Change and Stability - Glaciers

Glaciers are large masses of densely  packed ice that are constantly moving due to their surface slope, pressure and gravitational  forces. A glacier forms over many years when snow and ice builds up  faster than it is removed. The removal of snow and ice is called ablation and includes processes such as melting and evaporation.

A névé is the name for an area where  a glacier has formed. This is usually in bowl-shaped areas between mountains  where snow collects readily and compresses and compacts due to the weight of 
more snow falling on top. As individual snow flakes are crushed  by this immense weight pressure, air is squeezed from the snow turning it into  a very dense glacial ice. Glacial ice will continue to fill  the névé until eventually a geological weakening or gap between mountains means  the ice mass will start to move down a slope surface.

As glaciers move they erode the  terrain under them using two main processes. Plucking, whereby bedrock rock is  softened and levered out by subglacial water constantly re-freezing (expanding)  within it, the sediment then becomes part of the glacier's cargo. Abrasion  occurs when
the ice and now rock too slides over the bedrock essentially  smoothing and polishing it like sandpaper on wood.           

Researchers are able to determine  the direction of historical glaciers by examining bedrock scrapings such as glacial  striations (long carved scratches caused by large boulders moving with the  glacier) and chatter marks (crescent-shaped lines caused by boulders being constantly dragged and released).

Studies of glacial deposits also help show where historical glaciers were and how they moved. Linear mounds of  glacial sediment called moraines are formed and left by the deposition of material from a glacier. While drumlins are teardrop shaped groups of hills 
also containing left behind sediment deposits.  Usually mountain valleys are “V”  shaped. Glaciers deepen, smooth and widen the valleys into a "U"  shape. Within these glacial valleys, depressions and deposits left behind are filled  by water to create lakes and fjords.

Types of glaciers include: Alpine  glaciers (or mountain glaciers) located in mountain valleys. Ice caps (or ice  fields) are less than 50,000 km² (20,000 mi²) in size and sit on top of  mountains. While ice sheets (or continental glaciers) are usually found at the 
poles and are larger than 50,000km². Around 99% of glacial ice on Earth  is
contained within the polar ice sheets. Glaciers can be found in mountain 
ranges on every continent except Australia. Glacier ice stores approximately 75%  of
the Earth's entire freshwater supply. Around 10% of the Earth's land  surface
is covered by various types of glaciers.           

The word "glacier" comes  from the French language and the name is derived from the Latin word glacies  meaning "ice". The study of glaciers and their  related processes is called glaciology. The study of glaciers is very  important for scientists to keep track of unique variations in the Earth's  climate (such as global warming) as glaciers are very sensitive to climatic  changes.

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