Transcript Chapter 8: Major Elements

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)


Partial melts: low-T fraction is always more Si-Al-NaK-rich and Fe-Mg-poor than source rock.
Leaves behind Mg-Fe-rich refractory residue
Igneous Processes
Geotherm

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
(and last to melt)
Crystal Fractionation
More Sialic
(and first to melt)