Volcanoes

What are Volcanoes?
● A volcano is a rupture of the Earth's crust which allows hot
lava, poisonous gases and ash to escape from the magma
chambers below the surface.
● Volcanoes occur because the Earth's crust is separated into 17
rigid tectonic plates that float around on a hotter and
softer mantle below.
● This is why volcanoes are generally found around places
where the plates converge and diverge. For example, as
the plates move apart, a fissure opens in the ground,
allowing lava to pour out onto the surface. This is called a
fissure volcano.
● Scientist who study volcanoes are call Volcanologists.

Volcano Phases
● Volcanoes can be in one of three phases: Active, Dormant,
and Extinct.
● Active volcanoes are ones that have erupted in the pas
10,000 years, and that are likely to erupt again. An
example is Mt. Saint Helens in U.S.A.
● Dormant volcanoes are ones that have not erupted in the
past 10,000 years, but still have the possibility, though
unlikely. An example is Mt. Rainier in the U.S.A.
● Extinct volcanoes are ones that nobody think will erupt
ever again. An example is Mt. Ashitaka in Japan.

Types of Volcanoes
● There are four types of Volcanoes:
● Fissure Volcanoes,
● Cinder Cone Volcanoes,
● Shield Volcanoes,
● Composite Volcanoes,

Fissure Volcanoes
● Fissure volcanoes are cracks in the ground that are only
a few metres wide but can be several kilometres in
length.
● Fissure volcanoes are not usually explosive. Instead, the
lava seeps out of the gaps in the surface of the crust.

Shield Volcanoes
● Shield volcanoes are almost entirely made up out of fluid
lava flows.
● Vent after vent flows out through the volcano from the
centre vent.
● This builds a broad, gentle sloping cone of a flat, dome
shape, similar to a warriors shield.

Composite Volcanoes
● Composite volcanoes are some of the grandest on the
world.
● They are typically large, steep, symmetrical cones built
of alternating flows of lava ash and cinders.
● Most have a crater at the summit which contains a
central vent or a clustered group of vents.

Cinder Cone Volcanoes
● Cinder cone volcanoes are formed large globs of lava
being launched from a single vent.
● As the gas-charged chambers explodes, lava gets
launched into the air only to fall back down around
the main vent as cinders in an oval or circular cone.
● Most have a bowl-shaped crater in the centre.

What Causes Volcanoes?
● Volcanic activity frequently occurs on the boundaries of
tectonic plates as the pressure within causes the
magma below to rise up and explode or escape to the
surface.

The Ring of Fire!
● The Ring of Fire is a string of volcanoes that runs around
the edge of the Pacific Ocean.
● The Ring of Fire is quite a circle, more like 40,000
kilometre long horseshoe.
● A string of 452 volcanoes stretches from the southern tip
of South America, up along the coast of North
America, across the Bering Strait, down through
Japan, and into New Zealand.

Measuring Volcanic Eruptions
● Volcanic eruptions are measured using the Volcanic Explosivity Index
(VEI)
● Since the size and force of eruptions vary, Volcanologists take a
number of factors into account when measuring volcanic
eruptions, such as:
● Volume of material ejected, height of the eruptive column,
duration etc.
● Each eruption is given a rating of 0-8. 0 being non-explosive and
harmless, and 8 being “Run for your lives the planet is melting!”
● Each point on the scale is 10 times more powerful than the one
before. This makes the most devastating eruptions that we know
of thousands of times more powerful than the eruption that took
off the top 400m of Mt. St Helens almost a quarter of a century
ago.

VEI

Earthquakes

What are Earthquakes?
● An earthquake is the result of a sudden
release of energy in the crust that
creates seismic waves.
● The seismicity of an area refers to the
frequency, size, and type of earthquake
experienced over a period of time.

What cause Earthquakes?
● The Earth's crust is made up of several tectonic plates.
These plates are always moving around on the mantle.
● Because these plates are moving, they constantly grind
against one another and get stuck.
● When the rest of the plate moves far enough, one of the
two plates fault, which releases large amounts of
energy that was stored up by the tension.
● This causes an earthquake.

Focus and Epicentre
● The focus of an earthquake is where it begins, this is
where the plate slips on a fault line, usually at the
plate edges.
● The Epicentre is the point directly above the Focus on
the surface of the earth. This area will suffer from the
most direct damage.

Seismic Waves
● Seismic waves are the waves of energy caused by the
breaking of rock during an earthquake.
● The main two types of waves are body waves and surface
waves.
● Body waves occur in two types, primary waves (P) and
secondary waves (S).
● Surface waves occur after the body waves as lower
frequencies which are responsibly for most of the damage
and destruction on land.
● Surface waves have two types, Love waves and Rayleigh
waves.

Wave Types

Measuring Earthquakes
● The vibrations earthquakes produce are
detected, recorded and measured by
instruments called Seismographs.
● The line made by a seismograph is
called a seismogram and shows the
changing intensity of the earthquake
by responding to motion of the
ground below the instrument.
● From the data expressed in
seismograms, scientists the time,
the epicentre, the focal depth, the
type of faulting of an earthquake
and how much energy was released.

The Richter Scale

The Modified Mercalli Scale