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Describe the Three Types of Plate Boundaries Where Volcanic Eruption Can Occur

Volcanoes don̵7;t happen just anywhere. The earth's surface is a crust, broken into large rock slabs called tectonic plates. The plates are in slow but constant motion, and volcanoes usually happen at boundaries between plates. There are about eight major tectonic plates and many minor ones, with millions of people living near their boundaries. Plate movement creates three main plate-boundary types: divergent, convergent and transform. Boundary type largely determines the type of associated volcanic activity.

Divergent Boundaries
- A look at ocean floor topography reveals large volcanic ridges in the middle of the ocean basins. These continuous features encircle the earth like the seams of a baseball, and mark areas of crustal divergence. New crust is formed at these ridges as hot mantle material rises toward the surface, melting rock into magma and forcing plates apart. The molten material continuously adds new crust on both sides of the ridge as the plates move apart. The rocks produced are rich in metals such as iron, and poor in silica. Mid-oceanic ridges are the largest volcanic edifices in the world.
  Some rifting occurs in continental crust as well, marking the start of future ocean basins.
Convergent Boundaries
- Where plates converge, something must give. One oceanic plate will dive beneath the other plate, whether it is also oceanic or a thicker continental plate. A chain of volcanoes forms on the overriding plate as the subducted plate is consumed by the mantle. The Cascade volcanoes of western North America are examples of volcanoes produced when an oceanic plate dives under a continental plate. The resulting magma is rich in silica and poor in metals such as iron. The Mariana Islands are an example of volcanoes formed where one oceanic plate overrides another. Where two thick continental plates converge, neither plate can override the other. The result is a mountain-building pileup. Continental rock that partially melts at depth due to compression and heat is too viscous to rise to the surface, so no volcanism occurs.
Leaky Transforms
- At transform boundaries, plates are not created or destroyed by divergence or convergence. Instead they move past each other in a slow, grinding sideswipe. Typically, transforms are not associated with volcanism; when they are, they are called ̶0;leaky̶1; transforms. Mantle material wells up under a transform fault and creates basaltic magma, which makes its way to the surface.
Other Causes of Volcanism
- Volcanism can sometimes occur away from plate boundaries. This volcanism occurs when a mantle hot spot forms beneath a plate, and this type of volcanism is called ̶0;hotspot̶1; volcanism. The Hawaiian Islands and Yellowstone both are examples of hotspot volcanism. The islands have formed in succession from volcanism as the oceanic plate has moved over a hot spot. If a hot spot forms under a continent, a super volcano like Yellowstone can form, with eruptions so strong it can cause climate change.

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