SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
Mauna Kea, Hawaii short video 7c Hawaii; Etna; Iceland; Erta Image: S. Marshak “Earth, Portrait of a Planet” Ale, Nyamuragira/Africa Mt. Mayon, Philippines Fuji; Vesuvius; St. Helens; Pinatubo; Popocatepetl SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
Mt. Mayon, Philippines Mt. Fuji, Japan Mt. St. Helens Mt. Rainier “...anything that looks beautiful is potentially dangerous...” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
short video 7c small explosions effusive large explosions; lava fountains pyroclastic flows SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
Arenal, Costa Rica Mt. St. Helens (May 18, 1980) Kilauea, Hawaii (1983-87) Kilimanjaro Tanzania/Kenya (extinct) SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
• 90% of volcanism along plate boundaries (with 80% along mid-ocean ridges) • 10% at intra-plate hotspots/rifts Image: S. Marshak “Earth, Portrait of a Planet” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
• majority of volcanism (80% of total magma production) • non-explosive eruptions � pillow lava � black smokers SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
• common • subduction zones • dangerous on continents Image: S. Marshak “Earth, Portrait of a Planet” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
• relatively rare Mt. Etna • rifts • some hotspots Image: S. Marshak “Earth, Portrait of a Planet” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
• places with lots of magma in mantle • can be intra-plate (mantle plume) • dangerous on continents • overriding plate moves away -> • Yellowstone Earth’s worst! volcanoes go extinct -> chain • Hawaii most productive volcanoes Kauai (oldest/extinct) Oahu Maui Big Island (active) Loihi (youngest/active) Image: S. Marshak “Earth, Portrait of a Planet” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
• cont-cont collision • transform boundaries Image: S. Marshak “Earth, Portrait of a Planet” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
short video 7c Lecture 2: resistance of material to flow � high viscosity: lava clogs vents -> explosive volcanism � low viscosity: lava flows easily -> effusive volcanism crustal rock more viscous Image: S. Marshak “Earth, Portrait of a Planet” than mantle rock! SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
short video 7d OCEANIC CRUST • thin • dense, dark rock CONTINENTAL CRUST • thick • less dense, light rock • thicker crust higher viscosity • lighter rocks Image: S. Marshak “Earth, Portrait of a Planet” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
short video 7d � crustal thickness � composition (SiO 2 content) CONTINENTAL CRUST HAS MORE SiO 2 THAN OCEANIC CRUST SiO 2 : silica SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
1) MORE SiO 2 makes 2) HIGHER TEMPERATURE lava MORE VISCOUS makes lava LESS VISCOUS MORE VISCOUS � high-SiO 2 (Quartz) � cold LESS VISCOUS � low-SiO 2 (Olivine) � hot Image: S. Marshak “Earth, Portrait of a Planet” SiO 2 = silica short video 7d SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
geotherm Melting curve solid melt short video 7e Image: S. Marshak “Earth, Portrait of a Planet” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
geotherm Melting curve solid melt Image: S. Marshak “Earth, Portrait of a Planet” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
solid melt Image: S. Marshak “Earth, Portrait of a Planet” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
melting T or Magma/Lava freezing point: mix of: 650 - 1100 o C • solid parts • molten parts Quartz: 650ºC • dissolved gases Olivine: 1100ºC partial melt: y o F = mix of solid and x o C*9/5+32 molten parts 1200 - 2000 o F minerals: oven T: Quartz (> SiO 2 ) 260 o C/500 o F Olivine (<SiO 2 ) Image: S. Marshak “Earth, Portrait of a Planet” SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
• melting solid rock: Quartz first to melt • solidifying hot melt: Quartz last to crystallize -> lava has more SIO 2 than mantle rock left behind SIO15-SS1 2020: Lecture 9 Volcanoes and Plate Tectonics
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