Volcanic belts may be formed by multiple tectonic settings. They may be formed by
subduction zones, which is an area on
Earth where two
tectonic plates meet and move towards one another, with one sliding underneath the other and moving down into the
mantle, at rates typically measured in centimeters per year. An
oceanic plate ordinarily slides underneath a continental plate; this often creates an
orogenic zone with many volcanoes and
earthquakes. In a sense, subduction zones are the opposite of
divergent boundaries, areas where material rises up from the mantle and plates are moving apart. An example of a subduction-zone related volcanic belt is the
Okhotsk-Chukotka Volcanic Belt in northeastern
Eurasia, which is one of the largest subduction-zone related volcanic provinces in the world, stretching some and comprising about of volcanic and plutonic material. in
British Columbia,
Canada Volcanic belts may also be formed by
hotspots, which is a location on the Earth's surface that has experienced active
volcanism for a long period of time. These volcanic belts are called volcanic chains. Canadian
geologist John Tuzo Wilson came up with the idea in 1963 that volcanic chains like the
Hawaiian Islands result from the slow movement of a tectonic plate across a "fixed" hot spot deep beneath the surface of the planet, thought to be caused by a narrow stream of
hot mantle convecting up from the mantle-core boundary called a
mantle plume. But more recently some geologists, such as
Gillian Foulger view upper-mantle convection as a cause. This in turn has re-raised the antipodal pair impact hypothesis, the idea that pairs of opposite hot spots may result from the impact of a large meteor. Geologists have identified some 40-50 such hotspots around the globe, with
Hawaii,
Réunion,
Yellowstone,
Galápagos, and
Iceland overlying the most currently active. An example of a hotspot volcanic belt is the
Anahim Volcanic Belt in
British Columbia,
Canada, which was formed as a result of the
North American Plate sliding westward over the
Anahim hotspot. Most hotspot volcanoes are
basaltic because they erupt through oceanic
lithosphere (e.g., Hawaii, Tahiti). As a result, they are less explosive than subduction zone volcanoes, which have high water contents. Where hotspots occur under continental crust, basaltic magma is trapped in the less dense continental crust, which is heated and melts to form rhyolites. These rhyolites can be quite hot and form violent eruptions, despite their low water content. For example, the
Yellowstone Caldera was formed by some of the most powerful volcanic explosions in geologic history. ==Examples==