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Week 1 - Terrestrial Volcanism Overview

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8/30/2011 Week 1 - Terrestrial Volcanism Overview • Some definitions • Eruption products • Eruption triggers • Eruption styles • The role of water • Where do volcanoes occur • Monogenetic vs polygenetic • Some volcano and eruption examples GG711, Fall 2011 1 8/30/2011 Volcanoes: Places where molten Mid-ocean ridge schematic rock and gasses exit Earth’s (or another planet’s) surface Volcanic construction materials Magma molten or partially molten rock beneath the Earth's surface. When magma erupts onto the surface, it is called lava, or Magma chamber cinders, ash, tephra or other pyroclasts Sketch by B. Myers http://volcanoes.usgs.gov/Products/Pglossary/magma.html GG711, Fall 2011 2 8/30/2011 Eruption Products The relative proportion of these materials occur as a function of magma type, tectonic setting and local variables. Source: USGS Eruption Triggering Some important factors • Tectonic triggers (changes in stress field) • Tectonic setting (compressive or extensional) • Vent opening (pressure increase from new magma input and/or gas exsolution) • Vent plugging/clogging may promote flank eruptions • Closed-system magma differentiation (pressure increase) GG711, Fall 2011 3 8/30/2011 Eruption Styles Important Magmatic factors These work together to affect eruption style • Viscosity • Magma composition • crystallinity • gas content • temperature • pressure Hot runnier Mafic (Magnesium and iron rich) cold stickier silicic (Silicon-dioxide rich) Temperature vs. Magmatic water Crystallinity vs. viscosity vs. viscosity viscosity silicic (Silicon-dioxide rich) granite Mafic (Magnesium and iron rich) basalt GG711, Fall 2011 4 8/30/2011 Eruption Classifications Related factors • Effusive vs Explosive • Dry vs Hydrovolcanic (internal vs. external gas source) • Central vent vs Fissure eruption • Eruption rate • Submarine vs subaerial Eruption Styles Effusive Explosive Magma Mafic Silicic composition but not always but not always increasing Less More Fragmentation Less More Dispersal Longer shorter Usual duration decreasing increasing Column height GG711, Fall 2011 5 8/30/2011 Atmospheric subaqueous External Water: Dry amount of water wet Fragmentation from internal gas sources Water Pressure, Mass flux Water pressure also controls fragmentation Viscosity and density of water control dispersal Maximum explosivity at magma:water ~1 GG711, Fall 2011 6 8/30/2011 Koko Head and Hanauma Bay Surtseyan, shallow submarine explosive Tongatapu, 2009 GG711, Fall 2011 7 8/30/2011 Lava Meets the Sea from above 10m Littoral activity at Kilauea Fluidal pyroclasts collected in the deep sea Clague et al. 2009 Limu o Pele forming as the skin of a cooling lava bubble shell bursts at Puu Oo GG711, Fall 2011 8 8/30/2011 Water pressure effects Bubble rich basalt scoria from the NELSC, 1700m water depth GG711, Fall 2011 9 8/30/2011 Subaqueous Column Height Column height Water depth/ water pressure decreasing increasing What is the depth cut off for this process? Currents and water density affect submarine plume behavior Multiple wispy plumes caught right after a short duration eruption Baker et al., 2011 GG711, Fall 2011 10 8/30/2011 NW Rota Seamount in 2006 … Pyroclastic ejecta and a tiny bit of glowing red rock Courtesy of NOAA Vents Program Some submarine lava forms GG711, Fall 2011 11 8/30/2011 pillows Lobate flow Lava pillar GG711, Fall 2011 12 8/30/2011 Collapsed lobate lavas showing hollow interior Sheet flows Seismometer stuck in a submarine jumbled Hackly sheet flow and dead tubeworms – EPR sheet flow – Axial 1998 1992 Curtain folded sheets NELSC 2008 