Ch. 5: Volcanoes Flashcards
Magma chamber
body of molten
material that feeds a volcano
Flank
part of volcano that slopes
away from vent on top
crack on side
Crater
area above vent where lava
has piled up
Caldera
large depression formed when
volcano collapses into magma chamber
below it
Fissure
flood basalt, plateau basalt, lava curtain
elongated fracture
horizontal crack
Factors affecting viscosity:
Composition
silica content: higher silica content, higher viscosity
Factors affecting viscosity: Temperature
Temperature: higher T, lower viscosity
Factors affecting viscosity: Gas content
Gas content: higher gas content, lower viscosity
Effusive
low viscosity, high T, volatile-rich lava flows; usually basaltic, shield volcano, gas escapes easily, lava flows
Explosive
pyroclastic; usually andesitic & rhyolitic (int-high viscosity), strato
Lava flows
different compositions depend on plate tectonic setting
Pyroclastic flows
composed of tephra (ash, cinders, etc.) plus very hot gas
Lahars
volcanic mudflows
Volcanic gases
CO2, H2O, etc,—evidence in vesicles
Mafic low
low SiO2—1200°C—low viscosity— effusive—basalt, shield, runny, high temp, high gas, low si
Intermediate
andesite, pyroclastics, strata
Felsic/sialic high
high SiO2—800°C—high viscosity—explosive—rhyolite, pyroclastics, cindercone, low t, low gas, high si
Shield Volcanoe
broad with gentle slopes; basaltic; Hawaii
Pahoehoe (shield)
ropey lava; low viscosity basalt rich in gas
Columnar basalt (shield)
forms when lava flows cools & shrinks
Pillow basalt (shield)
forms when basalt erupts into water
Stratovolcanoes/Composite
steeper slope; andesitic; examples: Fuji, St. Helens, Vesuvius; Pliny the Younger’s letter Eruption of Mt. St. Helens 1980: earthquake-triggered landslide, lateral blast, pyroclastic flows, lahars, ash cloud Subduction Zone
Cinder cones
small conical piles of tephra
tephra
blocks, bombs, ash
pyroclastic flow or nuée ardente
Yellowstone
supervolcano; caldera; recurrence interval during past 2 million years
where do you expect stratovolcanoes to
form?
Subduction zone, convergent plate boundary
Active
Erupting, recently erupted or likely to erupt
dormant
Hasn’t erupted in hundreds to thousands of years
extinct
Not capable of erupting
Effect of volcanic eruptions on climate
cooler T, contributed to extinction of dinosaurs, acid rain
A’a lava
a’a forms when basalt loses gas, thickens, breaks
Mt Pinatous
Philipines 1991
dormant 500 years
plinian eruption: enourmous explosion of volcanic material lots of materials into atmosphere decrease avg global temp
Mt St. Helens
1980
convergent boundaries
magma. north flank (crack on side) bulged (stored magma), earthquake, landslide, release of presssure produced explosive lateral pyroclastic (explosive) eruption
Krakatou
1883 Indonesia
exploded for several months, caldera, new volcano appears
cool weather
brilliant sunsets (the scream) long twilight due to acid rain
Tambure
1815 Indonesia
Largest eruption of last 10,000 years
result is year without a summer
hit new england and europe with snow
Vesivous
79 c.e. pompeii
pliny the younger letter
