Inside EarthChapter 3: Volcanoes

Section 3-1Volcanoes and Plate Tectonics

Sec 3-1Volcano—a weak spot in the crust where magma has

come to the surfaceMagma—the molten mixture of rock-forming

substances, gases, and water from the mantleLava—liquid magma that reaches the surface; also

the rock formed when liquid lava hardensRing of Fire—a major belt of volcanoes that rims the

Pacific OceanIsland arc—a string of islands formed by the

volcanoes along a deep ocean trenchHot spot—an area where magma from deep within

the mantle melts through the crust above it

Sec 3-1: Volcanoes and Plate TectonicsWhat is a Volcano?Volcano

MagmaLava

A weak spot in the crust where

molten material, or

magma, comes to

the surface.

A molten mixture of

rock-forming

substances, gases, and water from the mantle.

What magma

that reaches the surface is

called.Forms solid rock.Builds up Earth’s surface.

Forms new islands and adds

new rock.

3-1…cont

Location of Volcanoes

About 600 active

volcanoes on land

Along diverging plate

boundaries (mid-ocean ridge), or in subduction

zones

Ring of Fire

Major volcanic belt that is formed by the many

volcanoes that rim the Pacific Ocean

Volcanic belts form along the boundaries of Earth’s

plates.Some volcanoes form at “hot spots” away from

boundaries.

3-1…cont

Volcanoes at Diverging

Plate Boundaries

Form along the mid-ocean ridge and in a few places (Iceland and the Azores Islands in the Atlantic

Ocean). Volcanoes rise above the surface.

3-1…cont

Volcanoes at

Converging Boundaries

Happens when oceanic and

continental plates collide and form

deep-ocean trenches. Crust sinks, forms

magma and erupts as lava to form volcanoes.

Island arc

String of islands caused by volcanoes. Curve of an island arc echoes the curve of

its deep-ocean trench.

3-1…cont

Hot Spot Volcanoes

An area where magma from deep within the mantle melts

through the crust.

A hot spot in the oceanic floor can gradually form a series of

volcanic mountains.Hot spots can also form under

continents.Yellowstone

Section 3-2

Volcanic Activity

Section 3-2: Volcanic Activity Objectives

Students will be able to describe what happens when a volcano erupts.

Students will be able to explain how the two types of volcanic eruptions differ.

Students will be able to identify some hazards of volcanoes.

Students will be able to identify types of volcanic activity other than eruptions.

Section 3-2: Volcanic ActivityMagma chamber—the pocket beneath a volcano

where magma collectsPipe—a long tube through which magma moves

from the magma chamber to Earth’s surfaceVent—the opening through which molten rock

and gas leave a volcanoLava flow—the area covered by lava as it pours

out of a volcano’s ventCrater—a bowl-shaped area that forms around a

volcano’s central opening

Section 3-2: Volcanic ActivitySilica—a material that is formed from the elements

oxygen and silicon; silica is found in magmaPahoehoe—a hot, fast-moving type of lava that

hardens to form smooth ropelike coilsAa—a slow-moving type of lava that hardens to

form rough chunks; cooler than pahoehoePyroclastic flow—the explusion of ash, cinders,

bombs, and gases during an explosive volcanic eruption

Active—said of a volcano that is erupting or has shown signs of erupting in the near future

Section 3-2: Volcanic ActivityDormant—said of a volcano that does not show

signs of erupting in the near futureExtinct—said of a volcano that is unlikely to erupt

againHot spring—a pool formed by groundwater that

has risen to the surface after being heated by a nearby body of magma

Geyser—a fountain of water and steam that builds up pressure underground and erupts at regular intervals

Geothermal energy—energy from water or steam that has been heated by magma

3-2: Volcanic Activity

How Magma Reaches Earth’s Surface

Magma Rises A Volcano Erupts

Magma rises until it reaches the

surface or a solid layer of rock.

Liquid magma is less dense than the surrounding

materials.

