Glacial Landforms

Following on from the previous post on glacial processes, the next thing to look at are the glacial landforms that occur as a result of these processes. Due to the forceful action of erosion and weathering, the landscape through which the glacier moves is left looking very different to many other landscapes created from erosional and weathering processes.

There are two different types of landform that are created from glaciers: erosional and depositional. 

First of all I will start by looking at erosional landforms.

Corries (also known as cwms or cirques) are found at the top of the mountain where the glacier first begins. They are bowl-shaped hollows which form as a result of plucking, abrasion and freeze-thaw action as the glacier moves further down the mountain or valley. If the ice within a corrie melts, a lake often forms and this is known as a tarn.

U-shaped valleys form as a result of a glacier moving down the valley. Glaciers usually follow the path of old river beds and so the glacier continues to erode the v-shaped river valley, cutting through harder rock that the river could not erode and thus creates a much wider U-shaped valley. Characteristically they have a flat floor with steep sides. Glaciers are also much like rivers in that when they erode through the upper course of the glacier, they leave behind truncated spurs (on a river they are known as interlocking spurs).

Arêtes are sharp, knife edge, ridges of rock which form when two corries form back to back. Each glacier continues to erode either side of the strip between the two corries which eventually leads to the creation of a very steep and narrow ridge.

Pyramidal peaks form as a result of the meeting of 3 or more corries and arêtes. The continued erosion eventually leads to the formation of a pyramidal peak (also known as a horn).

Diagram illustrating the above erosional land forms

Ribbon lakes form as a result of the erosion by the glacier on the valley floor. As it flows 

over this land, softer rock erodes much quicker and easier as opposed to hard rock and so the glacier creates deeper troughs in the soft rock. When the glacier has retreated, water will begin to collect in these deep troughs and can create long, thin, ribbon lakes.

Crag and tail also forms as a result of the differential erosion of the soft and hard rock over which a glacier flows. As the glacier flows over soft rock it eventually hits an area of hard rock and so instead of cutting right through it, it goes over the hard rock. This area of hard rock protects the softer rock behind it, creating a crag and tail. One good example of a crag and tail is Edinburgh castle.

 Diagram illustrating a crag and tail (BBC Bitesize)

Now that I have finished looking at the erosional landforms created by glaciers, I am going to move on to looking at the depositional landforms.

Till, also known as boulder clay, is the debris that is deposited when a glacier has retreated and is made up of a variety of material, including rock, sand, gravel and mud.

Moraines are deposits that have previously been carried by a glacier and dropped as the glacier retreats. There are four different types of moraine:

            Terminal – found at the furthest point that was reached by the glacier

            Lateral – found along the sides of the glacier

            Medial – found at the place where two glaciers have joined together to    create    one, larger, glacier

            Ground – variety of sizes and types of rock found at the bottom of the glacier

Not all material that was once carried by the glacier is deposited as a moraine. Material is sometimes carried by the melt water streams and is deposited as it flows. As a result, after many years of this small, steep mounds of debris accumulates adjacent to the glacier, known as kames.

Erratics are large, unsorted boulders that are deposited once a glacier has retreated. As they are so large they are often found individually, and not in piles and are often of a different rock to that of the surrounding area.

Drumlins are large, long hills which are created as a result of glacial deposits. Although there is much disagreement on how precisely they were formed, it is thought that they were created when subglacial material that had accumulated from various erosive and weathering processes was deposited. As the drumlins are shaped by glacial movement, all of those created by the same glacier face in the same direction; running parallel to the flow of the glacier.

Diagram above illustrates the above depositional landforms

As has been the case with other areas that I have already covered within this glacial topic, I think it is important to incorporate imagery into the teaching. Visual aids help to show pupils what they are learning and it could be easier for them to remember the different terms if they have been able to see it. Another way to help the learning of these terms would be to hand out a diagram of a glacier valley and ask students to add the labels for the different landforms created.

