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

Plumes under Continents yield more silica rich, explosive eruptions Great Basalt Plateaus Volcanic geomorphic provinces

A size comparison of the three main types of volcanoes 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 Exhalative (gas: H 2 O, CO 2, SO 2 ) Effusive (lava) Explosive (tephra) Hawaii, low silica, low viscosity, notice no tephra in view Lava Flow Upper surface pitted Scoria Pahoehoe Near vent Jagged A'a' away from vent

Basaltic Pillow Lavas The reason there is so much water carried down into a subduction zone

Volcanic Activities and their products Explosive (tephra) Intermediate to high silica - Andesitic to Rhyolitic nuée ardente = pyroclastic cloud

Tephra Coarse = close Thick = close

Lahars - volcanic mudflows Copyright © Stephane Veyrat-Charvillon 2002 Melting collapse of ice embedded cone

Characteristic Eruptive Types Special case: Phreatic eruptions occur when magma hits water. And the water flashes to steam explosively

Copyright © Richard Kesel 2002 Basaltic lava flows Layered –Lava/sediment Jointed –Columnar Rift Valley Flows Volcanic Landforms 1: Basaltic

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 +

Shield Volcanoes Mauna Kea from Mauna Loa Form above Plumes, hugeForm above Plumes, huge also Basaltic, gentle eruptions also Basaltic, gentle eruptions As plate moves old volcanoes become inactive, new volcano forms over the plumeAs plate moves old volcanoes become inactive, new volcano forms over the plume Volcanic Landforms, Basaltic continued

Andesitic - Composite cones Mt. Fuji in summer Volcanic Landforms 2: Andesitic Volcanoes Form above Subduction zones "Stratovolcano"

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 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 magmaphreatomagmatic eruption

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

Iceland 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 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 Source: Gerald & Buff Corsi/Visuals Unlimited, Inc. Ignimbrite or Welded Tuff

Erosional Remnants Plugs Dikes Ship Rock, NM

Intrusive terrains - Laccoliths Laccoliths - Henry Mts. Colorado Plateau First studied in by Grove Karl Gilbert. The term laccolith) is used to describe the characteristic shapes of some of the igneous intrusions that core the mountains.Grove Karl Gilbertlaccolith

Intrusive terrains - Sierra Nevada Batholith