Ring of Fire Facts
Pacific Ocean Volcanoes & Earthquakes
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.
Studying the ring of fire volcanoes
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
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.
Ocean Trenches
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
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.
Andesite LIne
Andesite line
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.
More Ring of Fire Links
Aleutian Trench in North Pacific Ocean
Cascadia Subduction Zone Great Quakes
What are Convergent Boundaries?
Redoubt is a Dangerous Volcano
Pacific Ring of Fire Volcanoes
Subduction Zones in the Pacific Ocean
Tectonic Plate Movement on Earth
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