In what ways does volcanic activity vary in relation to the type of plate margin along which it occurs? (10 marks)
Volcanic eruptions can occur along both divergent and convergent plate boundaries; however the eruptions are different at the two different plate boundaries. Generally the eruptions are considered to be more violent at convergent plate boundaries as opposed to divergent boundaries.
Firstly the characteristics of the lava which is erupted varies between the two plate boundaries. At divergent plate margins the lava is typically classified as the pahoehoe variety which is described as ‘ropey’ lava due to the fact that it has a low viscosity (it’s low in silica- basaltic). Comparatively the lava at convergent plate boundaries is typically described as ‘blocky’ lava due to the fact that it has a higher viscosity (high in silica- acidic). The fact that it has a higher viscosity can actually make the lava more dangerous because it typically has a higher density and is more explosive. This is because gas bubbles cannot escape from within the magma and so they expand from the heat and build up pressure before they are released. At divergent plate boundaries however, gas can easily escape and so pressure is constantly released, leading to less violent eruptions. In the 1991 Mt Pinatubo volcanic disaster, 52 of the deaths were thought to be caused from lava flows.
Linked with this is the frequency of the eruptions. As pressure is being constantly released at divergent plate boundaries, there are regular eruptions. This is much unlike what occurs on convergent plate boundaries as…