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Volcanoes
Ch. 12
80
Geology
Undergraduate 1
03/29/2011

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Cards

Term
asthenosphere
Definition
main source of magma
Term
volcanism
Definition
geologic processes that give rise to volcanoes and volcanic rocks
Term
volcanic geosystem
Definition
all magmas rocks and processes taken together
Term
basaltic lavas
Definition
erupt when hot fluid magmas fill up a plumbing syst. and overflow
-extrusive ig. rock (mafic); low in sillica--> fast flowing
-dark, erupt at high t's (1000-12000C)
Term
basaltic lava forms
Definition
pahoehoe - ropy, skin like (form thin, fluid lava)
Aa- lava that loses gasses cools to this rocky text.
Term
flood basalts
Definition
large basaltic lava plateaus; highly fluid lava erupted on flat plain-->thin sheets
Term
pillow lavas
Definition
basaltic eruptions underwater form these sack like deposits
Term
andesitic lavas
Definition
intermediate extrusive rocks; produced mostly above subduct. zones; temps lower than basalts
higher sillica contetnt-->lumpier masses & slower mvmnt
-phreatic - steam explosions; occur when hot, gas charged magma encounters water
Term
rhyolitic lavas
Definition
lower melt T.;(800-1000C)-extrusive, felsic (high silica)
-light color(often pink)
-produced where heat form mantle has melted large sections of cont. crust
-most viscous b/c of sillica cont
-pile up in thick bulbous deposits
-gasses easily trapped -->most explosive
Term
quick cooling
Definition
fined grained rocks
Term
slow cooling
Definition
coarse grained rocks
Term
pumice
Definition
very vesicular
Term
pyroclastic deposits
Definition
-hot ash and dust + gasses in flowing cloud - moves up too 200 km/hr
-classif according to size
Term
volcanic ejecta
Definition
a)volcanic ash (smallest) - come from sprays
b)volcanic bombs - blobs of volcanic magma thrown into the air
Term
tuffs
Definition
rocks formed from smaller fragments
Term
breccia
Definition
formed from larger fragments
Term
pyroclastic flows
Definition
often deadly
hot ash, dust and gas in a cloud
moves quickly
Term
central eruptions
Definition
discharge lava or pyroclasts from a central vent
Term
shield volcanoes
Definition

lava cone - built by successive flows of lava from a central vent --> shield shaped volcano

-accumulation of lava flows

Term
volcanic domes
Definition

rhyloitic and andesitic lavas (more viscous) - bulbous, steep sided mass

-often plug vents and trap gasses

-pressure can build and blast dome into fragments

Term
cinder cones
Definition

form from volcanic vents that discharge pyroclasts

-fragments from cinder cones

-concave accumulation of pyroclasts

-profile depends on angle of repose

Term
stratovolcanoes
Definition

volcanoes that emit lava and pyroclasts; alternating lava flows and blasts of pyroclasts build to concave shape

-strengthened by dikes and solidified lava in central feeder

-common above subduction zones

Term
craters
Definition
bows shaped pits found at summit of volcanic mountains
Term
calderas
Definition

large, steep walled basin-shaped depression

-when a violent eruption empties a volcano's magma chamber which cant support rock

-collapse and leave flat basin

-may reinflate (resurgent caldera)

 

Term
diatremes
Definition

when magma from earth's interior escapes explosively, the vent and the feeder channel are often left filled with volcanic breccia as eruption wanes

-kimberlite pipes

Term
kimberlite pipes
Definition

peridite ultramafic rock left behind (diamond)

-come from deep within earth

-assoc with deeper diatremes

Term
fissure eruptions
Definition

-largest eruptions; come from small, nearly vertical cracks in earth's surface (very long)

-basaltic lava; along mid ocean ridges wehere new oceanic crust forms

-flood basalts

-ash flow deposits

Term
flood basalts
Definition
lavas erupted from fissure to form plain/accumulate as a plateau
Term
ash flow deposits
Definition
eruptions of pyroclasts on continents-->sheets of tuffs
Term
hydrothermal activity
Definition
circulation of water thru hot volcanic rocks and magmas
Term
hot springs and geysers
Definition

continuous flow of water heated and returned to surface by buried magma

 

hot water fountains that spout intermittently

Term

volcanism at spreading centers

Definition

large volumes of basaltic lava erupt at mid ocean ranges (created sea floor)

-divergent boundaries - zig-zag pattern by transform faults

+short, parallel spreading centers

+axial volcanoes - spreading centers of parallel length

Term
volcanism at subduction zones
Definition

voncanic mountains lie parallel to convergent boundaries

(above sinking slab

-magmas made by fluid induced melting; varied in chem comp

-range from mafic to felsic (basaltic to rhyolitic;few intermediate)

