Transcript Volcanic Eruption

Earth Science Notes
Volcanic Eruptions
Our Objectives Today are…
I can …
• Explain the Factors that affect Volcanic
Eruptions
• Describe the Features of Volcanic Activity
– Intrusive Igneous Rocks (CH 5)
• Describe the destructiveness of Volcanoes
• The Circle of Life
Factors Affecting Eruptions
Trapped Gases
• Carbon dioxide and water vapor
get trapped in magma and
escape when pressure
decreases
• Gases that build up a lot of
pressure cause explosive
eruptions
Factors Affecting Eruptions
• Gases build up
more pressure in
thicker (more
viscous) magma.
• What type of
magma would
cause the greatest
explosion.
Recall: Unit 3
Viscosity means RESISTANCE
TO FLOW
Factors Affecting Eruptions
Silica Content
• Silica is a compound composed of silicon and oxygen
• Magma that is silica-rich (i.e. Granitic) produces
explosive eruptions
– Has a high viscosity (THICK)
– TRAPS more gasses
– RECALL: silica-rich magma formed granitic (felsic) rocks
Factors Affecting Eruptions
Silica Content
• Silica is a compound composed of silicon and oxygen
• Magma that is silica-poor (i.e. Basaltic) produces
quiet explosions
– Has a LOW viscosity (Thin)
– Forms nonexplosive eruptions
– RECALL: silica-poor magma formed basaltic (mafic) rocks
Hawaiian Volcano
Basaltic

Andesitic

Granitic (Rhyolitic)
Factors Affecting Eruptions
• Low Viscosity (Basaltic) Magma
– https://www.youtube.com/watch?v=qTTLYx4X
o2k
• Higher Viscosity (Granitic) Magma
– https://www.youtube.com/watch?v=e4PUOBI
wEv0
Volcanic Eruption Types
• Volcanic
eruptions are
characterized by
expolosivity and
height of plume.
Please Note: as with
classification scheme, there
are several forms and
eruptions may be difficult to
distinguish at times
Volcanic Eruption Types
Four Main categories of volcanic eruptions
(see EN: Kinds of Eruptions)
• Hawaiian
– weakest
• Strombolian
– weak
• Vulcanian
– kind of explosive
• Pelean
– massive explosions
Volcanic Eruption Types
Hawaiian Eruptions
https://www.youtube.com/watch?v=CSu_n
etRm8E
Volcanic Eruption Types
Strombolian Eruptions
https://www.youtube.com/watch?v=wS57sd7j9Y
Volcanic Eruption Types
Vulcanian Eruptions
https://www.youtube.com/watc
h?v=YF7ib5ToVs4
Volcanic Eruption Types
• Pelean Eruptions
Volcanic Eruption Types
• Even Larger than a Pelean Eruption are
Plinian Eruptions https://www.youtube.com/watch?v=IETUa_
nOk1g
Volcanoes Destructiveness
Mount Vesuvius - 79 AD
Volcanoes Destructiveness
• Mount St. Helen - Washington
Volcanoes Destructiveness
Features Of Volcanic Activity
Limnic Eruptions: Lake Nyos
Features Of Volcanic Activity
Limnic Eruptions: Lake Nyos
• Lake Nyos is a deep lake
high on the flank of an
inactive volcano in
Cameroon.
• A pocket of magma lies
beneath the lake, charging
the water with an estimated
90 million tonnes of carbon
dioxide (CO2).
• In 1986, a limnic eruption at
Lake Nyos triggered the
sudden release of about 1.6
million tonnes of CO2 that
rushed down nearby
valleys, displacing all the air
and suffocating
approximately 1,700 people
within 20 km of the lake.
Features Of Volcanic Activity
Limnic Eruptions: Lake Nyos
Elements for a
Limnic Eruption
• Very deep
volcanic lake.
• Lake has to be
over a slow source
of volcanic gas.
• Lake has to be
very, very still.
Features Of Volcanic Activity
Limnic Eruptions: Lake Nyos
Volcanoes Destructiveness
Volcanoes Destructiveness
This Diagram shows range of potential destruction
A super-eruption has
the potential to cover
the United States in 3
feet of ash from a
plume. Pyroclastic flow
would engulf the
greater part of three
states, and there is
evidence that the last
major 'super' eruption
plunged the world into
a freezing, volcanic
winter that lasted a
decade. An eruption
would devastate world
agriculture, severely
effect the distribution of
food and cause mass
famine.
After the Aftermath
Features Of Volcanic Activity
• Batholiths – formed when magma cools
underground
Features Of Volcanic Activity
• Volcanic Neck – magma inside volcano
cools and outside is eroded away
Features Of Volcanic Activity
• Dike – magma that cools in vertical cracks
Features Of Volcanic Activity
• Sill – magma that cools in horizontal
cracks
Features Of Volcanic Activity
• Caldera – top of volcano collapses on
emptied magma chamber
Photograph by M. Williams, National Park Service, 1977
Features Of Volcanic Activity
Features Of Volcanic Activity
Our Objectives Today were…
Can I …
• Explain the Factors that affect Volcanic
Eruptions
• Describe the Features of Volcanic Activity
– Intrusive Igneous Rocks (CH 5)
• Describe the destructiveness of Volcanoes
• The Circle of Life