11 terms

Formation of Volcanos-Leaving Cert Geography

Plate Tectonic Theory
Describes how earths lithosphere is split into large slabs called plates. Plates move because the earths core generates heat which causes slow moving convection currents in the upper mantle.
Convection currents drag plates with them causing different plate boundaries that can form volcanoes in three ways. Constructive. Destructive. Hotspots.
Constructive Plate Boundaries
Also divergent, where plates separate, and lava rises up to earth. Most constructive plate boundaries are in the ocean floor.
The separation of plates forms a long split in the crust called a Rift Valley, magma from the mantle then rises to the surface to fill the gaps and cools.
This creates a chain of volcanic mountains called mid ocean ridges. Example, Mount Helga, Iceland. Eurasian and North American.
Destructive Plate Boundaries
Plates collide due to convection currents dragging the plates to collide, then subduction occurs.
Subduction is where plates collide, the heavier sinks which is usually the oceanic, and the crust is melted in the mantle.
The melted oceanic crust is less dense than the mantle and the recycled material rises through the cracks in the crust until through a vent it reaches the surface, and forms volcanic island arcs. Example is Mount Pinatubo, Philippianes and Eurasian.
Where convection currents of earths mantle results in magma rising until it reaches the crust. The great heat of this magma causes the crust to melt and form pipes, which forms vents of a volcano.
Tectonics makes plates move but the plume of magma stays where it is, so the volcano becomes dormant.
Example currently over hotspot is Yellowstone Caldera USA.