A glacier is a large, slow moving river of ice, formed from compacted layers of snow, that slowly deforms and flows in response to gravity. Glacier ice is the largest reservoir of fresh water on Earth, and second only to oceans as the largest reservoir of total water. Glaciers cover vast areas of polar regions but are restricted to the highest mountains in the tropics.
The following topics below explain more about Glaciers and the environments they occupy.
About every 200 million years the Earth experiences a major period of ice activity – a glaciation.
The most recent of these started about 2 million years ago and finished (*) about 10,000 years ago.
A glaciation consists of glacials (cold periods ) separated by interglacials (warmer periods).
* Some people believe we are still in an interglacial!
About 30% of the world was covered by glacial ice when the glaciation was at its maximum.
The UK was covered by ice between 1-3kms thick as far south as a line from London to Bristol.
Causes of Glaciation
There are many theories as to the cause of glaciations:
Milankovitch cycle – changes in incoming radiation due to changes in orbit, tilt and position in space.
Variations in sunspot activity
Changes in the amount of carbon dioxide in the atmosphere
Changes in the movement of the ocean currents
Periods of extreme volcanic activity which put huge amounts of ash into the atmosphere
Formation of Glaciers
During the onset of a glaciation, more and more precipitation falls as snow.
In addition, less and less snow melts each summer so that successive layers of snow gradually build up until there is a year-round snow cover in more and more places.
Fresh snowflakes trap much air and have a low density.
As snow becomes more compacted, the air is driven out and density increases.
Eventually, this process forms neve or firn (compacted snow).
After 20-40 years the firn will turn into glacial ice which contains little air and has a density of about 0.9.
Glacial ice can begin to flow downhill under the influence of gravity as a glacier.
Types of Glacier
Glaciers can be classified according to their size and shape.
The main types are: Corrie glacier (also called a cirque glaciers or a cwm) – these occupy small hollows mainly on the sheltered north-facing slopes of mountains
Valley glacier – these are linear masses of ice which move along pre-existing river valleys in the mountains
Piedmont glacier – these form when valley glaciers spread out on to low-lying areas and merge to form a single ice mass.
The Malaspina Glacier, Alaska is a classic example of a piedmont glacier lying along the foot of a mountain range.
The main source of ice for the glacier is provided by the Seward Ice Field to the north which flows through three narrow outlets onto the coastal plain.
Ice caps or ice sheets are these are extremely large ice masses…