lithosphere - glaciation

plucking

when ice freezes on to bedrock pulling loose rocks away from the backwall

abrasion

when the angular rock embedded in the ice grinds the hollow

frost shattering

when water in cracks in the rock freezes, expands and contracts weakening the rock until fragments break off

corrie

• snow accumulates in north facing hollows

• north/ north east facing slopes are more shaded so snow lies longer

• glacier moves downhill due to gravity

• bergschrund crevasse opens up at back of hollow this allows meltwater and rock fragments to get to the base of the glacier increasing erosive power

• friction causes the ice to slow down at the front edge of the corrie allowing a rock lip to form which traps rain water

arete

• snow accumulates in north facing hollows

• north/ north east facing slopes are more shaded so snow lies longer

• glacier moves downhill due to gravity

• rotational slidingg over deepens the hollow

• an arete is formed when 2 corries erode back toward each other

• frost shattering can make the ridge more pronounced and can cause scree slopes to develop

pyramidal peak

• snow accumulates in north facing hollows

• north/ north east facing slopes are more shaded so snow lies longer

• glacier moves downhill due to gravity

• pyramidal peaks have a sharp summit and steep slopes on at least 3 sides

• pyramidal peaks form when 3 or more corries erode back to produce aretes with a pyramidal peak in between

u shaped valley

• north/north east facing slopes are more shaded so snow lies longer with accumulate snow compressing into ice

• gravity causes glacier to move downhill following existing v shaped valleys

• former interlocking spurs may be cut off by the glacier as it flows downhill leaving truncated spurs and steep valley sides

• valley becomes wider deeper and straighter

hanging valley

• north/ north east facing slopes are more shaded so snow lies longer with accumulated snow compressing into ice

• gravity causes glacier to flow downhill following existing v shaped valleys

• former interlocking spurs may be cut off as the glacier flows downhill leaving truncated spurs and steep valley sides

• the valley becomes wider deeper and straighter

• a thick glacier flows through the main valley while a smaller glacier flows through a tributary valley

• thick glacier has more weight to erode vertically than the smaller glacier

• after ablation the tributary valley is left hanging above the main valley

ribbon lake

• north/ noorth east facing slopes are more shaded so snow lies longer with accumulated snow compressing into ice

• gravity causes the glacier to flow downhill following existing v shaped valleys

• former interlocking spurs may be cut off by the glacier is it moves downhill leaving truncated spurs and steep valley sides

• valley becomes wider deeper and straighter

• as a glacier moves over softer rock the downcutting increases and a hollow is carved out valley floor, this later fills with water to create a ribbon lake

drumlin

• drumlins are made up of unsorted materials and consists of glacier till

• drumlins are formed as the glacier becomes overloaded with sediment and deposits i, streamlining the sediment as it flows over it

• if there is a small obstacle on the ground this may act as a trigger point and glacial till can build up around it

• drumlins may be reshaped by further ice movements after being originally deposited

• or when temperature rises the glacier melts

• the steep ‘stoss’ slope faces up valley and the more gently sloping ‘lee’ slope faces down valley

• drumlins are found in a basket of eggs topography

esker

• eskers are meandering ridges along a valley floor, formed by meltwater streams in or underneath the glacier

• they are made up of meltwater sands and gravels. these are sorted by size as heavier stones are dropped first by flowing water

• the stones also tend to be more rounded than glacial deposits because of the action of flowing water rounding the edges by erosion

• when temperature rises, glacier begins tto melt and sub glacial streams deposit into tunnels

terminal moraine

• terminal moraine is a ridge across the valley and made up of glacial deposits which is unsorted

• as the glacier moves downhill it acts like a bulldozer pushing sediment in front of its snout as it goes

• when temperatures rise the glacier melts losing power and depositing the moraine

• terminal moraine marks the furthest point that the glacier reaches

• once the ice has retreated the terminal moraine can often form a natural dam creating a ribbon lake