How to a volcano made
What are volcanoes and how are they formed?
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dramatic volcanic eruptions happen
all around the world humans are left in
both
fear and awe of these fiery powerful and
highly dangerous events
today there are over 600 active
volcanoes on earth
with at least 50 eruptions occurring
each year
but did you know there are many other
volcanoes out there that are
extinct or dormant
what is going on under the surface to
cause such a destructive event
to answer this question we must first
understand what a volcano is
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a volcano is essentially a rupture in
the earth's crust
the earth's rocky outermost layer that
lies on top of its hotter
inner layers
the earth's crust and the upper mantle
form the lithosphere
the lithosphere is broken up into slabs
known as tectonic plates
and they fit together like puzzle pieces
to make up the surface of the earth
most volcanoes are found along these
tectonic plate margins
either at a destructive or constructive
plate margin
both of these margins allow gas and
molten rock to escape from inside the
planet to the surface
at a destructive or convergent plate
margin
an oceanic tectonic plate which is a
plate mostly covered by the sea
and a continental plate which is mostly
covered by land
move towards each other
the denser oceanic plate sinks under the
continental plate
melting down into the earth's mantle
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this melting releases gases that make
their way through the crust above
and erupt through the surface
at a constructive or divergent plate
margin
the two plates move apart really slowly
less than five centimeters per year but
over time
this allows extremely hot magma to rise
up from deep within the planet
magma rises and fills the gaps created
by the plates moving away from each
other
and eventually new crust is formed
magma at the margin can sometimes
explode through this new crust
creating a volcanic eruption
many of these constructive margins are
found under the ocean
if you map the locations of volcanoes
you'll see that 75 of the world's active
volcanoes are along the margin of the
pacific plate
volcanologists refer to this as the ring
of fire
since 1850 approximately 90 percent of
the 16 most powerful volcanic eruptions
on earth
have occurred within the pacific ring of
fire making it one of the most dangerous
places on earth
however there are places on earth where
a volcano can
form away from tectonic plate boundaries
we call these
hot spot volcanoes
they form when rising magma from deep
within the planet
melts through the tectonic plate above
and begins to build up
an example of this is the hawaiian
islands
which are all made of a mixture of
extinct and active volcanoes that have
broken through the middle of the pacific
plate
now that you know where volcanoes form
let's learn about their different types
there are two main types composite
volcanoes
and shield volcanoes
the majority of volcanoes are composite
volcanoes
these are commonly found on destructive
plate margins
and have a distinctive conical shape
let's slice a composite volcano in half
to learn more about it
at the bottom of a composite volcano
lies a magma chamber
which is like a hot bubbling furnace
magma enters the chamber from the
earth's mantle
and collects here until pressure builds
causing gases to expand
and water to become steam
eventually the pressure becomes so high
that an explosion
or volcanic eruption occurs
most of the magma moves through the main
vent and exits the volcano through the
crater
some magma also makes its way through
secondary events and out through
secondary cones
craters can eject four different types
of materials into the atmosphere
these include lava which is the name for
magma that has reached the surface of
the earth
pieces of rocks called volcanic bombs
thick ash and gas
with every eruption the lava that
travels out of the crater
cools and solidifies along with ash to
form
alternate layers of ash and lava
composite volcanoes are also known as
strata volcanoes
because strato means layers
shield volcanoes on the other hand are
usually found on constructive plate
margins or at hot spots
they have gentle sloping sides caused by
runny lava
flowing quicker and covering longer
distances before it solidifies
they usually erupt less violently as
compared to composite volcanoes
volcanoes reflect the movements of
earth's major tectonic plates
and are signs of activity occurring
under the earth's surface
this gives us evidence that the earth is
not just a static and rigid rock
but one full of dynamic and powerful
forces
you
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