GLACIERS

A glacier is a thick mass of ice, composed of compacted and recrystallized snow that forms over thousands of years.

Glacier only flow or move over land

The movement is caused by the weight or by gravity

Icebergs and sea ice are not glaciers.

Glaciers cover nearly 15 million square km or about 10% of the Earth’s surface

They account for 75% of all freshwater.

Glaciers can be seen today on all continents except Australia

Glaciers form at high altitude or high latitude where snowfall in winter does not entirely melt in summer.

There are tow types of glaciers; Valley glaciers and Continental glaciers

VALLEY GLACIERS

Valley glaciers, also called alpine glaciers are confined to mountain valleys at high altitudes with temperatures low enough to accumulate snow.

Valley glaciers vary in length, width, and depth They move in response to gravity; they flow down hill. They have smaller tributary glaciers, like a river has

tributaries.

CONTINENTAL GLACIERS

These glaciers are not confined by topography and cover large landmasses. Also called ice sheets.

There are only two continental glaciers on Earth today;

Antarctic ice sheet and

Greenland ice sheet

These glaciers flow outward from the center where ice thickness is greatest.

The thickest part of a glacier can be up to 3km in the center and thins towards the margins of the glacier

FORMATION Glacier can form if an

area receives more snowfall in winter than melts in summer, resulting in a net accumulation of snow.

Snow turns into glacial ice through a process of compaction Firn are snow granules

fused together.

MOVEMENT

The movement of a glacier is termed flow.

When the ice reaches a critical thickness, about 50m, the pressure is enough to allow for plastic flow, having the ice move like toothpaste.

Above 50m depth the glacier does not move plastically.

The top portion is forces to move, such that it is brittle, that the ice fractures. This is known as the fracture or brittle zone.

Crevasses are formed due to this action.

Travel on a Glacier

The other mechanism of flow is termed basal slip.

This takes place at the bottom of the glacier, where the ice slides over a thin layer of water.

GROWTH & DECAY

Expansion and decrease in size of a glacier is in response to accumulation of snow and ice and melting, wastage.

It is described in terms of a glacial budget. The upper part of the glacier is the accumulation zone

The lower section is the wastage zone

Glacial ice is lost through melting, sublimation, and/or calving.

The line that separates the zone of accumulation from the zone of wastage is termed the snowline or equilibrium line.

When the equilibrium line moves down a glacier, terminus or toe is said to advance. A positive budget.

When the equilibrium line moves up the glacier it is said to be retreating or a negative budget.