Glaciers Lab Part 1. The basics A glacier is long living body of ice that moves

Question

Glaciers Lab

Part 1. The basics

A glacier is long living body of ice that moves under the influence of gravity and its own weight. It develops on land as compacted snow is transformed into ice. There are two main types of glaciers. Glaciers that are confined to valleys are called valley or alpine glaciers. Such glaciers are relatively common in the NW United States and in Alaska.

Those glaciers that are not restricted to a valley but cover large areas of continents are called continental glaciers. On a global basis, glaciers cover 1/10th of the Earth’s surface, and store over 75% of the world’s freshwater supply. If all of the global supply of land ice locked up in glaciers were to melt, then sea level would rise ~70 meters.

All glaciers consist of two parts. The upper part is perennially covered with snow, and is referred to as the zone of accumulation. In contrast, in the lower part calving, melting, and evaporation occur. The lower part is called the zone of wastage. The boundary between the zone of accumulation and the zone of wastage is the snow line, a line marking the highest point at which the glacier’s winter snow cover is lost during a melt season.

If, over a period of time, the amount of snow a glacier gains is greater than the amount of water and ice it loses, then the glacier will expand. If the amount of water and ice a glacier looses is greater than the amount of snow it gains, then the glacier will shrink.

Question #1: What do you think will happen to the snow line under these two different sets of conditions?

An expanding glacier is said to have a positive budget and, as a result, is said to be advancing. A shrinking glacier is said to have a negative budget and, and as a result, is said to be retreating. Throughout the 20th century most glaciers on a global basis have been retreating. Movement varies from a few millimeters a day to more than 15 meters a day.

Question #2: Why do you think the glaciers are retreating?

Basal sliding refers to the sliding motion of the whole glacier over underlying rock.

Such sliding is facilitated by a thin film of melt water. Plastic flow occurs in a zone of variable thickness lying immediately above the interface between the glacier and the underlying rock. Here flow takes place by slippage along internal planes of individual crystals. The rigid zone overlies the zone of plastic flow and extends upward to the surface of the glacier. Ice within the rigid zone is brittle; it rides passively on the underlying zone of plastic flow.

Question #3: Cracks in glaciers occur only in the rigid zone and commonly form crevasses. Why would you not expect to find such structures in the zone of plastic flow?

Explanation / Answer

Question #1: What do you think will happen to the snow line under these two different sets of conditions?

Glaciers can expand, shrink and retreat to balance the mass. It involves tow main process called accumulation of snow glacier in the zone of accumulation and ablation of ice occurs in the zone of ablation.

Zone of accumulation takes place in upper regions of Glaciers where additional snow exceeds the losses due to melting, evaporation and sublimation.

Below the zone of the accumulation lies zone of ablation where snow and ice losses takes place due to melting. Evaporation and sublimation which are greater than the additions.

The line of separation of these two zones is called snow line or firu limit.

In modern days. zone of ablation is more due global warming caused by pollutions of human activity. So glaciers are shrinking and ice is melting and adding into oceans which are causing sea level rising.

Most of the global glaciers retreating by losing ice from few millimetres to a day to more than 15m per day.

Question #2: Why do you think the glaciers are retreating?

Fossil fuel like coal, gas and oil increasing use emitting more and more CO2 gas into atmosphere. The more CO2 gas produces more heat due to solar radiation. It is increasing every year due industrialisation and transport. Heating of atmosphere causing global warming. This global warming melting snow more and more water is added to oceans than accumulation.

So glaciers retreat, melt and ablations occurs due to increasing temperature due to global warming. Due to melting of ice retreat of glaciers are occurring. Retreat means snow and ice melts in the glacier and flow down wards. In alpine glaciers 90% of retreat happening in glaciers due to global warming and increasing soot and dust effects coming form industry, transport and agricultural activity.

Basal sliding refers to the sliding motion of the whole glacier over underlying rock.

Such sliding is facilitated by a thin film of melt water. Plastic flow occurs in a zone of variable thickness lying immediately above the interface between the glacier and the underlying rock. Here flow takes place by slippage along internal planes of individual crystals. The rigid zoneoverlies the zone of plastic flow and extends upward to the surface of the glacier. Ice within the rigid zone is brittle; it rides passively on the underlying zone of plastic flow.

Question #3: Cracks in glaciers occur only in the rigid zone and commonly form crevasses. Why would you not expect to find such structures in the zone of plastic flow?

Lower layers of glaciers deform plastic like under pressure cause slow movements and glaciers as viscous fluid.

Glaciers are driven by continuous accumulation of new snow at the soruce, creates thicker ice and a surface slope. The upper layers of glaciers are more brittle and form deep cracks known as crevasses.

Crevasses created due to internal differences in glacier velocity between two quasi rigid parts above and the deeper plastic substrate below. As the parts move at different speed and directions, shear forces develops and causes break in two sections apart and creates the cracks and crevasse.

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