Ring of Fire

The Power under the Ring of Fire

Plate tectonics describes the Earth's crust as very large and thick plates (an average of 50 miles) floating very slowly (one to seven inches annually) on the underlying molten magma. The entire Pacific Ocean is over one large plate that is being pushed from the southeast to the northwest, causing great stresses all around the Pacific as it contacts the continents at plate boundaries. The stresses result in geologic activities like earthquakes, mountain formation, and volcanoes. Plates slide past each other on transform boundaries; move away from each other on divergent boundaries, creating rifts that allow magma to come to the surface and cool; and push against each other at convergent boundaries, causing one plate to slide under the other (subduction). Plate edges that slide under other plates are melted and recycled back into the magma, and water-saturated crust releases copious amounts of steam into the crust above it, creating the potential for explosive eruptions such as the one that occurred on Mount St. Helens in Washington State in 1980.

The Sarychev Volcano in the Kuril Islands, northeast of Japan, in an early stage of eruption on June 12, 2009

On a smaller scale, and fueled mainly by convergent and divergent plate boundaries, crustal faults provide the channel that allows magma to come to the surface—where it is then called lava—providing fire to the ring. Faults that slip by each other are called strike-slip, faults that pull away from each other are called normal, and faults that push into each other are called thrust faults.

Magma below the crust flows in relatively stable directions, much like the flow of ocean currents. Upflows in the magma provide for another type of geologic activity—the hotspot—where magmatic upflow pushes through to the surface, creating volcanoes and lava flows. The Hawaiian Islands were created by a hotspot, and island formation continues today. As the Pacific plate floats northwestward at 3.5 inches per year over the magma upflow, the hotspot appears to move to create more islands, and is currently under Hawaii, having created all the islands to the northwest over thousands of years.

In the Pacific Northwest, the Juan de Fuca plate, as well as part of the Pacific plate, plunge beneath the North American plate in a subduction zone. The stresses create the mountains and volcanoes of the Cascade Mountain range. Other subduction zones include the northwestward-moving [Page 607]Pacific plate plunging beneath the volcanic arc of the Aleutian Islands, the Pacific plate plunging beneath the Kamchatka Peninsula, and the Pacific diving beneath the Eurasian plate. That subduction is responsible for all of the Japanese islands, as well as picturesque volcanoes like Mt. Fuji.

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