marker beginning of glacial period forming corries and valleys

aspect, latitude and altitude in Snowdonia

aspect:

70% corries facing N/NE as sheltered by prevailing SW winds and solar energy

Manny drumlins orientated SW/NE in north Snowdonia indicated originated further north

Altitude/latitude

Snowdonia too far south to be considered cold based glacier

Changes over time in Snowdonia

• Glacial - interglacial cycles

• Loch Lomond stadial leading to smaller corries glaciers and lots of erosional and depositional landforms

• Weathering

• Winter temps below 0 - freeze thaw cycles creating block fields on mountains where rock is weathered in situ

• Human activity

• Agriculture, slate mining, infrastructure and footpath erosion

geology in Minnesota

laurentide shield

Oldest rocks between alternating belts in northern half of state and much of Minnesota river valley

Belts of volcanic and sedimentary rocks with granitic between

Oldest rocks formed 2700 million years ago when lava escaped through rifts

Volcanic debris released into sea settled forming sedimentary rock

Tectonic activity folded many formations and formed faults

Many volcanic rocks metamorphosed to greenstone

Tectonic compression created range of mountains 3km high in north

glaciation in Minnesota

75,000 years ago, lobes or tongues extended from ice sheet advancing and retreating, transporting and depositing till

Erosional impact on Minnesota

1km thick ice sheet wore down high mountains to now only 500-700m high

Large elipsoidal basin created and now studded with lakes such as upper and lower red lakes in north

Arrowhead region was particular deep as earlier tectonic tilting of landscape exposed weak shale rocks which were eroded more rapidly than surrounding resistant volcanic therefore creating lakes

As lobes advances, abraded striations in bare rock outcrops of gneiss and greenstone, indicating alignment of ice

Far southeast not covered so more varied

Considerable impact as shaped overall landscape but doesn’t form same landforms as in Snowdonia

depositional impact in Minnesota

Wadena lobe advanced from NE Canada and reached souther of Minneapolis

Till deposited was red and sandy as from red sandstone and shale to NE

Wadena lobe deposited Alexandria moraine and formed drumlin fields in Otter Tail

Proglacial lakes Minnesota

edge of a giant ice sheet and associated lobes also dammed natural drainage

Lake Agassiz occupying red river valley Belts of

Glaciers to north blocked natural north drainage and as ice melted, proglacial lakes developed south

Water overflowed watershed and drained, cutting the present Minnesota river valley

Changes over time Minnesota

• Glacial-inter glacier cycles

  Landforms during quaternary period including drumlins, till sheets and moraines and when melted carved out river valleys and lakes

• Soil formation

  Glacial till transformed into fertile soil centuries

• Climate change

  Warming temps causing faster snow and ice melt leading to higher water levels and flooding that reshape riverbanks and wetlands

Glacial-fluvial landforms

produced by meltwater from glaciers, supraglacially (top) englacially (within) and proglacially (in front)

High pressure and velocity of meltwater beneath glaciers causes erosion of underlying bedrock and leads to sub glacial meltwater channels

Both erosional and depositional

Meltwater released from glaciers during short, seasonal periods of melting but mostly during deglaciation

Kames

hill or hummock composed of stratified sand and gravel laid down by glacial meltwaters

delta and terrace

delta Kame formation

• en-glacial streams emerging at snout which lose energy at base of glaciers causes erosion and deposit load

• Supra-glacial streams deposit material on entering ice-marginal lakes, losing energy as enter static body of water

• Debris- filled crevasse collapses during ice retreat

Kame terrace formation

ridges of material running alongside edge of valley floor

Supraglacial streams on edge of glacier pick up and carry lateral moraine which is later deposited on valley floor as glacier retreats

Esker

long sinuous ridge composed of stratified sand and gravel laid down by glacial meltwaters

esker formation

material is deposited in subglacial tunnels as supply of meltwater decreases at end of glacial period

Sub-glacial streams carry huge amounts of debris under pressure and is confined at base

As glacier snout retreats, point of deposition gradually moves backwards dropping till

Outwash plains

flat expanse of sediment in the pro-glacial area

formation of outwash plains

as meltwater streams lose energy as enter lowland areas beyond ice front, deposit load

