Deck 6: Volcanic Eruptions: Plate Tectonics and Magmas

Question 1

Spreading centers are an ideal location for volcanism because ______________.

A)they sit above the high-temperature asthenosphere
B)the asthenosphere rock has low percentages of SiO₂
C)the oceanic plates pull apart causing hot asthenosphere rock to rise and undergo decompression melting to form magma that continues to rise
D)All of the choices are correct.

Answer 1

D

Question 2

The most famous of all volcanoes probably is Vesuvius,and the most famous of its eruptions are those of 79C.E. ,which buried the cities of ____________.

A)Pompeii and Herculaneum
B)Naples and Rome
C)Naples and Milano
D)Petra and Florence

Answer 2

A

Question 3

Areas of geyser activity include _______.

A)Iceland
B)Yellowstone Park in the United States
C)North Island of New Zealand
D)Kamchatka Peninsula of Russia
E)All of these are correct.

Answer 3

E

Question 4

The viscosity of magma is lowered by __________.

A)increasing temperature
B)decreasing crystal content
C)decreasing SiO₂ content
D)All of the choices are correct.

Question 5

The most peaceful eruptions are _____________.

A)Icelandic type eruptions
B)Plinian eruptions
C)Strombolian eruptions
D)Vulcanian eruptions
E)Surtseyan eruptions

Question 6

The presence of water ________ the melting point of rock.

A)raises
B)lowers
C)does not change
D)may raise or may lower

Question 7

The typical trend in a rising plume of subduction-zone magma is to increase ____________.

A)the percentage of SiO₂
B)the viscosity
C)the explosive potential of the magma by holding in the gases more tightly
D)All of the choices are correct.

Question 8

If basaltic lava reaches the sea or a lake,it cools rapidly into ____________.

A)bed lava
B)sheet lava
C)blanket lava
D)pillow lava

Question 9

The volcanic explosivity index (VEI)measures size of volcanic eruptions on a scale of 0 to 8.Between 1500 and 1981,one VEI 7 eruption occurred.This was ______________.

A)Tambora,in 1815
B)Krakatau,in 1883
C)Mt.St.Helens in 1980
D)Mt.Pelee in 1902
E)Mt.Vesuvius in 1631

Question 10

Slow flowing,more viscous basaltic lava commonly has a rough,blocky texture called ________.

A)aa
B)bb
C)cc
D)pahoehoe
E)poi

Question 11

Silicon and oxygen link up to form the silicon-oxygen ______________.

A)dihedron
B)trihedron
C)tetrahedron
D)hexahedron
E)dodecahedron

Question 12

Hawaiian volcanoes unlikely to erupt include _________________.

A)Haleakala on the island of Maui
B)any of the five volcanoes that make up the island of Hawaii
C)the growing but still sub-sea volcano of Loihi
D)Diamond Head,Oahu

Question 13

Over _________ of Earth's magma extruded through volcanism takes place at the oceanic spreading centers.

A)90%
B)80%
C)70%
D)60%
E)50%

Question 14

The dominant volcanic gas (commonly 90% or more of total gas)is _____________.

A)water vapor (H₂O)
B)carbon dioxide (CO₂)
C)sulfur dioxide (SO₂)
D)hydrogen sulfide (H₂S)with its rotten egg smell
E)carbon monoxide (CO)

Question 15

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?

A)differences in the chemical and mineral makeup of magmas
B)variations in the temperature,water and gas content,and viscosity of magmas
C)different geographic positions with respect to hot spots and edges of tectonic plates
D)All of these are correct.

Question 16

A shield volcano has a great ___________.

A)height compared to its width
B)width compared to its height
C)amount of pumice
D)proportion of pyroclastic material,compared with lava flows

Question 17

Over _________ of volcanism is associated with the edges of tectonic plates.

A)90%
B)80%
C)70%
D)60%
E)50%

Question 18

The three Vs of volcanology are __________________.

