Extreme landscapes: Glacial landforms 1

There are many different landforms created by glaciers, which is not surprising even their prevalence, size and power. I am going to split them into 2 types erosion and deposition, it could as easily be divided into upland and lowland formations. I am going to have a look at erosional landforms in this blog and depositional landforms in the next. This should allow me to use a few pictures of the magnificent landforms features.

Erosion formations This is a Cirque. generally found at the start of a glacier. It is a bowl-shaped depression eroded into the side of a mountain by an alpine glacier.









Pictures say a thousand words and this diagram shows how the cirque is formed.


This is a U shaped valley that typically have steep sides and flat floors. The glacier widens, steepens, deepens and smooths pre-existing V-shaped river valley.










A hanging valley occurs when a tributary rivers joins the U shaped valley that is lower. It often leads to spectacular waterfall.





When a river erodes the landscape, ridges of land form in its upper course which jut into the river. These are called interlocking spurs. A glacier cuts through these ridges leaving behind truncated spurs


An arête is a knife-edge ridge. It is formed when two neighbouring corries run back to back. As each glacier erodes either side of the ridge, the edge becomes steeper and the ridge becomes narrower, eg Striding Edge found on Helvellyn in the Lake District. (BBC bitesize)

















A pyramidal peak is formed where three or more corries and arêtes meet. The glaciers have carved away at the top of a mountain, creating a sharply pointed summit, eg Mont Blanc, The Matterhorn and Mount Everest. (BBC bitesize)












Other formations develop such as ribbon lakes that occur after the glacial has melted, they are often deep and flat bottomed. Roches moutonnée and Crag and tail are formations that develop when there is a change in the type of rock that the glacier passes over.

The erosional formations can create dramatic scenery and exciting places to visit often in National Parks.

Extreme landscapes: Glacial Processes

So from the previous blog we know that glaciers move, they ate massively heavy and as they move they change the land that they travel over.

The main erosional processes are Freeze/thaw, plucking and abrasion.



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.

Plucking is when melt water from a glacier freezes around lumps of cracked and broken rock. When the ice moves downhill, rock is plucked from the back wall. It leaves behind a jagged landscape.

Abrasion is when rock frozen to the base and the back of the glacier scrapes the bed rock. 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.

In terms of teaching glacial processes my view is that it should be linked to the landforms created so that they is something tangible to examine. The next blog will show the formations giving pictorial examples. I have found some great video's online but I am yet to work out how to upload them to the blog. These would be very helpful in providing a visual explanation. Also, if it were possible a field trip to the lakes would be great to show the students the processes and the results....money permitting of course!

Extreme landscapes: Glacial, general

Glaciers are huge masses if snow and ice that have been compacted over many thousands of years. Their weight is such that when they move they do so very slowly the bottom slowed by the ground. They originate from the 'ice age' (18,000 years ago, covering 1/3 of the earths surface) and as the earth has warmed they have melted and reduced in size. Having said that they still cover 10% of the earth. When the majority of the glaciers melted (after the ice age) they left behind changed landscapes that will be discussed in the next blog. A local example of a glacial landscape is the lake district.

In the high mountains of Britain we can see the effects of glaciers. This is the Buttermere valley in the Lake District. This valley would have been filled by ice. The valley has been straightened and deepened by the erosion. This type of valley is called a U-shaped valley.

Extreme Landscapes: Desertification/human processes

This is a subject that interests me as you can look at the interaction/juxtaposition of physical and human geography. It is a great example of how geography is a current and dynamic subject, by looking at the cause and effect of 'natural' (if there is such a thing) and anthropological impacts.

What is desertification?

The transformation of arable or habitable land to desert, as by a change in climate or destructive land use. This picture shows how with over farming a poor farming methods the soil has become infertile, allowing the desert to move in.













Human processes

The following is a quote from Kofi Annan (UN General Secretary) 2003, altering the world to the dramatic and devestaing effect of desertifcation on human populations. the quote is from mindfully.org. 'Desertification and drought pose an ever-increasing global threat. Human activities such as overcultivation, overgrazing, deforestation and poor irrigation practices, along with climate change, are turning once fertile soils into unproductive and barren patches of land. Arable land per person is shrinking throughout the world, threatening food security, particularly in poor rural areas, and triggering humanitarian and economic crises.'



The graph shows the type of land use in each world area that is causing desertification. The map below shows how vulnerable Africa is to this process especially when you bare in mind that level of poverty on this continent, which will affect their attempts to combat the problem.



