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Volcanos
What is a volcano?
A volcano erupting
The ground we walk on is actually similar to a
large jigsaw puzzle. It is made up of huge
pieces of flat rock called tectonic plates.
Where these plates meet is called a fault.
Volcanoes are often found where the tectonic
plates meet. However, volcanoes can also occur
over ‘mantle plumes’ – super hot areas of rock
inside the earth. Put simply, a volcano is an
opening (usually a mountain) in the Earth’s
surface from which hot magma, ash and gas can
escape.
How is the earth formed?
In order to find out more about volcanos, we need to
know how the earth is formed. The earth is made up
of layers: inner core, outer core, mantle and the
crust. Life as we know it, all vegetation and land
animals, live on this cool crust, either on the land or
within the ocean which covers the earth’s crust.
Underneath the earth’s crust, is the mantle which is
made up of super-hot melted rock called magma.
Magma is very, very hot liquid rock, ranging from
700°C to 1300°C.
Did you know that scientists have also found magma on
Mars, Venus and Mercury as well as our Moon?
The earth’s tectonic plates
We already know that the
earth’s crust is made up of
large tectonic plates of solid
rock and where the plates
meet together, is called a
fault. These faults, go right
down into the mantle of the
earth. We don’t normally see
them because they are either
covered by the land (soil) or
by the oceans.
The layers of the earth
Here we can see the cracks in the
earth’s crust along the edges of
two plates.
Why do volcanos erupt?
Volcanic eruption on land
Larva flowing into the sea
We know that the mantle (just under the earth’s crust)
is made up of magma (super-hot) rock. Magma is lighter
than the rock above it, so tries to rise up but is trapped
by the earth’s crust. As more melted rock from below is
added, this squeezes the magma, building up pressure.
The easiest way to relieve this pressure is for the
magma to ooze out between the cracks in the tectonic
plates.
Once the magma reaches the surface of the earth, it is
called larva. The larva, then cools and hardens into solid
rock. When there is no crack or fault in the crust, the
magma may push right through a weak part in the crust
and a volcanic eruption occurs. Molton rock may pour
out, or a cloud of larva, rock and ash may violently shoot
up into the air with all the pressure. Larva is orange or
red in colour and is very hot rock which cools when it
meets the air or water on the earth’s surface, hardening
over time into solid rock.
Sometimes larva rock is ‘blasted’ out during an
eruption, this rock is called tephra. It can be as
big as a house or as small as a piece of sand.
Volcanic-ash is sand sized tephra which has been
blown into the air by the erupting volcano.
Volcanos can erupt with a mixture of tephra,
volcanic ash, larva and gases. As well as danger
from the hot larva, an erupting volcano can trigger
life threatening events such as tsunamis, flash
floods, earthquakes, mud flows and landslides.
Did you know that the word ‘volcano’ comes from the Roman name ‘Vulcan’, the Roman god of fire?
What does a volcano look like inside?
Magma rising in the main volcano vent as the pressure increases from the chamber
When the magma cannot find a path upwards, it
gathers together in a magma chamber underneath
the earth’s crust. As the magma collects and the
pressure increases, the magma rises inside the
volcano. When enough pressure develops inside the
magma chamber, the volcano erupts. As more larva
spills out of the volcano and then hardens into rock,
the bigger the volcano becomes. The crater is a bowl
shaped dip at the mouth (top) of the volcano. The
vent is a channel in the neck of the volcano which the
Magma chamber
magma travels though when it erupts. The side vent
or secondary vent will allow some magma and gas to
escape, but the main vent is where the eruption takes place. Fumaroles are vents from
which volcanic gas escapes into the atmosphere. These volcanic gases; carbon dioxide,
sulphur dioxide, hydrogen chloride, and hydrogen sulphide gases are toxic and are just as
dangerous as the larva itself.
Did you know that some volcanos can take thousands of years to form whereas some
form overnight?
Why do some volcanos erupt with explosions and some don’t?
Some volcanos are explosive and
others are not. If the magma is thin
and runny, the gas can easily escape
from it. When this type of magma
erupts, the larva just flows out of
and down the sides of the volcano.
