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 rock-forming 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 _____________, cone-shaped 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 ___________________.