GG711, Fall 2011 13 8/30/2011 Explosive submarine eruption at W. Mata Volcano, 1200m water depth May 2009 Submarine strombolian eruption at W. Mata Volcano, 1200m water depth May 2009 GG711, Fall 2011 14 8/30/2011 Vent-proximal lobate lavas, W. Mata Volcano Note pyroclastic apron over the lavas Hydrothermal chimney Right after an eruption GG711, Fall 2011 15 8/30/2011 Where do we find Volcanoes? Most of Earth’s volcanism occurs at convergent Intra-plate and (hotspot) divergent boundaries, plus intraplate hotspots Subduction zones Ocean ridges Crustal ages in the ocean basins today. http://www.ngdc.noaa.gov/mgg/image/crustalimages.html GG711, Fall 2011 16 8/30/2011 Volcano Type and Plate Tectonic Setting Silicic Caldera – thick crust Shield Volcano – hotspots, especially oceanic Stratovolcano - convergent plate boundaries (subduction zones) Cinder Cones, Tuff Rings, etc.., Rift Volcano – divergent plate anywhere at or above sea level boundaries (spreading centers) Magma Type and Plate Tectonic Setting Basalt through Rhyolite, high volcatile content Tholeiitic + lesser alkalic basalt, moderate volatile content Basalt through Dacite, usually relatively high volatile content Usually restricted to basalt Usually restricted to basalt, low through andesite volatile content GG711, Fall 2011 17 8/30/2011 Monogenetic vs Polygenetic Volcanoes Monogenetic: Polygenetic: one eruption many eruptions Subaerial Monogenetic Volcano Shapes shield cinder cone dome tuff ring mixed cone GG711, Fall 2011 18 8/30/2011 Michoacán-Guanajuato Volcanic Field (Mexico) Photo: Jim Luhr El Jorullo 1759-1774 and Paricutin 1943-1952 Other photos: Ken Rubin Submarine Monogenetic? GG711, Fall 2011 19 8/30/2011 Subaerial Volcanoes come in 5 basic types plus hybrids. Submarine volcanoes are similar, with arguably steeper sides pyroclastic Stratovolcano cone Rift Volcano Shield Volcano Silicic Caldera Rift Zone Volcano Thingvallir, Iceland GG711, Fall 2011 20 8/30/2011 Stratovolcano Mayon Volcano, Philippines Stratovolcanoes St. Augustine, Alaska Shasta, California http://volcanology.geol.ucsb.edu/volcano.htm http://www.peakware.com Volcán Itztlazihuatl, Mexico http://es.wikipedia.org/wiki/ GG711, Fall 2011 21 8/30/2011 Composite volcanoes Hekla Volcano, Iceland Shield Volcano Mauna Loa, Hawaii – Earth’s tallest and broadest volcano GG711, Fall 2011 22 8/30/2011 usually calm, and steady … Puu Oo eruption of Kilauea, Hawaii some low spattering and fountaining Puu Oo eruption of Kilauea, Hawaii GG711, Fall 2011 23 8/30/2011 Halemaumau explosion May 2009 http://hvo.wr.usgs.gov/kilauea/timeline/20090508_00345_L.jpg 1924 Kilauea summit explosion GG711, Fall 2011 24 8/30/2011 Rare larger Kilauea explosions http://hvo.wr.usgs.gov/volcanowatch/2006/06_01_26.html Around 1,000-1,200 years ago, the largest explosion brought up rocks several kilometers (miles) from the volcano's depths. This explosion was likely caused by rapid expansion of carbon dioxide bubbles within Kilauea's deep plumbing system. Cinder Cones Pu`u ka Pele, Mauna Kea, Hawai’i Hverfell, Krafla, Iceland http://volcanoes.usgs.gov/Products/Pglossary/CinderCone.html Photo by Ken Rubin Red Hill, California GG711, Fall 2011 25 8/30/2011 Tuff Cones and Rings Koko Head and Crater, Hawaii Diamond Head, Hawaii Silicic Caldera Silicic magma is gooey and cooler than other common types Rhyolite tephra, Okataina New Zealand Yellowstone Caldera, Western USA GG711, Fall 2011 26 8/30/2011 lava domes Panum dome (and crater), California http://lvo.wr.usgs.gov/gallery/ Explosive Subaerial Eruptions Pinatubo, Philippines, 1991 GG711, Fall 2011 27 8/30/2011 Explosive Submarine Eruptions West Mata 2009 GG711, Fall 2011 28.
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