Volcanoes 4 Flashcards
Mafic explosivity characteristics
low gas content and low viscosity
= quiet effusive eruptions
- gas escapes cuz low viscosity, pressure released
= safe
felsic explosivity characteristics
high gas content + gooey
= explosive eruptions
gas kept under increasing pressure cuz high viscosity
= dangerous
is mafic or felsic eruptions dangerous? Why?
felsic
- gas kept under increasing pressure cuz high viscosity
which conditions most favour explosive eruptions?
- high viscosity
- high gas content
gas escapes easily from ___ magma
mafic
gas escapes more difficultly from ___ magma
felsic
why do bubbles form when magma rises?
exsolve gases
which factors are important in determining eruption style?
viscosity and gas content
what happens as magma rises?
pressure decreases so bubbles form
viscosity (helps/fights) bubble growth
fights
fragmentation occurs when ___
pressure rises inside bubbles until they overcome the strength of the magma
= pyroclastic material is produced
what is tephra
pyroclastic material
name the four parts of volcanic conduit
- disrupted magma (gas jet of pyroclastic material)
- fragmentation surface
- resolution interval (bubbly magma)
- saturation surface
how does pyroclastic material form?
- rising magma (w/ dissolved gas) decompresses fast
- gas bubbles expand and blow up magma foam
- magma particles freeze in flight
what controls viscosity?
temperature
___ contents are important for explosivity
silica and volatile (gas) content
-> also temp controls viscosity!
what magma property is least important for explosivity?
density
what are the 5 styles of explosive volcanic eruptions?
- hawaiian
- strombolian
- volcanian
- plinian
- phreatomagmatic
hawaiian explosive eruptions
- low viscosity
- basaltic magma
- effusive
- lava flows
- fire fountaining
- lava lake
are hawaiian explosive eruptions safe?
yes
Strombolian explosive eruptions
- basaltic/andesitic magma
- mildly explosive
- lava flows
- fire fountaining
- bombs
are Strombolian explosive eruptions safe?
still safe yeah
which explosive eruption has a pulsatory/cyclical nature?
Strombolian
vulcanian explosive eruptions
- andesitic/rhyolite magma
- super explosive
- sustained explosions of ash (plume & fallout)
- bombs / fragmentation
are vulcanian explosive eruptions safe?
nope
can be lethal :<
which explosive eruption can transition from effusive to explosive in seconds?
vulcanian
plinian explosive eruptions
- andesitic/rhyolite ash
- violently explosive!
- pyroclastic flows
- large sustained ash column + fallout
are plinian explosive eruptions safe?
nope super dangerous T^T
phreatomagmatic explosive eruptions
- contact btwn water and magma
- violently explosive
- water vapour cloud
- crater and water
- compressed ash
a resurgent dome in a lake (of a crater) might explode in what style?
phreatomagmatic
are phreatomagmatic explosive eruptions safe?
nope they super dangerous and exploooosive
what condition might turn an unexplosive volcano to a super explosive and dangerous one?
water around the conduit
pelean explosive eruptions
dome collapse
- violently explosive!
- ash fallouts
rank the types of eruptions from mafic to felsic
(low viscosity & gas = safe)
hawaiian
strombolian
vulcanian
pelean
plinian
(high viscosity & gas = danger)
eruption column height of hawaiian explosion
< 2km
eruption column height of Strombolian explosion
< 10 km
eruption column height of vulcanian explosion
< 20km
eruption column height of plinian explosion
< 55km
which is more explosive, vulcanian or plinian?
vulcanian :O
«go slides for chart: day 4»
3 characteristics that define the VEI scale
- volume of ash produced
- height of eruption cloud above vent
- duration of eruption
VEI
volcanic explosivity index
- describes size of an explosive eruption
- logarithmic
- mainly depends on total volume erupted explosively
(0 - 8)
Hawaiian explosion would mostly be categorized as what VEI?
VEI 1
vulcanian explosion would mostly be categorized as what VEI?
VEI 3
plinian explosion would mostly be categorized as what VEI?
VEI 5
example of ultraplinian eruption
VEI 6
Mt Pinatubo in 1991
- caused global temp to decrease cuz lots of SO2
