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Compressional Plate Boundary of a Volcano

The Earth's surface is made up of massive pieces known as tectonic plates. These plates are actually floating on a bed of partially molten rock located deep beneath the ground; currents in the molten rock cause the plates to move and grind against one another. When this happens, molten rock, or "magma," can sometimes be forced to the surface at the boundary between two plates, at which point it is known as "lava." The result is a volcanic eruption.

Types of Plate Boundaries
- Volcanoes can be defined by the type of plate boundary on which they are located; these include tensional and compressional plate boundaries. A tensional plate boundary is one in which the two plates are being driven away from each other by convection currents; a compressional plate boundary is one in which an oceanic plate is being driven into a continental plate. The oceanic plate is pushed under and absorbed into the continental plate along the boundary. Either of these types of plate boundaries can produce volcanoes.
Compressional Plate Boundaries
- Oceanic plates are denser than continental plates, so when the two collide at a compressonal plate boundary the oceanic plate sinks into the Earth's mantle below the continental plate. The intense heat of the mantle melts the oceanic plate as it sinks downward, and the molten rock can shoot to the surface and explode out in a volcanic eruption of lava and ash. Under the enormous pressures of the two plates colliding, the continental plate is sometimes pushed up to form mountain ranges.
Formation of Volcanoes
- When a volcanic eruption sends magma to the surface in the form of lava, the molten lava flows out in a circle and then cools into a layer of volcanic rock. Every eruption adds a new layer of lava and a new layer of volcanic rock, which slowly build up into a mountain with a distinctive cone-like shape. The explosive power of a new eruption can destroy the entire top of the volcano, causing it to collapse and form a crater. Volcanic mountains can be found along compressional and tensional plate boundaries, both above ground and underwater.
The Ring of Fire
- Compressional plate boundaries are also known as "destructive" plate boundaries because of the destruction of the oceanic plate as it is driven down into the mantle. The Pacific Ring of Fire is a long chain of volcanic mountains along the edges of the Pacific Ocean. The Ring of Fire occurs along the destructive or compressional plate boundary formed by the collision of the Pacific Plate with the Eurasian Plate.

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