Transcript Earthquakes - Station Camp High School

Volcanoes
Sections 7.1, 7.2
Section 7.1
Volcanoes and Plate Tectonics
The asthenosphere has very high
temperatures, but because it has so much
pressure around, it remains rock.
 There are some areas where it melts to
form Magma or liquid rock.
 Any activity where magma moves toward
the surface is called volcanism.

Section 7.1
Volcanoes and Plate Tectonics
Magma slowly moves to the crust because
it is less dense than solid rock
 Most magma forms near the edges of
plates
 Magma that erupts to the earth’s surface
is called lava

Section 7.1
Volcanoes and Plate Tectonics
The opening where molten rock flows to
the surface is called a vent.
 The structure that forms and builds up
around a vent is called a volcano.

Section 7.1
Volcanoes and Plate Tectonics
Like earthquakes, most volcanoes occur
near both convergent and divergent
boundaries
 When there is a subduction of one plate
under another, the plate that goes
underneath will melt and create a volcano
about 100 miles inland

Section 7.1
Volcanoes and Plate Tectonics
The greatest amounts of magma comes to
the surface where the plates are moving
apart.
 Large volcanoes are formed here
 One of those is the country of Iceland
 Half of Iceland is moving toward Europe
and the other half is moving toward North
America

Section 7.1
Volcanoes and Plate Tectonics
Not all volcanoes form on plate boundaries
 Some form over Hot Spots.
 Hot spots are just pockets of magma in
the middle of a plate
 The Hawaiian Islands were formed this
way

Section 7.2
Volcanic Eruptions
There are 2 different types of lava.
 The first type is dark colored when it
hardens and is rich in magnesium and iron
 It is called mafic lava.
 This forms much of the oceanic crust.

Section 7.2
Volcanic Eruptions
The second kind of lava is lighter in color
and is made of silica and lesser amounts
of iron and magnesium
 It is called felsic lava
 Felsic lava found in continental crust

Section 7.2
Volcanic Eruptions
When mafic lava cools quickly, a crust
forms on top, but the bottom still flows.
The rock wrinkles forming pahoehoe
 If the rocks break into jagged chunks, it is
called aa
 Rounded blobs of hardened lava on the
ocean floor are called pillow lava

Section 7.2
Volcanic Eruptions

Lava that has a lot of trapped gases will
produce large violent eruptions out of
continental volcanoes.
(like Mt. St. Helens)

Oceanic Volcanoes produced less violent
volcanoes with very hot and thin mafic
lava (like Hawaii)
Section 7.2
Volcanic Eruptions
Felsic lava explodes out of a volcano
throwing Pyroclastic material
 Volcanic ash is small particles, they are
less than 2mm in diameter
 Volcanic dust is the smallest particles,
they are less than 0.25mm in diameter

Section 7.2
Volcanic Eruptions
Dust and Ash can be carried all around the
world by wind
 Large pyroclastic material up to 64mm in
diameter is called lapilli
 Sometimes lava gets thrown into the air
while it is still hot, that’s called a volcanic
bomb
 If it is solid when it is blasted, it’s called a
volcanic block

Section 7.2
Volcanic Eruptions
There are 3 kinds of volcanoes.
 Shield volcanoes are very wide
volcanoes that are made from layers of
lava
 Cinder Cones are taller but are made
from ejected pyroclastic material
 Composite Volcanoes are the tallest and
look like mountains. They are made with
layers of lava and pyroclastic material.

Section 7.2
Volcanic Eruptions
Craters are formed on volcanoes when a
large explosion blows the top off.
 If the magma chamber below a volcano is
empty, the volcano can fall in. The hole
that is left in the ground is called a
caldera.
