Download Fukutoku-Okanoba, Japan

Earth Science
Chapter Six - Volcanoes
6-1 Volcanoes and Plate Tectonics
• A volcano is a weak spot in the crust where molten
material from the mantle comes to the surface.
• A mixture of rock, gases, and water create magma.
• Liquid magma that reaches the surface is called
lava. When lava cools it forms solid rock.
Volcanic activity adds new rock to existing land
and forms new islands.
6-1
• Volcanoes occur in belts. One major belt is
the Ring of Fire, formed by many
volcanoes.
Ring of Fire
Ring of Fire
6-1
• Volcanic belts form along boundaries where Earth’s plates
are diverging (pulling apart) or converging (pushing
together).
• Most volcanoes occur along diverging plates – the crust is
weakened allowing magma to reach Earth’s surface.
• Some volcanoes occur in the middle of a plate, far from
plate boundaries. At these places, there are HOT SPOTS,
magma from deep within the mantle that melts through the
crust above it.
6-1
• Over millions of years, a hot spot forms volcano
mountains. The Hawaiian Islands were formed as
the Pacific plate drifted over a hot spot.
– Lava erupted from the hot spot, and built a volcanic
island. The Pacific plate kept moving slowly, carrying
the island away from the hot spot. This process
continued, and over time a chain of islands formed.
Hawaiian Islands Formation
Hawaiian Islands and their Volcanoes
Hualalai Volcano
Hualalai Volcano
Kilauea volcano is one of the most active on Earth..
Kilauea volcano
Mauna Loa Volcano
6-1
–
Yellowstone National Park marks a major hot spot
under the North American Plate. (Old Faithful – hot
water and other materials erupt – this is called a
geyser.)
Old Faithful
Old Faithful
Volcano Diagram
6-2 – Volcanic Activity
• Lava begins as magma in Earth’s mantle. Magma
flows upward through cracks in the rock until it
reaches the surface or becomes trapped. As
magma rises, the pressure decreases and the
dissolved gases begin to separate out. A volcano
erupts when an opening develops in weak rock on
the surface. During a volcanic eruption, the gases
dissolved in magma rush out, carrying magma
with them.
Magma
6-2 Volcanic Activity
• The Volcano
– Inside a volcano, magma collects in a pocket called a
magma chamber.
– The magma moves through the pipe, a long tube that
connects the magma chamber to Earth’s surface.
– There, the magma leaves the volcano through an
opening called a vent.
– The area covered by lava as it pours out the vent is
called the lava flow.
– Lava then collects in a crater, a bowl-shaped area
around a volcanoes central vent.
Lava Flow
6-2 – Volcanic Activity
• The force of an eruption depends on the magma’s
gas content:
–
–
–
–
How the thick or thin the magma is
Temperature
Silica content
Silica is a material formed from oxygen and silicon.
Thick magma flows slowly and not so easily. The
hotter the magma is, the thinner and faster flowing the
magma becomes. Thick magma contains more silica.
6-2 Volcanic Activity
• The silica content of magma helps to
determine whether the volcanic eruption
will be quiet or explosive.
– If the magma has low silica, it flows easily and
the volcano erupts quietly. Quiet eruptions
produce two different types of lava:
• Pahoehoe: hot and fast moving lava
• aa: cooler, slow moving lava
6-2 Volcanic Activity
• A volcano erupts explosively if the magma
is thick. The magma plugs the pipe, and
pressure builds up until the trapped gases
explode, forcing the magma out. A
pyroclastic, pyro meaning fire, occurs when
an explosive eruptions hurls out ash,
cinders, and bombs.
6-2 Volcanic Activity
• A volcano that is erupting or has shown
signs that it may erupts in the future is
called an active volcano.
• A volcano that is dormant is not active now,
but may again erupt in the future.
• An extinct volcano is unlikely to ever erupt
again.
6-2 Volcanic Activity
• Other forms of volcanic activity:
– A hot spring forms when groundwater heated
by magma rises to the surface and collects in a
pool.
– A geyser is a fountain of water and steam that
erupts from the ground.
– Water heated by magma can provide a clean,
reliable energy source called geothermal
energy.
6-2 Volcanic Activity
• Hazards of volcanoes include:
–
–
–
–
–
Lava flows
Clouds of ash
Hot volcanic gases
Landslides
Avalanches of mud, rock, or snow.
Lava Flows
Clouds of Ash
Volcanic Gases
Landslides
Avalanches
6-3 Volcanic Landforms
• Some volcanic landforms are formed when lava flows build up
mountains and plateaus. Rock and other materials formed from lava
create a variety of landforms including:
– Shield Volcano: layers of lava that eventually build up into a
sloping mountain.
– Cinder Cone: Materials pile up around the vent, forming a steep,
cone-shaped hill or mountain.
– Composite Volcano: sometimes lava flows alternate with explosive
eruptions of ash, cinders, and bombs. The alternating layers form a
tall, cone-shaped mountain.
– Calderas: a huge hole left by the collapse of volcanic mountain.
Shield Volcano
Cinder Cone Volcano
Composite Volcano
Calderas
6-3 Volcanic Landforms
• Sometimes magma rises upward through cracks in
the crust but does reach Earth’s surface. The
magma cools and hardens into rock beneath the
surface.
Dike
A dike forms when magma forces itself across
rock layers and hardens.
Sill
A sill forms when magma squeezes between layers
of rock and hardens.
Batholiths
• Batholiths: forms when a large body of magma
cools inside the crust, a mass of rock forms.
Active Volcanoes Today
• Fukutoku-Okanoba, Japan
Merapi, Indonesia
Cleveland Volcano, Chuginadak
Island, Alaska
Colima Volcano - Mexico
Karymsky - Russia
Popocatepell, Mexico
6-4 Volcanoes in the Solar System
• Earth is not the only body in the solar system that
shows sign of volcanic activity.
– Earth’s moon has dark, smooth areas where lava flowed
onto the surface billions of years ago.
– Venus has volcanic mountains - shield volcanoes.
– Mars has large shield volcanoes similar to those on
Venus and Earth.
– Jupiter’s moon Io has shown ongoing volcanic
eruptions.
– Neptune’s moon, Triton, has also shown ongoing
volcanic eruptions.
Volcanism on the Moon
Volcanism on Mars
Volcanism on Venus
Volcanism on Jupiter - Io