SIHC - Glaciation

Glaciation Erosion by bodies of moving ice.

Erosion processes are very active in the SIHC because of climate. The cold temperatures, due to high altitude, have meant that glaciation is an important land modifying process.

Formation of Glaciers Over time snow turns to glacial ice high in the mountains. It is formed in three major steps. Glaciers move due to the structure of the crystals, melt water and the pull of gravity. There are two major zones within the glacial system: accumulation and ablation. Moraine often covers the lower extent of glaciers.

Hooker Glacier

Glacial ice is formed in three major steps. Feathery snowflakes - Snow falls high in the mountains and collects in neve as white powder. As more snow is added the structure of the snow alters. Firn or "old snow" - The pressure applied from the weight of snow above bears down on the snow below compacting and pressing the air out. Larger ice crystals form. These crystals are called firn or "old snow". Glacial ice - Over time as the depth of snow increases and the firn is buried more deeply. Now more air is forced out until the ice crystals are completely compacted forming clear blue glacial ice.

Neve

How do glaciers move? When the ice becomes thick enough to flow, about 50m, the glacier will begin to move away from its source. At this depth the ice creates enough pressure to allow the lowest ice to undergo plastic deformation, ie: it begins to flow like a soft or liquid plastic. Glaciers also have a thin film of water underneath and at the side, which helps the movement down the valley by the pull of gravity. The glacier will advance along the valley, remain stationary or retreat depending on the balance between the amount of new ice collected in the source area and the rate of ablation in the rest of the glacier.

The velocity of ice flow in all glaciers varies considerably from a few metres over a period of years to several metres per day. The rate depends on such factors as the thickness of the ice, the slope of the surface over which the glacier is advancing, and the amount of meltwater that is available to lubricate the base of the glacier.

A glacial formation

Within the glacial system there are two major zones Accumulation zone This is near the top of the glacier where snow and ice are added. This zone comprises mostly snowflakes, firn and glacial ice. Ablation zone Found towards the terminal end of the glacier where ice melts away. Old glacial ice is exposed with many crevasses. This zone comprises mostly glacial ice, water and accumulations of moraine. Between these zones is the equilibrium line. This is the balance point between the accumulation and ablation zones. No ice mass is lost or gained at this point.

Erosion by Glaciers The ice in glaciers causes a lot of erosion in alpine regions of the world. As glacial ice forms it presses on the sides of the valley. It makes a bowl shaped basin at the top of the mountain called a cirque. Water around the glacier and gravity help it slide down the valley.

Abrasion by a glacier Glaciers scrape the walls and floor of the valleys as they slide down. This is called glacial abrasion. The glacier has many rocks and boulders in the ice. The glacier acts like a huge belt sander eroding tonnes and tonnes of rock as it slides down the mountains.

Abrasion The millions of tonnes of rock come from the valley floor and walls. Other rocks fall on to the top of the glacier as it goes by. Some of these rocks fall into the glacier through crevasses. Glaciers carry tiny bits of rock as well as huge boulders. The tiny rock particles are called rock flour. All the rock around and on a glacier is called moraine. A glacier is like a bulldozer and pushes the moraine along in front of it. Other rocks are left at the side and the streams under the glacier carry some away.

Hooker Glacier

Moraine All the rocks in, on and around a glacier are called moraine. These rocks move along with the glacier. Moraine has different names when it is on different parts of a glacier. Lateral moraine is at the sides of a glacier Medial moraine is on top of the glacier Terminal moraine is at the end of the glacier Piles of moraine are left when a glacier melts. These moraine walls show how far a glacier has been down a valley.

Tasman Glacier

The Glacial System at Franz Josef and Fox  Inputs:  Processes: name types of  Outputs: describe the Climate_________________ Orogeny________________ Altitude_________________ Relief_________________ Gravity ________________ Erosion________________, _________, ____________ Transportation__________, _________, _____________ Deposition______________, ___________, ___________ Natural features ______________