Volcanism

• Extrusive activity
• Volcano - mountain built up by accumulation of material ejected from a vent (opening in crust)
• Products of extrusive activity
• lava
• pyroclastics - particles ejected from volcanic vent; tephra
• dust -> ash -> cinders -> lapilli -> bombs or blocks

• Felsic (Rhyolitic; Granitic magma)
• Intermediate (Andesitic)
• Mafic (Basaltic)

• magma chamber
• central vent
• crater
• pyroclastic layers (could also be lava layers or alternating lava and pyroclastics)

• Pyroclastic rocks
• tuff, welded tuffs - mostly cemented ash
• pumice - vesicular, glassy
• volcanic breccia - large angular fragments cemented together
• Features of lavas
• pahoehoe - ropy
• aa - blocky
• Pillow basalt - bulbous surface; extrusion under water
• Columnar basalt - fractures associated with shrinking

• Determined by nature of material (e.g., proportion of lava to pyroclastics)
• Shield volcano - low, broad slope; built mostly of basaltic flows (Hawaiian Islands, Iceland)
• Composite cone (Stratovolcano) - alternating lava and pyroclastics; classic cone-shape (Mt. Fuji, Mt. Rainier, Mt. St. Helens)
• Volcanic dome - viscous magma fills crater; forms dome; short-lived (Ex: Mono Craters, CA)
• Cinder cone - steep slopes; layers of pyroclastics; <300 m high (Ex.: Paricutin)
• Caldera - volcano with unusually large crater; collapsed or blown volcano (Crater Lake, Jemez Caldera)

• Fissure eruptions - eruptions through deep fractures rather than through central vents
• flood basalts (Columbia Plateau)

• Ash-flows -  eruptions of pyroclastics
• Lahars - catastrophic mudflows of volcanic debris
• Remnants of volcanoes
• Volcanic neck - basalt-filled remnant of vent
• Volcanic pipe  - cylindrical dike; conduit
• Kimberlite pipe
• Diatreme - breccia-filled remnant of vent (Ship Rock)

• Volcanic gases

• water vapor, 70 - 95%
• carbon dioxide (CO2)
• sulfur dioxide (SO2)
• others - nitrogen, hydrogen, carbon monoxide (CO), sulfur, and chlorine
• recycled groundwater and seawater
• some gases may be juvenile (from mantle)

• Divergent Plate Boundaries
• greatest volume
• basalt
•  fissure eruptions at MOR
• Convergent Plate Boundaries
• Ocean-ocean convergence
• basalts and andesites (Ex: Japan, Philippines)
• Ocean-continent convergence
• basaltic to felsic lava (Ex: Cascade Range, Parícutin)
• Intraplate Volcanism - Hot spots (Emperor Seamount Chain, Hawaii)

• Approaches
• Eruption history
• Radiometric dating of lava and/or fossilized wood
•  Terms
• Active - erupting or expected to erupt
•  Dormant - not erupting but will likely erupt in future
• Extinct - not expected to erupt
• seismic activity
• tilting
• gas emissions
• increased temperature of hot springs
• Success stories (Mt. St. Helens, Mt. Pinatubo