-subduction volcanoes form as island arcs where lithos is oceanic

Term
hot spot
Definition
volcanic manifestiations of hot, solid material rising from mantle plumes
Term
mantle plumes
Definition
thin magmatic jets deep in mantle
Term
large igneous provinces (LIP's)
Definition

fissure eruptions release large amts of lava

flood basalts can be LIP's

-large volumes of mostly mafic extrusive and intrusive ig. rocks

-origins lie in processes other than seafloor spreading

-continental flood basalts, assoc. intrusive rocks, oceanic basalt plateaus, aseismic ridges

 

Term
aseismic ridges
Definition
no earthquakes
Term
eruption clouds
Definition
clouds of ash lofted into air traffic lanes (dangerous to planes)
Term
lahars
Definition

torrential flows of wet volcanic debris

-occur when pyroclastic flow meets river/snow; when wall of a water filled crater breaks; when lava flow meets glacier; when rain pushes ash into mud

Term
flank collapse
Definition

volcanic mt. constructed from thousands of deposits of lava, or pyroclasts or both

-not very stable

-sides may break off

Term
caldera collapse
Definition

infrequent

earthquakes

carbon dioxide leaks

Term
geothermal energy
Definition
depends on heating of water as it passes thru a region of hot rock (heat reservoir) deep below earth's surface
Term
andesite
Definition
volcanic eq. of diorite; less silica, plagioclase feldspar, no qz
Term
basalt
Definition
mineral found at ocean/crust floors; grey-black fine grained extrusive; large in pyroxene and olivine
Term
batholith
Definition
larger pluton of magma chambers; thick, horizontal sheetlike; slow cooling at great depths
Term
bomb
Definition
pyroclasts hurled from volcanoes streamlined as hurdled through air
Term
concordant intrusion
Definition
boundaries parallel to country rock layers (horiz. or not)
Term
country rock
Definition
rock surrounding volc intrusions
Term
dacite
Definition
volcanic equivalent of grandiorite; qz, plagioclase feldspar
Term
decompression melting
Definition
when material rises and melts with decreased pressure; makes most of earth's magmas
Term
dike
Definition
sheetlike igneous bodies; cut across layers of country rock
Term
diorite
Definition
low silica, high plagioclase feldspar, little/no qz
Term
discordant intrusion
Definition
cuts across layers of country rock
Term
extrusive igneous rock
Definition
forms from erupted materials
Term
felsic rock
Definition
high in sillica, low in Mg and Fe, qz, plagioclase and orthoclase
Term
fluid induced melting
Definition
melting of rock induced by presence of water that lowers melting pt
Term
fractional crystallization
Definition
process by which crystals are fomed in cooling magma and are segregated from remaining liquid rock
Term
gabbro
Definition
coarse-grained, dark grey intrusive rock; pyroxenes (mafic); no qz, plagioclase feldspar
Term
granite
Definition
felsic intrusive; 70% sillica; qz, plagioclase, muscovite and biotite
Term
grandiorite
Definition
light rock, looks like granite; plagioclase
Term
intermediate igneous rock
Definition
not rich or sillica or low in Mg and Fe; grandiorite, diorite, dacite & andesite
Term
mafic rock
Definition
rich in pyroxene and olivine, Mg and Fe, low in silica, flows quickly, basalt & gabbro; magmatic
Term
magmatic differentiation
Definition
process where rocks of varying comp can arise from uniform parent magma
Term
obsidian
Definition
hard glass pyroclast; lots of pores
Term
ophilolite suite
Definition
essemblages of deep sea sediments
Term
partial melt
Definition
where some minerals melt before others in a rock
Term
pegmatite
Definition
veins of extremely course grained granite cutting across fine country rock
Term
peridotite
Definition
coarse grained ultramafic rock; olivine & pyroxene
Term
pluton
Definition
large magmatic chambers
Term
porphyry
Definition
ig rock with mixed texture; large cystals 'float' in mass of fined grained rock
Term
pyroclast
Definition
fragments of lava thrown into the air
Term
rhyolite
Definition
felsic extrusive; fine grained; volcanic glass
Term
sill
Definition
sheetlike magma between country rock
Term
stock
Definition
smaller plutons
Term
ultramafic rock
Definition
rock with 10% feldspar; rarely extrusive; solidify at hight temp
Term
vein
Definition
mineral deposits found in rock fracture
Term
viscosity
Definition
measure of a liquid's resistance to flow; goes up as silica content goes up
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