volcano basics I Flashcards
what is igneous rock?
formed of molten rock
melting of rocks in hot, deep crust and upper mantle
what is magma?
molten rock underground
what is lava?
molten rock on the surface of the planet
rocks that solidify underground are called?
plutonic or intrusive
what are rocks called that solidify on the surface or above ground?
volcanic or extrusive
if a rock has cooled more slowly, what size is it, and what kind of rock is it?
bigger (coarse crystals) + intrusive
if a rock has cooled more quickly, what size is it, and what kind of rock is it?
smaller (fine grain crystals) + intrusive
what is pyroclastic rock?
refers to deposits and rocks formed by the eruption of a volcano, extrusive rocks
what is a tephra?
material ejected through the air during eruption (volcanic ash or pumice)
what is igneous rock classification based on?
- intrusive or extrusive
- amount of silica content
(mineral assemblage + texture)
what is a mafic rock?
lower silica, higher magnesium and ferric
what is a felsic rock?
higher silica and feldspar, lower magnesium and ferric
what is an intermediate igneous rock?
varies in element content
what are some properties of mafic rocks?
- 45 - 50% silica
- low viscosity (runny / flowy)
- dark in color (magnesium and felsic)
- melt and forms are very hot
- abundant ferromagnesian mineral
- calcium rich feldspar
what is an example of mafic igneous rocks?
basalt (extrusive, fine grain) or gabbro (intrusive, coarse grain)
what are some properties of intermediate igneous rocks?
- 50 - 70% silica
- little or no quartz
- purple / green / grey color
what are some examples of intermediate igneous rocks?
dacite and andesite and nanocides (extrusive, fine grain) + diorite/granodiorite (intrusive, coarse grain)
what are some properties of felsic igneous rocks?
- > 70% silica
- formed in association with continental crust
- high viscosity (thick)
- melts and forms at low temperatures
- potassium rich feldspar
- sodium rich quartz
- low ferromagnesium
- lots of feldspar and quartz
what are some examples of felsic igneous rocks?
rhyolite (extrusive, fine grain) + granite (intrusive, coarse grain)
how to make partial melt magma
decrease overlying pressure (hard to melt with high pressure), raise the temperature, and/or add water
how can we decrease overlying pressure to make magma partially melt?
decompression melting
spreading zone (plates thinning apart and lowering pressure)
how can we raise the temperature to make magma partially melt?
mantle plume/hot spot
subducting plate (decreases into area)
how do we add water to make magma partially melt?
subducting plate (decreases into area, bringing water into area)
why does melt rise (if it can find a way)?
it is less dense than surrounding rock
when does a volcano form?
if some of the partial magma melt reaches the surface due to faults or weakness in rocks above
are all magma melts the same? why or why not?
NO! rocks are always made up of different minerals, and different minerals melt under different conditions
is the melt the same composition as the rock / solid version?
NO! rare to melt the entire rock, rocks are a mix of different minerals, so typically only some minerals are melting the rock, which makes it have a different composition
do we melt higher or lower silica content first?
higher silica (felsic -> ultramafic)
rock / melt changing from one compensation to another is called?
magma differentiation
what is partial melt recharge?
melt coming in from other areas
how can geography control magma composition?
the magma composition that makes it to the surface depends on how much crust the magma needs to travel through and how long it takes to get to the surface
when the crust is thicker and it takes longer to get to the surface, what happens to the melt?
the more the melt evolves (mafic to intermediate to felsic)
what are the magma types by tectonic setting?
subduction zone
hot spot under ocean crust
mid-ocean ridges
continental rifts
hot spot under crust
what are subduction zones magma type?
some magma evolving, but not an enormous amount (intermediate, crust thickness + time moderate)
what are hot spots under ocean crusts magma type?
ocean crust is much thinner (basalt, direct from mantle)
what are mid-ocean ridges magma type?
iceland: hot spot under rift (basalt, direct from mantle)
what is a hot spot under crusts magma type?
large volume, under thick continental crust
(rhyolite, lots of crust to travel through + long time)
what are continental rifts magma type?
rift that will eventually become ocean rift
(mix of rocks, thinning at rifts despite continents thick)
what is a volcanos magma type?
a central vent or fissure where molten rock, gas, and rock fragments are ejected during an eruption. anywhere where molten rock makes it
can be fissures, and may not always be the big cone shape you think
what are the types of volcanoes?
fissure, shield, lava dome, cinder cone, composite, caldera
what are the four typical volcanic settings?
- hot spots: mantle plumes under ocean and continents (formed when anonymously hot portion of the mantle is impacting the bottom portion of the crust)
- divergent boundaries (spreading zones): mid-ocean ridges
- young spreading zones: rifts in continents
- subduction / collision zones: subducting plate can cause melt
OR ANYWHERE MAGMA PRODUCE + CAN GET TO SURFACE
what are subduction zones volcanic type?
intermediate
stratovolcanoes
what are hot spots under ocean crusts volcanic type?
exclusively basalt
shield volcanoes and fissures
what are mid-ocean ridges volcanic type?
mostly basalt (fissures)
iceland exception
what are hot spot under crusts volcanic types?
rhyolite
calderas + flood basalts
what are continental rift volcanic types?
mix
what types of volcanoes are most common?
subduction zone volcanoes
what type of volcanoes have the most super-eruptions?
hot spot under crust