BBC Bitesize as well as National Geographic have been very useful with this area and are filled with useful pictures, diagrams and resources which could prove to be very useful!

Links used:

http://nsidc.org/cryosphere/glaciers/questions/land.html National Snow and Ice Data Centre

http://education.nationalgeographic.com/education/encyclopedia/glacier/?ar_a=1#page=1 National Geographic

http://www.bbc.co.uk/schools/gcsebitesize/geography/glacial_landscapes/glacial_deposition_landforms_rev1.shtml BBC Bitesize

Glacial Processes

This blog post is going to look at a variety of glacial processes; erosion, transportation, deposition and weathering.

Looking first at erosion, there are two main processes that occur here: plucking and abrasion.

Plucking occurs when ice at the bottom of the glacier melts slightly as it moves. Often, the ice melts around large boulders and then refreezes around them. As the glacier then continues to move, these boulders are ripped up off of the ground and move along with the glacier and contribute to the process of abrasion. This process of plucking leaves behind a very jagged landscape.

Abrasion occurs when rocks become embedded in the base and sides of the glacier itself. As the glacier moves, these rocks rub and scour the bedrock and rock faces, acting much like sand paper. This results in the rock surfaces becoming highly polished with large grooves in them, known as striations.

The above diagram gives a brief illustration of the processes of plucking and abrasion as well as where about on the glacier they would occur (http://www.bbc.co.uk/schools/gcsebitesize/geography/glacial_landscapes/glacial_erosion_landforms_rev1.shtml)

Secondly, we will be looking at weathering, in particular freeze-thaw.

Freeze-thaw weathering occurs when water enters joints and cracks in rocks and then freezes as the temperature drops. As water freezes, it expands and exerts pressure within these cracks and causes them to widen. As temperatures begin to rise again during the day, the water thaws and contracts. This recurring process causes the rock to weaken and eventually they break up. These rock pieces may then contribute to the process of abrasion.

The next section will be transportation.

Material carried within a glacier is known as moraine. Moraine can be transported on the surface of the glacier, known as supraglacial moraine, or internally (englacially). Debris collected from valley sides as the glacier moves is known as lateral moraine. If two valley glaciers meet and then merge together, the lateral moraine of the two glaciers also merges together and forms what is known as medial moraine and runs down the middle of the newly formed glacier.

The image above illustrates the different type of moraine that is transported within a glacier.

Lastly, we will be looking at deposition.

As temperatures begin to fall, the ice within a glacier begins to melt. This therefore means that the glacier cannot carry as much material and so it deposits it. The rocks and boulders that the glacier puts down is known as till or boulder clay and is an assortment of different sized and shaped material (unsorted). The main depositional feature of a glacier is the terminal moraine - material deposited at the very end of the glacier. However, it will also eventually deposit the lateral and medial moraines alongside the ground moraine (debris found at the base of the glacier).

Looking for information on this part of the topic led me to many revision and text book websites which has led me to see that this information is not only readily accessible but also very easy to use and explain. There have been a number of useful diagrams and explanations and some websites have even provided short videos to help show the written explanation. These will all be very useful when teaching as it is sometimes difficult to understand things purely from a written or spoken explanation. Often, within this topic, it is easier to show diagrams and videos as it gives a better idea of what is happening and helps to apply what has been learnt to a real life scenarios.

List of websites used:
http://www.bbc.co.uk/schools/gcsebitesize/geography/glacial_landscapes/glacial_deposition_landforms_rev1.shtml - BBC Bitesize
http://revisionworld.co.uk/a2-level-level-revision/geography/glacial-environments/glacial-processes-landforms/erosion-processes - erosion processes
http://www.pearsonhighered.com/christopherson8einfo/downloads/Christopherson_Chapter_17.pdf - Geosystems, Christopherson
http://www.s-cool.co.uk/gcse/geography/glaciers/revise-it/glacial-processes - S-cool revision
http://education.nationalgeographic.com/education/encyclopedia/glacier/?ar_a=1#page=2 - National Geographic

Types of Glacier

Firstly, I would like to apologise for the long break between my last blog post and this blog post (I have spent the past month in Chile - a geographers paradise!). However, blogging shall continue as normal from now on, resuming with types of glacier.

