glacial landscapes Flashcards
what is a global environment?
(UK) during the last ice age snow, ice covered most of the landscape. Temperatures barely rose above freezing even in the summer.
- Huge glaciers radiated from the north and west and carved depp glacial balleys and troughs. Further south and east the land was permanently frozen with some meltwater rivers.
Freeze-thaw weathering
In summer water flows into cracks in the rocks and freezes hard the following winter. The water expans by 9% when it freezes.
- It helps to shape jagged glacial mountain landscapes,
- Rocks become weakened by freeze-thaw making it easier for them to be eroded by glaciers,
- piles of large angular rock, called SCREE, collect at the foot of mountains- these become powerful erosion tools when trapped under moving glaciers
glacial erosion
Abrasion- ‘sandpaper’ effect caused by the weight of the ice scouring the valley floor. It leaves a smooth, polished surface. Scratches (called STRIATIONS) caused by large rocks beneath the ice can often be seen.
Plucking- when meltwater beneath a glacier freezes and bonds the base of glacier to the rocky surface below, like glue. As the glacier moves any loose fragments of rock are ‘plucked’ away- leaving a jagged rocky surface.
movement and transportation
basal slip- in the summer meltwater lubricates the glacier enabling it to slide downhill, this movement which can be quite sudden is basal slip.
rotational slip- in hollows high up on the valley sides, this movement may be more curved, in which it is called rotational slip.
transportation-
rock fragments resulting from freeze-thaw and eroded by the ice are transporated. this sediment is called MORRAINE- can be transported on the ice, in the ice (burried in snowfall) and below the ice.
As the glacier moves forward it pushes loose debris ahead of it effectively transporting it downhill. This is called BULLDOZING.
deposition – why glaciers deposit sediment (till and outwash).
- Deposition occurs when the ice melts. As most melting occurs at the front (the SNOUT) of the glacier, this is where most deposition takes place.
- As a glacier slowly retreats it leaves behind a bed of broken rock fragments called TILL. due to the lack of water to transport it, till is poorly sorted, with jagged rock fragments of all sizes. TILL is also known as BOULDER CLAY.
- Ahead of the glacier, meltwater ru=ivers will carry sediment away. The process of attrition will cause the rock fragments to become smaller and more rounded. Sediment is well sorted, with larger rocks deposited close to the ice and finer material carried many kilometres away. This sandy and gravel material is called OUTWASH.
corries
- also known as cirques and cwms
- large hollowed- out depressions found on the upper slopes of glaciated valleys. they are characterised by a steep back wall and a raised ‘lip’ at the front. They may contain a lake called a tarn.
Arêtes
- knife edge ridge often found at the back of a corrie separating two glaciated valleys
- often extremely narrow
- very popular with hill walkers
- although strong winds can make them very dangerous
- typically form when erosion in two back-to-back corrries causes the land in-between to become narrower.
pyramidal peaks
If 3 or more corries have formed on a mountain, erosion may lead to the formation of a single peak rather than a ridge. This feature is called a pyramidal peak
glacial troughs
- steep-sided, wide and flat-bottom valley
- formed by abrasion
- most start out at v-shaped river valleys
- when the landscape becomes glaciated, individual glaciers occupy the river valleys, eroding them through the process of abrasion to form spectacular U-shaped glacial troughs
truncated spurs
- unable to flow around existing interlocking spurs, the glacier cuts straight through them, forming steep-edged truncated spurs
hanging valleys
- smaller tributary valleys above the main glacial trough
- smaller glaciers in these valleys were unable to erode down to the same as the main glacier
- today they are often marked by spectacular waterfalls.
ribbon lakes
- long, narrow lakes often tens of metres deep
- often a result from severe erosion of the glacial trough
- this happens when the ice becomes thicker after a tributary glacier has joined, or where a weaker band of rock has eroded more easily
- sometimes a shallow ribbon lake may form in a glacial trough behind a dam of deposited morraine.
Types of Morraine
Ground morraine- the material dragged underneath the glacier and left behind when the ice melts, it often forms uneven hilly ground
Lateral morraine- the morraine forms at the edges of the glacier. It is mostly scree material that has fallen off the valley sides due to freeze-thaw weathering. When the ice melts, the morraine forms a low ridge on the valley side
Medial morraine- when a tirbutary glacier joins the main glacier two lateral morraines will merge to produce a single line of sediment that runs down the centre of the main glacier. On melting the medial morraine forms a ridge down the centre of the valley.
Terminal morraine- huge amounts og material pile up at the snout of a glacier to form a high ridge often tens of metres in ehight across the valley. This is terminal morrine it represents the furthest extent of the glacier’s advance, hence the name ‘terminal’
drumlins
- smooth egg-shapes hills about 10m high and several hundred metres long that are found in clusers on the floor of a glacial trough
- made of morraine that has been streamlined and shaped by the moving ice.
- They usually have a blunt end, which faces-up valley, and a more pointed end facing down-valley
- this indicates the direction of movement of a glacier
erratics
- large boulder that is out of place, resting on a different type of rock
- scientists have used erratics to trace the history of glaciation in areas like the UK
- by studying the geology of the area, it is possible to work out where the erratic rocks came from nd what route they followed as they were carried by glaciers
- most large erratics were probably transported on or in glaciers.