The dissolved gases trapped in magma are under

great pressure.As magma rises to

the surface, the pressure decreases and the gases form

bubbles.

During a volcanic eruption, the gases dissolved in magma rush out, carrying

the magma with them.

3-2…continued

Inside a Volcano

Magma chamber-a pocket of magma that collects underneath a volcano.

Pipe—a long tube in the ground that connects the magma chamber to Earth’s

surface.Vent—an opening in a volcano where molten

rock and gas escapeLava flow—area covered by lava as it pours

out of a ventCrater—a bowl-shaped area that may form at the top of a volcano around the central vent.

3-2…continued

Characteristics of Magma

The forces of a volcanic eruption depends partly on the amount of gas

dissolved in the magma.

Thick or thin, temperature, and silica content are important factors.

SilicaA material that’s formed from the

elements of oxygen and silicon.

One of the most abundant materials in Earth’s crust and

mantle. More silica =

thicker.Rocks

formed

Silica levels

High—rhyolite, pumice, obsidian

Obsidian—lava cools quickly

Pumice—gas bubbles are trapped in lava

Low--basalt

High—light-colored lava that’s too sticky to flow

very far.Low—flows readily and produces dark-colored

lava

3-2…continued

Types of Volcanic Eruptions

The silica content of magma helps

to determine whether the

volcanic eruption is quiet or explosive.

Quiet Eruptions

Explosive Eruptions

Thick magma builds up in the pipe and ends up

exploding out.Breaks the lava into

pieces—ash, cinders, and bombs.

Pyroclastic flow

Occurs when an explosive eruption

hurls out ash, cinders, and bombs

as well as gases.

Magma flows easily. The lava can flow many kilometers from the volcano’s vent.

Pahoehoe: fast-moving, hot lava.

Forms a solid mass of wrinkles, billows, and

ropelike coils.

Aa: cooler and slower-movingForms a rough

surface consisting of jagged lava

chunks.

3-2…continued

Stages of a Volcano

Active Dormant Extinct

A volcano that is erupting or has

shown signs that it may erupt in the

near future.

Sleeping or hibernating.

Expected to wake up in the future.

Dead: volcano that is unlikely to

erupt again.

3-2…continued

Other Types of Volcanic ActivityDoes not

involve the eruption of

lava.

Geothermal energy

Hot springs

Geyser

Forms when groundwater heated by a nearby body of magma rises to the surface and collects in a natural pool.

A fountain of water and steam that erupts from the ground.

Water heated by magma that

provides a clean, reliable energy

source.Used as a source of electricity and to heat homes.

3-2…continued

Monitoring VolcanoesMethods Monitor

Tiltmeter, laser-

ranging devices,

and other instruments

.

Magma moves underground and causes

elevation and tilt to change.

The local magnetic field, water level in a volcano’s

crater lake, and any gases escaping from a

volcano.Temperature of

underground water.Many small earthquakes caused by movement of magma into the magma

chamber and pipe.

3-2…continued

Volcano Hazards

Although quiet eruptions and explosive eruptions involve different volcano hazards, both types can cause damage far from the crater’s

rim.

Quiet Eruption Explosive Eruption

Volcanic Ash

Lava flows pour from

vents, setting fire to and then

burying everything in

their path.

A volcano can belch out hot, burning clouds

of volcanic gases as well as cinders and

bombs.

Can bury entire towns, damage crops, and clog

car engines.Ex.—Pompeii

Section 3-3

Volcanic Landforms

Section 3-3 Objectives

Students will be able to identify the landforms that lava creates on Earth’s surface.

Students will be able to explain how magma hardens beneath the surface creates landforms.

