Volcanoes

A volcano can be described as an opening, or break, in a planet's surface or crust, which allows hot magma, volcanic ash and gases to escape from the magma chamber below the surface.

In general, volcanoes are found at converging tectonic plates (two tectonic plates moving towards each other causing one of them to break). One example of this is the Pacific Ring of Fire which has examples of volcanoes caused by convergent tectonic plates coming together. They are also found at diverging tectonic plates (two tectonic plates move away from each other leaving a break in the layer of tectonic plates). One example of this is in the mid-Atlantic ridge whereby two plates are diverging leading to the formation of volcanoes.



Image courtesy of http://mail.colonial.net/~hkaiter/platetectonics.html 



There are many effects of a volcanic eruption; firstly the ash and dust particles thrown up into the air cause significant rainfall, lightning and thunder. This is because the ash particles are good at attracting water droplets due to their dipolar positive charge, therefore attracting the waters dipolar negative charge. Secondly, lahars can form if the erupting material comes into contact with large amounts of rainfall or melting snow, lahars are mixtures of ash, mud and water which can cause fast-flowing mud slides. Thirdly, there are obviously the human effects, many lives can lost and lava flows and lahars can destroy settlements and clear areas of woodland or agriculture, the land affected is often irreversible. In some severe cases, volcanic eruptions can cause large-scale disruption, such as the case in 2010 where the Eyjafjallajökull volcano in Iceland led to flights globally being cancelled.

 However, there are also positive effects; firstly the dramatic scenery created by volcanic eruptions attracts tourists and thus increases economic opportunities in an area. Secondly, the volcanic material can often break down to provide valuable nutrients for local soils acting as a great natural fertiliser increasing crop yields. And thirdly, the heat of a volcano can provide opportunities for the exploitation of geothermal energy which is becoming increasingly important and desirable as countries and companies seek to lower global emissions.

So although the effects of volcanic eruptions are often portrayed as negative by the media, these great natural wonders can have tremendously positive effects on areas and if managed and predicted properly, can prove to be a great source of income and a great source of natural beauty for many worldwide.

Is the Burgess Model still applicable today?

The land-use model (pictured below) is known as the Burgess Model or the Concentric Zone Model and was created by the geographer Ernest Burgess in 1924. But is it still applicable to the growing international cities of today?

Image courtesy of BBC

 

The model, originally based on the city of Chicago, was the first to give the explanation of the distribution of social groups within urban areas. It was designed to show what a typical city is most likely to look like in terms of land use. This model is based on the idea that land values are highest in the centre of a city because competition is high in the central parts of the cities which leads to high-rise, high-density buildings being found near the Central Business District (CBD), with low-density, sparse developments on the edge of the town or city. It can loosely be applied to a city such as London; in general land prices are most expensive in the CBD. This is because of the vast number of passers-by and also the expansive transport network. And in general, the further out of the city you go, the cheaper the land prices, although there are of course exceptions, for example, an area such as Knightsbridge in which the average asking price for a house is £2,443,942 is further out than Holborn but house prices in Holborn are cheaper at £1,535,033.

However, there are limits to the Burgess model:

•The model is now quite old and was developed before transport networks were so prominent in the lives of many people. Car's weren't widely owned and getting around was much harder than it is today.

•The development of the internet and telephone has led to increased business being done through technology, with some companies opting to locate in a cheaper location further out. Furthermore, many people now choose to live and work outside the city on the urban fringe -  this is not reflected in the Burgess model.

•Every city is different. There is no such thing as a typical city. Burgess based this model upon, one city, Chicago and it therefore cannot be applied globally.

So in conclusion, although the model can loosely be applied to most modern day cities, it is very hard to consider this as a precise model of the modern day city and there are now too many factors, independent to each city, that mean it is unlikely another model, of suitable precision, could be created.

The link between deforestation and soil erosion

With an area the size of Costa Rica being destroyed each year, deforestation to create land which can be used for agriculture is a growing problem, it needs to be addressed soon before it’s too late. Here, I will be looking at the effects of deforestation on soil erosion.

A forest will protect the soil lying beneath it from the immediate effects of rainfall as the canopy and other factors help to lower the rate of erosion in this type of environment. This is because the canopy reduces the fall of raindrops, reducing their velocity and therefore kinetic energy.

The forest is also helped by the presence of humus in its soils (see image). Humus is the term used to describe any organic matter that has reached a point of stability, where it will break down no further and might, if conditions do not change, remain as it is for centuries. Humus helps to absorb the impact of the raindrop and is very permeable therefore allowing the rain to infiltrate its soils and be absorbed by the roots which can then help the plants grow. This humus also helps to bind these soils together, reducing the impacts of wetting and water-drop impact

Another factor that increases the stability of forest soils is the large, deep, tree roots that tend to bind soils together, compacting them and increasing the total strength of the soils.

Therefore, we can expect that with an increase in deforestation; there will be an increase in soil loss and erosion. If the land is left bare, then the effects will be more dramatic than if the land were to be covered with crops, which would have similar (but to a lesser extent) effects as forests. Furthermore, the type of ploughing, time of sewing and type of crop will influence soil erosion rates.

It is evident that the effect of humans upon the soils of the earth has dramatically increased the rate at which soil is eroded and lost. In Colorado, USA, rates of erosion over the past 100 years have been at circa 1.8mm per year, whereas in the 200 years before that, rates were between 0.2 and 0.5mm per year, showing erosion rates have increased at a rate of 5x since 300 years ago. In this specific area, it is because of the number of cattle that now use the fields.

This situation is something that cannot be ignored and has to be dealt with soon before the damage to our environment is irreparable.

Humus in soil. Image courtesy of http://cookingrut.blogspot.co.uk/2011/05/gardening-tips.html#!/2011/05/gardening-tips.html