Volcanoes 3 Flashcards
name the four main types of volcanoes
- cinder cones (m, ex)
- shield volcanoes (m, non)
- stratovolcanoes (int-f, mixed)
- calderas / super volcanoes (f, ex)
True or false: diff types of volcanoes can exist together
true
ex/ small cinder cones on side of large shield volcanoes
which type of volcano can cause climate change?
calderas
(super volcanoes)
eruption type and trends for cinder cones
- explosive
- erupt for a few years then never again
size of cinder cones
height: < 0.5km
width: < 2km
cinder cones material, behaviour, slope
- gas rich mafic (basalt)
- fire fountaining creates beds of pyroclastic ejecta
- angle of repose = 30-40˚ (not very steep)
eruption type and trends for shield volcanoes
- effusive, not very explosive
- erupts often
size of shield volcanoes
height: 4-10km
width: 100km
shield volcanoes material, behaviour, slope
- mafic
- lava flows (pahoehoe then a’a)
- gentle slopes
eruption type and trends for stratovolcanoes
- explosive
- can erupt many times and stay active for 100k yrs
size of stratovolcanoes
height: < 5km
width: 10km
stratovolcanoes material, behaviour, slope
- intermediate or felsic
- interbedded lava flows, pyroclastic flows, lahars
- steeper cuz viscous magma
example of stratovolcano
mt st helens
mt baker
mt fuji
example of shield volcano
Mauna Loa, hawaii
example of cinder cones
opal cone, garibaldi park
can we get felsic magma from the mantle?
no
what causes stratovolcanoes? Where is it most common?
subduction
ring of fire
how does plate subduction generate mafic/felsic magma?
plate subduction creates mafic magma
which melts crust to produce felsic magma
eruption type and trends for calderas
- explosive
- not often
size of calderas
huge!
up to 10’s km across
calderas material
felsic pyroclastic
how are calderas created
created from large, explosive felsic eruptions
when the roof of magma chamber collapses
example of caldera
yellowstone
what is a resurgent dome
when eruption causes a collapse (caldera), continued effusive eruption causes resurgent dome (usually in water)
which type of volcano is the most explosive and most devastating?
calderas
frequency of global eruptions for the four types of volcanoes (cinder cone, shield, strato, caldera)
- cinder cones -> frequent
- shield -> frequent/continuous,
larger gaps btwn eruptions - stratovolcanoes -> frequent but discontinuous
(active vs dormant) - calderas -> rare
effusive eruption style
passive eruption of magma
- gas plume + pyroclastic material, pummus deposits
- laval flows
(maf-int) - lava domes
(fel-int) ex/ mt baker - gravitational collapse of flows/domes
(block and ash flows)
explosive eruption style
gas driven and violent
- pyroclastic deposits
- acid rain
- buoyant eruption column of ash
- pyroclastic airfall
- pyroclastic flows (column collapse)
- blocks & bombs (ballistics) proximal to vent
volcano with sheets means ___ viscosity
low
volcano with domes means ____ viscosity
high
pyroclastic falls
- eruption columns: 10s of kms
- wide distribution of ash in downwind direction
- ash blankets topography
ex/ pinatubo
pyroclastic flows
- gas-pyroclast mixtures
- gravity driven, channel in valleys
- super hot and fast
- velocity 40 to >400km/h
- temps 100-600˚C
ex/ pinatubo
primary volcanic processes
- lava flows, domes, graviational collapse
- pyroclastic falls and flows
- ballistics
secondary processes
- reworking of primary deposits during eruption
-> LAHARS
what are lahars
volcanic mud flows of water and ash
- super erosive and fast
