Glaciation
Glaciation
is
the study of ice and its impact on the environment.
The Ice Age in Britain lasted from about one million years
ago to about 20 000 years ago. During that time the Northern
and Eastern parts of the British Isles were covered in ice.
Glaciers were formed which move down valleys with great
erosive power. These glaciers carved new scenery.
Glacial
Erosion
There
are three main types of glacial
erosion - plucking, abrasion and freeze thaw.
Plucking
is when melt water from a glacier freezes around lumps of
cracked and broken rock. When the ice moves downhill, rock
is plucked from the back wall. Abrasion is when rock frozen
to the base and the back of the glacier scrapes the bed
rock. Freeze-thaw is when melt water or rain gets into cracks
in the bed rock, usually the back wall. At night the water
freezes, expands and causes the crack to get larger. Eventually
the rock will break away.
Glacial
Landforms - Upland Features
Upland
glacial features include:
Corrie - This is an arm chair shaped hollow found in the side of
a mountain, e.g. Helvellyn,
Lake District
Arete
- This is a narrow, knife edge ridge separating two corries,
e.g. Striding Edge, Helvellyn.
Pyramidal
Peaks - These are formed when three or more corries form
in the side of one mountain, e.g. The
Matterhorn, Austria or Mount Snowdon,
Snowdonia National Park, Wales
Tarn - This is a lake found in a corrie, e.g. Red Tarn,
The Lake
District
Glacial
Landforms - Lowland Features
Lowland
glacial features include:
U-shaped Valley - This a valley which was V-shaped but has
been eroded by ice. The valley sides are steeper and the
valley floor flatter after the ice melts. Hence the name
U-shaped valleys.
Truncated Spurs - These are spurs which have been cut through
by ice, e.g. Nant Francon Valley, Snowdonia.
Hanging Valleys - These occur when glaciers at higher levels
than the main valley didn't experience such powerful erosion.
Tributary streams enter the valley as waterfalls from hanging
valleys.
Ribbon Lakes - These are lakes found in U-shaped valleys,
e.g. Lake Windermere, Lake District.
Drumlins
- These are hills shaped like eggs! (see diagram below)
Drumlins
are blunt at one end and tapered at the other. Drumlins
are found in swarms called 'basket of eggs'
topography. This is because they look like eggs in a basket!
They are formed when ice is moving forward, but is also
melting. The ice deposits boulder clay and till when it
comes across a small obstacle (e.g. small rock outcrop).
Most material is deposition the 'up stream' end of the drumlin.
The down stream end is shaped by the ice.
Case
Study - Helvellyn, Lake District
The
following links are to web sites containing case study information
about Helvellyn, an area containing glaciated landforms
in the Lake District, England.
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