Download Volcanoes Study Guide

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Volcanoes Study Guide
1.
Where are most volcanoes located?
The Ring of Fire is a ring of volcanoes around the Pacific Ocean that result from subduction of
oceanic plates beneath lighter continental plates. Most of the Earth's volcanoes are located
around the Pacific Ring of Fire because that the location of most of the Earth's subduction
zones. This area is known as a volcanic belt. A volcanic belt is an area that has a large
amount of volcanic action. Volcanic belts usually form around the boundaries of Earth’s
plates.
2.
What is a hot spot? How are they different from most volcanoes?
Places known as hot spots are volcanic regions thought to be fed by underlying mantle that is
anomalously hot compared with the surrounding mantle. They differ from most volcanoes in
that they may be on, near to, or far from tectonic plate boundaries
Hot spots are due to hot mantle plumes that rise from the mantle.
Provide two locations in the United States where hot spots exist.
Hawaii and Yellowstone.
3.
Distinguish the difference between lava and magma.
If someone is talking about magma you know they are talking about when it is still
underground but if they are talking about lava you know they are talking about after it
has erupted.
4.
What controls the explosiveness of a volcano?
Three properties have the greatest impact on the explosiveness of a volcano. They are: 1. The
composition of the lava, 2. The temperature of the lava, and 3. The gas content in the lava.
5.
How does temperature affect density?
As the temperature increases, the melted rock becomes less dense than the solid rock surround it. The less
dense material will rise through more dense material. Magma continues to rise until it either erupts or
enters material with the same density, at which point it will form a magma chamber.
As the magma rises, bubbles can form from the gas in the magma. This gas increases in pressure in the
magma. If the pressure becomes great enough, the overlying rock can fracture, at which point an eruption
occurs
Magma flows at different rates when volcanoes explode. The more silica in the magma, the easier the
magma flows down the mountain.
6.
Explain the difference between and active, dormant, and extinct volcano.
An active volcano is a volcano that has had at least one eruption during the past 10,000 years.
A dormant volcano is an active volcano that is not erupting, but is supposed to erupt again.
An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in
a comparable time scale of the future.
7.
Contrast the three types of volcanoes. Provide their size/shape, explosiveness, and material
from the volcano.
Sheild
Cinder Cone
Composite
Lava flow pours out in all
directions from a group of vents,
building a broad gently sloping
cone of flat, domical shape.
These volcanoes are built up
slowly because the lava flow
called basalt lava spreads out
great distances.
These are the simplest type of
volcanoes. They are built from
particles and blobs of lava
ejected from a single vent.
Most cinder cones have a
bowl-shaped crater at the
summit.
Shield Volcanoes in the United States: Three Sister in Oregon
Mannakea in Hawaii
Medicine Lake in California
Some of Earth’s grandest
mountains are composite
volcanoes. They are typically
steep-sided, symmetrical cones
of large dimension built of lava,
volcanic ash, cinders, and blocks
of earth. Most have craters at the
summit. The essential feature of
a composite volcano is a conduit
system through which magma
from a reservoir deep in the
Earth’s crust rises to the surface.
The volcano is built up by the
accumulation of material
erupted through the conduit and
increases in size as lava, cinders,
ash, etc. are added to its slope.
Earthquakes
Rock stress causes 3 types of faults. A fault is a fracture in Earth’s crust where rocks on either side of
the crack have slid past each other.
Types of Faults:
Strike-slip- indicate rocks are sliding past each other horizontally with little to no vertical movement.
(refer to illustration D)
Normal- occurs when two blocks of crust pull apart, stretching the crust into a valley. ( refer to
illustration C)
Reverse- also called thrust faults, slide one block of crust on top of another. These faults are commonly
found in collision zones.
A- Before faulting occurs
B- Compression pushes rock together. Convergent: Tending to come together; merging.
When two plates collide (at a convergent plate boundary), some crust is destroyed in
the impact and the plates become smaller. The results are different, depending upon
what types of plates are involved in the collision.
Subduction: The process of which collision of the earth's crustal plates results in one
plate's being drawn down or or pushed on top of the other plate.
Oceanic Plate to Continental Plate - When a thin, dense oceanic plate collides with a
relatively light, thick continental plate, the oceanic plate is forced under the
continental plate; this is called subduction.
Oceanic Plate to Oceanic Plate - When two oceanic plates collide, one may be
pushed under the other and magma from the mantle rises, forming a volcano.
Continental Plate to Continental Plate - When two continental plates collide,
mountain ranges are created as the colliding crust is compressed (squished) and
pushed upwards.
C- The term "tension" refers to a stress which stretches rocks in two opposite
directions.( Divergent Plates) The rocks become longer in a lateral direction and thinner
in a vertical direction.
D- A transform boundary or transform fault is how earthquakes occur on the surface. This
happens when the mantel heats up rock into lava which rises because it is so hot. Then when it
cools, it sinks which causes convection currents. These convection currents cause the
asthenosphere to move. When the asthenosphere moves, it wants the lithosphere to move with it.
But when the lithosphere can’t move because it is already pushed up against another plate, lots of
pressure builds up and faults form. Then eventually the faults will break causing a sudden
earthquake.