volcano

A volcano is an opening in Earth’s surface
through which molten rock, hot gases, and rocks are
ejected. Volcanoes create new land and islands. They
can also produce economically important mineral
deposits, fertile soils, and beautiful landscapes.
However, volcanoes can also destroy lives and prop-
erty, and therefore constitute significant geologic haz-
ards in many parts of the world.
With regard to the hazard that they present, vol-
canoes can be classified as active, dormant, or extinct.
Active volcanoes are those that have erupted within
recorded history. Dormant volcanoes are those that
have not erupted during recorded history but may
erupt again, whereas extinct volcanoes are those for
which there is little or no chance of future eruptions.
Where volcanoes develop
Most of the volcanoes on Earth are located along
the boundaries between lithospheric plates, which can
be convergent (subduction zones) or divergent (mid
ocean ridges). The chain of volcanoes along the Pacific
Rim, often referred to as the Ring of Fire, is an exam-
ple of subduction zone volcanism. Iceland, in contrast,
is a volcanic island straddling the Mid-Atlantic Ridge
(a divergent plate boundary). Although they are not as
numerous as plate boundary volcanoes, intraplate vol-
canoes can occur where plates pass over mantle hot
spots or along continental rift zones where plates are
being pulled apart. The Hawaiian Islands, for exam-
ple, were formed as the Pacific Plate slowly passed
over a magma-generating hot spot within the mantle.
Oceanic ridges are chains of volcanoes located
along the boundary between two diverging oceanic
plates. New oceanic crust is formed along the ridges
as two oceanic plates move apart. Where the rate of
plate formation is rapid, older crust is quickly pushed
out of the way and only small volcanic vents form.
Where the spreading rate is slower, volcanic eruptions
may form large volcanoes.