Volcanic Eruptions - MAGMAS Flashcards
Volcanoes are mostly found along
convergent boundaries
Much magmas are expelled along
divergent boundaries
the type of ____and consequent type of _____ of a volcano depends on the _____ it is formed
magma ; eruption ; tectonic setting
what are the three types of magma
basaltic, andesitic, rhyolitic
what is a magma
a magma is an extremely hot mixture of solid, gas, and liquid, located under Earth’s surface
what is the solid part of the magma
crystals
what are the gaseous part of the magma
H2O, CO2, SO2
what is the liquid part of the magma
molten rock
what type of magma are formed in an oceanic-oceanic subduction zone
basaltic or andesitic magma
what type of magma are formed in an oceanic-continental subduction
andesitic or rhyolitic
what type of magma is found in oceanic hotspot
basaltic magma
what type of magma is found in continental hot spot
rhyolitic magma
how does continental hotspot produce rhyolitic magma?
silica-poor basalt still rises toward the surface; as the magma rises, it melts its way trough thick, silica-rich continental crust forming shallow silica-rich (rhyolitic) magma chambers
silica content of basaltic magma
48-52%
silica content of andesite/dacite magma
52-68%
silica content of rhyolite magma
68-77% or >66%
silica content of ultramafic magma
<45%
t or f: as silica content increases, the silica structure of the magma becomes more 3D
T
t or f: high temperature magma have high viscosity
F (low viscosity)
the viscosity of magma increases with ____ SiO2 and ______ tempeature
increasing ; decreasing
they are the least viscous type of magma
basaltic magma
why are basaltic magmas least viscous?
they form in the upper mantle where the temperature is high and the SiO2 content is low
t or f: basaltic magmas are formed in the deep and hot upper mantle while andesite and rhyolitic magmas form at much shallower and cooler depths
T
t of f: magmas evolve in different ways, one process can’t explain the entirety of its evolution
T
t or f: overtime, a volcano may extrude lavas that are uniform in composition
F (vary in composition)
depicts the sequence in which minerals crystallize to form magmas
Bowen’s Reaction Series
draw the bowen’s reaction series
mechanisms that allow evolution of magma
magmatic differentiation
crystal settling
assimilation
magma mixing
partial melting
it is the process where the early-formed minerals are denser than the liquid and sink toward the magma chamber
crystal settling
in crystal settling, when the remaining melt solidifies either in place or in another location, if it migrates into fractures in the surrounding rocks, it will form _____
a rock with mineralogy much different from the parent magma
what are the early-forming minerals?
olivine, pyroxene, ca-plag
in crystal settling, the remaining melt will become more enriched in ____
silica
crystal settling results in a change in the composition of the ______
remaining melt
it is the formation of one or more secondary magmas from a single parent magma
magmatic differentiation
magmatic differentiation results in _____ of ferromagnesian minerals and ______ of silica-rich minerals
depletion ; enrichment
t or f: crystal settling is part of magmatic differentiation
T
it is an intrusion extending from New York to New Jersey that was formed through magmatic differentiation
Palisades Sill
how long was the Palisades Sill intrusion and composed of what rock?
80 km long ; monzonite
what are the layers of palisades sill?
Sandstone
Basalt
Na-rich plag
Ca-rich plag, pyroxene
Olivine
Basalt
Sandstone
t or f: magmatic differentiation by itself cannot account for the entire compositional spectrum of igneous rocks
T
some of the surrounding rock (country rock) may be incorporated into the upwelling magma
assimilation
in assimilation, rising magma creates an _____ applied to overlying layer causing the country rock to ______
upward stress ; fracture
occurs during the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes the more slowly rising body
magma mixing
in partial melting minerals with _____ are the first to melt
lowest melting temperature
is the process that generates a magma that is nearer the felsic (granitic) end of the compositional spectrum than the parent rock from which it was derived, because silica rich minerals are first to melt
Partial melting
partial melting can be triggered by addition of ____ to the overlying rock layer
volatiles
how does volatile trigger partial melting?
as volatiles gets squeezed out from the subducting slab, it reacts with overlying rock, decreasing its melting temperature thus, low-temp rocks melt first
most magma that erupts on the earth’s surface is _____ in composition
basaltic
basaltic magma has a temperature of
1000 to 1250 degrees celsius
experiments show that under the ______ conditions calculated for the upper mantle, _____ of the ultramafic rock ____ will yield a magma of basaltic composition
high-pressure ;
partial melting ;
peridotite
basaltic (mafic) magmas that originate from partial melting of mantle rocks are called _____ or _____ because they have not yet evolved
primary or primitive magmas
partial melting caused by a reduction in the confining pressure
decompression melting
basaltic magmas are also generated at ______, where water driven from the ______ of _____ promotes partial melting of the rocks that lie above
subduction zones ; subducting slab ; oceanic crust
one way andesitic magma can be formed:
when rising mantle-derived basaltic magma undergoes magmatic differentiation thru crystal settling as it slowly makes it way through the continental crust
if iron-rich components are separated from the liquid by crystal settling, the remaining melt will have an _____
andesitic composition
evolved (changed) magmas are termed:
secondary magmas
andesitic magmas can also form when rising basaltic magmas _______ crustal rocks that tend to be silica-rich
assimilate
granitic magmas are mostly generated by _____
partial melting of continental crust
magmas also contain various types of gas molecules that form when
minerals within a rock body begin to melt
gaseous molecules in magmas remain dissolve until the magma gets _____, where the ______ allows the gases to escape
near the surface ; decreased pressure
t or f: higher content of dissolved gases within a magma will result to a more explosive volcanic eruption
T
one cubic meter of magma with 5% of dissolved water will expand to:
670 cubic meters
t or f: andesitic magmas contain more water molecules than basaltic magma
True
