Volcanism & Extrusive
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Volcanism & Extrusive. expulsion of molten rock (LAVA), gases and water onto the surface of the Earth. •. Igneous Activity. -. 550 active volcanoes. >. Active = erupted in historic times. -. e.g. Mauna Loa and Kilauea (Hawaii). -. Mt. St. Helens (Washington). -.

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Mt. Fujiyama, Japan

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Mt fujiyama japan

Volcanism & Extrusive

expulsion of molten rock (LAVA), gases and

water onto the surface of the Earth.

Igneous Activity

-

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


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Dormant

Extinct Volcanoes

vs

Dormant volcanoes

Dormant volcanoes

-

have not erupted recently, but may do so again.

-

have not erupted recently, but may do

>

Mt. Vesuvius (Italy)

>

Mt. Vesuvius (Italy)

Extinct volcanoes

Extinct or inactive volcanoes

-

have not recently erupted

-

nor do they give indications

of erupting in the future.

Thousands of these

>

>

types ofvolcanoes exist.

Mt. Kilamanjaro (Tanzania,Africa)


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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.


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Unzen Volcano, Japan shown with Lava dome and lahars (volcanic debris flows)


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Caldera


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Bathymetry map of Crater lake, Oregon


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Summit of Kilauea-inner crater


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Volcanoes types


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Olympus Mons, a shield volcano


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A small shield volcano in Iceland


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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)

Composite Volcanoes


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Stratovolcano formation


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Composite Volcanoes

Mayon volcano, Philippines, is a

Mayon volcano, Philippines, is a

View of Mount St. Helens,

View of Mount St. Helens,

nearly symmetrical composite

nearly symmetrical composite

Washington in 1978.

Washington in 1978.

volcano.

volcano.


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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.


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Cinders and volcanic ash


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Development of Cinder Cone

Development of Cinder Cone


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Lava Types

Pahoehoe lava (smooth & ropey) in

Aa lava (rough and blocky) also

Pahoehoe lava (smooth & ropey) in

Aa lava (rough and blocky) also

Hawaii.

in Hawaii.

Hawaii.

in Hawaii.


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Pillow Lavas

These bulbous masses of pillow

These bulbous masses of pillow

lava formed when lava erupted &

lava formed when lava erupted &

cooled under water.

cooled under water.

1 meter

1 meter


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Lava Fountain

Lava Fountain


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Pyroclastic Ash Flow

'

aka Nuee Ardentes

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

>


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Glowing Ash clouds-

Nuee Ardentes


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Ash plume from a stratovolcano eruption


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Pyroclastic flow

,

Nuee Ardente


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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


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The effects of explosive volcanic activity


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Gases and Magma

Volcanic gases

-

water vapor

- carbon dioxide

-

nitrogen

- sulfur oxides

-

hydrogen sulfide

- 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.


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Lake Nyos, a volcanic lake in Cameroon, Africa

CO2 emitted from the acidic lake killed 1700 villagers near the lake in 1986


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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)


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Distribution of volcanoes is not random

related to plate tectonics

commonly found along plate boundaries


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Eruption types are a function of plate tectonic setting, magma composition and water/gas content.


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Plinian eruption of Lascar Volcano in Chile


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A Vulcanean eruption


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Surtseyan eruption


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Vesuvian eruption


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Strombolian style eruption of Tungurahua Volcano, Ecuador


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Eruption styles and their relative explosiveness

* VEI stands for Volcanic Explosivity Index


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