Section 3-3: Volcanic LandformsShield volcano—a wide, gently-sloping mountain

gradually built by lava flows and formed by quiet eruptions

Cinder cone—a steep, cone-shaped hill or mountain made of volcanic ash, cinders, and bombs piled up around a volcano’s opening

Composite volcano—a tall, cone-shaped mountain I which layers of lava alternate with layers of ash and other volcanic materials

Caldera—the large hole at the top of a volcano formed when the roof of a volcano’s magma chamber collapses

Section 3-3: Volcanic LandformsVolcanic neck—a deposit of hardened magma in

a volcano’s pipeDike—a slab of volcanic rock formed when

magma forces itself across rock layersSill—a slab of volcanic rock formed when

magma squeezes between layers of rockBatholith—a mass of rock formed when a large

body of magma cooled inside the crust

3-3 Volcanic Landforms

Landforms from Lava and Ash

Shield Volcanos

Cinder Cone

Volcanoes

Composite Volcanoes

Lava Plateaus

Calderas

Thin layers of lava pour out of a vent and harden on top of

previous layers; builds a wide, gently sloping mountain

A steep, cone-shaped hill or mountain; if lava is thick and stiff, it may produce ash, cinders, and bombs that pile up around the

vent.Tall, cone-shaped

mountains in which layers of lava alternate with

layers of ash

Flows of lava that spread out on top of other layers; lava flows out

of several long cracks and spreads out

Mountain is empty and top collapses inward

Crater Lake,

Oregon

Columbia Plateau;

Washington, Oregon, &

Idaho

Mt. St. Helens,

Washington

Paricutin, Mexico

400 m high

Hawaiian Islands

3-3…continued

Soils from Lava and Ash

Originally barren Lava, ash,

and cindersHard

surface breaks

down to form soil

Breaks down into

soilRichest soils in the world Releases

potassium, phosphorus,

and other materials that plants need

3-3…continuedLandforms from MagmaBatholiths

Volcanic Necks, Dikes, and Sills

Dome Mountains

Mass of rock formed when a large body of magma

cools inside the crust

Volcanic Necks

Dikes Sills

Formed when rising magma is blocked by

horizontal layers of rock;

magma forces the

layers of rock to bend

upward into a dome shapeSierra Nevada

Mts., California Black Hills,

South Dakota

Magma hardens

in a volcano’s

pipe; softer rock

wears away

Hardened magma

tha forced itself

across rock

layers

When magma

squeezes between layers of

rock

Section 3-4

Volcanoes in the Solar System

Section 3-4 ObjectivesStudents will be able to explain how volcanoes

on Mars and Venus compare with volcanoes on Earth.

Students will be able to describe the volcanic activity found on the moons of Jupiter and Neptune.

3-4: Volcanoes in the Solar System

Earth’s Moon

Darker Area

Light-colored Crater

Unusually smooth; lava flows; more than 3 billion

years ago

Mark where meteorites have smashed into the moon over billions of

years

3-4…continued

Volcanoes on Venus

Signs of widespread volcanic activity

Made of thin, runny lava

Thousands of volcanoes

Largest volcano on Venus

150 large volcanoes measuring between

100 and 600 km across and about ½ a

km high

Gently sloping shield volcanoes with broad

bases

Long, riverlike lava flows

More than 6,800 km long

Theia Mons

800 km across and 4

km high

3-4…continuedVolcanoes on

MarsLong history of volcanic activity

Variety of volcanic features

Olympus Mons

Volcanoes are found in only a few regions on

Mars

Large shield

volcanoesCone-

shaped volcanoes

Lava flows

Biggest volcano

on Mars is the

largest mountain

in the solar

system

Shield volcan

o similar

to Mauna Loa;

covers an

area as

large as

Ohio

Over 8 times taller than Theia Mons

on Venus

3-4…continued

Volcanoes on Distant

Moons

Volcanic features are very different from those on Earth, Mars, and Venus

Volcanic eruptions have been observed

Io TritonA moon of Jupiter

NitrogenSulfur volcanoes

A moon of Neptune

Erupt like fountains or spread out like umbrellas above the

colorful surface

Most is frozen solid; some is melted by absorbing heat from the sun; expands and erupts

through the icy crust