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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. 2. 3. 4. Volcanoes and Volcanic Hazards How, Why, and Where Rock Melts Cooling and Crystallization 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 pyroclasts 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 (mainly unconsolidated Pyroclastic rock (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 Santorini, Greece Mt. Etna, Sicily Clast size Pyroclast Tephra (mainly unconsolidated Pyroclastic rock (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 (mainly unconsolidated Pyroclastic rock (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 gas and fragments of rock, volcanic glass and ash Eruptions, Landforms, and Materials Volcanoes and eruptions VEI Plume height Eruption type Frequency Example 0 <100 m (330 ft) Hawaiiann Continuous Kilauea 1 100–1,000 m (300– 3,300 ft) Hawaiian/Strombolian Months Stromboli 2 1–5 km (1–3 mi) Strombolian/Vulcanian Months Galeras(1992) 3 3–15 km (2–9 mi) Vulcanian Yearly Nevado de Ruiz (1985) 4 10–25 km (6–16 mi) Vulcanian/Peléan Few years Eyjafjallajökull (2010) 5 >25 km (16 mi) Plinian 5–10 years Mount St. Helens (1980) 6 >25 km (16 mi) Plinian/Ultra Plinian 1,000 years Krakatoa (1883) 7 >25 km (16 mi) Ultra Plinian 10,000 years Tambora (1815) 8 >25 km (16 mi) Ultra Plinian 100,000 years Lake Toba (74 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 • Produce pyroclastic flows https://www.youtube.com/watch?v=Cvjwt9nnwXY 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 avalanche Kalapana, Hawaii 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 avalanche Pompeii, Mt. Vesuvious 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 avalanche Lahar from Mount St Helens 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 avalanche Ijen, East Java 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 •Magmas (therefore lavas) differs in composition, temperature, and viscosity *molten rock below surface (magma) vs. magma when it reaches the surface(lava) Two types of lava flows How, Why, and Where Rocks Melt Magma and Lava Composition •45% to 75% of magma by weight is silica. •Water vapor and carbon dioxide are usually present Temperature •Lavas vary in temperature between 750°C and 1200°C •Magmas with high H2O contents melt at lower temperatures Viscosity •Lavas vary in their ability to flow • Influenced by silica content and temperature How, Why, and Where Rocks Melt Magma and Lava Three types of magma Basaltic •45% to 50% of magma by weight is silica •Little dissolved gas •Oceanic crust How, Why, and Where Rocks Melt Magma and Lava Three types of magma Andesitic •60% of magma by weight is silica. •2-4% dissolved gas (mainly water vapor) •Subduction zones How, Why, and Where Rocks Melt Magma and Lava Three types of magma Rhyolitic •70-75% of magma by weight is silica •3-8% dissolved gas (mainly water vapor) •Continents How, Why, and Where Rocks Melt Tectonic setting and volcanism Divergent and convergent plate boundaries, and hotspots How, Why, and Where Rocks Melt Tectonic setting and volcanism Oceanic, divergent margins • Lava is thin with a steep geothermal gradient. Midocean ridge: submarine basaltic pillow lavas How, Why, and Where Rocks Melt Tectonic setting and volcanism Continental divergent margins • Lava is high in silica. Continental rift: rhyolitic and lavas with unusual composition How, Why, and Where Rocks Melt Tectonic setting and volcanism Subduction zones •Typically have high water content and melt at lower temperatures. Ocean-ocean subduction zone Ocean-continent subduction zone How, Why, and Where Rocks Melt Tectonic setting and volcanism Hot spots • Lava tends to be hot and basaltic and build giant shield volcanoes Shield volcano Cooling and Crystallization Cooling and Crystallization Crystallization •The process whereby mineral grains form and grow in a cooling magma (or lava) •Classified as: • Volcanic • Plutonic Cooling and Crystallization Rate of Cooling Rapid cooling: Volcanic rocks and textures •Volcanic rock • An igneous rock formed from lava • Glassy • Aphanitic • Porphyritic • Pumice • Vesicular basalt Glassy texture Cooling and Crystallization Rate of Cooling Rapid cooling: Volcanic rocks and textures •Volcanic rock • An igneous rock formed from lava • Glassy • Aphanitic • Porphyritic • Pumice • Vesicular basalt Aphanitic texture Cooling and Crystallization Rate of Cooling Rapid cooling: Volcanic rocks and textures •Volcanic rock • An igneous rock formed from lava • Glassy • Aphanitic • Porphyritic • Pumice • Vesicular basalt Porphyritic texture Cooling and Crystallization Rate of Cooling Slow cooling: Plutonic rocks and textures •Plutonic rock • An igneous rock formed underground from magma • Phaneritic: A coarse-grained texture • Can have exceptionally large grains Plutonic rock textures Cooling and Crystallization Chemical Composition Igneous rocks subdivided into four categories based on silica content: felsic, intermediate, mafic, and ultramafic Cooling and Crystallization Fractional crystallization a) Filter pressing b) Crystal settling c) Crystal flotation •Separation of crystals from liquids during crystallization •This the reason of the diversity in kinds of igneous rocks Cooling and Crystallization Fractional crystallization Bowen’s reaction series •Predictable melting and cooling of minerals Plutons and Plutonism Plutons and Plutonism Plutons •Any body of intrusive igneous rock, regardless of size or shape Plutons and Plutonism Plutonic features Batholith A large, irregularly shaped pluton that cuts across the layering of the rock into which it intrudes Stock Is a smaller version of a batholith, only 10km or so its maximum dimensions Laccolith A mushroom-shaped pluton between pre-existing layers Plutons and Plutonism Batholiths are so huge that map views give us the best perspective. Plutons and Plutonism Plutonic features Dike A tabular pluton that runs perpendicular to preexisting layers They form when magma squeezes into a crosscutting fracture and solidifies Plutons and Plutonism Plutonic features Sill A sheet-like pluton that is parallel to preexisting layers They form when magma intrudes between two layers and is parallel to them. Plutons and Plutonism Plutonic features Dike Plutons and Plutonism Plutonic features Sill Plutons and Plutonism Plutonic features Volcanic neck Remnant of a volcanic pipe that once fed the magma to the volcanic vent Plutons and Plutonism Plutonic features Devil’s Tower, Wyoming Plutons and Plutonism Xenoliths A foreign rock (preexisting rocks) Plutons and Plutonism Xenoliths
