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Volcanoes
Volcanoes and Plate Tectonics
• A _____________ is a weak spot in the
crust where molten material, or
_______, comes to the surface.
• ________ is a molten mixture of rockforming substances, gases, and water
from the mantle.
• When magma reaches the surface, it is
called _________.
• Lava released during __________
activity builds up Earth’s surface.
Volcanoes and Plate Tectonics
• There are about ______ active volcanoes on
land.
Volcanoes and Plate Tectonics
• Volcanoes occur in ________ that extend
across continents and oceans
• One major volcanic belt is the _________
formed by the many volcanoes that rim the
____________ Ocean.
• Volcanic belts form along the
_____________ of Earth’s plates.
• At plate boundaries, huge pieces of the crust
_________ (pull apart) or _________ (push
together).
Volcanoes and Plate Tectonics
• Most volcanoes form along
____________ plate boundaries such as
______________ and along converging
plate boundaries where ___________
takes place.
• Along the _________, lava pours out of
cracks in the ocean floor, gradually
building new mountains.
• Volcanoes also form along diverging plate
boundaries on _________.
Volcanoes and Plate Tectonics
• Many volcanoes form near
________________ plate boundaries
where ________________ plates return
to the _____________.
• Volcanoes may form where _________
oceanic plates ____________ or where
an oceanic plate collides with a
___________________ plate.
Volcanoes and Plate Tectonics
Volcanoes and Plate Tectonics
• Many volcanoes occur near boundaries where two
________________ plates collide.
• Through _____________, the older, denser plate
_________ beneath a ______________ into the
mantle.
• Some of the rock above the subducting plate
___________ and forms magma.
• Because the magma is less _________ than the
surrounding rock, it rises toward the surface.
• Eventually, the magma breaks through the ocean
floor, creating _________________.
Volcanoes and Plate Tectonics
• The resulting volcanoes create a string of
islands called an ______________. The
curve of an island arc ____________ the
curve of its deep-ocean trench.
• Major island arcs include:
– _______________________________________
_______________________________________
_______________________________________
_______________________________________
Volcanoes and Plate Tectonics
• Volcanoes also occur where an oceanic
plate is subducted beneath a
continental plate.
• Collisions of this type produced the
volcanoes of the ____________
Mountains in South America and the
_____________ of the Pacific
Northwest in the United States
Volcanoes and Plate Tectonics
• Some volcanoes result from
______________ in Earth’s mantle.
• A hot spot is an ___________ where
material from deep within the mantle
______________________, forming
magma.
• A _____________ forms above a hot
spot when magma erupts through the
crust and reaches the surface.
Volcanoes and Plate Tectonics
Volcanoes and Plate Tectonics
• A hot spot in the ______________ can
gradually form a series of volcanic
mountains.
• The _______________ Islands formed
one by one over millions of years as the
_____________ plate drifted over a hot
spot.
• Hot spots can also form under the
_______________.
Volcanic Eruptions
• Lava begins as _________, which usually
forms in the __________________.
• The materials of the asthenosphere are
under great ____________.
• Liquid magma is less _________ than the
solid material around it.
• As magma rises, it sometimes becomes
_____________ beneath layers of rock.
• But if an opening in _____________ rock
allows the magma to reach the surface, a
volcano forms.
Volcanic Eruptions
Volcanic Eruptions
• A volcano is more than a large,
______________________
• All volcanoes have a ___________ of
magma beneath the surface and one or
more _____________ through which
the magma forces its way.
• Magma collects in a pocket called a
________________ beneath a volcano.
Volcanic Eruptions
• The magma moves upward through a
__________, a long tube in the ground that
connects the magma chamber to the Earth’s
surface.
• Molten rock and gas leave the volcano
through an opening called a ___________.
• There is _________ central vent at the top of
a volcano. However, many volcanoes also
have _________ vents that open on the
volcano’s _____________.
Volcanic Eruptions
• A _____________ is the area covered
by lava as it __________ out of a vent.
• A _____________ is a bowl-shaped
area that may form at the top of a
volcano around the central vent.
• The _____________ of a volcano is
similar to the soda water bubbling out of
a warm bottle of soda pop.
