Volcanoes are associated with plate boundaries and hot spots
What do you remember about oceanic and continental crust? Oceanic crust: – Composition? Continental crust: – Composition?
Oceanic crust: – Lower in silicon and oxygen – Higher in magnesium and iron Continental crust: – Higher in Si and O – Lower in Mg and Fe What do you remember about oceanic and continental crust?
Who cares about the composition? Composition determines the explosivity of a volcano
Volcanic rock names are based on the composition BasaltAndesiteRhyolite Lowest % of silicon and oxygen Intermediate % of silicon and oxygen Highest % of silicon and oxygen Oceanic crustMixture of oceanic and continental crust Continental crust Divergent plate boundaries and hot spots under oceanic crust (Hawaii) Subduction zones: Ring of Fire (Cascadia subduction zone) Hot spot under continental crust (Yellowstone)
Magma or lava? Within the crustOn the Earth’s surface
The more silicate tetrahedrons in a lava, the more explosive the volcano. Which lava contains the higher percentage silicon and oxygen? Rhyolitic or andesitic lavas
Viscosity Resistance to flow Which test tube contains the fluid with high viscosity? Left? Right?
Viscosity: resistance to flow Lavas with higher percentage of silicon and oxygen have a high viscosity-pasty Lavas with a lower percentage of silicon and oxygen have a low viscosity-fluid
Rhyolitic lava is associated with continental crust Rhyolite is cooled from pasty or thick lavas.
Andesitic lava is a combination of oceanic and continental crusts Andesite is cooled from pasty or thick lavas.
Rhyolitic and andesitic lavas produce pyroclastic debrisdebris
BasalticBasaltic lava is associated with oceanic crust Basalt is cooled from fluid lava.