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.

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.

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".