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Inside a Volcano
Beneath a volcano, magma collects in a pocket called a magma chamber. The magma moves upward through a pipe, which is 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 volcanic eruption
Dissolved gases are trapped in magma and
are under great pressure. As magma
reaches the surface, the dissolved gases
begin to expand and exert an enormous
force. When a volcano erupts, the force of
the expanding gases pushes magma from
the magma chamber through the pipe until it
flows or explodes from the vent.
Kinds of volcanic eruptions
Geologists classify volcanic eruptions as
quiet or explosive. The properties of
magma determine how the volcano erupts.
The type of eruption depends on the
magma’s silica content. Silica is the
material found in magma that is formed
from the elements oxygen and silicon
Quiet eruptions
A volcano erupts quietly if its magma is
low in silica. Low silica magma is thin,
runny and flows easily. The gases in the
magma bubble out gently.
Quiet eruptions
Quiet eruptions can produce two types of
lava. Pahoehoe is fast moving, hot lava that
is thin and runny. It looks like wrinkles
when it hardens. Aa is cooler and slower
moving. It is also thicker and has a rough
surface when it hardens.
Explosive eruptions
A volcano erupts
explosively if its
magma is high in silica.
High silica magma is
thick and sticky. The
gases cannot escape the
thick magma so they
build up pressure until
they explode!
Explosive eruptions
An explosive volcano breaks lava into
pieces that cool and harden in all different
sizes. A pyroclastic flow is a type of
explosive eruption that hurls out a mixture
of hot gases, ash and cinders.
What do you think
Identify if each of the following is an example of a high silica or low silica lava.
1) A lava river flowing away from a volcano
2) A plug of lava covering a volcano’s vent
3) Small pieces of lava being blasted high into the air.
Volcano hazards.
Both types of eruptions can cause damage
far from the volcano’s location. During a
quiet eruption lava flows from vents setting
fire to, and then burying everything in its
path..
Volcano hazards
During an explosive eruption, a volcano can
release deadly gases, as well as ash and
cinders
Life cycle of a volcano
The activity of a volcano may last from less
than a decade to more than 10 million
years. Geologists use the terms active,
dormant and extinct to describe a
volcano’s stage of activity.
Life cycle of a volcano
An active, or live volcano, is one that is
erupting or showing signs to erupt in the
future. A dormant, or sleeping volcano is
expected to awaken and become active in
the future. An extinct, or dead volcano is
unlikely to erupt again.
Hot Springs and Geysers
Hot Springs and geysers
are found in areas of
present or past volcanic
activity. A hot spring
forms when water deep
underground is heated by
magma or hot rock. The
hot water rises to the
surface and collects in a
pool.
Hot springs and geysers
Sometimes, the rising water and
steam become trapped in a narrow
crack. The pressure builds until it
sprays above the surface as a geyser.
A geyser is a fountain of steam and
water that erupts from the ground.