It is important to note that glaciers are classified based on two factors: size and topography. Due to this, they are broadly classified into two groups: alpine glaciers and ice sheets. Firstly, we will look at alpine glaciers.

Alpine glaciers classifies those which are formed on mountains and can be found in the world's highest mountains and are found on most continents (although there are none in Australia, alpine glaciers can be found in New Zealand). Due to this, they are often known as mountain glaciers.

Mountain glacier found in the Andes. (http://www.unep.or.jp/ietc/publications/short_series/lakereservoirs-2/4.asp)

Valley glaciers are those which have commonly originated from mountain glaciers. They begin to move down into valleys and can be very long, some often exceeding the snow line and may even reach sea level.

Mer de Glace Valley Glacier, France (http://www.aber.ac.uk/en/iges/research-groups/centre-glaciology/research-intro/valley-glaciers/)

Hanging Glaciers are so called due to the fact that they cling to the side of steep mountains. They usually form at the top of a mountain or valley but doesn't descend into the main glacier or valley below. Instead, the ice often calves in avalanches to the glacier or valley below (making them often extremely hazardous).

Mt.Kefton, Antarctica Hanging Glacier (http://nsidc.org/cryosphere/glaciers/gallery/hanging.html)


Piedmont glaciers are found when valley glaciers flow from a relatively narrow valley into a much wider valley or plain. Due to this, they then spread out into large, bulb like features. The largest Piedmont glacier in the world is found in Alaska: the Malaspina glacier. It spreads over 5,000 square kilometres and can be seen in the picture below:

(http://nsidc.org/cryosphere/glaciers/questions/types.html)

Cirque glaciers are named after the bowl shaped hollows that they occupy which are known as cirques. They are most usually found high up on the side of mountains and are most often wider than they are long.

Teton cirque glacier, Wyoming, USA (http://www.swisseduc.ch/glaciers/glossary/cirque-glacier-en.html)

Tidewater glaciers are valley glaciers which have flown far enough that they reach the sea. The leading edge of the glacier lifts up and floats in the water which thus forms cliffs of ice. Huge chunks of ice may break off at the edge of the glacier, a process known as calving.

Kronebreen tidewater glacier, Svalbard (http://www.swisseduc.ch/glaciers/glossary/tidewater-glacier-en.html)

The last type of glacier that we will look at will be ice sheets. These can only be found in Antarctica and Greenland and are not restricted to mountainous areas; instead they spread out in all directions from the center and cover vast areas. The largest of ice sheets are known as continental glaciers.

The edge of the East Antarctic Ice Sheet (http://www.swisseduc.ch/glaciers/glossary/ice-sheet-en.html)

This blog post has looked at the different type of glaciers that can be found and has identified each type with a photograph. When teaching this section, I think it would be important to illustrate each glacier with a picture as it is often easier to remember and learn about them with a visual aid. It is a brief section which could be taught in the form of a simple game, matching pictures and definitions, as was done for the key vocabulary table in a previous blog post. This would help to make the lesson a bit more fun for students and would help to further engage them with the topic.

I just want to round this blog post off with a good video I found on the BBC website showing a glacier in action (definitely helped by the fact that Sir David Attenborough is the narrator!): Glaciation In Action - Frozen Planet

Links used:
http://nsidc.org/cryosphere/glaciers/questions/types.html - National Snow and Ice Data Centre
http://iceland.vefur.is/iceland_nature/glaciers_in_iceland/ - Icelandic Glaciers
http://education.nationalgeographic.com/education/encyclopedia/glacier/?ar_a=1 - National Geographic
http://www.swisseduc.ch/glaciers/glossary/ice-sheet-en.html - Glaciers Online
http://www.unep.or.jp/ietc/publications/short_series/lakereservoirs-2/4.asp - UNEP