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Volcanoes Volcano The Dynamic Earth ESSC 1010 The Dynamic Earth Prof. Kennet E. Flores Visualizing Geology 3rd Edition Barbara W. Murck Brian J. Skinner Chapter 6 Volcanoes and Igneous Rocks 1. Volcanoes and Volcanic Hazards 2. How, Why, and Where Rock Melts 3. Cooling and Crystallization 4. Plutons and Plutonism Copyright © 2012 by John Wiley & Sons, Inc. Volcanoes and Volcanic Hazards Volcanoes Volcano •A vent through which lava, solid rock debris, volcanic ash, and gasses erupt from Earth’s crust to its surface Volcanoes Volcano •Can be explosive or nonexplosive Volcanoes Volcano •The most common perception of a volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit. • This describes just one of many types of volcano, and the features of volcanoes are much more complicated http://video.nationalgeographic.com/video/news/150 220-volcano-drones-vin?source=relatedvideo Volcanoes Volcanic materials •Lava, fragments of rock, and glassy volcanic ash Volcanoes Lava •Molten rock that reaches Earth’s surface Volcanoes Pyroclast • Fragment of rock ejected during volcanic eruptions Volcanoes Tephra • All the pyroclas ejecta from a volcano • It range from car-size rocks (blocks) to ultrafine volcanic ash Volcanoes Bishop Tuff, Long Valley Caldera (California) Clast size Pyroclast Tephra Pyroclastic rock (mainly unconsolidated (mainly consolidated) <0.063 mm Fine ash Fine ash Fine tuff <2 mm Coarse ash Coarse ash Corse tuff <64 mm Lapillus Layer of lapilli or lapilli tephra Lapilli tuff or lapillistone >64 mm Block, bomb Agglomerate Pyroclastic breccia Volcanoes Mt. Etna, Sicily Santorini, Greece Clast size Pyroclast Tephra Pyroclastic rock (mainly unconsolidated (mainly consolidated) <0.063 mm Fine ash Fine ash Fine tuff <2 mm Coarse ash Coarse ash Corse tuff <64 mm Lapillus Layer of lapilli or lapilli tephra Lapilli tuff or lapillistone >64 mm Block, bomb Agglomerate Pyroclastic breccia Volcanoes Clast size Pyroclast Tephra Pyroclastic rock (mainly unconsolidated (mainly consolidated) <0.063 mm Fine ash Fine ash Fine tuff <2 mm Coarse ash Coarse ash Corse tuff <64 mm Lapillus Layer of lapilli or lapilli tephra Lapilli tuff or lapillistone >64 mm Block, bomb Agglomerate Pyroclastic breccia Volcanoes The different kinds of eruptions and the volcanoes they build have much to do with the physical properties of the magma that lies at their source Volcanoes Magma •Molten rock, which may include fragments of rock, volcanic glass and ash, or gas Eruptions, Landforms, and Materials Volcanoes and eruptions VEI Plume height Eruption type Frequency Example 0 <100 m (330 ft) Hawaiiann Continuous Kilauea 100–1,000 m Hawaiian/Strombo 1 Months Stromboli (300–3,300 ft) liann Strombolian/Vulca 2 1–5 km (1–3 mi) Months Galeras(1992) nian Nevado de 3 3–15 km (2–9 mi) Vulcanian Yearly Ruiz (1985) 10–25 km (6– Eyjafjallajökull 4 Vulcanian/Peléan Few years 16 mi) (2010) Mount St. 5 >25 km (16 mi) Plinian 5–10 years Helens (1980) Plinian/Ultra Krakatoa 6 >25 km (16 mi) 1,000 years Plinian (1883) Tambora 7 >25 km (16 mi) Ultra Plinian 10,000 years (1815) Lake Toba (74 8 >25 km (16 mi) Ultra Plinian 100,000 years ka) VEI: Volcanic Explosivity Index Eruptions, Landforms, and Materials Volcanoes and eruptions Eruption types It depends of two factors (a) Viscosity of the magma and (b) amount of gas dissolved in it Eruptions, Landforms, and Materials Volcanoes and eruptions Viscosity • Degree to which a substance resists flow. • A less viscous liquid is runny, whereas a more viscous liquid is thick. Eruptions, Landforms, and Materials Volcanoes and eruptions Volcanic Gases • Water vapor, carbon dioxide, sulfur dioxide, etc. • They can cause a volcano to explode Eruptions, Landforms, and Materials Volcanoes and eruptions Hawaiian eruptions https://www.youtube.com/watch?v=6VfsKoH-ScA •Consist of very runny lava that flows easily •These flows gradually build shield volcanoes Eruptions, Landforms, and Materials Volcanoes and eruptions • Shield volcanoes are broad, flat volcanoes with gently sloping sides, built of successive lava flows Eruptions, Landforms, and Materials Volcanoes and eruptions • Tallest mountains in Earth (10 Km from b.s.l. to a.s.l.) Eruptions, Landforms, and Materials Volcanoes and eruptions • In shield volcanoes sometimes the lava rises to the surface through long fissures rather than central craters Eruptions, Landforms, and Materials Volcanoes and eruptions • These fissures produce flood basalts or basalt plateaus Eruptions, Landforms, and Materials Volcanoes and eruptions The classic volcano profile of a shield volcano Eruptions, Landforms, and Materials Volcanoes and eruptions https://www.youtube.com/watch?v=6I5rC-ibqi4 Strombolian eruptions •More explosive than Hawaiian •Create loose volcanic rock called spatter