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