Chapter #6 Geology 1010

about _______ of volcanism is associated with the edges of tectonic plates

90%

over _______ of Earth's magma extruded through volcanism takes place at the oceanic spreading centers

90%

analysis of global sites of magma extrusion found that hot spots, such as hawaii, represent _______ of the total magma extrusion

15%

the most famous of all volcanoes probably is Vesuvius, and the most famous of its eruptions are those of 79 CE, which buried the cities of __________

Pompeii and Herculaneum

_______ in the aegean sea underwent an explosive series of eruptions around 1628 BCE that buried the Bronze Age city of Akrotiti on Thera to depths of 70 meters

Santorini

spreading centers have relatively peaceful eruptions of magma because the _______

SiO2-poor magma is at high temperatures

the formation of a giant continental caldera includes all but which of the following

basaltic eruptions begin forming circular fractures surrounding the bulge

volcanic _______ are big fragments that are liquid when airborne

bombs

mineral growth in magmas at the surface with temperatures around 1,000 to 1,200 C occurs in the following way

both of these are correct

pyroclastic debris is _______

chunks of magma and rocks blown into the air by gas in a volcanic eruption

_______ melting occurs when a rock melts due to a lowering of pressure

decompression

hawaiian volcanoes unlikely to erupt include

diamond head, oahu

a well-formed conical volcano located above an active subduction zone that has not erupted in 12,000 years is

dormant, but will likely erupt again at some point

Because volcanologists are aware of the potential hazards, no volcanologist has ever been killed studying a volcano.

false

airborne pyroclasts have their finest grains settle down from the atmosphere first, closest to the volcano, followed by progressively coarser material at greater distances away

false

antarctica does not lie above any hotspots

false

at oceanic spreading centers, magmas are rhyolitic in composition

false

eruptions in hawaii are always peaceful

false

gas bubbles decrease in number and volume as magme keeps rising upward to lower pressures, helping to propel magma upward through fractures or pipes toward an eruption

false

hawaiian volcanoes produce andesitic lava

false

hot spots occur only under oceanic plates

false

if the magma cools and solidifies below the surface, it crystallizes as volcanic rocks

false

less than 20% of Earth's magma extruded through volcanism occurs at oceanic spreading centers

false

most basaltic rocks are high in potassium-rich feldspar and muscovite mica

false

most volcanism is associated with hot spots

false

no magmas contain dissolved gases

false

scoria cones form from repeated eruptions over the course of many decades

false

the higher the viscosity of magma, the more fluid is its behavior

false

the highest temperature and the highest SiO2 contects are in basaltic magma, giving it the lowest viscosity and easiest fluid flow

false

the volcanic explosivity index (vei) ranges from 1 to 100

false

transform faults have lots of associated volcanism because the strike0slip motions keep a lid on the hot atmosphere below, allowing it to melt

false

crater lake in oregon is which type of caldera?

formed from the summit of a stratovolcano

The most peaceful eruptions are __________ eruptions

icelandic type

as minerals form in magma kept at a constant temperature, what happens to the viscosity of that magma?

it increases

this volcano erupted in 18883 in the sunda strait between sumatra and java, exploding with a loudness heard 3,000 miles away, then collapsing into its magma chamber, making a caldera and setting off a tsunami that killed at least 36,000 people

krakatoa

most rifting occurs at spreading centers _______

located below sea level

the presence of water ____________ the melting point of rock

lowers

the number of active "hot spots" on earth over the last 10 million years active is

more than 100

crater lake, oregon, fills the caldera of _______ which collapsed about 7,600

mt. mazama

which of the following correctly lists the order in which the listed minerals form in a cooling magma from the first to the last to form?

olivine, pyroxene, amphibole, biotite mica, and quartz

if basaltic lava reaches the sea or a lake, it cools rapidly into _____________ lava

pillow

_______ eruptions are the most violent types of explosive eruptions

plinian-type

if all of the following rocks were to completely melt and reach the same final temperature, which would produce magma with the highest viscosity?

rhyolite

a mantle hot spot has generated a long-lived plume beneath yellowstone national park, and the north american continent is moving _______ above it about 2 to 4 centimeters a year

south westward

_______ 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 earth's most beautiful mountains are ________. including mt. killimanjaro in tanzania, mt. shasta in california, mt. rainier in washington, and mt. fuji in japan

stratovolcanoes

what erupts in a geyser?

