1. Volcanoes & Tectonics Seamounts and Guyots

2. 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.

3. Plate Tectonics and Volcanism

4. Volcanism on a tectonic plate moving over a hot spot

5. Pacific Basin 90%Volcanic Output Seamounts and MOR => ocean floor

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

7. 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

8. 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

9. http://volcanoes.usgs.gov/Products/Pglossary/ancientseq.html Basaltic Pillow Lavas The reason there is so much water carried down into a subduction zone

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

11. Tephra Coarse = close Thick = close

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

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

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

15. Columbia Plateau Deccan Traps Very large in scale, worldwide effects Basalt Plateaus - Flood Basalts

16. Basaltic Cinder and Spatter Cones Projectiles –Ballistic –Wind-borne Divergent Margin +

17. 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

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

19. The Cascades, Washington State

21. Composite cones - section Lava and tephra alternate

22. Andesitic Eruptions Extensive Welded Tuff, Pumice Lavas, and Lahars Cleveland Volcano, Aleutians

23. Plug Domes

24. Rhyolite Eruptions Rare, extremely explosive Size of ash cover = violence Toba and our near-extinction

25. Volcanism on a tectonic plate moving over a hot spot

26. Calderas

27. Caldera – Crater Lake Copyright © Ann Dittmer 2002

28. Caldera topography – Crater Lake

29. 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

30. 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

31. 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 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

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

33. Erosional Remnants Plugs Dikes Ship Rock, NM

34. Intrusive 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.Grove Karl Gilbertlaccolith

35. Intrusive terrains - Sierra Nevada Batholith