Download Volcanoes

Volcanoes
• EEn.2.1.1 Explain how the rock cycle, plate tectonics,
volcanoes, and earthquakes impact the lithosphere.
Anatomy of a Volcano
• Magma chambers fuel
volcanoes
• When magma reaches
Earth’s surface it is called lava
• Lava erupts through an
opening called a vent
• Over time, lava can
accumulate to form a
mountain called a volcano
• At the top of a volcano is a
bowl-shaped depression
called a crater
• Larger craters are called
calderas – can form when the
side of a volcano collapses
into the magma chamber
Types of Volcanoes
• What factors affect the
appearance of a
volcano:
– Type of material that
forms the volcano
– Type of eruptions that
occur
Volcanic Characteristics
SHIELD VOLCANOS
This type has a slope that is small
This type usually has flowing lava that does not shoot out in the air
The lava flow is very slow and you could outrun it
This type makes large chunks of basalt
Ex. Hawaiian Islands
CINDER CONES
This type has the steepest slope of the volcanoes
This type shoots lava in the air and has a faster lava flow
The lava hardens in the air
The hardened lava helps reform the volcano again
COMPOSITE VOLCANOS
This type is the worst of the volcanoes because it is very explosive
It usually has poisonous gases, ash and lava
The ash can blanket an area with over an inch of it
The ash can fly faster than 200 miles an hour
Kills more people than any type of volcano
Ex. Mount St. Helens
Volcanic Material
Tephra- rock
fragments
thrown into
the air
Classified
according to
size
Dust
Ash
Lapilli- little stones
Less than
.25mm
diameter
Larger than
dust but less
than
Larger than 2 mm
but less than
2 mm
64 mm
Volcanic
blocks/volcanic
bombs
Volcanic Material
Pyroclastic flow
• Fast moving clouds of gas,
ash, and other tephra
• Travel at speeds of 200
km/hr
• Contains hot poisonous
gases
Lahar
• Hot and cold mixture of
water and rock fragments
flowing down volcano
– Mud flow
– Debris flow
Volcanic Material
Magma
• Molten material found
beneath earth’s surface
with large crystals when it
cools slowly and forms
minerals with small crystals
when it cools rapidly
Lava
• Magma that flows onto
earth’s surface
Volcanic Effects
Lithosphere
• Volcanic activity adds:
– rocks and boulders to
lithosphere
– minerals to soil
– material to lithosphere in
layers
Atmosphere
• Volcanic activity adds:
– Ash into atmosphere
– Gases into atmosphere
Volcano Occurrence
• Most volcanoes form at
plate boundaries
• 80% of all volcanoes are
found along convergent
boundaries
• 15% are found along
divergent boundaries
• Only 5% occur far from
plate boundaries
Convergent Volcanism
• Where slabs of oceanic
crust descend into mantle
and melt
• The magma is forced
upward through the plate
and forms volcanoes
• Volcanoes associated with
convergent plate
boundaries form two
major belts:
– Circum-Pacific Belt (Pacific
Ring of Fire) – larger
– Mediterranean Belt
(includes Mt. Etna and Mt.
Vesuvius) - smaller
Divergent Volcanism
• Magma is forced upward
into fractures and faults
(rift zones) that form as
plates separate
• Most of the world’s rift
volcanism occurs under
water at ocean ridges
• Results in the formation of
new ocean floor
• One of the few places
where rift volcanism
occurs above sea level is
in Iceland
Hot Spots
• Some volcanoes are located far
from plate boundaries
• Hot spots – unusually hot
regions of Earth’s mantle
where plumes of magma rise
toward the surface
– Trail of progressively older
volcanoes form as the plate
moves over a hot spot
• Example: Hawaiian islands
– The volcanoes on the oldest
island (Kauai) are inactive
because the island no longer
sits above the hot spot
– The world’s most active volcano
(Kilauea) is on the big island of
Hawaii and is currently located
over the hot spot
Volcanoes and Society
• Volcanic activity is
proof that Earth is a
dynamic planet
• While many volcanic
eruptions can be
spectacular events,
these geologic
phenomena can
pose risks to
humans and their
environment.