Volcanoes Flashcards
Lecture __ 9/19 thursday
what is a volcano?
a hole in the ground
what is the mountain etifis?
the mountain
where do we find volcanoes?
- pacific ring of fire
- subduction zones: hydrated magma
why do ocean ridges cause volcanoes?
What are hot spots?
burns through lithosphere
but lithosphere moves
chain islands
primitive
deep mantle
high He/Ne isotope ratio
how is volcanism associated with plate tectonics?
volcanoes and convergent plates
what controls the composition and nature of an eruption?
where the volcanoes are located
what are refractory elements?
everything that isn’t silica
how does silica determine magma type, extrusive rock, and instrusive rocks?
weight percent
how does water affect magma?
lowers melting temperature
what are flood basalts?
- monstrous eruptions
- volumetric
- a lot of rocks melted and came up
what are shield volcanoes?
low slope
broad
fluid basalt
can run down a shallow hill
lava viscosity
what are cinder cones?
- pieces spit out that pile-up and get steep
- by the time they hit the ground they are hard
what is the angle of repose?
stratovolcanoes
-stratified
- composed a different in nature magma
- spatter, ash,
- very steep
volcanic dome
- viscous
- cool
- close to solidus
- comes out and solidifies right away
caldera
what is left after a very explosive eruption
- magma chamber comes out of the ground
-a hole in the ground that subsides
controls style of eruption
effusive
molten magma oozing out and flowing
explosive
viscous magma fragments and shoots into the air
pahoehoe
move quickly
- slower than a walk
Aa
the same stuff as pahoehoe but breaks up
- more force
- steep
- past stress
- little bit faster
what does flow type depend on?
rheology and strain rate
fissure eruptions
crack in the ground
erupt basalt
flood basalts
hexagonal
flood basalts
light rare earth enrichment
La/Sm ratio
tell us primitive source melt
- minerals don’t want
-first thing to go into melt
Capatability
isotope ratios
where do hot spots come from?
whole or layered mantle convection
scoria cone
- cinder
- steep
composite cones
- stratovolcanoes
- pyroclastic (fire particles)
- bigger than cinder
volcano influence on atmosphere
ash and water vapor
why do they erupt
- ## bubbles of gas in magma
plutonic
what kind of relationship does viscosity have with water diffusivity?
inverse
surtseyan explosion
water explosion
chills and breaks up
small
plinian explosion
sustained, fire hydrant
strombolian explosion
pop gun
vulcanian explosion
kaboom
how do we measure explosivity?
VEI: volume of tephra (stuff that comes out of the ground, hard to do)
Simplified VEI
what comes out of volcanoes?
basalt andesite
what size is ash?
less than 2 mm
what size is lapilli
2-64 mm
what sizes are blocks and bombs?
more than 64 mm
- surface tension irrelevant
what is tephra?
what is tuff?
PDC
hundreds of km/hr
large particles dragged down by air, dense
deadly
