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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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


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)


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.



Caldera (volcanic debris flows)


Bathymetry map of Crater lake, Oregon (volcanic debris flows)


Summit of Kilauea-inner crater (volcanic debris flows)


Volcanoes types (volcanic debris flows)


Olympus Mons, a shield volcano (volcanic debris flows)


A small shield volcano in Iceland (volcanic debris flows)


a.k.a.- stratovolcanoes (volcanic debris flows)

-

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


Stratovolcano formation (volcanic debris flows)


Composite Volcanoes (volcanic debris flows)

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.


Cinder Cones (volcanic debris flows)

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 (volcanic debris flows)


Development of Cinder Cone (volcanic debris flows)

Development of Cinder Cone


Lava Types (volcanic debris flows)

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.


Pillow Lavas (volcanic debris flows)

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


Lava Fountain (volcanic debris flows)

Lava Fountain


Pyroclastic Ash Flow (volcanic debris flows)

'

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

>


Glowing Ash clouds- (volcanic debris flows)

Nuee Ardentes



Pyroclastic flow (volcanic debris flows)

,

Nuee Ardente


, (volcanic debris flows)

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



Gases and Magma (volcanic debris flows)

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.


Lake Nyos, a volcanic lake in Cameroon, Africa (volcanic debris flows)

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


Mt. St. Helens (volcanic debris flows)


Effects of Volcanic activity (volcanic debris flows)

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 (volcanic debris flows)

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 magma composition and water/gas content.


A Vulcanean eruption magma composition and water/gas content.


Surtseyan eruption magma composition and water/gas content.


Vesuvian eruption magma composition and water/gas content.


Strombolian style eruption of Tungurahua Volcano, Ecuador magma composition and water/gas content.


Eruption styles and their relative explosiveness magma composition and water/gas content.

* VEI stands for Volcanic Explosivity Index


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