A)viscosity,volatiles,velocity
B)viscosity,volatiles,volume
C)viscosity,velocity,volume
D)volatiles,volume,variability
E)volatiles,velocity,variability

Question 19

Rock may melt by _______________.

A)lowering the pressure on it
B)raising its temperature
C)increasing its water content
D)All of the choices are correct.

Question 20

Mineral growth in magmas at the surface with temperatures around 1000 to 1200 ^$\circ$ C occurs in the following way:

A)Iron and magnesium will link up with aluminum and the silicon-oxygen tetrahedron as magma temperature decreases to sequentially form four distinct and discontinuous families of minerals-olivine,pyroxene,amphibole,and biotite mica.
B)Calcium will combine with aluminum and the silicon-oxygen tetrahedron to begin forming the plagioclase feldspar family,a continuous and gradational series of minerals.
C)Both of these are correct.
D)Neither of these is correct.

Question 21

_________ eruptions are common first phases in the eruptions of volcanoes as they "clear their throats" before emitting larger eruptions.

A)Hawaiian-type
B)Icelandic-type
C)Vulcanian-type
D)Plinian-type
E)Surtseyan-type

Question 22

The number of "hot spots" worldwide is ________________.

A)only 4
B)about 20
C)about 50
D)more than 100
E)no more than 10

Question 23

__________ eruptions are the most violent types of explosive eruptions.

A)Icelandic-type
B)Vulcanian-type
C)Plinian-type
D)Hawaiian-type
E)Pompeiian-type

Question 24

Crater Lake,Oregon,fills the caldera of ____________ which collapsed about 7600 years ago.

A)Mt.Mazama
B)Mt.Shasta
C)Mt.St.Helens
D)Mt.Baker
E)Mt.Rainier

Question 25

A mantle hot spot has generated a long-lived plume beneath Yellowstone National Park,and the North American continent is drifting ___________ above it about 2 to 4 cm/yr.

A)southeastward
B)northeastward
C)southwestward
D)northwestward
E)in random directions

Question 26

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

Question 27

On 20 February 1943,a new volcano,a scoria cone,was born when an eruption rose up through a farm field near a village in Mexico.The volcano is ________________.

A)Mt.Fuji
B)Mt.St.Helens
C)Mt.Kilimanjaro
D)Mt.Popocatepetl
E)Paricutin

Question 28

Water circulating at thousands of feet below the surface can be heated to temperatures far above 100 ^$\circ$ C (212 ^$\circ$ F)without boiling because the pressure of the overlying groundwater body is so great.

Question 29

What is the cause of volcanism at Italy's Vesuvius,Stromboli,Vulcano,and Etna?

A)The subduction of Mediterranean sea floor beneath Europe.
B)The subduction of Mediterranean sea floor beneath Africa.
C)The continent-continent collision of Africa and Europe.
D)
Rifting along Mid-Atlantic Ridge.

Question 30

____________ in the Aegean Sea underwent an explosive series of eruptions around 1628B.C.E.that buried the Bronze Age city of Akrotiri on Thera to depths of 70 meters.

A)Vesuvius
B)Krakatoa
C)Santorini
D)Mt.Pele

Question 31

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

Question 32

A caldera collapse occurs ________________.

A)before the eruption starts
B)in the middle of the eruption
C)after the magma chamber is mostly empty
D)millions of years after the volcano's final dying eruption
E)at the onset of Vulcanian activity

Question 33

__________ 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.

A)Stratovolcanoes
B)Scoria cones
C)Shield volcanoes
D)Calderas

Question 34

This volcano erupted in 1883 in the Sunda Strait between Sumatra and Java,exploding with a loudness heard 3000 miles away,then collapsing into its magma chamber,making a caldera and setting off tsunami that killed at least 36,000 people.