The economic problems that will develop as a consequence of desertification are significant, including reduced food production leading to rural communities breaking down, internal migration, external migration and possible conflict. The situation is urgent and needs a global response, but whether this will happen given that those most affected have little 'global power' remains to be seen. it is this type of issue that students can reflect upon and consider possible solutions and developing their own ideas on global issues.

Extreme Landscapes: Desert Landforms

Deserts have a variety of landscape features. Teaching this subject could be tricky but there are some fab web sites on teaching methods and resources, including howstuffworks.com, enchantedlearning.com. This is one of the alien environments that we will learn about and it is important to reflect of the method of teaching to try and bring the subject to life.

Sand dunes: the landforms commonly thought of as typical of deserts, occupy only a relatively small part of the world's deserts. Some deserts, however, have great expanses of dunes, known as sand seas, or ergs.



Yardangs: Bare rock surfaces they occur where wind and water have removed the surface particles and left the hard bedrock exposed. Commonly, flat areas are covered by what is known as a desert pavement, a closely compacted layer of rock and gravel. In some places, especially at the foot of a mountain, there are large deposits of gravel and other coarse debris, which are sometimes quite deep.


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Arroyos: Floods occur and form temporary rivers that carve steep-sided valleys called dry washes or wadis.



Playas: occur when water is carried by floods sometimes accumulates in shallow depressions in the desert floor. Playa lakes usually disappear quickly and leave behind sand, silt, and dissolved minerals, which may form salt flats. There can be permanent water features—such as the Great Salt Lake, in Utah, USA.



Ventifacts: Rocks that are shaped by the wind and occur in deserts due to the Strong winds that carry sand particles. They are shaped by this process of saltating.



There are many more examples of the desert feature but the ones i have shown here are the basics!

Extreme Landscapes: desert processes

What is a desert?

It is a region with so little vegetation that no significant population can be supported on that land. This implies that it is dry, but not necessarily hot. However, for the purposes of this blog I will consider mid latitude deserts in the interior of continents characterized by low rainfall and high summer temperatures, e.g., Gobi Desert of Mongolia.

The dominant force in a desert is wind. Wind can also cause erosion and deposition in environments where sediments have been recently deposited or disturbed. Erosion by wind is slower than water or ice, but it can move material up and down a slope unlike water. But as the wind velocity increases as does the winds erosive power.

Wind erosion

Removal of loose sediment by the wind. Sediment must be dry. Sand and silt sized material will be moved. Larger material is generally left behind
Abrasion is a physical weathering process. AKA Sand blasting. Impact of windblown particles on exposed surfaces will remove material from that surface
Abrasion will also reduce the size of the particles that are being moved
Generally limited to heights of 1 meter (2 meters max.)

Deposition

In a desert, material moves primarily by the wind through a process called saltation. Deposition occurs in areas where a pocket of slower moving air forms next to much faster moving air. Such pockets typically form behind obstacles like the leeward sides of slopes. As the fast air slides over the calm zone, saltating grains fall out of the air stream and accumulate on the ground surface. (PhysicalGeography.net).

There are different types of sand dunes and desert landforms that i will look at in the next blog. Perhaps to help the students understand the movement of sand we cold look at sand closer to home that is the beach where dunes occur.

Riparian Environments: Landforms

Landforms: A way of teaching this element could be by way of a quiz, differentiating on learning abilities, using graphics and basic pictures to learn where certain landforms are located on the length of a river (that is upper middle or lower course of the river). I love the formations that rivers create, the diversity of physical shapes formed by the shear power of water. Amazing!

Upper Course

The steep gradient and narrow flow of the river helps to form features such as V-shaped valleys, waterfalls, gorges and interlocking spurs. These formations can be spectacular:

Interlocking spurs





Waterfall: formed as water passes over a variation hard rock and softer rock causing erosion of the soft rock.








Middle Course
the gradient is more gentle but the river has high volumes of water and energy. It travels along through flatter areas allowing it to create different types of land forms, including large meanders (bends in the river). As the river meanders the speed of the the water on the inside of the curve is slower so that it deposits material, whereas on the outside of the curve it travels more quickly and therefore erodes the bank. This makes the bends even more extreme



Over time the horseshoe become tighter, until the ends become very close together. As the river breaks through, eg during a flood when the river has a higher discharge and more energy, and the ends join, the loop is cut-off from the main channel. The cut-off loop is called an oxbow lake.



Lower Course

This element has high volume and large deposits. the river is moving slowly often towards its mouth. It can have a large flood plain which over time has deposited very fertile alluvium (sediment) that is great for farming. On reaching the mouth a delta is formed. See my previous blog on river processes and the picture of the Okavango Delta.