Volcanic Eruptions
• As magma rises toward the surface, the
pressure of the surrounding rock on the
magma _____________.
• When a volcano erupts, the _________
of the expanding gases pushes magma
from the ____________________
through the __________ until it
_________ or explodes out of the vent.
• Once magma escapes from the volcano
and becomes _________, the
remaining ___________ bubble out.
Volcanic Eruptions
• Geologist classify volcanic eruptions as
_____________________.
• The ________________ properties of
its magma determine how a volcano
erupts.
• Eruptions depends on the magma’s
_____________ and _____________
content.
Volcanic Eruptions
• _________________ is the ____________ of
a liquid to flow.
• The ____________ the viscosity of a liquid,
the _____________ it flows.
• The viscosity of magma depends on its
______________________________.
• The compound ___________ is made up of
particles of ___________ and
________________.
Volcanic Eruptions
• A volcano erupts _________ if its
magma is ________ in silica.
• Low-silica magma has low __________
and flows ___________.
• Lava with low viscosity _________
quietly from the vent and can flow for
many __________________.
• The _______________ Islands were
formed from ___________ eruptions.
Volcanic Eruptions
• A volcano erupts _____________ if its
magma is _________ in _________.
• ___________ magma has _________
viscosity, making it _______________.
• The high-viscosity magma does not always
flow out of the ___________.
• Instead, it builds up in the volcano’s
_________, plugging it like a ______ in a
bottle.
• The trapped gases build up pressure until
they ____________.
Volcanic Eruptions
• An ______________ eruption breaks
lava into _____________ that quickly
cool and harden into pieces of different
sizes.
• The smallest pieces are
_____________ – fine, rocky particles
as small as a speck of dust.
• Pebble-sized particles are called
_____________.
Volcanic Eruptions
• Larger pieces, called ____________, may range
from the size of a baseball to the size of a car.
• A ____________________ occurs when an
explosive eruption hurls out a mixture of hot gases,
ash, cinders, and bombs.
• _______________ forms when lava cools very
___________, giving it a smooth, ____________
surface like glass.
• _____________ forms when gas bubbles are
trapped in fast-cooling lava, leaving spaces in the
rock.
Volcanic Eruptions
• Both types of eruption can cause
damage far from the ___________ rim.
• During a ____________ eruption, lava
flows from __________, setting fire to,
and then burying, everything in its path.
• During an ___________ eruption, a
volcano can __________ out hot clouds
of deadly gases as well as ash,
______________, and bombs.
Volcanic Eruptions
• ______________ can bury entire towns.
If it becomes wet, the heavy ash can
cause roofs to collapse.
• If a jet plant sucks ash into its engine,
the engine may stall.
• Eruptions can cause _____________
and ________________ of mud, melted
snow, and rock.
Kinds of Volcanic Eruptions
• Within the last ______ years, major volcanic
eruptions have greatly affected the land and
people around them.
Volcanic Eruptions
• The activity of a volcano may last from
______ than a decade to more than
_____ million years.
• Most long-lived volcanoes, however, do
not erupt _______________.
• Geologists often use the terms
___________, ___________, or
_________ to describe a volcano’s
stage of activity.
Volcanic Eruptions
• An active, or ________, volcano is one
that is erupting or has shown signs that
it may erupt in the near future.
• A dormant, or _____________, volcano
is like a sleeping bear.
• Scientists expect a _______________
volcano to awaken in the future and
become ____________.
• An ___________, or dead, volcano is
unlikely to erupt again.
Volcanic Eruptions
• The time between volcanic eruptions
may span __________ to many
________________ of years.
• People living near a ___________
volcano may be unaware of the danger.
• But a dormant volcano can become
___________ at any time.
Volcanic Eruptions
• Geologists have been more
______________ in predicting volcanic
eruptions than in predicting earthquakes.
• Geologists use _________________ to
detect changes in and around a volcano.
• Geologists use ________________ and
other instruments to detect slight surface
changes in _____________ and _______
caused by magma moving underground.
Volcanic Landforms
• Volcanoes have created some of
Earth’s most ________________
landforms.
• ____________ activity on and beneath
the surface has built up Earth’s land
areas.
• Volcanic activity also formed the rock of
the ______________ floor.
