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3.1.5.3 Volcanic hazards
Volcanic Hazards
Most volcanic activity is associated with plate tectonic processes and is mainly located along plate margins. Volcanic activity is therefore found at:
Volcanic eruptions vary in both scale, frequency and magnitude. There are two predominant types of volcanic eruptions: Effusive eruptions – magma rises through the surface and flows out of the volcano as a viscous liquid called lava. Explosive eruptions – magma is torn apart as it rises and reaches the surface in pieces known as pyroclasts. This is measured on the Volcanic Explosivity Index (VEI), a logarithmic scale from 0-8, quiet eruptions score 1 and increase in number as the volcano becomes more explosive. A magnitude 7 has only been experienced in Tamboro, Indonesia (1815), so are relatively uncommon. To measure frequency, the number of previous eruptions must be recorded and analysed. The Impacts of Volcanic Activity The impacts can be classified into primary and secondary effects. Primary effects include:
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