Location of ice sheets

Icebergs

Icebergs are large pieces of land ice that have broken off from ice shelves or glaciers. This is caused by warm temperatures. The process of them breaking off of the larger ice mass is called calving.Between 10,000 to 15,000 icebergs are calved each year.

They float in the sea, as ice is less dense than water, and the wind and the current causes them to move.

Although all icebergs form the same way, those that originate in Artci and Antarctic regions differ. Ice bergs with steep, narro pinnacles, sometimes know as castle icebergs, only form in Arctic regions, while large, flat (tabula) icebergs are only calved in Antarctica. These differences are caused by the ice itself and the land underneath. Pinnacle icebergs are steep because they are calved from mountain glaciers, whil tabular icebergs form from much flatter ice sheets.

Only around one tenth of an iceberg is visible above water.

They generally range in size from 1 to 75 metres (3 to 250 feet) and they can weigh up to around 200,000 tonnes.

Pictures of hanging glaciers

http://www.ece.cmu.edu/~koopman/dsn08/excursion.html

http://www.swisseduc.ch/glaciers/earth_icy_planet/glaciers02-en.html?id=10

 http://blog.travelpod.com/travel-photo/profbrainstorm/2/1222901160/summit-of-ama-dablam.jpg/tpod.html

http://www.swisseduc.ch/glaciers/glossary/hanging-glacier-cook-en.html

Glaciers: Forms

Ice Sheets
Found only in Greenland and Antarctica, ice sheets are enormous masses of glacial ice expanding over 50,000 kilometres squared. The ice sheet over Antarctica is over 4.2 kilometres thick in some areas. It covers almost all of the land features except for the Transantarctic Mountains.

Ice Shelves

Ice shelves occur when ice sheets extend over the sea and float on the water. They vary in thickness from a few hundred metres to over a kilometre. They surround most of Antarctica.

Ice Caps

Ice caps are smaller ice sheets, that cover less than 50,000 kilometres squared.They mostly form in polar and sub-polar regions that are relatively flat and high in elevation.

Outlet Glaciers/Ice Streams

Channelised glaciers that flow more rapidly than the surrounding body of ice.

Ice Fields

Ice fields are similar to ice caps, except that they are usually smaller than ice caps and their flow is influenced by the underlying surface area.

Mountain Glaciers

These are glaciers that develop in high mountainous regions, often flowing out of icefields that span several peaks or even mountain ranges.

Valley Glaciers

Often originating from ice fields and mountain glaciers, these glaciers flow down valleys. They can be very long, sometimes even reaching sea level.

Piedmont Glaciers

These are formed when valley glaciers spill out onto relatively flat plains and spread out to cover a large area.

Cirque Glaciers

Glaciers that reside in cirques, large bowl-like hollows, usually found high up in mountains.

Hanging Glaciers

Similar to valley glaciers, they cling to steep mountainsides and are wider than they are long. They are rather common in the Alps.

Tidewater Glaciers

Glaciers that reach the sea. They create small icebergs that can be problematic for ships.

Glaciers: Formation and Movement

Glaciers are formed when snow remains in the same place throughout the year, and enough builds up to turn it into ice. New layers of snow bury and compress the previous layers.  This compression causes the snow to re-crystallise, forming grains similar in size to sugar. These grains gradually grow larger and the air-pockets among the grains get smaller, causing the snow to compact and increase in density. Crystals can reach several inches in length in older glaciers.

The fact that glaciers deform, added to their sheer weight and the force of gravity, causes glaciers to flow downhill.

Glaciers periodically retreat or advance, depending on the amount of snow they gain or lose. This movement takes a very long time, with more rapid movementh only being noticible over several months or years.

Ice Storm