GEO Midterm 2
water circulating at thousands of feet below the earth's surface needs to be heated to temperatures _________ 100C (212F) in order to reach its boiling point because the pressure of the overlying groundwater body is so great
above
which of the following is a poor choice when trying to reduce the likeihood of a slope failure?
adding water to the slope during a cold snap to freeze it in place
a caldera collapse occurs ___________
after the magma chamber is mostly empty
the typical trend in a rising plume of subduction-zone magma is to increase the _______
all of the above
external processes that increase the probability of a slope failure include ________
all of these choices are correct
many hill-slope masses are weak due to preexisting geologic conditions such as ______
all of these choices are correct
mt. rainier, washington, is number one on the danger list of many u.s. volcanologist because of its __________
all of these choices are correct
rock may melt by __________
all of these choices are correct
the viscosity of magma is lowered by ________
all of these choices are correct
violent causes of death from volcanic eruptions include _________
all of these choices are correct
why does the magma from some volcanoes flow smoothly and relatively peacefully, while the magma from other volcanoes blast forth violently and deals death over wide areas?
all of these choices are correct
at oceanic spreading centers, magmas are rhyolitic in composition
false
less than 20 percent of earth's magma extruded through volcanism occurs at oceanic spreading centers
false
several geologic phenomena are being studied as signs of an impending volcanic eruption. these include seismic waves, __________, and the release of gases
ground deformation
magma at great depths usually does not contain gas bubbles because ________
high pressure at depth keeps gas dissolved in solution
beneath continents, rising basaltic magmas are contaminated by sediments and continental-crust rocks, altering magma composition; the resultant andesitic to rhyolitic magmas have __________ contents of sio2, relatively low temperatures, and ________ viscosity
high, high
the most peaceful eruptions are ______ eruptions
icelandic type
as minerals continue to form in the magma kept at a constant temperature, the viscosity of that magma will _______
increase
a mantle hot spot has generated a long-lived plume beneath yellowstone national park, and the north american continent is moving ______ about it about 2 to 4 cm/yr
southwestward
__________ are steep-sided, symmetrical volcanic peaks built of alternating layers of pyroclastic debris capped by high-viscosity andesitic to rhyolitic
stratovolcanoes
although there are 92 naturally occurring elements, a mere eight make up more than 98 percent of earth's crust
true
if basaltic lava reaches the sea or a lake, it cools rapidly into _______ lava
pillow
among different types of volcanic eruptions, ________ eruptions are the most violent type of explosive eruptions
plinian-type
the most famous of all volcanoes probrably is vesuvius, and the most famous of its eruptions are those of 79 ce, which buried the cities of __________
pompeii and herculaneum
when gas escapes quickly and violently from lava it may produce a frothy glass full of holes left by former gas bubbles; this porous material, known as __________, contains so many holes it can float on water
pumice
if all of the following rocks were to completely melt and reach the same final temperature, which would produce magma with the highest viscosity? [hint gabbro and diorite are plutonic rocks, their composition equivalent volcanic rocks are basalt and andesite, respectively]
rhyolite
of the following types of mass movements, which can move the fastest?
rock fall
spreading centers have relatively peaceful eruptions of magma because the __________
sio2-poor magma is at high temperatures
the volcanic explosivity index (vei) of historical events ranges from ________
0 to 8
about _______ of volcanism is associated with the edges of tectonic plates, and close to about ______ of earth's magma extruded through volcanism takes place at the oceanic spreading centers
90%, 80%
the formation of a giant continental caldera includes all but which of the following?
basaltic eruptions begin forming circular fractures surrounding the bulge
pyroclastic debris is ____________
chucks of magma and ricks blown into the air by gas in a volcanic eruption
the process of mineral formation in a cooling magma is usually called _________
crystallization
__________ melting occurs when a rock melts due to a lowering of pressure
decompression
the primary reason magma forms at subduction zones is that the subducting plate carries a cover of sediments, water, and hydrated minerals down with it, which usually _____________ the temperatures required for the adjacent overlying mantle lithospheric rock to melt
decreases
when it comes to volcanic hazards, the key problem is how easily the ________ can escape from the magma
dissolved gases
below the ocean basins, the basaltic magmas have ________ contents of sio2, high temperature, ______ viscosity, and allow easy escape of gases, producing peaceful eruptions
low, low
if two magmas have the same composition but at different temperature, the hotter of teh two magmas will have a _________ lower viscosity
lower
the presence of water usually _____ the melting point of rock
lowers
spreading centers are an ideal location for volcanism because all but which of the following?
magma formation due to the melting caused by incorporation of water in asthenosphere minerals
crater lake, oregon, fills the caldera of ________ which collapsed about 7,600 years ago
mt. mazama
a genuine success story of advance warning before a large eruption occurred in the philippines in 1991 before the climatic eruption of ______
mt. pinatubo
the two most active cascade range volcanoes over the past 4,000 years are ___________
mt. st. helens and mt. shasta
highly fluid basaltic lava may cool with a smooth, ropy surface called _________, whereas lower temperature, slower flowing, more viscous basaltic lava commonly has a rough, blocky texture called ________
pahoehoe, aa
mt. kilimanjaro in tanzania, mt. shasta in california, mt. rainier in washington, and mt. fuji in japan, are _______, which are steep-sided, symmetrical volcanic peaks built of alternating layers of pyroclastic debris capped by high-viscosity andesitic to rhyolitic lava flows that solidify to form protective caps
stratovolcanoes
some of earths most beautiful mountains are ______, including mt. kilimanjaro in tanzania, mt. shasta in california, mt. rainier in washington, and mt. fuji in japan
stratovolcanoes
magma rising in a ________ tends to get more "contaminated" with _______ than does magma rising in a spreading ridge
subduction zone, high silica content minerals
in magma, silicon and oxygen often link up to form the silicon-oxygen __________
tetrahedron
active volcanoes today in oregon and washington, including mt. st. helens, result from_________
the subduction of the juan de fuca place beneath north america
the immediate causes of slope failures, such as earthquakes or heavy rainfall, are called ____________
triggers
hot spots can be under the ocean, under the continents, in the center of plates, and at spreading centers
true
oxygen and silicon are so abundant in earth's crust that their percentages dwarf those of all other elements
true
stratovolcanoes are often associated with subduction zones
true
the radiocarbon process of documenting major eruption dates for volcanoes int he past 50,000 years or so is the same as that used to work out dates of major prehistoric earthquakes
true
the three most recent catastrophic yellowstone eruptions occured at 2.6 million, 1.29 million, and 640,000 years ago
true
when it comes to volcanic hazards, the key problem is how easily the dissolved gases can escape from the magma
true
the three v's of volcanology are _______
viscosity, volatiles, volume
if the magma reaches the surface, it forms _________, names for vulcan, the roman god of fire
volcanic rocks
________ eruptions are common first phase in the eruptions of volcanoes as they "clear their throats" before emitting larger eruptions
vulcanian-type
in magma, __________ is the most abundant dissolved gas
water vapor (h2o)
a shield volcano has a great __________
width compared to its height
the huston-galveston, texas, area has been sinking due to the _________
withdrawal of ground water by pumping
