Glaciers Flashcards
What is a glacier
A river of ice which advances and retreats over the land e.g. Mer de Glace
What is the zone of accumulation?
The area of an ice sheet/cap or glacier where snow fall exceeds the rate of ablation
What is ablation
The process by which snow or ice melts.
What is firn or neve?
A layer of granular, crystalline snow which has been compressed under the weight of continued falling snow
How does a glacier form
Snow falls on a zone of accumulation
The weight of the continued snow fall builds a layer of firn which is a layer of granular, crystalline snow
As the weight of snow continues to rise this layer of firn is compressed into glacial ice
The ice eventually starts to move downhill owing to gravity, it is then known as a glacier
What are the two different types of glacier that covers the earth
An ice sheet covers more than 50,000km and represents approximately 90% of all of the ice on earth e.g. Greenland Ice Sheet
An ice cap covers less than 50,000km e.g. Vatnajokull ice cap in Iceland
A glacier is a river of ice which advances or retreats over the land e.g. Mer de Glace
How do glaciers move
Glaciers move as a result of gravity
However they advance and retreat dependent upon the glacial budget which is the difference between rate of accumulation (snow deposit) and the rate of ablation (snow melting)
If the rate of accumulation is higher than the rate ablation the glacier builds and advances.
If the rate of ablation is higher than the rate of accumulation the glacier retreats.
how does a glacier shape the landscape
A glacier shapes the landscape by plucking out rocks from the landscape as the glacier flows over them leaving a jagged landscape (plucking)
Stones which are trapped in the base of the glacier then grind and gauge the landscape, (Abrasion) often leaving grooves in the rock it travels over called striations
Glaciers also simply bulldoze the landscape as they move forwards clearing everything in its path
Freeze thaw weathering contributes to glacial erosion be weakening the rock around the glacier. Freeze thaw weathering is the process by which water from the glacier melts into cracks in the bedrock. As the temperature falls the water freezes and expands. As the temperature rises the water melts and contracts. As this process repeats itself the rock weakens and breaks.
What is a good example for highlighting glaciers
The Mer De Glace is the largest glacier in France at 7km long and 200m deep and the second largest glacier in Europe
It flows from the Northern Slopes of Mont Blanc towards Switzerland and is near Chamonix.
The glacier is thinner and shorter today than it was in 1850
Even though the glacier advanced by 150m during the period 1970-80, because the glacial budget was high i.e. rate of accumulation was greater than Ablation
Since 1994 however the glacier has retreated by 30m per year because the rate of accumulation less than the rate of ablation
Why are glaciers such as the Mer De Glace retreating?
The Mer De Glace is retreating because of global warming and associated climate change.
Temperatures today are 1 degree celsius higher than they were 100 years ago at sea level and 3 degrees celsius higher at 1800m
Drier winters have also led to less snow fall which has meant the rate of ablation is higher than the rate of accumulation
What evidence is there that the Mer De Glace has advanced and retreated
There are a number of sources of evidence which illustrates the way the Mer De Glace glacier has retreated and advanced including aerial photographs taken today vs old 19th century paintings and photographs taken by for e.g. Jean Antoine Lick (1766 - 1843),
old maps and moraine mapping in the valley itself provide further evidence
