The Ring of Fire
The Ring of Fire is an area around the Pacific Ocean that is volcanically and seismically active. Subduction zones have formed around the Pacific Ocean as continental plates and younger oceanic plates converge with the Pacific Plate. The dense Pacific Plate is subducting beneath the lighter plates and in the process is shrinking in size.
Location 75% active and dormant volcanoes
More than 75% of the world’s active and dormant volcanoes are located along the Ring of Fire in the Pacific Ocean. Ten percent of these volcanoes are located in the United States. The northwestern area of the Ring of Fire includes the Pacific Northwest, the coast of British Columbia and the coastline of Alaska including the Aleutian Islands.
Prior to the Theory of Plate Tectonics
Scientists were already studying the ring of volcanoes and the accompanying earthquakes before the theory of plate tectonics explained many of the processes that create volcanic mountain ranges. We now know that the Ring of Fire is located along a line of deep trenches that separates the Pacific Plate and other tectonic plates.
Overriding the Pacific Plate
The plates surrounding the Pacific Plate are both continental plates and oceanic plates. Continental plates and younger sea plates always override the Pacific Plate creating subduction zones.
Activity in North Pacific Ocean
The Aleutian Islands were created as the Pacific Plate subducts beneath the North American Plate. The Cascade Range in the Pacific Northwest is an arc of volcanoes that formed as the Juan de Fuca Plate subducts beneath the North American Plate.
Tracking plate movement on the Ring of Fire
Scientists believe that in the future the Ring of Fire will continue to be volcanically and seismically active. Plate movement, direction, and speed of plates are being tracked by global positioning satellites using lasers.
Tracking plate movement with GPS
Scientists use global positioning satellites to determine the rate that the different plates move. The average plate movement is about the speed your fingernails grow. In the Pacific Ocean the Cocos Plate and the Nazca Plates are moving about 10 cm/yr. These are the two fastest moving plates in the Pacific Ocean.
Where Ocean Trenches Form
Ocean trenches form between two crustal plates in subduction zones. Volcanoes always form on the landward side of trenches. Trenches develop as the subducting plate is bent downward and forced beneath the other plate into the crust and upper mantle.
Formation of island arcs
The volcanoes in island arcs are clustered along narrow mountainous belts where the folding and fracturing of the crust provide channels for the magma to move to the surface and erupt at a vent on the ocean floor.
Cascadia Subduction Zone (CSZ)
The Cascadia Subduction Zone (CSZ) stretches from Cape Mendocino in California along the Pacific Northwest coastline to Northern Vancouver Island in British Columbia. The fault is 1000 km long separating the Juan de Fuca and the North American Plates.
Earthquakes in the past
Recent studies of the coastline in the Pacific Northwest have found areas which have been repeatedly inundated by tsunamis due to subduction zone earthquakes. The last great earthquake along the Cascadia Subduction Zone occurred on January 26, 1700.
The andesite line is an important geologic distinction. It separates the mafic basalt rocks of the Central Pacific Basin from the volcanoes on the continental side of the line that contain felsic rocks.
Volcanoes on the continental side of a subduction zone
The volcanoes that form on the continental side of the andesite line are typically composed of viscous andesite and dacite lavas. Volcanoes usually alternate between tephra eruptions and lava flows. Plinian eruptions are common on these volcanoes.
Thick lava flows of viscous lavas
Viscous lavas flow slowly down a slope forming thick lava flows on the flanks of stratovolcanoes. The lavas erupted by stratovolcanoes can be a combination of andesite, dacite and rhyolite. Because stratovolcanoes often erupt a combination of lavas they are often referred to as composite volcanoes.
Check out Myrna Martin's award winning textbooks, e-books, videos and rock sets. The Kids Fun Science Bookstore covers a wide range of earth science topics. Click here to browse.