cones or cinder cones Eruptions, Landforms, and Materials Volcanoes and eruptions https://www.youtube.com/watch?v=mIX43uy4Zvg Vulcanian eruptions • More explosive than Strombolian and, as a result, can generate billowing clouds of ash up to 10 km. Eruptions, Landforms, and Materials Volcanoes and eruptions Pyroclastic flows are hot volcanic fragments (tephra), buoyed by heat and volcanic gases, flow very rapidly Vulcanian eruptions https://www.youtube.com/watch?v=Cvjwt9nnwXY • Produce pyroclastic flows Eruptions, Landforms, and Materials Volcanoes and eruptions https://www.youtube.com/watch?v=CCujnt68bVg Plinian eruptions • Named after Pliny the Elder, who died during eruption of Mount Vesuvius Eruptions, Landforms, and Materials Volcanoes and eruptions Plinian eruptions • Most violent eruptions, generating ash columns that can exceed 20 kilometers Eruptions, Landforms, and Materials Volcanoes and eruptions Plinian eruptions • Produce steep-sided volcanoes, called stratovolcanoes Eruptions, Landforms, and Materials Volcanoes and eruptions • Stratovolcanoes are composed of solidified lava flows interlayered with pyroclastic material. • Steep sides curve upward Eruptions, Landforms, and Materials The classic volcano profile of a stratovolcano Eruptions, Landforms, and Materials Other volcanic features • Craters Eruptions, Landforms, and Materials Other volcanic features • Resurgent dome Eruptions, Landforms, and Materials Other volcanic features • Thermal spring Eruptions, Landforms, and Materials Other volcanic features • Geysers Eruptions, Landforms, and Materials Other volcanic features • Fumaroles Volcanic Hazards Volcanic Hazards Deadly eruptions Volcanic Hazards Primary effects •Lava flows •Pyroclastic flows •Volcanic gases Secondary effects •Related to, but not a direct result of, volcanic activity • Fires • Flooding • Mudslides • Debris Kalapana, Hawaii avalanche Volcanic Hazards Primary effects •Lava flows •Pyroclastic flows •Volcanic gases Secondary effects •Related to, but not a direct result of, volcanic activity • Fires • Flooding • Mudslides • Debris Pompeii, Mt. Vesuvious avalanche Volcanic Hazards Primary effects •Lava flows •Pyroclastic flows •Volcanic gases Secondary effects •Related to, but not a direct result of, volcanic activity • Fires • Flooding • Mudslides • Debris Ijen, East Java avalanche Volcanic Hazards Primary effects •Lava flows •Pyroclastic flows •Volcanic gases Secondary effects •Related to, but not a direct result of, volcanic activity • Fires • Flooding • Mudslides • Debris Lahar from Mount St Helens avalanche Volcanic Hazards Tertiary and beneficial effects •Change a landscape •Affect climate on regional and global scale •Renew mineral content and replenish fertility •Geothermal energy •Provide mineral deposits Volcanic Hazards Tertiary and beneficial effects •Change a landscape •Affect climate on regional and global scale •Renew mineral content and replenish fertility •Geothermal energy •Provide mineral deposits Volcanic Hazards Tertiary and beneficial effects •Change a landscape •Affect climate on regional and global scale •Renew mineral content and replenish fertility •Geothermal energy •Provide mineral deposits Volcanic Hazards Tertiary and beneficial effects •Change a landscape •Affect climate on regional and global scale •Renew mineral content and replenish fertility •Geothermal energy •Provide mineral deposits Volcanic Hazards Tertiary and beneficial effects •Change a landscape •Affect climate on regional and global scale •Renew mineral content and replenish fertility •Geothermal energy •Provide mineral deposits Predicting Eruptions Volcano monitoring from the ground Predicting Eruptions Predicting Eruptions Establishing a volcano’s history •Active •Dormant Monitoring changes and anomalies •Earthquakes •Shape or elevation •Volcanic gases •Ground temperature •Composition of water Monitoring volcanoes from orbit How, Why, and Where Rocks Melt How, Why, and Where Rocks Melt Geothermal gradient Heat and pressure inside Earth: • Continental crust: temperature rises 30°C/km, then about 6.7°C/km. • Ocean crust: temperature rises twice as rapid. How, Why, and Where Rocks Melt Effect of temperature and pressure on melting How, Why, and Where Rocks Melt Heat and Pressure Inside Earth Fractional melt •A mixture of molten and solid rock How, Why, and Where Rocks Melt Heat and Pressure Inside Earth Fractionation •Separation of melted materials from the remaining solid material during the course of melting How, Why, and Where Rocks Melt Magma and Lava Magma •Molten rock below surface Lava •Magma when it reaches the surface •Differs in composition, temperature, and viscosity Two types of lava flows How, Why, and Where Rocks Melt Magma and Lava Composition •45% to 75% of magma by
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