Volcanic Activity

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Plate tectonics and Volcanoes Activity

Explain how the study of plate tectonics has helped us to understand the global distribution of volcanoes?

Two of the forces at work along the crustal plates boundaries are Collision and Separation. Plates tectonics theory describes how the earth crust is split into large section called plates. The plates move because heat from the earth's core causes the upper mantle to flow in huge slow moving convection currents. These convection currents drag plates along with them causing them to collide and separate, forming destructive and constructive plates boundaries.

Volcanoes occurs where tectonic plates collide and separate. Volcanoes also occurs where a fountain or plume of hot mantle material rises to the surface in the middle of a plate. These are called hotspots. These locations are linked to the operation of tectonics cycle. The tectonic cycle is the constant destruction and generation of crust.

1. Volcanoes at Constructive Plate boundaries , e.g. Mount Hekla Iceland

Most constructive boundaries are found under the ocean. At constructive plate boundaries, mantle currents pull the earth's plate apart, e.g. the Eurasian Plate is pulled from the North American Plate. The separation of plates forms a long split in the crust called rift valley. Magma rises from the mantle to fill the gap creates by the rift. The magma reaches the surface and cools, forming a long ridge of volcanic mountains called mid-ocean ridge. Sometimes volcanic islands are formed, e.g. Iceland is part of Mid-Atlantic Ridge.

2.Volcanoes at Destructive Plate Boundaries, e.g. Mount Fuji Japan

Volcanoes occur where two oceanic plates collide, e.g. the Pacific plate collides with the Philippine plate. Here one plate sinks beneath the other and is absorbed back into the mantle. This process is called subduction. The melted oceanic crust is less dense then mantle and recycled material rises through cracks in the crust until it reaches the surface through a vent to form volcanic islands arc. These curved chains of volcanic islands which mark the subduction zone. The magma at these destructive plate boundaries is very acidic and tends to form steep-sided volcanic cones,eg. Mountain Pinatubo in the Philippine Islands

3. Volcanoes at hotspot, e.g. the Hawaiian Island of the Pacific

Sometimes magma from the mantle is able to reach the surface of the earth in the middle of a plate. This location is called hotspot. Hotspot occur because a large fountain or plume of magma rises to the surface and forces its way through the crust to form volcanoes.

Mantle plumes generally contain very basic magma(less than 55% silica) which is not very gaseous and can flow for many km. The volcanic mountain that result

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