'the Extent to Which Volcanic Processes Represent Hazards Depends on Where and When They Occur.' Discuss This Statement.

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'The extent to which volcanic processes represent hazards depends on where and when they occur.' Discuss this statement. Volcanic processes become a hazard when they impact upon the human and built environments, killing and injuring people, burying and collapsing buildings, destroying infrastructure and bringing agricultural activities to a halt. Volcanic hazards are influenced by several factors including location, time and frequency of eruptions, and the materials ejected. It is the viscosity of magma that largely determines the nature and power of an eruption and the resultant severity of the hazard. Basic magma has a high proportion of dissolved gases and low silica content, making it very fluid. On the other hand, acidic magma is very rich in silica and has a relatively lower temperature, making it very thick and slow moving. The more viscous the magma, the greater the potential for explosive eruptions and these represent the greatest potential hazards. Non-explosive eruptions tend to produce mostly lava flows, which do not represent a particularly serious hazard to people, however they will destroy farmland and buildings. Ash clouds are explosive eruptions that blast solid and molten rock (called tephra or pyroclastics) into the air with tremendous force. Ash clouds pose a considerable threat to aircraft, can cause buildings to collapse and can also cause death by asphyxiation. Pyroclastic flows are a potential product of volcanic activity; clouds of incandescent gas, ash and rocks with temperatures up to 800°C and speeds of over 200kph. They can cause widespread destruction, such as the 1980 eruption of Mt St Helens. Lahars are a secondary effect of a volcanic eruption and are cement-like mudflows consisting of volcanic ash and water. They often occur in the days following an eruption when people are at their most vulnerable and with the capacity to travel up
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