Volcanic Landforms
• Volcanic eruptions create
____________ made of lava, ash, and
other materials.
• These landforms include:
– _____________________
– _____________________
– _____________________
– _____________________
Volcanic Landforms
• Shield Volcanoes
– At some places on __________ surface,
_________ layers of lava pours out of a
vent and harden on top of previous layers.
– Such lava flows gradually build a wide,
gently ___________________.
– Shield volcanoes rising from a hot spot on
the ocean floor created the
___________________.
Volcanic Landforms
• _______________________
– If a volcano’s lava has _________
viscosity, it may produce
__________, __________, and
______________.
– These materials build up around the
vent in a _____________, coneshaped hill or small mountain called a
__________________.
Volcanic Landforms
• _________________ Volcanoes
– Sometimes, lava flows
_____________ with explosive
eruptions of ash, cinder, and bombs.
– __________, cone-shaped mountains
in which layers of lava alternate with
layers of ash.
– Examples are Mount Fuji in
___________ and Mount St. Helens
in __________________.
Volcanic Landforms
• Lava ________________
– Instead of forming mountains, some eruptions of
lava from high, level areas called
_______________.
– First, lava flows out of several long
_______________ in an area.
– The thin, runny lava travels far before cooling
and _________________.
– Again and again, floods of lava flow on top of
earlier __________________.
– Example is the _______________ Plateau,
which covers parts of the states of Washington,
Oregon, and Idaho.
Volcanic Landforms
• __________________
– ______________________________
______________________________
– The hole is filled with pieces of the
volcano that have fallen
___________, as well as some lava
and ash.
How a Caldera Forms
How a Caldera Forms
How a Caldera Forms
Volcanic Landforms
• ____________ From Lava and Ash
– The lava, ash, and cinders that erupt from
a volcano are initially ________.
– Over time, however, the _________
surface of the lava breaks down to form
soil.
– When ______________ breaks down, it
releases _______________,
_______________, and other substances
that plants need.
– Some volcanic soils are among the
_____________ soils in the world.
Volcanic Landforms
• Landforms From _____________
– Features formed by magma includes;
• ______________________
• ______________________
• ______________________
• ______________________
• ______________________
Volcanic Landforms
• Volcanic Necks
– ______________________________
______________________________
– Forms when ____________ hardens
in a volcano’s ___________.
– The ______________ rock around
the pipe wears away, exposing the
hard rock of the volcanic neck.
Volcanic Landforms
• Dikes and Sills
– Magma that forces itself across rock
layers hardens into a ___________.
– When magma squeezes
______________ layers of rock, it
forms a sill.
Volcanic Landforms
Volcanic Landforms
• Batholiths
– ______________
______________
______________
______________.
– A mass of rock
formed when a
_________ body
of magma cools
inside the crust.
Volcanic Landforms
• ______________ Mountains
– Other, smaller bodies of hardened
magma can create ________
mountains.
– Forms when uplift pushes a
_____________ or smaller body of
hardened magma toward the surface.
– The hardened magma forces the
layers of rock to bend ___________
into a dorm shape.
Volcanic Landforms
• Geothermal Activity
– The word ______________ comes
from the Greek ________ meaning
“___________” and __________
meaning “_________.”
– In geothermal activity, magma a few
kilometers beneath Earth’s surface
heats _________________ water.
Volcanic Landforms
• A ______________ of geothermal
features occur in volcanic areas.
• _______________ and ____________
are types of __________________
activity that are often found in areas of
present or past volcanic activity.
Volcanic Landforms
• Hot Springs
– __________________________________
__________________________________
______________________
– The ______ water rises to the surface and
collects in a __________ pool.
– Water from hot springs may contain
dissolved _________ and other
_____________ from deep within Earth.
Volcanic Landforms
• _______________
– Sometimes, rising hot water and steam
become trapped underground in a narrow
______________.
– _________________ builds until the
mixture suddenly sprays above the
surface.
– A __________________ of water and
steam that erupts from the ground.
Volcanic Landforms
• Geothermal Energy
– ______________________________
______________________________
– Can also be used as a source of
_________________.
– Provides some electrical power in
_______________ and
___________________.