Volcanic Eruptions Flashcards
Where does volcanoes mostly found?
Convergent boundaries
Continents generate more what type of magma?
Rhyolitic magma
Hot spots generate more what type of magma?
Basaltic magma
The viscosity of magma depends on ________.
SiO2
The process where the early formed minerals are denser than the liquid.
Crystal setting
SiO2 content of Basaltic lava
41-52%
SiO2 content of Andesite/Dacite
52-68%
SiO2 content of rhyolite
68-77%
Which magma is hotter when ejected?
Basaltic magma
Which type of magma is cooler when ejected?
Rhyolite
True or False. 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 a mineralogy much different from the parent magma
TRUE
The richer _______, ________, and ________ crystallize and settles at the bottom of the magma chamber.
iron, magnesium, and calcium
The remaining melt will be enriched with _____, ______, and ______. Should a subsequent eruption occur, the rocks generated will be more ________ and closer to the __________ end of the compositional range than the initial magma.
sodium, potassium, and silica
silica-rich
felsic (granitic)
What is Magmatic Differentiation?
The formation of one or more secondary magmas from a single parent magma.
What is Assimilation?
Surrounding country rock may be incorporated to the upwelling magma.
What is magma mixing?
Occurs during the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes the more slowly rising body
True or False. Minerals with the highest melting temperatures are the first to melt
FALSE. lowest
The process that generates a magma that’s nearer the felsic (granitic) end of the compositional spectrum than the parent rock from which it was derived.
Partial melting
Basaltic magma have a temperature of __________
1000 degrees celsius to 1250 degrees celsius
TRUE or FALSE. Under the high-pressure conditions for the upper mantle, partial melting of the ultramafic rock peridotite will yield a magma of granitic composition.
FALSE. basaltic composition
Basaltic (mafic) magmas that originate from partial melting of mantle rocks are also called ___________.
primary or primitive magma
What is decompression melting?
Partial melting that produces mantle derived magmas may be triggered by a reduction in confining pressure
TRUE or FALSE. Basaltic magmas are also generated at subduction zones where water driven from the descending slab of oceanic crust promotes partial melting of the mantle rocks that lie above
TRUE
How andesitic magma formed?
When rising basaltic magmas assimilate crustal rocks that tend to be silica rich.
One way andesitic magma can form is when a rising mantle derived basaltic magma undergoes ______________ as it slowly makes its way through the continental crust
magma differentiation
What are the various types of gas molecules form when rock body begin to melt?
H2O, CO2, SO2, H2, CO, H2S
Gases remain dissolved within the magma until the magma gets near the surface , where the __________ allows the gases to escape.
Decreased pressure
TRUE or FALSE. Lower content of dissolved gases within a magma will result to a more explosive volcanic eruption.
FALSE. Higher content.
A type of landform when lava eventually cools and solidifies into an igneous rock body
Lavaflow
A type of landform is a steep-sided mound formed from viscous lava ( rhyolitic lava). They can also act like a ________ when it begins to solidify and thus allow pressure to build in the magma chamber and result in a more explosive eruption.
Lava dome; plug