Volcanoes Shield Volcano Typically Basalt Lava Flows Low

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!

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

Ash Volcanic Hazards

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 (and last to melt) More Mafic More Sialic (and first to melt) l l 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 l l id Liqu id Sol l 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 l Decompression partial melting at divergent zones

Igneous Processes l “Hot Spots”

Igneous Processes “Hot Spots”

Igneous Processes “Hot Spots”

Igneous Processes Subduction zones: F Conveyor of basalt to melt ® andesite F 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)