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Volcanic Activity

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Alicia Bartels

on 9 December 2015

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Transcript of Volcanic Activity

Volcanic Activity
How Magma Reaches Earth's Surface
Lava begins as magma in the mantle.
Types of Volcanic Eruptions
The silica content of magma helps to determine whether the volcanic eruption is quiet or explosive.
How Magma Reaches Earth's Surface
Magma Rises:
Because liquid magma is less dense than any surrounding rock, magma flows upward into any cracks in the rock above.
Magma rises until it reaches the surface, or until it becomes trapped beneath layers of rock.
Inside a Volcano
All volcanoes have a pocket of magma beneath them and one or more cracks for magma to force through.
Characteristics of Magma
How thick the magma is, its temperature, and its silica content are important factors to determine the size or type of eruption.
There, magma forms in the asthenosphere, which lies beneath the lithosphere.
Materials of the asthenosphere are under great pressure.
A Volcano Erupts:
The dissolved gases trapped in magma are under tremendous pressure; as magma rises toward the surface, the pressure decreases.
Dissolved gases begin to separate out, forming bubbles.
Volcanoes erupt when an opening develops from weak rock on the surface.
During volcanic eruptions, the gases dissolved in magma rush out, carrying magma with them.
Beneath a volcano, magma collects in a pocket called a
magma

chamber
.
The magma moves through a
pipe
, a long tube in the ground that connects the magma chamber to the Earth's surface.
Molten rock and gas leave the volcano through an opening called a
vent
.
A
lava

flow
is the area covered by lava as it pours out of a vent.
A
crater
is a bowl-shaped area that may form at the top of a volcano around the volcano's central vent.
page 185 in textbook has diagram
Some magma moves and flows easily, others move slowly and are more thick.
The hotter the magma, the more fluid-like it is.
The amount of
silica
, material that is formed from the elements oxygen and silicon, helps determine how easily magma flows.
The more silica magma contains, the thicker it is.
Magma that is high in silica produces light-colored lava that is too sticky to flow very far.
Magma that is low in silica flows readily and produces dark-colored lava.
Quiet Eruption:
Erupts quietly if its magma flows easily.
Gas dissolved in magma bubbles out gently.
Thin, runny lava oozes quietly from the vent; usually cracks in the crust.
Examples: islands of Hawaii and Iceland
Produces two types of lava:
pahoehoe:
fast moving, hot lava that cools to form wrinkles
aa:
cooler, slower moving lava that hardens to form a rough surface.
Explosive Eruptions:
Thick and sticky magma produces an explosive eruption.
Magma slowly builds up in the volcano's pipe, plugging it like a cork in a bottle.
Dissolved gases cannot escape from the thick magma, they build up pressure, and eventually explodes.
The explosion breaks the lava into fragments that quickly cool and harden into pieces
the smallest being volcanic ash
the largest ranging from the size of a baseball to the size of a car
A
pyroclastic

flow
occurs when an explosive eruption hurls out ash, cinders, and bombs as well as gases
Stages of a Volcano
The activity of a volcano may last from less than a decade to more than 10 million years.
An
active
volcano, or live, is one that is erupting or has shown signs that it may erupt in the near future.
A
dormant
, or sleeping, volcano is like a sleeping bear; scientists expect the volcano to awaken in the future and become active.
An
extinct
, or dead, volcano is unlikely to erupt again.
Other Types of Volcanic Activity
Hot springs and geysers are two examples of volcanic activity that do not involve the eruption of lava, and can occur in any volcanic area, even extinct.
A
hot

spring
from when groundwater heated by a nearby body of magma rises to the surface and collects in a natural pool.
May contain dissolved gases, like lava, from within Earth.
A
geyser
is a fountain of water and steam that erupts from the ground from built up pressure of trapped steam.
Water heated by magma can provide clean, reliable energy source called
geothermal

energy
.
For example, in Iceland, people have hot water warmed by magma piped directly to their homes.
Monitoring Volcanoes
Geologists more successful at predicting volcanic eruptions than earthquakes.
Geologists use tiltmeters, laser-ranging devices, and other instruments to detect slight surface changes in elevation and tilt caused by magma moving underground.
Geologists monitor local magnetic field, water level in a volcano's crater lake, and any gases escaping from a volcano.
They take the temperature of underground water to see if it is getting hotter, which is a sign that magma may be nearing the surface.
Geologists, however, cannot be certain what type or eruption or how powerful it may be.
Volcano Hazards
Time between volcanic eruptions may span hundreds of years.
Although quiet eruptions and explosive eruptions involve different volcano hazards, both types of eruption can cause damage far from the crater's rim.
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