Specifications *GCSE-AQA-Ice on the land http://filestore.aqa.org.uk/subjects/AQA-4030-W-TRB-DSOW6-PHYS.PDF *GCSE-OCR-Mountain Environments http://www.ocr.org.uk/Images/82576-specification.pdf
Key terms: Glacial period: A period when ice advances due to falling temperatures. Interglacial: A period when ice retreats due to rising temperatures. Ice sheet: A large body of ice over 50,000 km2 in extent. Ice cap: A smaller body of ice (less than 50,000 km2) usually found in mountain regions. Glacier: A finger of ice usually extending downhill from an ice cap or occupying a valley.
Climate Change Global warming may have an impact on our climate and sea levels. BUT some scientists believe that there is talk of another ice age. Climate change in the past has been entirely natural although now it is linked to human activities.
Ice age part of the Pleistocene age which was a period of two million years.
evidence from ice cores and deep sea sediments that there may have been twenty cold periods or glacials during this period.
In these glacial periods ice advanced south in the northern hemisphere and the ice covered large parts of Europe and North America. 18,000 years ago ice reached its maximum extent during the last glacial period.
The ice that covered the British Isles had a thickness of hundreds of metres.
Below is an image of the ice sheets that covered Europe.
Between glacial periods there were periods called interglacials.
These changes happened over thousands of years and were not influenced by humans.
Present day global ice coverage
Currently two large areas of ice in the world called ice sheets, the largest is in Antarctica and is 14million km2 (holds 90% of freshwater on earth's surface) Greenland ice sheet is 1.7 million km2 and is currently showing signs of melting due to global warming.
Ice caps are usually found in mountains such as the European Alps or Iceland.
Spreading out from these ice caps are glaciers (individual fingers of ice) they often follow former river valleys and flow fown to an altitude when the ice turns to flowing water.
Glaciers are found in every continent of the world and in 47 countries.
A glacier is a system of inputs (accumulation) and outputs (ablation).
The image above shows the glacier as a system of inputs (accumulation) and outputs (ablation).
The main input to the glacier is snow. The more snow that falls, the more it compacts. Air is expelled and snowflakes turn to granular ice crystals. The ice then gets denser and becomes clear.
Avalanches of snow and ice are also counted as inputs into glaciers.
The outputs (ablation) usually tends to be melting. This happens at the snout of the glacier. The air temperature tends to be warmer in this part.
When chunks of ice break away at the bottom of the glacier it is called calving (this could be another output).
Another outputs (ablation) is evaporation of the water.
Glacier budget
A balance between the inputs and outputs.
If accumulation exceeds ablation then the glacier will advance.
If ablation exceeds accumulation then the glacier will retreat.
The glacier budget varies between the seasons.
Processes operating in glacial environments
Freeze-thaw weathering
Glacial erosion (rock fragments created by freeze thaw weathering and enable the ice to grind away at the valley floor and sides).
Abrasion - sandpaper effect - weight of the ice scours the valley floor and sides using the rock material that is trapped underneath ( a glacier will only move a few centimetres a year but can cause a lot of damage in this time). Plucking - meltwater beneath a glacier freezes, bonds the glacier surface to rocky surface below like glue. When the glacier moves loose fragments of rock are plucked away like extracting loose teeth.This leaves a jagged rocky surface as opposed to the smooth surface that abrasion leaves.