Chapter 14 Flashcards
(34 cards)
Continental Drift
Alfred Wegner
old theory that continental landmasses were “drifting” across the earth (Pangea)
evidence: similar fossils and glaciated continents fit
Plate Tectonics Theory
lithospheric plates move as a result of slow convection in Earth’s mantle; plates float on the asthenosphere
Evidence of plate tectonics
paleomagnetism: iron cooled magma orients itself with the magnetic poles of earth; this is used to verify age of ocean floor rock and seafloor spreading
Divergent Boundaries
plates move away from each other
- midocean ridges; earthquakes and volcanoes; seafloor spreading
Oceanic-continental convergent boundaries
oceanic plate sinks bc it is more dense (SUBDUCTION)
- forms oceanic trenches and continental mountains
- earthquakes and volcanoes along this boundary
- forms metamorphic rocks
Oceanic-Oceanic convergent boundaries
results in an undersea trench formation
- deep shallow earthquakes
- Pacific Ring of Fire (75% of volcanoes are here)
* SO MUCH SUBDUCTION HERE
continental-continental convergent boundaries
NO SUBDUCTION bc plates are highly buoyant
- builds huge mountain ranges
- shallow earthquakes
- no volcanoes
Transform boundaries
two boundaries slip past each other laterally
- transform faults (san andres fault)
- produces earthquakes
Mantle Plumes
localized hot areas NOT associated with plate boundaries
- move with the plate so eventually become inactive
- explains anomalous volcanoes
Accreted Terranes
piece of lithosphere carried by a plate that eventually collides and fuses with another plate
Extrusive Volcanism
occurs on Earth’s surface; lava cools quickly->no time for atoms to bond->fine igneous rocks
Intrusive volcanism
occurs below the surface; plutonic activity; lava cools slowly->atoms have time to bond-> coarse-grained igneous rocks
viscosity
resistance to flow
high silica: high viscosity: SLOW FLOW
low silica: low viscosity: FAST FLOW
Explosive Eruptions
high silica, high viscosity, pyroclastic, granite
Gentle Eruptions
low silica, low viscosity, basalt
Volcanic HAZARDS
volcanic gases: can cause acid rain, alter global climate
eruption clouds: gas and ash material clouds
pyroclastic flows: avalanche of hot gases
volcanic mudflows (LAHARS): result from heavy rain and or snow melt during an eruption
Volcanic POSITIVES
- much of earth’s water originates from water vapor from volcanoes
- magma contains elements required for plant growth
- provides soil fertility
Flood Basalt
A vast accumulation of lava build up; correlated with mass extinctions
Shield Volcanoes
layer upon layer of solidified lava flows; little pyroclastic material; not steep (Hawaiian islands)
Composite Volcanoes
emit higher silica lava (andesite lava); form symmetric, steep sided volcanoes; pyroclastics from explosive lava flows alternate with nonexplosive lava; pyroclastic flow produces steep slopes, lava holds it together
Lava Domes
masses of viscous lava that does not flow far; lava bulges from the vent, done grows by expansion from below and lava within; some domes form inside composite volcanoes
Cinder Cones
baby volcanoes; grow on big volcanoes; basaltic magma is common; slopes form from pyroclastic materials
Calderas
result from a volcano that explodes, collapses, or both; immense basin-shaped depression; larger than original crater
volcanic necks
pipe or throat of an old volcano that filled with solid lava