superheated water and steam

the volcanic explosivity index (VEI) measures size of volcanic eruptions on a scale of 0 to 8. Between 1500 and 1980, one VEI 7 eruption occurred. This was _____________

tambora in 1815

silicon and oxygen link up to form the silcon-oxygen

tetrahedron

what is the cause of volcanism at italy's vesuvius, stromboli, vulcano and etna

the subduction of mediterrenean seafloor beneath europe

the lowest temperatures and highest SiO2 contents occur in rhyolitic magma, material so viscous that is commonly does not flow

true

the most abundant dissolved gas in magmas is H2o

true

on february 20 1943, a new volcano names _______ a scoria cone, was born when an eruption rose up through a farm field near a village in Mexico

Paricutin

slow-flowing, more viscous basaltic lava commonly has a rough, blocky texture called

aa

a caldera collapse occurs _______

after the magma chamber is mostly empty

rock may melt by _______

all of these choices are correct

spreading centers are an ideal location for volcanism because _______

all of these choices are correct

the typical trend in a rising plume of subduction-zone magma is to increase the _______

all of these choices are correct

the viscosity of magma is lowered by

all of these choices are correct

why does the magma from some volcanoes flow smoothly and relatively peacefully, while the magma from other volcanoes blasts forth violently and deals death over wide areas?

all of these choices are correct

Beneath continents, rising basaltic magmas are contaminated by sediments and continental-crust rocks, altering magma compositions; the resultant andesitic-to-rhyolitic magmas have high contents of SiO2, relatively low temperatures, and high viscosity.

true

If lava reaches the sea or a lake it cools rapidly into ellipsoidal masses called pillow lava.

true

When gas escapes quickly and violently from lava it may produce a frothy glassful of holes left by former gas bubbles; this porous material, known as pumice, contains so many holes it can float on water.

true

about 80% of the magma reaching Earth's surface is basaltic, with only about 10% andesitic and 10% rhyolitic

true

although there are 92 naturally occurring elements, a mere eight make up more than 98% of Earth's crust

true

at a depth of 32 km, basaltic rock melets at around 1,400 but this same rock will melt at only 1,250 C at Earth's surface

true

at the end of the triassic (201 million years ago), flood basalts occurred during the opening of the atlantic ocean

true

basaltic magma has the lowest viscosity, so more of it reaches the surface; the more viscous rhyolitic magmas are so sluggish that they tend to be trapped deep below the surface where they cool, solidify, and grow into the larger mineral crystals of plutonic rocks

true

decreasing the pressure on hot rock generates most magma

true

highly fluid basaltic lava may cool with a smooth, ropy surface called pahoehoe, whereas lower temperature, slower flowing, more viscous basaltic lava commonly has a rough, blocky texture called aa

true

hot spots can be under oceans, under the continents

true

if the magma reaches the surface, it forms volcanic rocks, named for vulcan, the roman god of fire

true

if two magmas have the same composition, the hotter of the two magmas will have a lower viscosity

true

lava domes from when high-viscosity magma with low-volatile content cools quickly, forming a hardened dome a few meters to a kilometer or so in height

true

magma at great depth does not contain gas bubbles because the high pressure at depth keeps gas dissolved in solution

true

magma rising in a subduction zone tends to get more "contaminated" with high-silica minerals than magma rising in a spreading ridge does

true

oxygen and silicon are so abundant in Earth's crust that their percentages dwarf those of all other elements

true

the basaltic magmas that erupt on the ocean floor have a low SiO2 content, high temperature, and allow gas to escape easily, all resulting in non-explosive eruptions

true

the largest number of hotspots lies beneath africa

true

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 lowers the temperature required for the adjacent overlying mantle lithospheric rock to melt

true

the process of mineral formation in a cooling magma is called crystallization

true

the three most recent catastrophic yellowstone eruptions occurred at 2.06 million, 1.29 million, and 64,000 years ago

true

the variations in the composition of magmas govern whether eruptions are peaceful or explosive

true

water circulating at thousands of feet below the surface can be heated to temperatures far above 1000 C (212 F) without boiling because the pressure of the overlying groundwater body is so great

true

when it comes to volcanic hazards, the key problem is how easily the dissolved gases can escape from the magma

true

while there are many hundreds of different minerals, the overwhelming majority of Earth's crust is composed of just eight common rock forming minerals

true

the three 'v' of volcanology are

viscosity, volatiles, and volume

_______ eruptions are common first phases 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