A)Vesuvius
B)Krakatoa
C)Santorini
D)Mt.Pele
E)Stromboli

Question 35

Magma at depth does not contain gas bubbles because the high pressure at depth keeps gas dissolved in solution.

Question 36

Most magma is generated by decreasing the pressure on hot rock.

Question 37

Although there are 92 naturally occurring elements,a mere eight make up more than 98 percent of the Earth's crust.

Question 38

The process of mineral formation in a cooling magma is called crystallization.

Question 39

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

A)Rising magma forms a low-density cap rich in SiO₂ and gases,bulging the ground surface upward.
B)Basaltic eruptions begin from circular fractures surrounding the bulge.
C)Magma pours out in high-volume pyroclastic flows,causing the ground surface to sink into a caldera.
D)Removal of magma decreases the pressure on the magma below the caldera,causing new magma to bulge up the caldera floor.
E)All of these are correct.

Question 40

Some of Earth's most beautiful mountains are ________,including Mt.Kilimanjaro in Tanzania,Mt.Shasta in California,Mt.Rainier in Washington,and Mt.Fuji in Japan.

A)stratovolcanoes
B)cinder cones
C)shield volcanoes
D)calderas
E)oceanic seamounts

Question 41

No magmas contain dissolved gases.

Question 42

If the magma reaches the surface,it forms volcanic rocks,named for Vulcan,the Roman god of fire.

Question 43

At oceanic spreading centers,magmas are rhyolitic in composition.

Question 44

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 a.

Question 45

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

Question 46

The higher the viscosity of a magma,the more fluid is its behavior.

Question 47

The lowest temperatures and highest SiO₂ contents occur in rhyolitic magma,material so viscous that it commonly does not flow.

Question 48

Magma compositions are independent of the amount of crustal rock melted and incorporated into the rising magma.

Question 49

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

Question 50

Over 80 percent of Earth's magma extruded through volcanism occurs at oceanic spreading centers.

Question 51

Basaltic magmas have low contents of SiO₂,low temperature,low viscosity,and allow easy escape of gases,producing peaceful eruptions.

Question 52

The highest temperatures and highest SiO₂ contents are in basaltic magma,giving it the lowest viscosity and easiest fluid flow.

Question 53

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

Question 54

Over 90 percent of volcanism is associated with the edges of tectonic plates,and most of the rest is caused by hot spots.

Question 55

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.

Question 56

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

Question 57

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.

Question 58

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.

Question 59

If lava reaches the sea or a lake it cools rapidly into ovoid or toothpaste-looking forms called pillow lava.

Question 60

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,which make it difficult for gases to escape,causing explosive eruptions.

Question 61

The most abundant dissolved gas in magmas is water.

Question 62

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

Question 63

The Volcanic Explosivity Index (VEI)ranges from 0 to 10.

Question 64

At a depth of 20 miles,basaltic rock melts at around 1400 ^$\circ$ C but this same rock will melt at only 1250 ^$\circ$ C at the Earth's surface.

Question 65

Hot spots can be under the oceans,under the continents,in the center of plates,and at spreading centers.

Question 66

Eruptions in Hawaii are always peaceful.

Question 67

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

Question 68

Transform faults have lots of associated volcanism because the strike slip motions keep a "lid" on the hot asthenosphere below,allowing it to melt.

Question 69

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

Question 70

Hawaiian volcanoes produce andesitic lava.

Question 71

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 pumice,contains so many holes it can float on water.

Question 72

Hot spots occur only under oceanic plates.

Question 73

The largest number of hot spots lie beneath the Juan de Fuca plate.

Question 74

A scoria cone is likely to form if lava is low in gas content and high in viscosity.

Question 75

When magma nears the surface,gases come out of solution and help cause volcanic eruption.

Question 76

In the last 2 million years,three catastrophic eruptions have occurred at Yellowstone at about 2 million,1.3 million,and 600,000 years ago.

Question 77

Antarctica does not lie above any hot spots,partly explaining its massive volumes of ice.