The extent to which volcanoes represent a hazard to human populations depends on where they are experienced. To what extent do you agree with this view?

‘The extent to which volcanoes represent a hazard to human populations depends on where they are experienced’. To what extent do you agree with this view?

Sam Burton

In 1992, a German by the name of Alfred Wegener published his theory to the world, stating that around 300 million years ago the separate continents as we know them now were once joined. He called this super continent ‘Pangaea’ and explained that it later split into two main continents and that our current continent layout was formed as a result from even further splitting. There is much geological evidence to support his theory, such as matching rock samples in north Scotland and parts of Canada indicating that they were once joined. Similar fossils have also been found of the same animal in South America and Africa. It is unlikely that these two animals have evolved without contact and in sync. Paleomagnetism is also a contributing factor to the idea that supports the theory of plate tectonics. Paleomagnetism describes the process at a mid Atlantic ridge where magma rises, cools and creates new crust. The iron particles when they cool are aligned to the Earth’s polar magnetism. At intervals of around ¾ million years the Earth’s polarity reverses itself. As magma is continually rising to the surface the new magma will now be aligned with the inverted poles. This creates ‘magnetic stripes’ on the sea floor and supports the theory of sea floor spreading.

As these plates move due to convection currents, where they collide they form different types of boundaries. Constructive margins form where two plates move apart from one another such as the North American plate and the Eurasian plate to from the mid Atlantic ridge. Another rift valley would be the African rift valley, which has a number of volcanoes along it including Mt Kenya and Mt Kilimanjaro. Destructive margins form when the denser continental plate slides underneath the crust and often forms fold mountains. A good example of this is where the Nazca plate and South American plate collide to form the Andes. At subduction zones a line of volcanoes often forms such as the ‘ring of fire’ that surrounds the Pacific Ocean. Conservative margins is the other boundary formed when continental plates come into contacts and is where two plates move side by side one another, such as the North Atlantic plate and the Pacific plate to form the San Andreas Fault.

Most volcanic activity is associated with plate tectonic processes and mainly located along plate margins. Hotspots are an exception to this. A hotspot is a point on the surface of the Earth located above a plume of rising magma. Where lava breaks through to the surface active volcanoes occur above the hotspot. A hotspot is stationary so as a plate moves over it a line of volcanoes is created. The Hawaiian Islands are an example of this over the Pacific Ocean. There are variations in the form, frequency and type of volcanic eruption and it often depends upon the type ...

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In some ways I agree with the title, in simple terms the closer your proximity to a volcano the greater a hazard it becomes. However, you could be the same distance from a volcano at a Destructive margin and the same distance from a volcano at a Constructive margin but the hazard would be very different. At a constructive margin shield volcanoes usually occur. Shield volcanoes are characterised by their long gently sloping sides and small height in comparison to their sides. An example of a shield volcano would be the Mauna Loa and is one of five volcanoes that form the Island of Hawaii. It consists of mainly basaltic lava and is usually not very viscous. They erupt mainly lava and can erupt for long periods of time and can be quite regular. At a destructive margin the volcanoes that form are often much more of a hazard than at constructive margins. Composite cone volcanoes form at destructive margins. Mount St Helens is a volcano that formed as the Juan De Fuca plate was forced under the North American Plate. In the United States’ history it is the most economically destructive killing 57 people and destroying over 250 homes. One main thing to consider when discussing the title is to take into account at what boundary the volcano is at, whether it is constructive or destructive.

Partial melting is the name that describes the process of melting crust. As the denser oceanic crust slides under the continental crust, the oceanic crust is melted by the magma. The silica that is trapped in the oceanic crust is released from the rocks and raises the silica content of the surrounding magma. This increased silica content produces very viscous lava which is acidic, otherwise known as Felsic (rhyolitic) lava. It also results in the eruptions being highly explosive releasing lava bombs and is often the type of volcano that releases pyroclastic flows. This is why I think the title is not specific enough; you could be miles away from a volcano but still suffer from some of the effects produced by an eruption.

Some eruptions have global effects whereas some eruptions have minor effects and only affect a small radius of the surrounding area. The eruption of the Soufriere Hills, Montserrat in 1995 through to 1997 was a localised problem in comparison to other eruptions. The eruption affected those on the island only in terms of actual volcanic impact as it erupted 4-5 million m3 of material. Only 40km2 of the island’s 100km2 was safe to live on. The island’s capital was buried by 10m of ash and all residents had to be evacuated to the north of the island. The UK gave aid of more than £100 million in assisting migration, service restoration and agriculture restoration. The eruption of Mount St Helens in 1980 however was a far more global problem. The magma inside of the volcano burst into a large scale pyroclastic flow that flattened buildings over 230 square miles. More than 1.5 million metric tonnes of sulphur dioxide were released into the atmosphere creating a much more sever situation. The eruption was rated at five (a Plinian eruption). Ashes from the eruption were found collecting on top of cars and roofs next morning, as far as the city of Edmonton in Alberta, Canada. The radius of destruction for this volcano is far greater than that of Soufriere Hills’ radius. This is why I believe that the title is faulted; it does not take into account the boundary at which the volcano occurs nor does it consider the scale and size of the volcano.

In some cases it is possible to live in a close vicinity of the volcano and still live there with minimal hazard. Mt Etna is a volcano that was constructed over an older shield volcano. It has persistent explosive eruptions sometimes with minor lava emissions. Although it can be destructive it is not considered particularly dangerous. Thousands of people live on its slopes. Towards the end of 1991 lava flows began to pour from the high vents on the eastern flank. A large earth barrier was constructed at the end of the val calanna at the southern end of the Valle del Bove. It was several tens of metres high and more than 400m long. This managed to hold back the lava for several months and after the lava spilled over engineers in 1992 blasted a new opening to encourage a new flow path. This shows that you can be in a closer vicinity than that of Mount St Helens and still have very little impact on the surrounding area. Those that were miles away from Mount St Helens received greater impacts that those living on the slopes of Mount Etna. It is possible to somewhat manage a volcano however this form of management would not have worked with Mount St Helens. This does show however that the hazard to human populations does not necessarily depend upon where you are experienced.

The destruction and hazards to people are also different in MEDCs and LEDCs. The Nevado del Ruiz eruption of 1985 in Colombia had not erupted since 1845. The town of Armero was built on the debris of the previous event. The eruption killed in total around 24,000 people. They were not prepared for any kind of eruption and as they were an LEDC there was little primary responses given. The eruption of Soufriere Hills is a good example of an eruption in an MEDC. Evacuation took place, aid was given, safe zones were set up and further monitoring of the volcano took place. In many MEDC there is constant monitoring of the volcano for signs of eruptions. Scientists are hired to look for slight changes in activity. In most LEDCs there is not this funding for monitoring and little preparations for if/when there is an eruption.

I do agree with the statement to some extent and it is hazardous to the human population the closer you go, however the degree of danger does change dependent upon several other factors. The degree of danger is far greater at a destructive margin due to the rise in silica content and more acidic lava as well as the more violent eruptions. The type of volcano also changes the severity and whether it takes place in an LEDC or MEDC is also a contributing factor. I do agree with the statement but other factors need to be included.

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