The Pacific Ring of Fire is a zone of frequent earthquakes and volcanic eruptions encircling the basin of the Pacific Ocean. In a 40,000 km horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, island arcs, and volcanic mountain ranges and/or plate movements. It is sometimes called the circum-Pacific belt or the circum-Pacific seismic belt.
The Ring of Fire is a direct consequence of plate tectonics and the movement and collisions of crustal plates. The eastern section of the ring is the result of the Nazca Plate and the Cocos Plate being subducted beneath the westward moving South American Plate. A portion of the Pacific Plate along with the small Juan de Fuca Plate are being subducted beneath the North American Plate. Along the northern portion the northwestward moving Pacific plate is being subducted beneath the Aleutian Islands arc. Further west the Pacific plate is being subducted along the Kamchatka—Kurile Islands arcs on south past Japan. The southern portion is more complex with a number of smaller tectonic plates in collision with the Pacific plate from the Mariana Islands, the Philippines, Bougainville, Tonga, and New Zealand. Indonesia lies between the Ring of Fire along the northeastern islands adjacent to and including New Guinea and the Alpide belt along the south and west from Sumatra, Java, Bali, Flores, and Timor. The famous and very active San Andreas Fault zone of California is a transform fault which offsets a portion of the East Pacific Rise under southwestern United States and Mexico. The motion of the fault generates numerous small earthquakes, at multiple times a day, most of which are too small to be felt.
In the past 25 years, scientists developed a theory called plate tectonics explaining the locations of volcanoes and other large-scale geologic features.
According to tectonic theory, the surface of the Earth is made up of a patchwork of massive rigid plates, about 80km thick, which float in slow motion on top of the Earth's hot, pliable interior. The plates change size and position over time, moving at speeds of between 1cm and 10cm every year - about the speed at which fingernails grow. New sea bed is constantly being created in the middles of the oceans - flowing out as hot lava, and rapidly cooling on contact with cold deep sea water.
To make room for the continual addition of new ocean crust, all the earth's plates move. And as they move, intense geologic activity occurs at the plate edges. At the edges, one of three things may occur. The plates can be moving away from each other, leaving space for new ocean floor. Some plates are moving towards each other, causing one to submerge beneath the other. Other boundaries slide past each other without much disturbance.