When magma is thicker or has a lot
Thin and runny magma
of gas dissolved in it, then the Thicker magma or
eruption
eruption is more explosive. In this trapped gas eruption
type of eruption, the larva blasts
into the air, breaking apart into pieces of larva rock called tephra. (Remember, tephra can
be very small pieces of rock like sand, or large pieces of rock similar to a house). Larva may
also be blasted from the main vent.
What are the different stages of volcanoes?
Scientists have categorised volcanoes into three main categories: active, dormant, and
extinct. An active volcano is one which has recently erupted or one which may possibly
erupt soon. A dormant volcano is one which has not erupted in a long time but there is a
possibility it can erupt in the future. An extinct volcano is one which has erupted thousands
of years ago and there’s no possibility of eruption.
What are the different types of volcanoes?
Volcanoes are grouped into four types: cinder cones, composite volcanoes, shield
volcanoes and lava volcanoes.
Cinder
Cones
Composite
Volcanoes
Shield
Volcanoes
Lava
Volcanoes
Cinder cones are circular or oval cones made up
of small pieces of lava from a single vent which
have been blown into the air, cooled and fallen
around the vent.
Composite volcanoes are steep-sided volcanoes
composed of many layers of volcanic rocks,
lava, ash and rock debris. Mount. Rainier and
Mount St. Helens are examples of this type of
volcano.
Shield volcanoes are volcanoes shaped like a
bowl or shield in the middle with long gentle
slopes made by basaltic lava flows. (Basalt lava
is where magma contains partially melted
rock).
Lava domes are formed when erupting lava is
too thick to flow and makes a steep-sided
mound as the lava piles up near the volcanic
vent. The eruption of Mount St. Helens in 1980
was caused partially by a lava dome shifting to
allow explosive gas and steam to escape from
inside the mountain.
How many volcanoes are there?
There are more than 1500 active volcanoes on the earth. Scientists have recorded around
80 volcanos which are under the oceans. Active volcanoes are found all over the world but
we don’t have any in the UK. Most volcanoes occur near the edges of the earth's tectonic
plates but Britain is now a long way from such geologically active areas.
What is a pyroclastic flow?
A pyroclastic flow is an extremely fast moving collection of gas, ash
and rock which travels at over 100km/h (hurricane speed) down the
sides of a volcano. This type of flow looks very similar to a snow
avalanche, except it is fiercely hot, contains toxic gases, and moves
at phenomenal, hurricane-force speeds.
The pyroclastic flow is the deadliest of all volcanic phenomena.
Pyroclastic flow from a volcano
What is lahar?
Lahar is a type of mudflow of pyroclastic material (gas,
ash and rock), rocky debris, and water. It flows down
from a volcano, typically along a river valley. It is very
dangerous because it is very similar to cement. It is
liquid when it's moving, but when it stops, it solidifies,
causing just as much devastation as the lava itself.
Lahar flowing from a volcano
What is pumice stone?
Pumice is a very light, porous volcanic rock which forms during
explosive eruptions. It is similar to a sponge because bubbles
are ‘frozen’ within it. These bubbles are made by trapped gas.
Some people rub a pumice stone on their skin (normally their
feet) to remove dead or rough skin.
Pumice stone
What is the largest active volcano?
The world's largest, active volcano is Mauna Loa in
Hawaii, where famous coffee is grown in the rich
volcanic soils. Mauna Loa is taller than Mount Everest.
Mauna Loa Volcano
What is the Ring of Fire?
The Pacific Ring of Fire is an area of
frequent earthquakes and volcanic eruptions
within the basin of the Pacific Ocean. The
Ring of Fire has 452 volcanoes and is home
to over 50% of the world's active and
dormant volcanoes. Ninety percent of the
world's earthquakes and 81% of the world's
largest earthquakes occur along the Ring of
Fire.
The Pacific Ring of Fire
Information sourced from: http://www.weatherwizkids.com/weather-volcano.htm
http://www.ngkids.co.uk/science-and-nature/Volcano-Facts
http://www.kidsdiscover.com/infographics/infographic-volcanoes-inside/