I didn't come across glaciation until university, looking into why the climate deteriorated in the Late Cenozoic and relative sea level change since the last glacial maximum but I'll just cover the basics here. A lot of the information I will use on the blog will be from Geography: An Integrated Approach by David Waugh - a must have for anybody who wants to teach geography. Glaciers are just like rivers of ice, in lessons I think I would try and draw comparisons between the hydrological and glacial system (if previous lessons had covered rivers). I would use pictures and videos to illustrate features and processes in glacial environments in a PPT. Hopefully, the pictures and videos will stimulate pupils' curiosity into the topic. At various intervals of the lesson, I would get students to discuss images and videos that they have seen, to the whole class or as a group. For example, describe what a glacier is like? Then I would get students to write this in their book and draw a simple sketch of a glacier.
Glaciers are found at high altitude, including mountains close to the equator and at lower altitudes at high latitudes close to the North and South Poles. The most recent and significant period of ice activity occurred during the Pleistocene epoch of the Quaternary, when ice reached its maximinum extent, it covered 30% of the Earth's land surface. 18,000 years ago, glaciers covered Britain as far as the Midlands and Norfolk.
There are various explanations given for this ice coverage.
- Milankovitch cycle, illustrates the Earth's position in spaces, its tilt and orbit around the sun changes
- Variations in sun spot activity-changes in amount of radiation received by the Earth.
- Injections of volcanic dust into the atmosphere reflect and absorb radiation.
- Changes in carbon dioxide in the atmosphere.
- Movements in plates.
- Changes in ocean currents.
Snow accumulation and ice formation
When the climate gets colder, more precipitation is likely to be in the form of snow in winter and there is less time for that snow to melt in the shorter summer. Snow flakes have an open and feathery appearance, trapping air and have a low density. Snow collects in hollows, it is compressed by the weight of subsequent falls, it gradually develops into a more compact dense form called a firn. The hollow is deepened and widened by the corrie glacier through the processes of abrasion and plucking. This overdeepening leads to an ‘armchair’ shape characteristic of a corrie and causes a ‘rock lip’ to be formed. I have a picture animation below that I would show (I can't seem to paste the animation on to the blog). There are also several videos covering glaciation on BBC learning Scotland that could be used to demonstrate glacial processes (http://www.bbc.co.uk/scotland/learning/learningzone/clips/3248/). .
Glacial systems and budgets
A glacier can be seen as a system of inputs, outputs, transfers and storages, again
I would draw comparisons with rivers.
Inputs- snow, rain
Outputs- evaporation, calving (formation of ice bergs), meltwater stream
Storage - as glacier ice
Transport - moving ice
Where input exceeds outputs, this is known as the zone of accumulation.
Where outputs exceeds inputs, this is know as the zone of ablation. I think it would be important for students to have a list of key words in their book, particularly as there are many technical words students would have to learn.
A diagram illustrating snowfall vs melting/evaporation.
Glacial erosion
Moving ice can alter the landscape dramatically, it is able to melt and refreeze, in order to overcome obstacles in its path and has the ability to lower landscape perhaps ten more times quickly than running water can.
Glacial erosion
Frost shattering- Freeze-thaw is when melt water or rain gets into cracks in the bed rock, usually the back wall. At night the water freezes, expands and causes the crack to get larger. Eventually the rock will break away. This produces loose material, that falls onto the edges on of the glacier to form lateral moraine.
Abrasion- Sand papering effect of angular material embedded in the glacier as it rubs against the valley slides and floors. This causes the wearing away of the landscape as the glacier behaves like sandpaper. It leaves behind smooth polished surfaces which may have scratches in them called striations. Striations are carved out by angular debris embedded in the base of the glacier. The angle of these striations are often measured, to estimate the direction of the glacial flow.
Plucking- The water at the bottom of the glacier freezes onto rock on the valley base. As the glacier moves the rock is pulled away from the valley base. Plucking mainly occurs when the rock is well-jointed.
Glacial deposition
- Moraine carried by the glacier gets left behind when the glacier retreats.
- Drift is often the term used to refer to all glacier deposits.Sediments that were deposited by melting ice or by glacial streams are called fluvio-glacial. Debris deposited directly by the glacier, such as moraine and intra-glacial material dropped 'in situ' by retreating ice, is known as till.
- Deposition occurs in upland valleys and across lowland areas.
I have just given a brief overview of glacial processes, I will cover glacial landforms, in greater depth, in the next post.
