Volcanoes & Volcanic
Activity
By Philipp S., 3rd hour
Shield Volcano
They are a large
volcano which has
shallow-sloping sides
 They have basaltic
magma that is not
viscous -> so it flows
very far
 Shield volcanoes are
not explosive because
of the basaltic magma

http://en.wikipedia.org/wiki/Shield_volcano
http://www.alohablooms.com/img/snow012302/maunak
ea_snow_coconut_leaf.jpg
Stratovolcano
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Is composed of many
layers of hardened lava,
tephra, and volcanic ash
Is a tall, conical volcano
Has andesitic or rhyolitic
magma which doesn’t
flow good because it’s
very viscous
They are very explosive
because of the nonviscous magma
http://en.wikipedia.org/wiki/Stratovolcano
http://en.wikipedia.org/wiki/Image:Popocat%C3%A9petl_
sunrise.jpg
Cinder Cone
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Made from rock
fragments that
accumulate around and
downwind from volcanic
vent
They are steep, conical
hills
They are located on the
flanks of shield
volcanoes,
stratovolcanoes and
calderas
http://en.wikipedia.org/wiki/Paricutin
http://en.wikipedia.org/wiki/Image:Paricutin.jpg
Caldera
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Forms after a big
eruption of a volcano
The volcano collapses
because there is no more
magma under it.
They can explode in huge
eruptions that are 2500
times as big as the
eruption of Mt. St. Helens
http://en.wikipedia.org/wiki/Caldera
http://en.wikipedia.org/wiki/Image:Santorini_Landsat.jpg
Lava Dome
Forms in the crater of
a volcano
 It is formed by a slow
eruption of rhyolitic
magma
 Most stratovolcanoes
have a lava dome in
their crater

http://en.wikipedia.org/wiki/Lava_dome
http://en.wikipedia.org/wiki/Image:MSH06_aerial_crater
_from_north_high_angle_09-12-06.jpg
Flood Basalt
They are results of
gigantic volcano
eruptions
 Have lava with low
viscosity -> basaltic
 They can be from
200,000km2 to
1,500,000km2

http://en.wikipedia.org/wiki/Flood_basalt#Struct
ures
http://en.wikipedia.org/wiki/Image:3-Devils-gradeMoses-Coulee-Cattle-Feed-Lot-PB110016.JPG
Basaltic Lava
High temperature:
1200°C
 Silica-poor, low viscosity
(flow very good), low gas
content
 The thin lava flows form
shields
->Shieldvolcano
 Is not explosive, it’s
flowing

http://www.teara.govt.nz/EarthSeaAndSky/Natur
alHazardsAndDisasters/Volcanoes/1/ENZResources/Standard/3/en
http://www.earlham.edu/~yeakech/pics/basalt.jpg
Andesitic Magma
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Moderate temperature:
1000°C
Moderate silica content,
moderate viscosity,
moderate gas content
It’s flowing and moderate
explosive
Forms thick lava flows
Mainly in Stratovolcanoes
http://www.teara.govt.nz/EarthSeaAndSky/Natur
alHazardsAndDisasters/Volcanoes/1/ENZResources/Standard/3/en
http://www.ufrsd.net/staffwww/stefanl/Geology/volcano/p
ahoehoe.jpg
Rhyolitic Magma
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Low temperature: 850°C
Silica-rich, very high
viscosity (doesn’t flow
very good), high gas
content ->very explosive
Eruption product:
pyroclastic flows, ash fall
Mainly in calderas
http://www.teara.govt.nz/EarthSeaAndSky/NaturalHazar
dsAndDisasters/Volcanoes/1/ENZResources/Standard/3/en
http://www.discoverourearth.org/student/volcanoes/image
s/st_helens_mosaic3.gif
Plinian Eruption
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Is characterized by large
gas blast eruptions which
are very loud
Extends columns of
smoke and ash high into
the stratosphere
The ash deposits over
large areas
Erutpions can last from
one day to several
months
http://en.wikipedia.org/wiki/Plinian_eruption
http://upload.wikimedia.org/wikipedia/commons/f/f4/Vesuvi
us1822scrope.jpg
Strombolian Eruption
Eject lava bombs to
altitudes of tens to
hundreds of meters
 Is a low level eruption
but can last very long
 The lava flows are
more viscous
-> andesitic

http://en.wikipedia.org/wiki/Strombolian_eruption
http://upload.wikimedia.org/wikipedia/commons/9/93/Stro
mboli_Eruption.jpg
Hawai’ian Eruption
Low level eruption,
with basaltic lava
 The lava flows flow
very far because
basaltic lava has low
viscosity
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http://www.ldeo.columbia.edu/news/2005/images/eruption.
jpg
http://en.wikipedia.org/wiki/Hawaiian_eruption
Phreatic Eruption
Occur when magma
makes contact with
ground water
 The water evaporates
nearly instantaneous
 This causes a steam
explosion
 It typically include
rock fragments
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http://en.wikipedia.org/wiki/Phreatic_eruption
http://upload.wikimedia.org/wikipedia/commons/
8/8a/Phreatic.jpg
Sill
Is a intrusion that
intruded between
older layers of
sedimentary rock
 They can be from
fractions of an inch to
hundreds of feet thick
and up to hundreds of
miles long
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http://en.wikipedia.org/wiki/Sill_%28geology%29
http://z.about.com/d/geology/1/0/J/S/sill.jpg
Batholith
Forms from cooled
magma deep in the
Earth’s crust
 When the surrounding
rock erodes the
batholith stays
because it is made
out of very hard rock
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http://whatonearth.olehnielsen.dk/img/batholith.jpg
http://en.wikipedia.org/wiki/Batholith
Dike
It’s an intrusion that
cuts cross pre-existing
or old bodies of rock
 They sometimes
appear as swarms
 They are made from
either basaltic,
rhyolitic or granitic
magma
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http://en.wikipedia.org/wiki/Dike_%28geology%
29
http://www.calvin.edu/academic/geology/pics/adirondacks/
dike.jpg
Stock
Have a surface
exposure of less than
40 square miles
 Is like a small
batholith
 Most stocks are
probably the tops of
hidden batholiths
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http://en.wikipedia.org/wiki/Stocks_%28geology
%29
http://www.geo.arizona.edu/tectonics/Ducea/projects/Huat
ulco%20batholith2.jpg
Laccolith
Is between two layers
of sedimentary rock
 Looks like a dome or
mushroom
 Are formed by viscous
magma -> andesitic
or granitic magma
 It cools slowly down
and forms large
crystals
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http://en.wikipedia.org/wiki/Laccolith
http://mason.gmu.edu/~sharlan/adelmountainvolcanics_fil
es/image014.jpg