Volcano Types |
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Some volcanoes crown island areas lying near the continents,
and others form chains of islands in the deep ocean basins. Volcanoes tend
to cluster along narrow mountainous belts where folding and fracturing
of the rocks provide channelways to the surface for the escape of the magma.
Significantly, major earthquakes also occur along these belts, indicating
that volcanism and seismic activity are often closely related, responding
to the same dynamic Earth forces. -- Excerpt from: Tilling, 1985,
Volcanoes: USGS General Interest Publication
In a typical "island-arc" environment, volcanoes lie along the
crest of an arcuate, crustal ridge bounded on its convex side by a deep
oceanic trench. The granite or granitelike layer of the continental crust
extends beneath the ridge to the vicinity of the trench. Basaltic magmas,
generated in the mantle beneath the ridge, rise along fractures through
the granitic layer. These magmas commonly will be modified or changed in
composition during passage through the granitic layer and erupt on the
surface to form volcanoes built largely of nonbasaltic rocks. -- Excerpt
from: Tilling, 1985, Volcanoes: USGS General Interest Publication
In a typical "oceanic" environment, volcanoes are alined along
the crest of a broad ridge that marks an active fracture system in the
oceanic crust. Basaltic magmas, generated in the upper mantle beneath the
ridge, rise along fractures through the basaltic layer. Because the granitic
crustal layer is absent, the magmas are not appreciably modified or changed
in composition and they erupt on the surface to form basaltic volcanoes.
--
Excerpt from: Tilling, 1985, Volcanoes: USGS General Interest Publication
In the typical "continental" environment, volcanoes are located in unstable, mountainous belts that have thick roots of granite or granitelike rock. Magmas, generated near the base of the mountain root, rise slowly or intermittently along fractures in the crust. During passage through the granite layer, magmas are commonly modified or changed in composition and erupt on the surface to form volcanoes constructed of nonbasaltic rocks. -- Excerpt from: Tilling, 1985, Volcanoes: USGS General Interest Publication Cascade Range: In the Pacific Northwest, the Juan de Fuca Plate plunges beneath the
North American Plate. As the denser plate of oceanic crust is forced deep
into the Earth's interior beneath the continental plate, a process known
as subduction, it encounters high temperatures and pressures that partially
melt solid rock. Some of this newly formed magma rises toward the Earth's
surface to erupt, forming a chain of volcanoes (the Cascade Range) above
the subduction zone. -- Excerpt from: Brantley, 1994, Volcanoes of the
United States: USGS General Interest Publication
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