Download 18.1-notes-volcanoes

18.1 Volcanoes
Volcanism
 All the processes associated with the
discharge of magma, hot fluids, and gases.
 Most form at plate boundaries
 Majority at convergent and divergent
boundaries.
 Only about 5% of magma erupts far from
plate boundaries.
Convergent volcanism –
 Most volcanoes on land are a result of
oceanic-continental subduction.
 These volcanoes are characterized by
explosive eruptions.
Divergent volcanoes –
 In the ocean at ocean ridges, the magma
rises and fills the gap.
 The lava takes the form of giant pillows
and is called pillow lava.
 Volcanism here is non-explosive, with
giant flows of large amounts of lava.
 About 2/3 of Earth’s volcanism occurs
underwater at divergent boundaries at
ocean ridges.
Hot Spots –
 Volcanoes that form far from plate boundaries over hot spots.
 Hot spots are unusually hot
regions of Earth’s mantle where
high-temperature plumes of
magma rise to the surface.
 The Hawaiian Islands are over a
plume of magma.
 Rising magma melted through the
crust and formed volcanoes.
 The hot spot formed by the
magma plume remained
stationary while the Pacific Plate
moved slowly northwest.
 Over time, the hot spot left a trail
of volcanic islands on the Floor of the Pacific Ocean.
 The oldest volcanoes in the Hawaiian chain are no longer active because they are not longer over
the hot spot.
Anatomy of a Volcano –
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As lava cools and solidifies, it will begin to layer and form a volcano.
Conduit- tube-like structure that lava travels to the surface through
Vent-opening that lava comes out of
Crater- a bowl-shaped depression around the vent
Caldera- large depression that is formed after the magma chamber
empties completely of magma. The summit or side of the volcano will
then collapse into the empty chamber, leaving an expansive, circular
depression.
conduit
Types of volcanoes
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Volcanoes are categorized by two things:
 the type of material that forms the volcano
 the type of eruption that occur.
There are three main types of volcanoes.
Shield volcanoes
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broad , gently sloping sides
nearly circular base
form when layers of lava accumulate during quiet non-explosive
eruptions
largest type of volcano
Cinder cone volcano
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formed when small pieces of material are ejected, fall back to Earth and
pile up around the vent
steep sides
generally small, most less than 500m (1,640ft) high
form on or very near larger volcanoes
explosive eruptions
Composite volcano
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formed of layers of hardened chunks of lava from violent eruptions
alternating with layers of lava that oozed downslope before solidifying
generally cone-shaped with concave slopes
larger than cinder cones
very explosive eruptions,
very dangerous to humans and the environment
tall, majestic mountains