Largest material is deposited nearest ice front and finest further away

modifications

repeated advance and retreat modify and alter appearance which are also subject to weathering, erosion and colonisation by vegetation in post-glacial times

As temps rise, further melting and retreat of glaciers results in production of more meltwater and therefore greater expanse and accumulation of outwash material

Kames and eskers exposed in greater number and length

Temps increase so does growing season for vegetation

Exposed outwash material is colonised by mosses then grass and shrubs

periglacial environment

at or near ice sheets

Have permafrost

Seasonal temperature variations

Freeze-thaw cycle dominating geomorphic processes

Found in high latitude and altitudes

climate change effects on geomorphic processes in periglacial environment

freeze thaw dominant due to fluctuations in temperatures

Frost heave (sub surface process that leads to vertical sorting of material in active layer)

patterned ground

collective term for number of fairly small-scale features of periglacial environments

As a result of frost-heave, large stones reach surface and ground surface is domed

Stoned move more radially under gravity, down each dome surface to form network of stone polygons

pingos

Rounded ice-cored hills that can be as much as 90m in height and 800m in diameter formed by ground ice developing during winter months

open system pingo

form in valley bottoms where water from surrounding slopes collects under gravity, freezes and expands under artesian pressure

Overlying surface material is forced to dome upwards

Closed-system pingo

develop beneath lake beds where supply of water is from immediate local area

As permafrost grows during cold periods, groundwater beneath a lake is trapped by permafrost below and frozen lake above

Saturated talik is compressed by expanding ice around and under hydrostatic pressure

When talik freezes it forces up overlying sediment

modification of landforms in periglacial

patterned ground is minor and small scale

As temps rise, patterned ground is colonised by vegetation and so hard to find and identify

Mass movement by creep degrades frost-heaved domes, making landforms less obvious

Pingos collapse when temperatures rise and ice core thaws - dome collapses leaving rampart surrounding circular depression called an ognip

need for oil in Alaska

2014 USA consumed 6.95 billion barrels of oil products

oil reserves Alaska

1968 vast deposits oil found in Prudhoe bay and trans-Alaskan pipeline built

impact of oil extraction on periglacial landscape of Alaska

• Gravel is extracted from stream and river beds and used as insulating base layer for road construction - loss of gravel from systems alters rate at which gravel is transported further downstream altering equilibrium between erosional and depositional processes

  Gasses burnt (flaring) releases carbon dioxide and methane is vented without bringing which are both greenhouse gasses contribute to enhanced greenhouse effect

  Urban heat island is a small town in Barrow that found mean temperatures were 2.2 degrees higher than surroundings

  Heat from domestic systems in poorly insulated buildings contributor

Changing landforms in Alaska

permafrost is perennially frozen

Heat released by infrastructure can thaw permafrost and longer period of melting of active layer

If building is constructed onto ground surface some heat produced by be transferred to ground, melting permafrost

Can lead to subsidence and increase mobility of active layer allowing solifluction

thermokarst

landscape dominated by surface depression due to thawing of ground ice

Removal of vegetation leads to more thawing And deeper lakes

Grande Dixence Dam, Switzerland

285m tall and stores over 400 million m3 of water each year

Aggregates obtained from moraines in adjacent valleys

energy created by Grande Dixence dam

drives 4 power stations with enough capacity to power 400,000 Swiss households

Operates by storing glacial meltwater during summer and then using it generate electricity during high demand in winter

Grande Dixence dam impact on environment

minimised to ensure area remains attractive to walkers, cyclists and hikers

Pumping stations built underground or well concealed to retain aesthetics with increased tourism

Reduced flow in Borgne river has led to higher concentrations of pollutants from agriculture and domestic resources

impacts of Grande Dixence dam on glacial system

15% of energy used dealing with sedimentation problems

When water is stored behind dam, lack of flow means loss in energy and deposition of sediment load behind dams with less than 20mg/L 3km

To solve water is used to purge sediment, flushing it and moving downstream

Water levels high turbidity and high sediment concentrations

impacts of Grande Dixence dam on river channels

• increased channel erosion

  Dam traps sediment so no energy used on transportation

• Below dam rivers dry up in summer

  Lack of discharge

• Scale of concentration increases downstream

  Amount of sediment flowing into lake Geneva halved since dam

• Increased risk of floods and unexpected flooding when excess water has to be realised