EQ3- Glaciation Flashcards
Freeze thaw weathering
- Water enters cracks in the day with precipitation
- but freeze overnight when temps fall below 0 + expand 9% volume
- repetition causes breaking of rock
Glacial plucking (quarrying)
- Underneath glacier meltwater gets into cracks+ freezes
- ice attached + ‘locks’ itself to rock
- as ice moves forward pulls out rock
- loose rock is now found as bedrock
Glacial abrasion
Sand papering effect of ice as it grinds over + scours landscape
Formation of a Corrie(cirque)
- snow builds up in hollow high up on N face mountain sides (less sun)
- yr later small glacier forms
- ice moves under own weight circular way ROTATIONAL MOVEMENT
- small Corrie full ice flows into main valley glacier
- mountain top weathered by FREEZE-THAW persistent freezing+ melting breaks sediment off fall into ice
- erosion back wall caused PLUCKING water freezes+ pulls off rock - develops vertical jagged appearance
- rocks fallen into glacier ice scrape away floor by ABRASION- deep bowl shape formed
- less erosion front Corrie as ice thinner so lip/ rock bar forms also moraines formed here
- when ice melts small but v deep lake often forms hollow called tarn
Formation arête
- Plucking and abrasion on back wall 2 corries on mountainside mean they erode backwards towards each other creating a narrow ridge
- +freeze thaw important
Formation pyramidal peak
- Plucking (especially) + abrasion on 3+ corries erode backwards create
- sharp pointed mountain summit
Formation glacial trough
- v-shaped valley widened+ deepened by powerful plucking+ abrasion valley glacier goes thru landscape
- create u-shaped valley w/steep sides+ wide, flat floor
Formation Hanging valley
- Powerful thicker glacial ice in main glacial trough eroded vertically downwards more rapidly than thinner ice/ rivers tributary valley
- create small tributary (v/u) valley high above main glacial trough often w waterfall
Formation Truncated spur
- Valley glaciers less flexible than rivers + remove ends interlocking spurs by plucking+ abrasion as move down river valley
- steep rocky valley side (where spurs river used to interlock)
Formation Ribbon lake
- areas increased plucking+ abrasion by valley glacier deepen part of valley floor cos of confluence glaciers/ weaker rocks
- create long, narrow lake along floor glacial trough
Formation Roche mountonnée (ice sheet scouring)
- bare outcrop rock on valley floor sculpted moving ice
- stoss end increased pressure due resistance outcrop moving ice caused localised pressure melting as PMP reached
- leads basal slip w/ regelations, abrasion+ polishing creating striations+ chatter marks
- lee end reduced pressure caused meltwater freeze forming bond between rocky outcrop+ overlying ice
- leading plucking+ lots mechanical weathering(freeze thaw) creating jagged, craggy appearance
Formation crag+ tail (ice sheet scouring)
- where hard rock provides ‘pressure shadow’ on lee side resulting soft rock behind eroded less
- but before crag softer rock eroded+ sediment deposited shadow zone (lee side) forming tail deposited material (till)
- e.g. Edinburgh castle on igneous rock w/ softer limestone around it forming tail to L
Formation of knock +Lochan (ice sheet scouring)
- glacially scoured lowland areas when ice sheets+ glaciers (typically temperate) expand out beyond constrained mountain valleys
- eroding beneath (subglacial) landforms different rates depending rock types
- displaying alternating roche moutonnées: more resistant rock (KNOCK)+ areas eroded hollows (often containing small lakes) less resistant rock/ lots cracks, fractures+ joints (LOCHANS)
- e.g. NW highlands, Scotland
Formation medial moraine (ice contact, depositional)
- 2 valleys converge 2 lateral moraines combine to form
- material carried+ deposited when melting occurs parallel ice flow
- form ridge moraine down middle valley flood
Formation lateral moraine (ice contact, depositional)
- exposed rock on valley side weathered+ fragments fall down onto edge glacier
- then carried along valley+ deposited when ice melts parallel ice flow
- form ridge moraine along edge valley floor
Formation terminal/end moraine (ice contact, depositional)
- advancing ice carries moraine forward+ deposits at pt max advance when retreats
- up-valley (ice contact) side generally steeper than other side as advancing ice rose over debris
- transverse ice flow
- forms ridge moraine extending across valley at furthest pt glacier reached
Formation drumlins (ice contact, depositional)
-example equifinality unsure about formation
-surge theory: suggest surging glacier deposits excess till that carrying at base, as some consist (at least partly) glacial till
-Boulton-Menzies theory: suggests deposition in lee of slowly moving obstacle in deforming layer, obstacle of bedrock/thermally frozen material forms core drumlin+ ground moraine plastered around
-Shaw theory: suggests subglacial meltwater in flood caused irregularities form in river bed which moulded into drumlins+ streamlined by advancing ice
(rounded mounds parallel ice flow w/ broad upstream end (stoss)+ tapered downstream end (lee))
Formation Recessional moraine (ice contact, depositional)
- each represent still-stand during ice retreat (gd indicator cycle advance+ retreat)
- transverse ice flow
- series ridges running across valley behind terminal moraine
Formation till plains (lowland depositional landscape)
- sheet ice retreating deposits lrg amounts material over sizeable area
- form lrg, relatively flat plain/ undulating landscape till
- e.g. ground moraine
Formation lodgement till (lowland depositional landscape)
- actively moving ice deposits till lodged/ pressed into valley floor beneath glacier
- forming deposits angular rock fragments in fine matrix- unstratified, unsorted + containing erratics
- e.g. Drumlins
Formation of ablation till (lowland depositional landscape)
- stationary/ retreating glaciers deposit till by melting ice
- forming (same lodgement) deposits angular rock in fine matrix- unstratified, unsorted + containing erratics
- e.g. terminal+recessional moraines
Mass movement
- Downslope movement of material (rock+soil) under force of gravity
- term for wide range specific movements e.g. landslides, rotational movement+ block fall
Basal melting
- When melting point water decreases under pressure thus water melts at lower temps under thicker glaciers
- can lead to basal sliding where glacier ‘floats’ above layer meltwater (acts as lubricant) therefore the glacier can move faster
