Transcript Volcanic Geomorphology

Volcanoes & Tectonics
Seamounts and Guyots
Lava 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 Volcanism
Volcanism on a tectonic
plate moving over a hot
spot
Pacific Basin 90%Volcanic Output
Seamounts and MOR => ocean
floor
Great Basalt Plateaus
Volcanic geomorphic provinces
Plumes under Continents yield more silica rich, explosive eruptions
A size comparison of the three
main types of volcanoes
Seamounts are these largest
Plume below ocean
Above subduction zone
Divergent Zone Cinder Cones
Volcanic Activities and their products
Upper surface pitted Scoria
• Exhalative (gas: H2O, CO2, SO2)
• Effusive (lava)
• Explosive (tephra)
Jagged A'a'
away from vent
Pahoehoe
Near vent
Hawaii, low silica, low viscosity, notice
no tephra in view
http://volcanoes.usgs.gov/Products/Pglossary/ancientseq.html
Basaltic Pillow Lavas
The reason there is so much
water carried down into a
subduction zone
Volcanic Activities and their products
• Explosive (tephra)
nuée ardente = pyroclastic cloud
Intermediate to high silica - Andesitic to Rhyolitic
Tephra
• Coarse = close
• Thick = close
Lahars - volcanic mudflows
Melting collapse of ice embedded cone
Copyright © Stephane Veyrat-Charvillon 2002
Characteristic Eruptive Types
Special case: Phreatic
eruptions occur when magma
hits water. And the water
flashes to steam explosively
Rift Valley Flows
Volcanic Landforms 1: Basaltic
Basaltic lava
flows
• Layered
– Lava/sediment
• Jointed
– Columnar
Copyright © Richard Kesel 2002
• Columbia Plateau
• Deccan Traps
• Very large in scale,
worldwide effects
Basalt Plateaus - Flood Basalts
Basaltic Cinder and
Spatter Cones
• Projectiles
– Ballistic
– Wind-borne
• Divergent
Margin +
Volcanic Landforms, Basaltic continued
Shield Volcanoes
Mauna Kea from Mauna Loa
•Form above Plumes, huge
• also Basaltic, gentle eruptions
•As plate moves old volcanoes
become inactive, new volcano
forms over the plume
Volcanic Landforms 2: Andesitic Volcanoes
Andesitic - Composite cones
"Stratovolcano"
Mt. Fuji in summer
Form above Subduction zones
The Cascades, Washington State
Composite cones - section
Lava and tephra alternate
Andesitic Eruptions
Extensive Welded Tuff, Pumice Lavas, and Lahars
Cleveland Volcano, Aleutians
Plug Domes
Rhyolite
Eruptions
• Rare, extremely
explosive
• Size of ash
cover = violence
• Toba and our
near-extinction
Volcanism on a tectonic
plate moving over a hot
spot
Calderas
Caldera – Crater Lake
Copyright © Ann Dittmer 2002
Caldera topography – Crater Lake
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
Ukinrek Maars
Mono Co, CA
Rhyolite, very high silica, very viscous, can’t get rid of gas bubbles, explodes
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
Iceland
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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 Tuff
Ignimbrite or Welded Tuff
Source: Gerald & Buff Corsi/Visuals Unlimited, Inc.
Erosional
Remnants
• Plugs
• Dikes
Ship Rock, NM
Intrusive terrains - Laccoliths
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.
• Laccoliths - Henry Mts.
• Colorado Plateau
Intrusive terrains - Sierra Nevada Batholith