Presentation on theme: "1 What happened in the Ice Age. 2 At present about 10% of the Earth's surface is ice covered, but about two million years ago the Planet's climate became."— Presentation transcript:
2 At present about 10% of the Earth's surface is ice covered, but about two million years ago the Planet's climate became much colder and as a result of this the polar ice caps extended into lower latitudes to cover over 30% of the Earth's surface at their maximum. This period of time is known as the Ice Age.
3 As snow layers built up year after year, the lowest layers were compacted into ice, making the base more slippery. This glacier gradually moves down slope under the force of gravity. Masses of ice which covered large areas of a continent were called ice sheets whilst those which occupy mountain valleys were called valley glaciers. In many parts of Northern Europe, which are now free from ice, striking features of both glacial erosion and deposition can be seen.
4 As we have seen; Scenery is changed by a combination of Erosion Weathering Transportation Deposition These processes were present in the Ice Ages. But because although the glaciers moved slowly, they were very large and made more changes that either rivers or oceans currently can.
5 Glacial processes Glacial Erosion: Abrasion - Glaciers carry a large amount of material with them. Sharp boulders embedded in the bottom of the glacier act as erosive agents for the glacier. These rocks mean that the glacier acts like sandpaper, scouring along the valley floor. The effects of abrasion are that the rock surface of the valley will be polished and may have deep grooves cut in them. These grooves are called striations.
6 Glacial processes Erosion: Plucking -This is the tearing away of blocks of rock which have become frozen onto the base and sides of a glacier. (tip! never grab a metal gate on a very cold frosty morning and pull your hands away quickly as the ice - skin bond may prove stronger than the skin - flesh bond and the skin may be plucked from your hand! OUCH !..... This is why scaffolders wear gloves in such conditions). Weathering: Freeze-Thaw - Water enters cracks in the rock during the day. Overnight the temperature drops and the water freezes. As it freezes, it expands. The expanded ice places pressure on the rocks around it. Over time this constant pressuring of the rock causes it to crack and split.
7 Glacial processes Glacial Transportation: Glaciers carry a huge amount of material. These rocks are called moraine and can be carried great distances by a glacier. The rocks are mainly carried once they have been plucked away from the valley surface by the glacier. Most of the material is carried near to the base of the glacier. But the glacier also carries frost shattered material from the valley sides that has fallen onto the its surface. This lateral moraine is carried at the sides of the glacier. When two valley glaciers meet and merge the two lateral moraines will form a medial moraine, running down the centre of the new, larger glacier. Glacial Deposition: Glaciers will always reach a point when they will start to melt, mainly due to the rise in temperature as they descend in height down the valley. As the ice melts it cannot carry as much material and so this is deposited. The main depositional feature of a glacier is its terminal moraine, but it will also leave behind lateral, medial and ground moraines.
9 Upland Glacial Landforms (formed by erosion) You should be able to recognise the following landforms on maps or diagrams, describe them, explain how they were formed.
10 Corrie Description - This is a steep sided hollow at the head of a glaciated valley. It is often described as an 'armchair' shaped hollow. We often find a small lake in it. Explanation - At the start of a period of glaciation we would find that some snow which fell on a mountainside, in small north - facing hollows, may not all melt during the following summer
11 Corrie Over a number of years as more and more layers of snow build up, then the lowest layers would be compacted and turn to ice Eventually, as this ice continues to build up, it starts to move down slope under the force of gravity and so a glacier is born. But a lip usually remains, so that eventually when the glacier melts, a hollow is left, it fills up with water. These have many local names – but tarn is the one most often used in England
12 Which numbers go with which? Scree slope Wearing away of rock by ice and rock fragments Lake deep in the floor of the corrie Steep rocky back to corrie Raised rocky lip to mouth of corrie 3 4 1 2 5
14 Arete description - This is a sharp ridge on the mountainside. explanation - An arete is formed where two corries 'eat' into a mountainside leaving a sharp ^ - shaped ridge.
15 Pyramidal Peak If you get 3 or more corries forming around the upper levels of a mountain then you may get a pyramidal peak forming See Mount Everest on the right
16 U- Shaped Valleys Description - This is a valley whose typical cross section is shaped like a 'u'. Explanation - A glacier is much bigger and more powerful than a river and so glaciers deepen and widen the v-shaped valleys formed by rivers in mountain areas. These glacial formed valleys have flat bottoms and steep sides and are called u-shaped valleys.
17 Notice how straight they are! These would have been winding river valleys before See how the wiggles have been worn away by the glacier – these are called truncated spurs
18 Hanging valley Explanation - Where a tributary glacier was much smaller than the main valley glacier, it would be much less able to erode the landscape and so its valley would not be as wide or deep. Description - This is a smaller u-shaped valley 'perched' on the mountainside above the main u-shaped valley
19 Erratic Description - This is a large boulder. These can range in size from the size of a washing machine upwards. Explanation - This boulder has been transported by ice from its source area and deposited when the ice melted or was no longer able to transport it.
20 A large Borrowdale Volcanic erratic on Whitbarrow about 14 miles
21 But what about the lowlands? Glaciers first accumulate on higher ground as it is colder there. But as the temperatures drop they grow down the hillsides and begin to flow onto the lowland areas Similar processes of flowing and eroding takes place but the features are different. At the edge or the snout of the glacier, which is where the melt water comes out, a lot of material comes out with the water.
22 This is because deposition of the load occurs whenever there is a decrease in pressure and/or velocity so at the snout there is a lot. On the edges of ice sheets, a large number of melt-water streams transport an immense amount of sand, silt, clay and rock particles from the melting ice. These streams merge, sometimes into a single tangle of waterways and the discharge of the channels varies both over 24 hours and also from season to season. Why? As a result, debris is constantly being picked up and deposited.
23 Drumlins These are smooth mounds of deposited material that are formed parallel to the direction of the movement of the glacier. They are quite large, usually between 30 and 40 metres high and up to 500 metres long. They look similar to eggs that have been stuck lengthways into the ground, and are described as being a "swarm of drumlins" as there are usually a number in one single area. They seem to occur when the glacier cannot carry its full load any more and the moraine drops out of the bottom – why they form this particular shape no-one is really sure!
24 And afterwards … The glacier has retreated back into the hills It has shrunk back up the U-shaped valley, with a stream or 2 taking the melt water away Some times its retreat is fast leaving all sorts of debris as it melts. Sometimes it stands still and leaves a high wall of terminal moraine Then once it has left the valley altogether, the river flows down When it meets a high wall of terminal moraine, a lake forms behind it, filling the whole valley bottom. These lakes are long and thin and called ribbon lakes
26 What am I talking about? Abrasion Striations Plucking Freeze-thaw Lateral moraine Terminal moraine Medial moraine Ground moraine Corrie Tarn Scree Arête Pyramidal peak U-shaped valley Truncated spur Hanging Valley Erratic Drumlins Ribbon lake
27 Homework Listen to Uncle Tonys bedtime tale on the wiki. Then think up your own bedtime story about another aspect of glaciation. Try to include as many glaciation words as you can Could be about a rock that was freeze-thawed off and travelled down as a lateral moraine – did it meet up with another lateral moraine to become part of a medial moraine? Where did it end up? Or a lump of rock plucked from its surroundings? Like the erratic? Or maybe its about a snowflake that joined a glacier? You may do it in WORD or PP or even as sound if you like.