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 surface
Magma—the molten mixture of rock-forming substances, gases, and water from the mantle
Lava—liquid magma that reaches the surface; also the rock formed when liquid lava hardens
Ring of Fire—a major belt of volcanoes that rims the Pacific Ocean
Island arc—a string of islands formed by the volcanoes along a deep ocean trench
Hot spot—an area where magma from deep within the mantle melts through the crust above it
Sec 3-1: Volcanoes and Plate Tectonics
What is a Volcano?
VolcanoMagma
Lava
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 collects
Pipe—a long tube through which magma moves from the magma chamber to Earth’s surface
Vent—the opening through which molten rock and gas leave a volcano
Lava flow—the area covered by lava as it pours out of a volcano’s vent
Crater—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 magma
Pahoehoe—a hot, fast-moving type of lava that hardens to form smooth ropelike coils
Aa—a slow-moving type of lava that hardens to form rough chunks; cooler than pahoehoe
Pyroclastic 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 future
Extinct—said of a volcano that is unlikely to erupt again
Hot 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 Volcanoes
MethodsMonitor
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 Landforms
Shield 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 Landforms
Volcanic neck—a deposit of hardened magma in a volcano’s pipe
Dike—a slab of volcanic rock formed when magma forces itself across rock layers
Sill—a slab of volcanic rock formed when magma squeezes between layers of rock
Batholith—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…continued
Landforms 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 Objectives
Students 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…continued
Volcanoes 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