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During the last Ice Age, 2 million to 10,000 years ago, many areas across the world were permanently covered by ice. During that time all of Scotland and the north of England was covered by ice and the Southern and Eastern parts of the British Isles had a climate like the modern Tundra areas just north of the Arctic Circle. Here the Tundra climate is defined by short, chilly summers, long, bitterly cold winters and the ground is frozen, forming a mixture of soil and ice called permafrost.
Scafell Masif in the English Lake District
Since then, the climate has become warmer resulting in the melting of the majority of the glaciers but these ancient glaciers helped to form lots the countryside in the British Isles like the Lake District and Cairngorms.
There are two main types of glacier - continental glaciers (or ice sheets) and valley or alpine glaciers and they are found in very specific climate conditions.
East coast of Greenland
High latitudes - close to the North and South Pole. In areas such as Antarctica, the low temperatures are ideal for glacier growth. Earth currently has two ice sheets – one covering Greenland, the other covers Antarctica.
High altitudes - Mountains have to be high enough to ensure cool temperatures in the summer and high snowfall in the winter, so none of the accumulated snow is lost in the summer.
Grindelwald Glacier, Switzerland
Glaciers form in hollows on the colder, sheltered side of a mountain. These hollows are called corries. Snowflakes collect in the hollow and as more and more snow falls on top of the flakes; the overlying snow starts to compress the bottom flakes, increasing the density.
The snow that forms glaciers is subject to repeated freezing and thawing. This process changes the snow into a form of granular ice called névé.
After a year or so, under the pressure of the layers of ice and snow above it, this granular ice fuses into a more compact substance called firn. Eventually over a period of years, the layers of firn undergo further compression and become glacial ice. Glacial ice has a distinctive blue tint to it as it contains only minute air bubble due to the compaction process it undergoes.
Eventually, under the pressure of its own weight and the forces of gravity, the glacial ice will move over the lip of the corrie and begin to flow outwards and downwards. Glaciers do not need a slope to flow, as they are driven by the continuing accumulation of new snow at their source.
Valley glaciers flow down valleys, and continental glaciers (ice sheets) flow outward in all directions from a central point. This flowing movement causes the bottom layer of ice to behave plastically, allowing the glacier to move slowly as a whole – rather like toothpaste out of a tube. The upper layers of glaciers are more brittle, and often form deep cracks called crevasses as they flex. Crevasses make unprotected travel over glaciers extremely hazardous as every polar explorer will know!
When valley glaciers reach the sea or a lake, large pieces can break off, or calve, and form icebergs. Usually these pieces are irregular shaped and contain lots of rock material. Where ice sheets or continental glaciers meet the sea, huge chunks break off as icebergs.
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Glaciers & Glaciation