glaciated landscapes- fluvioglacial and periglacial landforms (3a + b)

How does the influence of climate change during post-glacial period affect geomorphic processes

• Temperatures get warmer, more meltwater, more erosion occurs to valley sides- more water volume and increased lubrication

• Meltwater rivers have high discharge in summer, carry large cobbles and boulders

• Landforms produced during seasonal melting and retreat are often severely modified/ degreased during periods of subsequent readvance

Influence of geomorphic processes forming landforms (kames, eskers, outwash plains)

Kames: rounded mounds or fluvio-glacial deposits made of stratified gravels and sands laid down by meltwater

• Glaciers have crevasses, surface streams, en/subglacial tunnels filled with sediment, as glacier melts it leaves this sediment. Warmer temperatures, more melting occurs

• Forms isolated hills/ hummocks—> delta kames. Delta kames formed when meltwater deposits sediment into a proglacial lake

• kame terraces—> sediment deposited at sides of valley, pressure between valley sides and glacier forms ice-marginal channels. Water travels into valley and collects in the channel, carries sediment. Material deposited, glacier retreats and sediment left at valley side.

• Crevasses kame- sediments accumulate in crevasses, left behind when ice melts

• Erosion, abrasion forms kames, sediment eroded and carried englacially to then be deposited

• Supra glacial streams on the edge of glacier pick up and carry lateral moraine later deposited on valley floor when glacier retreats

• Mass movement provides glacier with debris which can be transported and deposited by meltwater to form kames

Eskers:

• long narrow steep sided ridge formed of stratified sand and gravel deposited by meltwater

• Large quantities of meltwater produced, flow at high hydrostatic pressure, carry lots of sediment

• This erosion and high velocity of water forms subglacial tunnels

• Glacier retreats, subglacial stream stops flowing, hydrostatic pressure lost

• Deposits material, doesn’t have the energy to carry it. Sediment dumped in a path of where the channel was in a long line

• Show path of former meltwater tunnels under/ within ice

• Material sorted, more rounded than glacial debris due to fluvial erosion and attrition

• Form in subglacial tunnels unlike kame terraces which form along sides of glacier

Outwash plains: flat expanse of sediment deposited in front of a glacier

• meltwater emerges from snout, loses energy—> no longer flowing under immense pressure

• Larger sediment deposited first

• As meltwater flows out of glacier, velocity decreases- deposition

• Well sorted, layered sediment because meltwater flow varies seasonally (with temperature)

Subglacial streams:

• meltwater flows beneath ice in tunnels

• Streams under high pressure, flow rapidly, carry lots of sediment, meltwater erodes bedrock—> hydraulic action, abrasion, attrition

• Ice melts away, channels exposed, depositional landforms created

Modification of glacio-fluvial landforms by processes associated with present and future climate changes

• landforms subject to weathering, erosion over time

• Kames and eskers colonised by vegetation, this can alter original shape or stabilise them

• As temperature rises there is a greater outwash material

• Rivers may rework outwash plains- redistribute sediment

• Human use—> sand + gravel extraction, reshape features

• Present and future climate changes can influence how meltwater behaves, new deposition/ erosion created, modifying landscape

How the influence of climate changes during a specific era in a periglacial landscape effect geomorphic processes

Influence of geomorphic processes in forming Periglacial landforms and how climate changes affect them.

Solifluction lobes:

• occurs in areas of permafrost

• In summer, top layer of soil melts, ice below acts as impermeable membrane, not allowing melted water in surface layer to train. Surface layer supersaturated with water as percolation into permafrost cannot happen

• No vegetation to hold it together so slumping occurs

• Greater slope angle, greater flow

Patterned ground:

• stones brought upwards to ground surface due to frost heave and frost pull.

• Stone remains uplifted when active layer thaws in summer—> finer sediments take place of ice

• Frost heave shapes ground into mounds, stones roll down to form circles providing basis for each of the other patterns

• Up-doming of ground due to frost heave- larger stones roll outwards, finer sediments central and raised in middle

• Elongated stone polygons on steeper slopes

• May be colonised by vegetation due to climate change

Pingos:

• form when there is discontinuous areas of permafrost

• Ice cored mounds of earth, stand alone in flat plains of periglacial landscape

• Range in size 30-600m diameter, 3-70m tall.

• Mound grows- central ice core expands over time, causes mound to stretch, break. Cracking of pingo summit exposes ice core—> thawing occurs as temps rise in summer. Pingos support from ice core reduced as ice melts—> collapses.

• As it collapses, structure formed similar to volcanic crater. Crater hollow may be filled with meltwater, sediments

• Collapsed pingo—> ognip

• Open system pingo- hydraulic pingo. Not fed by contained pressure within system, fed by hydraulic pressure as water is coming from outside of system. Water freezed in talik trapped between freezing active layer and the permafrost- ice lens.

• Closed system pingo- fed by contained pressure- water trapped inside.

• More likely to collapse as a result of climate change- warmer temps ice melts

Thermokarst landscape:

• areas of hummocks, irregular ground with waterlogged depressions created as ground ice thaws

• Irregular topography, irregular pits and depressions

• Thermokarst increases due to climate change

Modification of periglacial landforms associated with present and future climate changes