Glacial+Landforms

Ice is an incredibly powerful agent of erosion and it can form spectacular landforms in mountaious areas. You need to be able to draw simple diagrams with three labels and a description.

Excellent BBC videos looking at the formation of glacial landforms. Highland landforms - before and after glaciation - [] Landforms of upland glaciation in Loch Lomond - [] Loch Lomond glacial landforms - [] Lochaber - a glaciated landscape - [] Lochaber - a high level glaciated landscape - []


 * __Corries:__**

Corries They have deep, rounded hollows with a steep back wall and a rock basin Snow accumulates in hollows on hillsides, especially in hollows on hillsides with a less sunny north and east facing aspect Snow turns into ice and then the ice moved downhill Freeze-thaw and plucking loosened and removed material from the back of the hollow creating a steep back wall Moraine dragged along the base of the glacier, deepened the floor of the hollow by abrasion and formed a __rock basin__ A __rock lip__ was left where the rate of erosion decreased The lip was often heightened by the deposition of moraine When the ice melted the rock lip and moraine acted as a natural dam to meltwater Many rock basins are occupied by a deep, round __corrie lake__ or __tarn__

[] __-__ a useful animation to show how a corrie is formed


 * __ Aretes and Pyramidal peaks __**

[] - a very good flash file showing how Aretes are formed!!

An **arete** is a knife-edged ridge often found at the back of a corrie or separating two glaciated valleys. **Aretes** are often extremely narrow features. A typical **arete** forms when erosion in two back-to-back corries causes the land in between to become even narrower. If three or more corries have formed on a mountain, erosion may lead to the formation of a single peak rather than a ridge. This is called a **pyramidal peak.**

 The above diagram shows the formation of pyramidal peaks and aretes in a glaciated landscape.

Glacial valley landforms:

Glaciers tend to form in river valleys. Ice is a solid and thus unable to flow round obstacles and generally calve straight paths down the valley. The incredible erosive power of the glacier leads the creation of dramatic features including:
 * glacial troughs
 * truncated spurs
 * hanging valleys
 * ribbon lakes


 * __Glacial troughs:__**

Glaciers form in river valleys. These are generally v-shaped. As the glacier moves down the valley it creates a valley which is more u-shaped. This leaves a valley which is steep-sided, wide and relatively flat-bottomed. Abrasion is the key agent of erosion in this process. The moving glacier grinds into the base and sides of the valley over a period of many hundreds of years. The glacier is unable to flow past the preivous interlocking spurs and simple cuts through them, forming **steep-edged truncated spurs.**

On the side of the main valley are smaller valleys which feed into the main valley. The main valley is eroded more quickly and deeper than the tributary valleys. This leaves the tributary valleys at a much higher level than that of the main valley. The tributary valleys are then called **hanging valleys** and often end in spectacular waterfalls which flow into the main valley.

Erosion of the valley floor is erratic. Cetain parts of the valley are more likely to eroded more deeply. This could be as a result of thicker ice or areas of softer rock. At the end of the glacial period water may occupy this deepened section to form a long narrow **ribbon lake** often several tens of metres deep. Loch Ness is a classic example of a ribbon lake.

Ribbon Lakes

A **ribbon lake** is a long and narrow, finger-shaped lake, usually found in a glacial trough. Its formation begins when a glacier moves over an area containing alternate bands of hard and soft bedrock. The sharp-edged boulders that are picked up by the glacier and carried at the bottom of the glacier erode the softer rock more quickly by abrasion, thus creating a hollow called a rock basin. On either side of the rock basin, the more resistant rock is eroded less and these outcrops of harder rock are known as rock bars, which act as dams between which rainwater may accumulate after the retreat of the ice age, filling up the rock basin and creating a ribbon lake.


 * __Landforms of glacial transportation and deposition:__**
 * Moraines:**


 * Moraine** is the term given to the angualr material transported and then deposited by the ice. Morraine can also be called **till** or **boulder clay** due to the range of sizes of sediment present.


 * Ground moraine** - this is the material which was dragged underneath the glacier and is simply left behind whne the ice melts. It often forms hummocky or uneven ground.
 * Lateral moraine** - this forms at the edges of the glacier. It is mopstly scree (brokern pieces of rock from freeze-thaw weathering) that has fallen off of the valley sides. When the ice melts it leaves a slight ridge on the side of the valley.
 * Medial moraine** - When a tributary glacier joins the main glacier, two lateral morianes merge to produce a single line of sediment that runs down the centre of the main glacier. On melting, the medial moraine forms a ridge down the centre of the valley.
 * Terminal moraine** - huge amounts of material pile up at the snout of a glacier to form a high ridge, often tens of metres high across the valley. The termianl moraine represents the furthest extent of the glacier's advance.




 * __Drumlins:__**

Drumlins are smooth egg-shaped hills which may be 10m in height and several hundred metres long. They are usually found in 'clusters' or 'fields' on the florr of glacial troughs. They are made of morranic material which has been shaped and moulded rather than dumped. Drumlins usually have a blunt end, which faces up-valley, and a more pointed end, which faces down-valley. This makes them useful indicators of the direction of glacial movement.




 * Key terms:**


 * Corrie**: a deep depression on a hillside with a steep back wall, often containing a lake
 * Arete**: a knife-edged ridge, often formed between two corries
 * Pyramidal peaks**: a sharp-edged mountain peak
 * Glaical trough**: a wide, steep-sided valley eroded by a glacier
 * Truncated spur**: an eroded interlocking spur characterised by having a very steep cliff
 * Hanging valley**: a tributary glacial trough perched up on the side of a main valley, often marked by a waterfall
 * Ribbon lake**: a long narrow lake in the bottom of a glacial trough
 * Lateral moraine**: a ridge of frost-shattered sediment running along the edge of a glacier where it meets the valley side
 * Medial moraine**: a ridge of sediment running down the centre of a glacier formed when two lateral moraines merge
 * Terminal moraine**: a high ridge running across the valley representing the maximum advance of a glacier
 * Drumlin**: an egg-shaped hill found on the floor of a glacial trough