Ice on the land

Ice ages
1. An Ice Age is a period of time in which part of the surface of the Earth is covered in ice permanently.
2. The last ice age was called the Pleistocene age (not plasticene!) and it began approximately 2 million years ago. We are still (technically) in the Pleistocene age. The pleistocene age's peak was around 18,000 years B.P. (before present; actually means before the year 1950) and at this point, 30% of the Earth's surface was covered in ice permeanently. During this time, Earth's mean temperature fluctuated significantly between warm periods, known as "interglacial periods" and cold periods, known as "glacial periods". Fom both ice cores and deep sea sediment, we can tell that there have been around 20 cold periods. During the Pleistocene age, the UK was covered in 2-3km of solid ice.
3. A map showing valley glaciers and the limit of the Pleistocene glaciation (bit scruffy, I made it after all!)
The amount of ice on Earth depends on the glacial budget; the glacial budget is the net result of accumulation and ablation. Accumulation is basically the amount of precipitation and moraine are inputted into the glacial system, and ablation is how much is lost to global warming, friction and other factors.
Current global ice cover
1. Ice now covers only 10% of Earth on a permanent basis. This ice is found in 2 main areas, the first being areas of high latitude (above 66° south or north) and the second being areas of high altitude (high in the mountains).
2. An ice sheet is an area of ice with an area of 50,000 km² or over. There are just two large ice sheets left on Earth; the Greenland ice sheet and the Antarctica ice sheet. Both are declining in size.
3. Valley glaciers are found in the Alps (Europe), the Himalayas (Asia), the Andes (South America) and also in New Zealand; glaciers are found in all of Earth's continents and in 47 countries.
4. The Antarctica ice sheet covers 14 million km² and conatins 90% of Earth's fresh water. It is in places several kilometres thick.
5. The Greenland ice sheet covers an area of 1.7 million km² (80% of Greenland!)
6. A diagram to show the basic positions of the remaining large glaciated areas and ice sheets.
What is ice?
1. A diagram showing how snowflakes turn into granular snow, then to firn, and then finally, glacial ice.
2. Many people think of ice as frozen water, but in glaciation, that is incorrect. In glaciation, ice is supercompressed snow. The ice is formed by the following process:
  1. When snow falls to the ground, there are pockets of air between the crystals. Over time, as more snow falls every year, the crystals become compressed under the weight of the new snow and the crystals stick together to form a form of granulated snow which is stuck together; this is called firn. Once all air has been completely squeezed out of the firn and there are no more air spaces left, this is ice.
Features of glacial erosion
1. A diagram to show features of glacial erosion. A Pater noster lake is one of a series of glacial lakes connected by a single stream or a braided stream system.
2. Corries/Cwms/Cirques
  1. Snow accumulates in a nivation hollow. As more snow falls, gradually the snow becomes compressed and the air is squeezed out to become firn. Over thousands of years the firn becomes a glacier. Erosion and weathering by abrasion, plucking and freeze-thaw action gradually make the hollow bigger. Gravity can cause the ice trapped in the corrie to move. This circular motion is known as rotational slip and can cause the ice to pull away from the backwall creating a crevasse or bergschrund. Plucked debris from the backwall causes further erosion through abrasion which deepens the corrie. Some of this debris is deposited at the edge of the corrie, building up the lip. These processes create a characteristic rounded, armchair shaped hollow with a steep back wall. When ice in a corrie melts, a circular lake is often formed at the bottom of the hollow. This is known as a tarn.
3. Arêtes and Pyramidal Peaks
  1. An arête is a knife-edge ridge. It is formed when two neighbouring corries run back to back. As each glacier erodes either side of the ridge, the edge becomes steeper and the ridge becomes narrower. A pyramidal peak is formed where three or more corries and Arêtes meet. The glaciers have carved away at the top of a mountain, creating a sharply pointed summit.
4. Glacial troughs, hanging valleys and truncated spurs
  1. Glaciers cut distinctive U-shaped valleys or troughs with a flat floor and steep sides. The glacier widens, steepens, deepens and smoothes V-shaped river valleys. Glaciers also have tributaries. As the main glacier erodes deeper into the valley, the tributary is left higher up the steep sides of the glacier. These U-shaped valleys ending with a water fall at the cliff-face are called hanging valleys. When a river erodes the landscape, ridges of land form in its upper course which jut into the river. These are called interlocking spurs. A glacier cuts through these ridges leaving behind truncated spurs.
5. Roche Moutonnes
  1. Roche moutonnées often have steep, jagged faces created by plucking on the far (lee) side and a gradual incline which is smoothed and polished by abrasion on the other (stoss) end. It may have striations on it indicating the direction of glacier movement.
6. Crag and Tail
  1. Crag and tails tend to be larger than a roche moutonnée. Crag and tail is the opposite of the roche moutonnee as the ice hits the steep resistant rock outcrop first. This protects the lee (far) side of the obstacle from erosion. Edinburgh castle is built on crag and tail.
Valley glaciers
1. This diagram shows an average valley glacier
2. A glacier is a system of inputs and outputs, as well as stores and flows. The inputs mainly occur in the zone of accumulaton in the form of snow from precipitation and avalanches, as well as moraine (sediment) from freeze-thaw weathering The outputs mainly occur ikn the zone of ablation, in the form of meltwater, evaporation and moraine deposits.
  1. As with any system, the relationship between the inputs and outputs alters the behaviour of the glacier. We call the study of these things the glacial budget. The budget or balance of the glacier is usually a net gain or a net loss over a 2-month period.
    1. If:
      1. Accumulation > ablation, snout of the glacier will advance (net gain)
      2. Accumulation = ablation, the snout of the glacier will remain in a state of equilibrium
      3. Accumulation < ablation, the snout of the glacier will retreat (net loss)
Glacial processes
1. Abrasion
  1. Abrasion - rocks stuck in the ice grind away the bedrock under the glacier
2. Plucking
  1. Plucking - the base of glacier ice melts due to pressure and friction. This allows water to freeze into cracks in rocks, and when the glacier moves it pulls out chunks to leave a jagged surface. This provides material for abrasion
3. Freeze-thaw weathering
  1. Freeze Thaw - water in cracks in the rock freezes and expands forcing open the gap. When the ice melts more water can get into the crack and freeze again. After many cycles of freezing and thawing lumps of rock are broken off the surface.
Moraines

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Ice on the land

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	Erstellt von Henry Kitchen vor etwa 11 Jahre