I thought that I'd start this section on glaciation with a look at how glaciers form in case, like me, the students haven't studied glaciers before. An icy worldThe Earth goes through cycles of ice ages, cold periods which last for millions of years. During these ice ages, there are cooler glacial periods and warmer interglacial periods. The last glacial period began about 100,000 years ago and ended about 10,000 years ago. Around 20,000 years ago over 30% of the land on Earth was covered by ice, including almost all of the UK. Ice sheets in the UK were up to 3 miles thick and one reached as far south as London. Today, we're in an interglacial period and only 10% of the Earth's land surface is covered by ice. How do we know about these past changes in temperature? There are three types of evidence for the changes: chemical evidence from the changing chemical composition of ice and marine sediments, from fossil remains showing the adaptations of the organisms to the past climate and, importantly for geographers, from the landforms that were created by glaciers. How are glaciers formed?Glaciers are often described as rivers of ice (see photo right). They move downhill and are so powerful that they carve valleys out of mountains. Glaciers form when multiple snowfalls in mountainous or polar regions fill valleys and sheltered hollows. Summer temperatures are important, as this snow must remain on the ground year round in order for glaciers to form. As these successive layers are compacted by further snowfall on top, they turn into ice. This process is demonstrated in this BBC video How glaciers form. This section of the glacier where the snow accumulates is called the zone of accumulation. As the snow and ice continue to pile up, the lower layers get pushed downwards under the force of gravity to the section of the glacier where less snow falls and where the ice melts to form meltwater. This part of the glacier is known as the zone of ablation. As it travels, the glacier transports this ice along, and in doing so erodes the landscape and picks up, transports and deposits material, creating the landforms that I'll look at in detail in the next few posts. The glacier is constantly transporting the ice from the upper part of glacier where it fell and moving it forward along the glacier, so even when the glacier as a whole is getting smaller and retreating, the ice is still being transported along. Whether a glacier advances or retreats depends on the difference between inputs and outputs of the glaciers. The difference between the accumulation (snow and ice) and ablation (ice melting) for one year is known as the glacial budget. If more snow forms and ice forms than the amount of ice that melts, there is a positive glacial budget and the glacier advances. However, if more ice melts than is formed in the zone of accumulation, there is a negative glacial budget and the glacier gets smaller and retreats up the valley. There is evidence that the world's remaining glaciers, in places such as Greenland, Antarctica and Europe, are shrinking and some are in danger of disappearing. The main cause of this is global warming as average global temperatures have increased by about 0.9°C in the last 150 years. Sources: BBC (2015) 'Glaciers' BBC Science. [Accessed on 19/08/15] Available from: http://www.bbc.co.uk/science/earth/water_and_ice/glacier British Geological Society (2015) 'Ice and our landscape' Geology of Britain. [Accessed on 19/08/15] Available from: http://www.bgs.ac.uk/discoveringGeology/geologyOfBritain/iceAge/home.html?src=topNav Coordination Group Publications Ltd. (2010) GCSE Geography: The Revision Guide. CGP. Royal Geographical Society (no date) 'Glaciation and geological timescales - Not an ice cube: how glaciers work' Teaching resources: Key stage 3 resources. [Accessed 19/008/15] Available from: http://www.rgs.org/OurWork/Schools/Teaching+resources/Key+Stage+3+resources/Glaciation+and+geological+timescales/Not+an+ice+cube+-+how+glaciers+work.htm
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AuthorMy name is Heather and I am going to begin my SCITT course to train as a Geography teacher. ArchivesCategories
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