VOLCANO NOTES
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Transcript of VOLCANO NOTES
• There are 2 types of volcanismThere are 2 types of volcanism
IntrusiveIntrusive--------magma magma cools below the cools below the surface and makes plutons (igneous surface and makes plutons (igneous intrusions)intrusions)
Extrusive-Extrusive---liquid rock --liquid rock lava lava cools on the cools on the surface (volcanoes, lava plateaus)surface (volcanoes, lava plateaus)
Igneous IntrusionsIgneous Intrusions
Dikes•Small magma intrusions (no more than a few 100 m wide)•Cut across other rock layers•Force their way along lines of weakness such as faults.
Shiprock, NM ---volcanic plug Shiprock, NM ---volcanic plug and dikeand dike
DikeDike
Igneous IntrusionsIgneous Intrusions
Sills• Small magma intrusions (no
more than a few 100 m wide)• Run parallel to rock layers• Force their way along lines of
weakness such as bedding planes.
A sill in the Salt River A sill in the Salt River Canyon, Arizona Canyon, Arizona
COLUMNAR JOINTINGCOLUMNAR JOINTING• Form in sills and dikes that cool Form in sills and dikes that cool
slowly and form six-sided columns slowly and form six-sided columns
These pictures were taken on Oregon These pictures were taken on Oregon 19, just north of US 20 19, just north of US 20
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Columnar
jointing in
basalt at
Devil’s
Postpile near
Mammoth
Lakes, CA
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Top of jointed basalt columns, Devil’s Postpile, CA
Igneous IntrusionsIgneous Intrusions
Laccoliths - • Lens shaped igneous intrusion• Have a “floor”---there are sedimentary rock layers
beneath the base
Batholiths -• larger • have no “floor”
A batholith exposed by erosionA batholith exposed by erosion
Enchanted Rock Enchanted Rock batholith; exfoliation domebatholith; exfoliation dome
Intrusive Igneous BodiesIntrusive Igneous Bodies
Locations of some of EarthLocations of some of Earth’’s s major volcanoesmajor volcanoes
• A volcano is active, or alive, when it erupts often.
• When a volcano is dormant, it has not erupted for a long time – but it might in the future.
• A volcano is extinct when it hasn’t erupted for at least 100,000 years.
Active, Dormant, or Extinct?Active, Dormant, or Extinct?
Types of EruptionsTypes of Eruptions
Depends on trapped gases and magma composition
•Violent and explosive•Quiet and flowing
• http://dsc.discovery.com/convergence/pompeii/videogallery/videogallery.html
Trapped GasesTrapped Gases•Water vapor and carbon
dioxide are trapped in magma•At low pressure, they escape
quietly when they reach the surface
•At high pressure, they escape violently when they reach the surface
Magma CompositionMagma Composition
•Two types:–Basaltic – less silica and very fluid; produces quiet eruptions
–Granitic – lots of silica, high water vapor content, and very thick; produces very violent eruptions
GLOSSARYGLOSSARY
Bomb – a lump of rock thrown out in an eruptionCrater – a deep hollow at the top of a volcanoLava – melted rock that flows down the volcanoMagma – melted rock inside the EarthMolten – melted, liquidVent – a crack on the side of a volcano where magma can
escape
Forms of VolcanoesForms of Volcanoes
•Three forms:–Shield–Cinder Cone–Composite
Shield VolcanoShield Volcano
•Formed by quiet eruptions•Basaltic lava builds up in flat layers
•Gently sloping sides•Ex: Hawaiian Islands (Mauna Loa)
Shield volcanoShield volcano
Mauna Kea
Shield volcanoHot Spot
Mauna Loa inbackground
Kilauea is behind MaunaLoa (erupting since 1983)
Kilauea
Pahoehoe (smooth, ropy) lava flowPahoehoe (smooth, ropy) lava flow
aa lava flow (slow, chunky)aa lava flow (slow, chunky)
• http://www.learner.org/interactives/volcanoes/movies/movies3.html
Cinder Cone VolcanoCinder Cone Volcano•Caused by explosive eruptions•Granitic lava thrown high into
the air•Lava cools into different sizes of
volcanic material called tephra•Steep-sided, loose slopes•Ex. – Paricutin (Mexico)
Cinder coneCinder cone
Composite/StratovolcanoComposite/Stratovolcano
•Alternating layers of ash and lava
•Quiet or violent•Basaltic or granitic•Steep or gentle slopes•Ex. – Mt. St. Helens
Composite volcano Composite volcano
Guagua Pichincha, EcuadorQuito in foregroundComposite volcanoes - explosive
Arenal Volcano – Costa RicaArenal Volcano – Costa Rica
Photo by E. L Crisp, 2007
Mt. St. Helens Mt. St. Helens –– a typical a typical composite volcanocomposite volcano
Mt. St. Helens following the Mt. St. Helens following the 1980 eruption 1980 eruption
http://www.youtube.com/watch?v=bgRnVhbfIKQ&feature=related
NueNueéé ardente (hot pyroclastic ardente (hot pyroclastic flow) flow) on Mt. St. Helenson Mt. St. Helens
Mt. Vesuvius – 79 a.d.Mt. Vesuvius – 79 a.d.
A A laharlahar (mud flow caused by melting (mud flow caused by melting snow) along the Toutle River near snow) along the Toutle River near
Mt. St. HelensMt. St. Helens
Composite VolcanoMt Rainier
Subduction zones
A size comparison of the three A size comparison of the three
types of volcanoestypes of volcanoes
Other volcanic landforms Other volcanic landforms Calderas
• Steep walled depression at the summit • Formed by collapse • Nearly circular • Size exceeds one kilometer in diameter
Fissure eruptions and lava plateaus • Fluid basaltic lava extruded from crustal
fractures called fissures • e.g., Columbia Plateau
Crater Lake, Oregon is a good Crater Lake, Oregon is a good example of a calderaexample of a caldera
Crater Lake in OregonCrater Lake in Oregon
Lava PlateausLava Plateaus• Magma seeps through
cracks on surface, spreads out and cools
• Process can go on for millions of years and cover very wide areas
The Columbia River basaltsThe Columbia River basalts
Other volcanic landforms Other volcanic landforms
Volcanic pipes and necks • Pipes are short conduits that connect a
magma chamber to the surface • Volcanic necks (e.g., Ship Rock, New
Mexico) are resistant vents left standing after erosion has removed the volcanic cone
Formation of a volcanic neckFormation of a volcanic neck
Shiprock (volcanic neck) New Shiprock (volcanic neck) New MexicoMexico
Devil’s Tower---WyomingDevil’s Tower---Wyoming
EyjafjallajokullEyjafjallajokull
• http://www.boston.com/bigpicture/2010/04/more_from_eyjafjallajokull.html