Managing Volcanic Hazards

Volcanic eruptions are hazards resulting from tectonic activity. During your GCSE geography lessons, you will have made a case study of a volcanic eruption. For your exams, you need to know what causes an eruption, the primary and secondary effects and that these can be positive as well as negative. You should also know and understand the immediate and long term responses and how volcanic eruptions are monitored. Millions of people throughout the world live close to volcanoes and benefit from them. Managing the hazards from volcanoes is necessary to their survival.

The Earth's crust is extremely thin compared to the overall size of the planet and is cracked into large plates. These plates move around, driven by convection currents in the Earth's mantle.

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As they move, they collide, move apart and slide sideways past each other, creating earthquakes and volcanoes close to their boundaries. When the volcanoes erupt, the materials produced by the eruption can be hazardous.

There are several different types of volcano, two common types are shield and composite cone. Eruptions from shield volcanoes tend to be less explosive than from composite cone volcanoes because the lava is much less viscous. Ash is erupted and is carried high into the air by the rising air above the volcano. This is a hazard to aviation and flights are sometimes diverted or even cancelled when there is a large eruption beneath an air corridor. As the lava cools and solidifies, new crust is formed. Where this happens on land, the lavas will eventually weather, forming mineral-rich soils.

Eruptions occur when magma reaches the surface of the Earth. Magma is intensely hot and the heat is transferred into the rocks around the rising magma. Any groundwater that is circulating will be heated and where the water reaches the surface, it becomes a hot spring. Some of these are cool enough to supply warm water for public baths, something that was noticed and often used by the Roman Empire. During the eighteenth and nineteenth centuries, hot springs became very popular with the middle and upper classes who believed that the mineral-rich warm water had health-giving properties. In the UK, although there are currently no volcanoes, heat from magma deep in the crust still warms groundwater in some places.

Volcanic eruptions are entirely unpredictable and the best that monitoring can do is to alert the authorities shortly before an eruption occurs. Volcanoes that are close to centres of populations are the most-closely monitored, for example Mt. Etna in Sicily. Scientists look for clusters of small earthquakes (caused by the magma pushing its way upwards through the crust), an increase in temperature around the volcano and any sudden increase in gases given off by the volcano. The only effective management for most eruptions is to evacuate the area. In MEDCs, the emergency services can be mobilised very quickly, so medical aid and shelter can reach the stricken area soon after the eruption. In LEDCs, it takes a lot longer. Often the bulk of the aid will be donated by MEDCs which takes time to organise. That means more people are likely to die, either as a result of the eruption, from untreated injuries, infections or even disease.

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  1. There are several reasons why communities in LEDCs are more vulnerable than those in MEDCs. Which of the following statements is false?
    Rural populations in LEDCs have less access to broadcast media and so warnings may not reach them before the eruption occurs
  2. Which of the following would be classed as a secondary effect of a volcanic eruption?
    A secondary effect is something that is not caused directly by the eruption. In this case, although the flooding is caused by the ash, the destruction is actually caused by the water and not the eruption
  3. Which of the following is not a hazard from a volcano?
    There are other hazards too such as nuée ardentes, toxic gases and volcanic bombs
  4. Why are more people likely to die when a volcanic eruption occurs in a poor country?
    Monitoring is not as effective as in countries that are wealthy so there is a lot less warning before an eruption occurs, taking people by surprise. Aid often needs to come in from abroad and that always takes several days to organise
  5. What is the most effective way to protect a population during a volcanic eruption?
    The only way that a population can be protected is by evacuation. If the lava from an eruption is of the viscous (thick and slow moving) type then it may be possible to build a wall from pre-cast concrete blocks to deflect it, however, there are still the other dangers to contend with
  6. Which type of volcano is most likely to cause loss of life and property when it erupts?
    Sword is not a type of volcano. The lava from shield volcanoes is much less viscous than in a composite volcano and therefore eruptions are less explosive
  7. Some volcanoes are closely monitored for signs of an eruption. Which of the following is not an indicator that an eruption is likely to occur?
    Volcanoes emit many gases, but never oxygen
  8. In MEDCs, people living near volcanoes are generally better prepared for an eruption. Which of the following is the most likely reason?
    Preparing people for a volcanic eruption includes education. That is more difficult where literacy levels are low because fewer people can read leaflets and posters
  9. Volcanic eruptions can have a devastating effect on communities and the environment yet people still live close to volcanoes and volcanically-active areas. Which of the following is not a reason for this?
    The heat underground can be used to generate geothermal energy, the extra nutrients in soil make them more fertile and tourism brings cash into the local economy
  10. Montserrat is a small island in the Caribbean and is a LEDC. A volcano on the south of the island started to give warning signs that an eruption was imminent. Two years later, the most intense eruptions occurred, however, there had been plenty of time to evacuate the population from the island. Which of the following would be classed as a long term response or result of the eruption?
    Since the volcano has calmed down again, the tourist industry has recovered

Author: Kev Woodward

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