Volcanic Arcs

Introduction
Volcanic arcs are volcanic mountain ranges that form in subduction zones. They form a belt of stratovolcanoes on the continental side of a subduction zone. Mount Washington, pictured below, is a stratovolcano in the Cascade Range.

Mount Washington, Photo by Myrna Martin
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Mount Washington, a volcanic mountain 
in the Cascade Range
, Myrna Martin

Stratovolcanoes
A volcanic chain of stratovolcanoes is created in subduction zone when a continental plate and an oceanic plate converge. The heavier oceanic plate bends and moves slowly into the mantle. The water soaked oceanic crust begins to melt as it descends beneath the ocean floor.

Molten rock above melting plates
The molten rock is hotter than surrounding rock in the lithosphere making it buoyant. Large plutons full of magma, molten rock, form above the melting plate. These plutons feed volcanoes on the continental side of the subduction zone.

Cascadia Subduction Zone
The Cascade Range is the result of the Juan de Fuca Plate subducting beneath he North American Plate. The Cascadia Subduction Zone that has formed between the two plates is approximately 700 miles long. The fault line runs from British Columbia in the north to the Mendocino Triangle in northern California.

Cascade Range volcanoes
Mount Rainier, Mount Saint Helens, Mount Hood, and Mount Shasta are four of the stratovolcanoes that make up the Cascade Range. The mountain that have formed parallel to the Cascadia Subduction Zone on the continental side of the subduction zone.

Aleutian Arc
The Aleutian Arc is located in a subduction zone with the Aleutian Trench as the boundary line between the North American Plate and the Pacific Plate.

Aleutian Islands
The Aleutian Islands formed on the north side of the Aleutian trench.The entire Aleutian Arc is 1500 miles long with over 100 volcanoes and extends from the Kamchatka Peninsula in Russia to Southeast Alaska.

More Pacific Ring of Fire Links

Ring of Fire Volcanoes Learn more about the Ring of Fire volcanoes that form in subduction zones.

Convergent Boundaries Learn how convergent boundaries have created the Ring of Fire in the Pacific Ocean.

Mt. Spurr Find out more about Mt. Spurr which is the tallest peak in the Aleutian Volcanic Arc.

Challenger Deep Learn more about the deepest point on the ocean floor that lies seven miles beneath the ocean's surface.


Composite Volcano Learn more about these towering mountains that form on the continents near subduction zones.

Volcanic Arcs Find out how and where volcanic arcs form on the Pacific Ring of Fire.

Pacific Ring of Fire Learn more about the Ring of Fire which is home to towering volcanoes and great earthquakes.

Kids Fun Science The links on our home page include information about volcanoes, science activities, plate tectonics, the rock cycle and much more.

Ring of Fire Science

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