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Glacier And Desert Landforms

Glacier Landforms

A glacier is a thick mass of ice that forms over hundreds or thousands of years. Most glaciers tend to originate on land, but generally make there way over water due to the glacial flow, and are always moving. Glaciers are formed by the crystallisation and compaction of snow in particular climates. During the last ice age more than 30% of the Earth's surface was covered in glaciers and is currently at approximately 10%, with plenty of evidence of previous glaciers still in many areas. Glaciers are part of both the rock cycle and hydrological cycle and plays a major part of both these cycles and also have a strong correlation with global climate and sea levels. Many mountains, valleys, fiords and other landforms are a direct result of glacial movement and also move large amounts of sediment and other smaller biomasses though the path it takes. Around 75% of the Earth's freshwater is trapped within glaciers, and is not readily accessible. When the glacier moves out to the ocean and melts and then through condensation turns into water vapour is the only way in which this fresh water can be accessed. There are five main types of glaciers: Valley or Alpine Glaciers (formed in mountainous areas), Continental Glaciers (large glaciers which cover entire land masses such as Antarctica), Ice Shelves (glaciers which sit on the edge of large land masses), Floating Glaciers and Ice Caps (glaciers which cover entire mountain tops) 1).

Melting

The increased rate in which glaciers have been melting in the past 30 years is of great concern. This increased rate has in turn contributed to the rising of sea levels, and promises to keep doing so in the near future. Sea ice has already displaced its volume when it comes to sea levels, but any new addition can invariably keep raising sea levels, which is bad news for humans as we tend to want to live near the coastline. If all glaciers and perched ice was to melt, it would create a net sea level rise of 70m, which would be a complete catastrophe for the human race. Glaciers also play an integral part in the planet's climate. They have what is called a high albedo, or reflectiveness which helps to reflect large amounts of solar energy back out into space. The loss of this albedo would cause a significant increase in temperature worldwide, thus potentially creating a runaway heating effect 2).

glacier.jpg

The Sphinx Glacier, Canada 3).

How They Form

For a glacier to form, it requires a very specific types of geographical and climatic conditions. The first requisite is high levels of snowfall combined with low temperatures year round,usually in areas that have an average temperature of 0 degrees Celsius or less, such as the conditions found in polar or alpine regions on the planet. The basic element required is snow, and the amount of snow that falls must exceed the amount of snow that is melted in summer, and if this is met, the glacier should keep growing year after year. As the snow keeps falling on top of the old snow, it turns to ice and the weight keeps compacting it further. As these particles keep getting compressed, they turn into grains roughly the size of rock salt. As time goes by, these grains keep getting compacted and eventually turn into massive sheets of ice. This is a very slow and long process, and can take thousands of years. Once the glacier has reached a certain mass, usually over 50 metres in depth, the sheer weight of it and the force of gravity will start to make the glacier move downhill and eventually out to sea. This glacial movement causes mass erosion but is also beneficial as it grinds rocks and other organic material, creating what we call soil. Countries which have had large glacial movements have a higher quality of soil in comparison to other countries 4).

Consequences

It has been noted that glaciers have been disappearing at rates never seen before. Glaciers in Europe, Iceland and Alaska lost nearly half of their ice in the last century, and at current rates will not last this century. The Glacier National Park in Montana, USA, will have no glaciers left on it by the year 2050. Winter temperatures in Antarctica have risen 4 degrees Celsius in the last 25 years, and over 13,000 square kilometres of perched ice has been lost in the last 40 years. The Greenland continental ice sheet is thinning at 5 metres per year and the Arctic ice cap is receding at rapid levels. For example if the West Antarctic Ice Sheet were to fall into the water, it would add 7 metres to world sea levels, displacing almost a quarter of all human habitats, and the melting of all perched ice would see a 70 metre rise in sea levels, which would be considered an extinction event 5).

Desert Landforms

Deserts play a significant part in the geological make up of the Earth. A desert can be defined as a dry place, but how do we determine how dry it needs to be to become classified as a desert? One of the most widely accepted definitions is if an area receives less than 250mm of rainfall per annum, it is considered to be a desert. However there are exceptions to this rule, and some climatologists define desert areas as areas where the amount of evaporation exceeds the amount of precipitation. Despite this, we know deserts as dry, hot and arid places, and immediately the Sahara Desert would come into our minds. It must be remembered that deserts do not necessarily need to be hot places. There are areas that can be extremely cold, such as the Siberian Tundra, which are also considered to be deserts. Generally deserts are divided into two categories, arid and semi-arid. Arid areas are your classic desert, such as the Sahara, and semi-arid areas or steppes as they are sometimes called, are not as east to define. These areas can sometimes be humid, and are generally transitional zones which exist between deserts and other geological landforms 6).

sahara.jpg

Sahara Desert 7)

Types Of Deserts

Temperatures in deserts can vary significantly. Deserts can be very hot or alternately very cold, with a wide range between maximum and minimum temperatures. Despite this wide range, the one thing that remains constant is the dryness. Approximately 30% of the Earth's surface is made up of desert, which is around 42 million square kilometres, and is the most dominant type of landform on the planet. Arid deserts can be divided into four sub-groups: Subtropical, cool coastal, cold winter and polar. Subtropical desert areas are the hottest types of desert, and these are found in between the latitudinal degrees of 30 and 35, both north and south of the equator, an area in which the trade winds blow towards the equator, dissipating any cloud cover which reduces the amount of rainfall in these areas. The Saharan, Australian, Arabian and Sonoran deserts are all subtropical. Cool coastal deserts are lower in temperature due to being close to the ocean and gaining the benefit of cooling breezes, however this does not increase the rainfall. These deserts are usually a mix of salt, sand and lava. The most notable of the coastal deserts are the Atacama, Namibian and Peruvian Deserts. Cold winter deserts are generally cold and dry, and are located closer to the poles and made up of gravel, basalt and very rarely sand dunes. The Siberian Steppes, the Patagonian Desert and the Gobi Deserts are good examples of cold winter deserts. Polar deserts are made up mostly of ice or ice covered land, and have very little rainfall or any living species. A good example of a polar desert is most parts of Antarctica 8).

Earth Sciences

1) Benn, D. I., 2007, 'Glaciers', Progress in Physical Geography, vol.31, no.3, pp.337-34
2) Gurney, S. D., 2005, 'Glaciers', Sedimentary Geology, 1vol.79, no.3, pp.329-330
3) The sphinx glacier headwall by McKay Savage, licence CC 2.0, Available: http://commons.wikimedia.org/wiki/File:Trips_05_-_Garibaldi_-_06_-_Sphinx_(90953668).jpg
4) Evans, D. J. A., 2005, 'Glaciers', Progress in Physical Geography, vol.29, no.1, pp.114-121
5) Showstack, R., & Tretkoff, E., 2010, 'Melting Glaciers', Transactions American Geophysical Union, vol.91, no.51, p.504
6) James, E., 2008, 'Deserts', Science Scope, vol.32, no.1, p.102
7) Sahara Desert by Globalatlas Adventures, licence CC 3.0, Available: http://commons.wikimedia.org/wiki/File:By_Globatlas_Adventures.JPG
8) Stone, R. O., 1978, 'Deserts of the world' Earth Science Reviews, vol.14, no.2, pp.183-184

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