Volcanoes Shield Volcano Typically Basalt Lava Flows Low Slope Angle
Volcanoes Composite or Strato-Volcano Typically Andesite Lava Flows and Tuffs (pyroclastic) Higher Slope Angle
Volcanoes Cinder or Scoria Cone Typically Basalt Gas-charged spray Not very violent
Volcanoes
Volcanoes Lava Dome Typically Rhyolite Slow extrusion following violent explosion
Volcanoes Spatter Cone Typically Basalt Gas-charged spray Not very violent Returns to ground before solidifies
Volcanoes Vent vs. Fissure
Volcanoes Plateau Basalt Eruptions
Volcanoes Plateau Basalts are Fissure Eruptions
Volcanoes Columnar Joints
Caldera Formation
Volcanic Hazards Lava Flows Basalt flows in Kalapana area, Hawaii
Volcanic Hazards Geologists outpace lava in Hawaii!
Basalt from Mt Nyiragongo invades Goma, Congo, 2002 Volcanic Hazards San Juan Parangaricutiro engulfed by basaltic aa from Paricutin, 1944 Lava Flows Basalt from Mt Nyiragongo invades Goma, Congo, 2002
Volcanic Hazards Wind-blown ash deposits Heimay, Iceland 1973 Ash
Volcanic Hazards Ash Vertical plinian ash column from Mt. St. Helens, 1980 Mount Pinatubo, Philippines, on June 12, 1991
Volcanic Hazards Ash
Volcanic Hazards Pyroclastic Flows Video of pyroclastic flow on Mt. Unzen Soufriere erupts on Montserrat, August 1997 Glowing ash cloud descends Mt St Helens, August 1980
Volcanic Hazards Pyroclastic Flows St. Pierre, Martinique after Nuée Ardente from Mont Pelée, 1902
Volcanic Hazards Rhyolite Eruptions
Plutonic Rocks
Plutonic Rocks
Igneous Processes
Igneous Processes Hotspots can also create volcanism within continental plates Subduction zones create chains of volcanoes Melting creates volcanoes (e.g. Iceland) and oceanic crust at divergent plate boundaries Mid-Ocean Islands (e.g. Hawaii) created at enigmatic “hotspots” with elevated T
Igneous Processes More Mafic (and last to melt) More Sialic (and first to melt) Partial melts: low-T fraction is always more Si-Al-Na-K-rich and Fe-Mg-poor than source rock. Leaves behind Mg-Fe-rich refractory residue
Igneous Processes Geotherm Liquid Solid Decompression partial melting at divergent zones Partial melts: low-T fraction is always more Si-Al-Na-K-rich and Fe-Mg-poor than source rock. Leaves behind Mg-Fe-rich refractory residue
Igneous Processes Decompression partial melting at divergent zones
Igneous Processes “Hot Spots”
Igneous Processes “Hot Spots”
Igneous Processes “Hot Spots”
Igneous Processes Subduction zones: Conveyor of basalt to melt ® andesite Water lowers melting point of mantle wedge
Igneous Processes Subduction zones: water lowers melting point
Magma Generation and Evolution
Magma Generation and Evolution More Mafic Crystal Fractionation (and last to melt) More Sialic (and first to melt)