DESCRIPTION OF GLACIAL EROSION

SMALL SCALE GLACIAL EROSION

· Striations – lines (metre or more short), on sloping, level vertical curved surface of fine grained rock surface. Mostly on gently inclined smooth surface where ice is forced to ascend.

· Grooves – Larger Striations (Mackenzie Valley Canada)
Means of understanding ice motion – Direction of Ice Movement
Nature and Behaviour of Basal Ice
Direction Studies of Ice Movement in Nasijarvi, Finland by Virkkala

· Friction Cracks – Medium grain rock
Gouges of crescentic shape
Semi vertical fractures with crescentic outer crops
Chattermarks

· Plastically Moulded surface – smoothing and scouring (Northern Norway)

Cavetto Forms – channels oriented to ice flow
Grooves – Open Flat surface
Sichelwannen – Axis with Ice flow
Curved and winding Channels – Fluvial Activity
Bowls and pot holes

Four Media –

1 .Basal ice containing rock debris
2. Water soaked ground moraine squeezed between bedrock and
overlying ice
3. Subglacial meltwater under pressure
4. Ice water compounds

· Potholes

Giant Kettles in Oslo Region
Brogger and Reusch

Glacier Moulin hypothesis
Streams pouring down crevasses creat potholes at the point
3 types of potholes – Plunge pool holes, broad open, have flaring walls

Gouge holes – shallow depression in stream beds
Eddy holes – deep, sharp edges

· Plucked surface

· Roches Moutonnees ( Stoss & Lee Topography)

Norwegian coast, Aland Islands of Baltic

GLACIATED VALLEYS

In Alps, Norway (Glacial Troughs)

Glacial erosion – thick well nourished temperate glaciers flowing rapidly down steep slopes towards free outlet à case of maximum erosion

Vatbajokul, Iceland
Jostedalsbreen, Norway

Modification of both transverse and longitudinal trough profile

Austerdalsbreen, Norway
Lauterbrunen, Switzerland
Lapporten Valley in Sweden – parabolic cross section

Erosion Mechanism suggested by M. Boye

· Ground Preparation (valley Floor) by permafrost.
· Slope water drain valley to increase moisture content
· Frost action

V-profile à U-shaped profile with Greater Gradient

Otztal, Austria
Turtagro, Norway
Aberglaslyn Pass, North Wales
Gorge du Guil, French Alps

Longitudinal profile – Irregular compared to river

Glacier Flow, J.F. Nye’s theory of “Extending and Compressing Flow”

Longitudinal Valley profile mapping

North Wales
Cuillin Hills, Skye

Ice scoured lakes in Alps
Lake Garda, Lake Maggiore, Lake Como

Glacial Diffluence and Transflucence: Watershed breaching by Ice

Outlet blocked by ice – level of ice in valley increases – glacier surface above col – all cols used up à Case of Transfluence

Rhine Valley in Sargans
Zell-am-See
Diffluence in Britain
Nant Froncon valley
Llanberis Valley
Guynant Valley
Nantle Valley
Cairngorns
Loch Avon Valley

Classification of Glacial Trough

Alpine Trough
Icelandic Trough
Composite Trough
Intrusive Trough

o Alpine Trough

o Accumulation Area should be surrounded
o Overlooked by higher ground
o Source – cirque
o Occupies preglacial valley

Hameswater and Ullswater

o Icelandic Trough

o Originates in mountain ice cap
o Flows through series of outlet glaciers

Jostedalsbreen ice cap
Austerdalsbreen
Grampian plateau

o Composite type

5 stages of evolution

1. simple diffluent trough – Strath Nethy
2. Multiple diffluent trough – Loch fine
3. Simple transfluent trough – Beattock Summit
4. Multiple Transfluent Trough – Glen Falloch
5. Radiative dispersal system – Southern Norway

o Intrusive or Inverse Trough

Ice pushes up the valley against the directionof preglacil drainage. Highlands of Scotland – Kilpatrick, Campsie, Ochil Group of Hills

CIRQUES

Cirque Morphology

Small & shallow of few tens of metres to kilometres – great cirques

4 Elements of cirque

o Head & side walls, steep and shattered
o Rock floor showing evidence of smoothing and polishing
o Near the junction of headwall & cirque floor, projecting node of rock
o Lip in the basin, convexly rounded and often shattered

Vesl-Skoutboln, Jotunheim, Norway

Cirque development stages

W.H. Hobbs

o Grooved upland – Bighorn Range of Wyoming
o Early Fretted Upland – Snowdon Massif, Northwales
o Mature Fretted Upland – Galdhopiggen, Jotunheim, Monch & Weissmeis in Swiss Alps
o Monumented Upland

Cols – breaking down of arêtes

Cirque orientation and morphology

Middle latitudes facing north and east in northern hemisphere
Elevation Related to firnline or snowline

Cirque erosion

o Abrasion
o Joint Block removal – by attachment to the bedrock surface, ice could only
remove materials already loosened by
frost riving or well jointed block – frost action helps
o Freeze-thaw – repeated freezing and thawing

Theodolite surveys, thermographs to measure temperature

GLACIAL EROSION IN AREAS OF LOW RELIEF

Knock and Lochan – northwest highland of Scotland
Faults, weak dykes, zones of weakness
Glacial fluting – small dimension, considerably elongated
Streamlined forms – rock drumlins, lower old red sandstone lavas of Lorne
Hummocky glaciated surface –

Karelia in Finland
Norland in Sweden
Quebecc, Great Lakes

Differential erosion – Lake Roxen in Sweden

Ice-sheet erosion reducing relief – South-East England

GLACIATION IN COASTAL ENVIRONMENT

1. Fjords – British Columbia, Southern Alaska, Southern Chile, Eastern Canada
(East Baffin Island), Greenland, Norway, Iceland, Spitsbergen, South-west of South Island, New Zealand

Erosional development of fjord

Maximum deepening of ice at centre and threshold at mouth, fjord erosion because of ice

2. Skjaergard and Strandflat

Zone of low rock islands – partially submerged platforms of erosion

3. Fjards – Coastal Inlets associated with glaciations of a lowland coast, lack steepwall characteristics of glacial trough, shallow basins

4. Fohrden – Coasts of Denmark
coast of Germany
Vejle Fjord, Flensburg Fjord, Limfjord