Volcanism & Extrusive
Igneous Activity
• expulsion of molten rock (LAVA), gases and
water onto the surface of the Earth.
- 550 active volcanoes
> Active = erupted in historic times.
- e.g. Mauna Loa and Kilauea (Hawaii)
- Mt. St. Helens (Washington)
- Mt. Pinatubo (Philippines)
- Mt. Fujiyama (Japan)
- Mont Serrat (Caribbean)
Mt. Fujiyama, Japan
Dormant vs Extinct Volcanoes
•• Dormant volcanoes
- have not erupted recently, but may do so again.
> Mt. Vesuvius (Italy)
Extinct or
volcanoes
• -Extinct
inactive
volcanoes
have not recently
erupted
nor do they give indications
of erupting in the future.
> Thousands of these
types of volcanoes exist.
Mt. Kilamanjaro (Tanzania,Africa)
Volcanoes, Craters, Domes, Calderas
• Conical mountains
- central vent where lava, gases, and
pyroclastic materials are erupted.
- Craters
- circular opening at summit
- generally less than 1 km in diameter
- Dome
- a large mound of viscous, felsic lava
- commonly plugs the central vent
• Calderas
- a collapsed volcanic summit
- greater in diameter
- have steep sides.
Unzen Volcano,
Japan shown
with Lava dome
and lahars
(volcanic debris
flows)
Caldera
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Bathymetry map of Crater lake, Oregon
Summit of Kilauea-inner crater
Volcanoes types
Olympus Mons, a shield volcano
A small shield volcano in Iceland
Composite Volcanoes
• a.k.a.- stratovolcanoes
- interbedded pyroclastics and lavas.
- typically andesitic to rhyolitic lava
> intermediate to felsic magma composition
- Found on continents and island arcs
> mostly associated with convergent plate
boundaries (subductive)
>
examples of composite
Mt. St. Helens, Mt. Vesuvius, Mt. Pinatubo,
Mt. Fujiyama, Mt. Kilamanjaro., Mt. Rainier
(photo)
Stratovolcano formation
Composite Volcanoes
Mayon volcano, Philippines, is a
nearly symmetrical composite
volcano.
View of Mount St. Helens,
Washington in 1978.
Cinder Cones
Primarily cinder-sized (0.25-1.0 mm) material.
but may have other sizes too.
Cinders fall to Earth and collect around the vent.
have steep slopes up to 33 degrees
smaller than shield volcanoes, usually less than
400 m tall
Form on the flanks of larger volcanoes.
Cinders and volcanic ash
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Development
of of
Cinder
Cone
Development
Cinder
Cone
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Lava Types
Pahoehoe lava (smooth & ropey) in
Hawaii.
Aa lava (rough and blocky) also
in Hawaii.
Pillow Lavas
These bulbous masses of pillow
lava formed when lava erupted &
cooled under water.
1 meter
Lava Fountain
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Pyroclastic Ash Flow
'
aka Nuee Ardentes
Pyroclastic ash- lava blown up into the air
• smaller stuff is ash, larger stuff are
called "bombs"
Pyroclastic Ash Flow
• extremely fast (100's m/sec)
• extremely hot
- sometimes glowing redhot
• extremely lethal
- many deaths associated with volcanic
eruptions are related to these events
>
e.g., Pompeii and Herculanum
Glowing Ash cloudsNuee Ardentes
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Ash plume from a stratovolcano eruption
Pyroclastic
flow
,
Nuee Ardente
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Lahar - volcanic
mudflow
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,
Lahars & Nuee Ardentes
• Lahars are mud flows that often occur after eruptions.
• Nuée ardentes are mobile dense clouds of incandescent ash that can move downhill at
speeds up to 100
, km/hr.
Mt Pelee destroyed St. Pierre on the island of Martinique, West Indies in 1902
The effects of explosive volcanic activity
Gases and Magma
• Volcanic gases
- water vapor
- nitrogen
- hydrogen sulfide
- carbon dioxide
- sulfur oxides
- chlorine
• Felsic magmas
-
highly viscous : Si-rich
inhibits the expansion of gases
pressure builds up
explosive eruptions, like Mt. St. Helens.
• Mafic magmas
- lower viscosity
- lower gas pressure
- erupt rather quietly, like Hawaiian Volcanoes.
Lake Nyos, a volcanic lake in Cameroon, Africa
CO2 emitted from the acidic lake killed 1700 villagers
near the lake in 1986
Mt. St. Helens
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Effects of Volcanic activity
• builds up mountains and new land; also destroys land
- (Lithosphere-aka. GEOSPHERE)
• destroys many living things
- (biosphere)
• ejects ash and gases into the air blocking sunlight
(exosphere)
• Changes weather and climate patterns for several
months to a year
- (atmosphere)
• Causes changes in drainage patterns, and pollutes
many water sources
- (hydrosphere)
Distribution of volcanoes is not random
• related to plate tectonics
• commonly found along plate boundaries
Eruption types are a function of plate tectonic setting,
magma composition and water/gas content.
Plinian eruption of Lascar Volcano in Chile
A Vulcanean eruption
Surtseyan eruption
Vesuvian eruption
Strombolian style eruption of Tungurahua Volcano, Ecuador
Eruption styles and their relative explosiveness
* VEI stands for Volcanic Explosivity Index