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 ___________________.