VOLCANISM
WHAT IS VOLCANO?
• A volcano is a vent or
'chimney' that connects
molten rock (magma)
from within the Earth’s
crust to the Earth's
surface.
• The volcano includes
the surrounding cone of
erupted material.
vent
cone
conduit
WHY DO VOLCANOES ERUPT?
• Hot, molten rock (magma) is buoyant (has a lower density
than the surrounding rocks) and will rise up through the
crust to erupt on the surface.
• When magma reaches the surface it depends on how easily
it flows (viscosity) and the amount of gas (H2O, CO2, S) it
has in it as to how it erupts.
TYPES OF ERUPTIONS
•
Explosive eruptions eject large amounts of gas and a high
viscosity (sticky) magma (Andesitic or Rhyolitic magma).
EXPLOSIVE ERUPTIONS
• Explosive volcanic eruptions
can be catastrophic
• Erupt 10’s-1000’s km3 of
magma
• Send ash clouds >25 km
into the stratosphere
• Have severe environmental
and climatic effects
Above: Large eruption column and
ash cloud from an explosive eruption
at Mt Redoubt, Alaska
EXPLOSIVE ERUPTIONS
• Three products from
an explosive eruption
– Ash fall
– Pyroclastic flow
– Pyroclastic surge
Pyroclastic flows on
Montserrat, buried the
capital city.
EXPLOSIVE ERUPTIONS
Direct
measurements of
pyroclastic flows
are extremely
dangerous!!!
TYPES OF ERUPTIONS
• Effusive eruptions release small amounts of gas and (or)
low viscosity (runny) magma (Basaltic magma).
EFFUSIVE ERUPTIONS
EFFUSIVE ERUPTIONS
• These form at hot
spots or spreading
centers creating
either a shield
volcano or basalt
flood plane.
VOLCANIC DANGERS
1.
2.
3.
4.
5.
6.
Pyroclastic flow
Pyroclastic surge
Pyroclastic fall (Tephra)
Lava flow
Earthquakes
Noxious Gases
1. PYROCLASTIC FLOWS
• They are hot, turbulent, fast-moving, high particle
concentration clouds of rock, ash and gas.
• They can reach > 100 km from a volcano.
• They can travel 100’s km/h and are commonly >400°C.
• They will destroy everything in their path including
buildings, agriculture and forests. Although because they
contain a high concentration of particles and a low
concentration of gas,
• they are dense and usually are confined to, and flow along,
topographic lows (valleys).
• It is extremely important to understand them as they are
often the most hazardous component of an explosive
eruption.
1. PYROCLASTIC FLOWS
1. PYROCLASTIC FLOWS
1. PYROCLASTIC FLOWS
2. PYROCLASTIC SURGE
• These are low particle/high gas concentration (low
density) flows of volcanic material.
• Pyroclastic surges can travel up to 360 km/h and be
greater than 600oC
• They can go overtop of high topographic features, and
therefore are not confined to valleys.
• Pyroclastic surges can travel up to at least 10
kilometers from the source.
3. PYROCLATIC FALL (TEPHRA)
• rock fragments thrown into the air by an
explosive eruption.
• They can range in size from dust to the
size of cars (lava bomb)
• They can collapses roofs, brings down
power lines, kill plants, contaminates
water supplies, and be a respiratory
hazard for humans and animals.
4. LAVA FLOW
• It is not just explosive volcanic activity that can be
hazardous. Effusive (lava) activity is also
dangerous.
4. LAVA FLOWS
• Lava flows have temperatures in excess of 200oC.
Therefore will burn any flammable material it
contacts with.
4. LAVA FLOWS
• Thick lava flows will bury all in it’s path including
infrastructure (buildings, roads, waterways etc.)
and agricultural land…
5. EARTHQUAKES
• Earthquake activity commonly precedes an eruption
• Earthquakes are a result of magma pushing up towards the
surface. The increase volume of material in the volcano
shatters the rock.
6. NOXIOUS GASES
• Volcanoes produce large quantities of gases, mostly water
(H2O), but also significant amounts of carbon dioxide (CO2),
hydrogen sulphide (H2S), sulphur dioxide (SO2), and
hydrofluoric acid (HF) as well as some chlorine (Cl) and
nitrogen (N) compounds.
• Each of these gases has caused loss of life and damage.
• Sulphur dioxide vented from the Laki volcano in Iceland in
1783 damaged crops and killed livestock and people.
• When SO2 reacts with water in the atmosphere, it forms
sulphuric acid and acid rain. Acid rain formed from
volcanic clouds can damage crops.
• When CO2 gas, which is heavier than air, is released by a
volcano, it collects in low areas; concentrations can become
high enough to be deadly.
6. NOXIOUS GASES
•
•
•
Lake Nyos (Cameroon) is a crater lake inside a
dormant volcano.
The lake had become laden with carbon dioxide
gas.
This gas had suddenly bubbled out of the lake and
asphyxiated nearly every living being in the
surrounding valley.
TYPES OF VOLCANOES
1. Shield Volcano
–
–
–
A large, circular
volcano with gentle
sloping sides.
Created from
layers of nonexplosive, basaltic
lava flows.
Has a large caldera
in the middle.
TYPES OF VOLCANOES
TYPES OF VOLCANOES
2. Cinder Cone Volcanoes
–
–
Form from the fallout of the ejected material of an
explosive eruption.
Have steep sides and are generally less than 500 m
high.
TYPES OF VOLCANOES
• Mt Edziza (B.C.)
Paricutin volcano began to erupt in a corn field
in Mexico in 1943 and continued until 1952.
The farmer had noticed a fissure (vent) had
opened in the field one morning and from it
was pouring black ash.
In the first year the volcano grew to 336 m
(almost 1 metre per day).
Rate of growth decreased steadily; by 1952 the
volcano was 424 m in height.
TYPES OF VOLCANOES
• Cinder Cone volcanoes sometimes appear on old
Shield volcanoes
TYPES OF VOLCANOES
3. Composite or
Stratovolcanoes
–
–
–
Volcanoes that alternate
between periods of lava
flows (constructive phase)
and periods of explosive
eruptions (destructive
phase).
Commonly called
“composite volcanoes”
because they are made up
of both lava and
pyroclastic deposits.
Can be much larger than a
Cinder Cone volcano
CANADIAN VOLCANOES
Mt. St. Helens Before
Mt. St. Helens After
Extensive ash falls and ash flows are commonly produced
during explosive phases.
OTHER TYPES OF VOLCANOES
• http://www.youtube.com/watch?v=xExdEXOaA9
A&feature=channel
• http://www.youtube.com/watch?v=NBPwwt0Hu
Vo&feature=related
• http://www.youtube.com/watch?v=Bz7WCttwXQ
k&feature=related
• http://www.cbc.ca/documentaries/passionateeye
showcase/2010/volcano/