The Influence of Geology in the Development of Glacial Landforms.

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Rock character (lithology)

Porosity / perviousness allows water to enter rock and assist plucking process

What landform?

Raised Beach at Low Tide - Little Gruinard, Scotland

Earth movement processes e.g. isostatic uplift in post glacial times

Weathering – freeze thaw creates scree. E.g. post glacial north Wales on Snowdon.

Most effective in uplands created by uplift. With well jointed rocks.

Mass Movements – affected by steepness of slope, porosity,Weathered / rock layering

e.g. Solifluction on gentle periglacial slopes (lobes), falls on steep slopes (scree)

Solifluction in weathered layer above permafrost layer

Tal-y-Llyn – a landslide dammed lake (below Cader Idris

Erosion more effective on steep slopes

e.g. mountain glaciers in the tropics (Pakistan Himalayas)

Differential erosion of hard and soft layers

Produces Paternoster Lakes, Washington State, USA (Mount Rainier)

Almost vertically tilted bedding planes allowed steep back wall to Llyn Cau, Cader Idris to develop

Resistant sill of igneous rock deflected the glacier from Llyn Cau round to the east

SILL

Fault controlled valley of Tal-y-Llyn

• effectiveness of erosion

• direction of erosion

Striations –material carried in the ice. Scratches caused by resistant hard material in the ice by the process of abrasion

Less resistant material gets ground down by abrasion into rock flour.

Lake Louise, Canada has a turquoise colour due to ground down rock flour sediment in the meltwater.

Transport and Deposition –

change of gradient perhaps from high land hard rock to lowland softer rock

Knock and Lochan landscape of eroded resistant roche moutonnnees (knocks) and eroded hollows (lochans)

Braided meltwater stream depositing outwash just beyond the ice front of a glacier

Fluvioglacial deposits – coarser gravels are deposited nearer the snout and finer material is transported further away before deposition.