Volcanoes & TectonicsVolcanoes & Tectonics
Seamounts and Guyots
Lava Viscosity (silica, Temp.) & explosivenessLava Viscosity (silica, Temp.) & explosiveness
• Basaltic lava - less silica and higher temperature, low viscosity, gasses escape at surface low pressures, not explosive
e.g. Shield volcanoes, Rifts, MOR, cinder cones• Intermediate silica, explosive, composite =
stratovolcanoes, Andes, Cascades, Aleutians Japan, Philippines, often pyroclastic clouds = nuée ardente
• Rhyolitic lava - more silica and lower temperatures, high viscosity, gasses cannot escape, explosive.
Plate Tectonics and VolcanismPlate Tectonics and Volcanism
Volcanism on a tectonic Volcanism on a tectonic plate moving over a hot plate moving over a hot
spotspot
Pacific Basin 90%Volcanic Output Pacific Basin 90%Volcanic Output Seamounts and MOR => ocean Seamounts and MOR => ocean
floorfloor
Plumes under Continents yield more silica rich, explosive eruptionsPlumes under Continents yield more silica rich, explosive eruptions
Great Basalt PlateausGreat Basalt Plateaus
Volcanic geomorphic provinces
A size comparison of the three A size comparison of the three main types of volcanoesmain types of volcanoes
Seamounts are these largestSeamounts are these largest
Plume below ocean
Above subduction zone
Divergent Zone Cinder Cones
Volcanic Activities and their productsVolcanic Activities and their products
• Exhalative (gas: H2O, CO2, SO2)
• Effusive (lava)
• Explosive (tephra)
Hawaii, low silica, low viscosity, notice no tephra in view
Lava
Flo
w
Upper surface pitted Scoria
Pahoehoe Near vent
Jagged A'a'away from vent
http://volcanoes.usgs.gov/Products/Pglossary/ancientseq.html
Basaltic Pillow LavasBasaltic Pillow Lavas
The reason there is so much water carried down into a subduction zone
Volcanic Activities and their productsVolcanic Activities and their products
• Explosive (tephra)
Intermediate to high silica - Andesitic to Rhyolitic
nuée ardente = pyroclastic cloud
TephraTephra• Coarse = close
• Thick = close
Lahars - volcanic mudflowsLahars - volcanic mudflows
Copyright © Stephane Veyrat-Charvillon 2002
Melting collapse of ice embedded cone
Characteristic Eruptive TypesCharacteristic Eruptive Types
Special case: Phreatic eruptions occur when magma hits water. And the water flashes to steam explosively
Copyright © Richard Kesel 2002
Basaltic lava Basaltic lava flowsflows
• Layered– Lava/sediment
• Jointed– Columnar
Rift Valley FlowsRift Valley Flows
Volcanic Landforms 1: BasalticVolcanic Landforms 1: Basaltic
• Columbia Plateau
• Deccan Traps
• Very large in scale, worldwide effects
Basalt Plateaus - Flood BasaltsBasalt Plateaus - Flood Basalts
Basaltic Cinder and Basaltic Cinder and Spatter Cones Spatter Cones
• Projectiles– Ballistic– Wind-borne
• Divergent Margin +
Shield VolcanoesShield Volcanoes
Mauna Kea from Mauna Loa
•Form above Plumes, hugeForm above Plumes, huge• also Basaltic, gentle eruptionsalso Basaltic, gentle eruptions•As plate moves old volcanoes As plate moves old volcanoes become inactive, new volcano become inactive, new volcano forms over the plumeforms over the plume
Volcanic Landforms, Basaltic continued
Andesitic - Composite conesAndesitic - Composite cones
Mt. Fuji in summer
Volcanic Landforms 2: Andesitic Volcanoes
Form above Subduction zones
"Stratovolcano"
The Cascades, Washington State
Composite cones - sectionComposite cones - section
Lava and tephra alternate
Andesitic EruptionsAndesitic Eruptions
Extensive Welded Tuff, Pumice Lavas, and Lahars
Cleveland Volcano, Aleutians
Plug DomesPlug Domes
Rhyolite Rhyolite EruptionsEruptions
• Rare, extremely explosive
• Size of ash cover = violence
• Toba and our near-extinction
Volcanism on a tectonic Volcanism on a tectonic plate moving over a hot plate moving over a hot
spotspot
CalderasCalderas
Caldera – Crater LakeCaldera – Crater Lake
Copyright © Ann Dittmer 2002
Caldera topography – Crater LakeCaldera topography – Crater Lake
MaarsMaars
Tuff Ring
Ukinrek Maars
A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma
Panum Crater is a good example of both a tuff ring and a Rhyolite dome
Rising magma hit groundwater, explosion left crater, then fountain of hot cinders made ring, then remaining magma rose as dome
Mono Co, CA Rhyolite, very high silica, very viscous, can’t get rid of gas bubbles, explodes
IcelandIceland• Is on the mid-Atlantic Ridge, • 13 volcanoes have erupted since AD 874.• most active & volatile is Grímsvötn.• Over the past 500 years, Iceland's
volcanoes have erupted a third of the total global lava output.
• • One quarter of Iceland ‘s population died
due to eruption of the craters of Laki in 1783-84. The craters are a part of a larger volcanic system with the subglacial Grímsvötn as a central volcano. Because most of Grímsvötn’s eruptions have been subglacial, the interaction of magma and meltwater from the ice causes phreatomagmatic explosions
Tephra forms TuffTephra forms Tuff
Source: Gerald & Buff Corsi/Visuals Unlimited, Inc.
Ignimbrite or Welded Tuff
Erosional Erosional RemnantsRemnants• Plugs
• Dikes
Ship Rock, NM
Intrusive terrains - LaccolithsIntrusive terrains - Laccoliths
• Laccoliths - Henry Mts.
• Colorado Plateau
First studied in 1875-1876 by Grove Karl Gilbert. The term laccolith) is used to describe the characteristic shapes of some of the igneous intrusions that core the mountains.
Intrusive terrains - Sierra Nevada BatholithIntrusive terrains - Sierra Nevada Batholith
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