Icebergs and Glaciers in the Arctic
Ice sheets hold about 77% of the World’s freshwater, of this 90% is frozen in Antarctica and 10% in the Greenland Icecap, so 69.3% is stored in Antarctica and 7.7% in Greenland. The Greenland Icecap (or more correctly, ice sheet) is the second largest body of ice after Antarctica, covering a staggering 1,71 million sq km. Much of it is over 2km thick and it is 3kn at its thickest point. If the whole 2.85 million cubic kilometres of ice were to melt it would raise global sea levels by 7.2m or 23.6ft. This huge volume of ice has weighed down the land in the centre of Greenland and much of it is at sea level, this would start to raise up again if the ice was gone.
The Greenland Ice sheet is drained by a number of outlet or tidewater Glaciers along its coast, the most dramatic of these is the Sermeq Kujalleq or Jacobshavn Isbrae, which flows at speeds of 20-22 metres a day. The Greenland Ice sheet has experienced record melting in recent years. Rising temperatures cause the outlet glaciers to move faster on a base layer of meltwater and the surface of the ice sheet will also thaw in above zero temperatures. At the moment it is estimated that Greenland icecap is losing 195 cubic kilometers a year.
GlaciersGlaciers are rivers of ice moving over land, as they flow they erode and shape the land around them, The classic shape of a glacial valley is U shaped where the ice has plucked the sides of a V shaped alluvial valley away and carried the debris down to the sea. Sometimes a glacier will pick up a large rock and carry it several hundreds of km before dropping it. These rocks are called Glacial Erratics and will differ from the rock type in the area where it has come to rest. It is believed that in some instances these rocks fell onto the glacier in landslides and were carried along on top of the ice before being left stranded.
Many landforms are glacial in origin, Eskers are the sediments deposited by a river flowing under a glacier, parts of the Denali Highway are built along an esker. Moraines are the debris dropped at the sides and front end of a glacier and many are familiar landmarks, In the USA, Martha’s Vinyard, Cape Cod and Long Island are all moraines. Glaciers are responsible for the Fiords of Norway, not Slartibartfast who was credited with their award winning design in the Hitchhikers Guide to the Galaxy.
There are several types of glacier, a cirque glacier is formed in a bowl shaped depression on the side of a mountain. There are icestreams in the Arctic glaciers, these are rivers of ice flowing faster than the ice around them. A rock glacier is mostly rock with ice in the mix and flows very slowly, it sometimes originated from a cirque glacier, other rock glaciers are believed to have their origins in permafrost. A tidewater or outlet glacier flows from a large body of ice either an icecap or icefield, or an ice sheet, usually into the sea, where the ice breaks off and forms icebergs.
IcebergsCalving off the end of tidewater Glaciers, unless the glacier is huge, the icebergs produced in this are often small, the really big ones break off glaciers where the ice is floating. At the John Hopkins Glacier the wash made when the huge lumps of ice crash into the sea are so substantial that the boats visiting the glacier have to stay 2 miles away from the glacier front to not be swamped by the wash.
Only one tenth of the volume of an iceberg is above the water, and as a rule icebergs are usually 1 to 75 m visible above water, but the tallest ever recorded was 168m or 550 ft tall. In the waters off Newfoundland icebergs have been recorded travelling as fast as 17km or 10 mile a day, extraordinary when one considers the bulk below the waterline. You can read the history of an iceberg since it calved, in the sculpting of its surfaces. There are the clean shear lines where it was attached to the glacier and the softer rounder surfaces sculpted underwater, You can also read how it had shifted angles in the water by its tidelines.
Text © B & C Alexander