Glaciers transport and deposit materialAs I looked at in the previous post, glaciers erode rock, creating distinctive landforms. This eroded material is then transported and deposited by the glacier, forming different landforms. A glacier works like a conveyor belt, constantly transporting material downhill. The ice continues to move downhill, even when the zone of ablution at the bottom of the glacier is receding. The material can be frozen inside the glacier, carried on its surface or bulldozed, which means material is pushed in front of the glacier. Material can include rock, gravel, sand and clay, but even ancient human remains have been found transported in glaciers. Deposition occurs when the ice melts at the snout (or end) of the glacier, which is why this part of the glacier, the zone of ablution, often looks grey and dirty, or if the ice is overloaded with material. Glacial deposits are deposited when the ice melts, and unlike river deposits which are sorted by weight, glacial deposits can be rocks of all shapes and sizes, from fine clay to rocks the size of a house. Fluvo-glacial deposits are washed out of the ice by meltwater, and these are sorted by weight, with heavier materials deposited first. Landforms produced by transportation and depositionMoraines These are piles formed from material deposited by the glacier as it melts. There are four different types depending on their position.
Drumlins Elongated hills of glacial deposits. They can be 1km long and 500m wide, and often occur in groups. They are formed from the debris carried along and then accumulated under a glacier, which was deposited when the ice became overloaded with sediment. One end is round, blunt and steep and the other tapered, pointed and gently sloping, showing the direction the glacier moved in. There is still disagreement among glaciologists as to how exactly drumlins were formed. Erratics As I said, glacial deposits come in a mix all shapes and sizes. Extremely big deposits are called erratics. They are large rocks or boulders and are often found on their own. They are often unusual shapes and a rock type which is uncommon in the area they were deposited in. This video from the BBC gives more information about and examples of erratics: Erratics in Switzerland Till Till is a poorly sorted mix of mud, sand and gravel-sized material deposited directly by glacier ice. Outwash plain A flat spread of sediment deposited by meltwater streams from a glacier. Photo examples of these landforms are shown in the slideshow below. Sources:
Coordination Group Publications LTd. (CGP) (2010) GCSE Geography: The Revision Guide. CGP. Royal Geographical Society (no date) 'How glaciers shape the land and what they leave behind' Teaching resources: KS3 teaching resources. [Accessed on 24/08/15] Available from: http://www.rgs.org/OurWork/Schools/Teaching+resources/Key+Stage+3+resources/Glaciation+and+geological+timescales/How+glaciers+shape+the+land+and+what+they+leave+behind.htm BBC (2014) 'Landscapes of glacial deposition' Geography: Glaciation. [Accessed on 24/08/15] Available from: http://www.bbc.co.uk/bitesize/standard/geography/glaciation/glacial_deposition/revision/4/
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Although the main focus of the exam specifications is the current glaciated landscapes of the UK, the specifications do refer to the processes of erosion, transport and deposition that once took place in the UK. GCSE students should understand different types of erosion from previous geography topics such as rivers and coasts, but may not have studied them in the context of glaciers. How glaciers erode the landscapeAlthough glaciers move extremely slowly, they are incredibly powerful and have a huge effect on the landscape. One of the processes that it caused by the advance of a glacier is erosion. Note that 'weathering refers to the weakening and breakdown of rock in its position (without being moved); whereas erosion refers to the picking up and removal of the weathered rock, thereby wearing away the land' (Royal Geographical Society, no date) The weight of the ice in the glacier causes it to move downhill, and as it does it erodes the landscape in two main ways:
Then as the glacier moves, it rips out the pieces of rock.
of the glacier and wear it away, like sandpaper. The rock above glaciers is also weathered by freeze-thaw weathering. This is when water gets into cracks in rocks and freezes, causing the rock to expand and putting pressure on it. When it then thaws, the pressure is released. Repeated freezing and thawing widens cracks and causes parts of rock to fall off. At the top of the glacier, in the zone of accumulation, the ice doesn't move in a straighten line. Instead it turns in a circular motion called rotational slip. This erodes hollows and deepens them into bowl shapes. Landforms produced by glacial erosion
the valleys and forming a sharp edge between them.
eroding the mountain.
Formed by a hollow containing a small glacier which is eroded by rotational slip. It often contains a tarn - a small circular lake formed when the glacier melts.
eroded by a river are cut off as the glacier moves past, leaving truncated spurs.
tributary glaciers (similar to a river's tributaries) flow into the main glacier, but the glacial trough is eroded much more deeply by the larger glacier so when the glaciers melt the hanging valleys are left "hanging" at a higher level.
resistant rock was eroded more than the surrounding hard rock.
moutonnee can result. It often has a steep, jagged face as a result of plucking on the far side, and a gradual incline on the other side which is smoothed and polished by abrasion. Striations on the rock indicate the direction the glacier moved in. Examples of all these glaciated landforms in the UK can be seen in the slideshow below. Sources:
BBC (2014) 'Landscapes of glacial erosion' BBC Bitesize Geography: Glaciation. [Accessed 20/08/15] Available from: http://www.bbc.co.uk/bitesize/standard/geography/glaciation/glacial_erosion/revision/1/ Coordination Group Publications Ltd. (CGP) (2010) GCSE Geography: The Revision Guide. CGP Glaciers online (2015) Photoglossary: Alphabetic list. [Accessed on 20/08/15] Available from: http://www.swisseduc.ch/glaciers/glossary/ Royal Geographical Society (no date) 'Glaciation and geological timescales - How glaciers shape the land and what they leave behind.' Teaching resources: KS3 teaching resources. [Accessed on 20/08/15] Available from: http://www.rgs.org/OurWork/Schools/Teaching+resources/Key+Stage+3+resources/Glaciation+and+geological+timescales/How+glaciers+shape+the+land+and+what+they+leave+behind.htm |
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