Exam Prep Volcanic Eruptions Plate Tectonics And Magmas Ch6

Natural Disasters, 11e (Abbott)

Chapter 6 Volcanic Eruptions: Plate Tectonics and Magmas

1) 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 ________.

A) Pompeii and Herculaneum

B) Naples and Rome

C) Naples and Milano

D) Petra and Florence

E) Florence and Pisa

2) Over ________ of volcanism is associated with the edges of tectonic plates.

A) 90%

B) 80%

C) 70%

D) 60%

E) 50%

3) 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%

4) 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 these choices are correct.

5) Silicon and oxygen link up to form the silicon-oxygen ________.

A) dihedron

B) trihedron

C) tetrahedron

D) hexahedron

E) dodecahedron

6) The typical trend in a rising plume of subduction-zone magma is to increase the ________.

A) percentage of SiO2

B) viscosity

C) explosive potential of the magma by holding in the gases more tightly

D) All of these choices are correct.

7) The viscosity of magma is lowered by ________.

A) increasing temperature

B) decreasing crystal content

C) decreasing SiO2 content

D) All of these choices are correct.

8) In magma, ________ is the most abundant dissolved gas.

A) water vapor (H2O)

B) carbon dioxide (CO2)

C) sulfur dioxide (SO2)

D) hydrogen sulfide (H2S)

E) carbon monoxide (CO)

9) Rock may melt by ________.

A) lowering the pressure on it

B) raising its temperature

C) increasing its water content

D) All of these choices are correct.

10) The presence of water ________ the melting point of rock.

A) raises

B) lowers

C) does not change

D) may raise or may lower

11) Mineral growth in magmas at the surface with temperatures around 1,000 to 1,200°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) None of these choices are correct.

12) 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 choices are correct.

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

A) aa

B) bb

C) cc

D) pahoehoe

E) poi

14) If basaltic lava reaches the sea or a lake, it cools rapidly into ________ lava. 

A) bed 

B) sheet 

C) blanket 

D) pillow 

15) What erupts in a geyser?

A) superheated water and steam

B) liquid hydrogen

C) magma

D) oil and natural gas

E) All of these choices are correct.

16) 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 ________.

A) Tambora in 1815

B) Krakatau in 1883

C) Mt. St. Helens in 1980

D) Mt. Pelee in 1902

E) Mt. Vesuvius in 1631

17) The three 'Vs' of volcanology are ________.

A) viscosity, volatiles, and velocity

B) viscosity, volatiles, and volume

C) viscosity, velocity, and volume

D) volatiles, volume, and variability

E) volatiles, velocity, and variability

18) 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

19) 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

20) The most peaceful eruptions are ________ eruptions.

A) Icelandic type 

B) Plinian 

C) Strombolian 

D) Vulcanian

E) Surtseyan 

21) On 20 February 1943, a new volcano named ________, a scoria cone, was born when an eruption rose up through a farm field near a village in Mexico.

A) Mt. Fuji

B) Mt. St. Helens

C) Mt. Kilimanjaro

D) Mt. Popocatepetl

E) Paricutin

22) ________ 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

23) 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

24) ________ 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

25) ________ eruptions are the most violent types of explosive eruptions.

A) Icelandic-type

B) Vulcanian-type

C) Plinian-type

D) Hawaiian-type

E) Pompeiian-type

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

A) the subduction of Mediterranean seafloor beneath Europe

B) the subduction of Mediterranean seafloor beneath Africa

C) the continent-continent collision of Africa and Europe

D) the rifting along the Mid-Atlantic Ridge

27) The number of active "hot spots" on Earth over the last 10 million years active is ________.

A) only 4

B) about 20

C) about 50

D) more than 100

E) no more than 10

28) 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 cm/yr.  

A) southeastward

B) northeastward

C) southwestward

D) northwestward

E) in random directions

29) 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

30) 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 forming 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.

31) Crater Lake, Oregon, fills the caldera of ________ which collapsed about 7,600 years ago.

A) Mt. Mazama

B) Mt. Shasta

C) Mt. St. Helens

D) Mt. Baker

E) Mt. Rainier

32) This volcano erupted in 1883 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.

A) Vesuvius

B) Krakatoa

C) Santorini

D) Mt. Pele

E) Stromboli

33) ________ in the Aegean Sea underwent an explosive series of eruptions around 1628 BCE that buried the Bronze Age city of Akrotiri on Thera to depths of 70 meters.

A) Vesuvius

B) Krakatoa

C) Santorini

D) Mt. Pele

E) Stromboli

34) Most rifting occurs at spreading centers ________.

A) in the interior of continents

B) and subduction zones

C) located below sea level

D) on the margins of continents

E) and hot spots

35) A well-formed conical volcano located above an active subduction zone that has not erupted in 12,000 years is ________.

A) likely extinct

B) extinct and will not erupt again

C) dormant, but will likely erupt again at some point

D) considered active

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

A) basalt

B) gabbro

C) andesite

D) diorite

E) rhyolite

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

A) It increases.

B) It decreases.

C) It remains the same.

D) It increases briefly before decreasing quickly.

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

A) quartz, biotite mica, amphibole, pyroxene, and olivine

B) olivine, pyroxene, amphibole, biotite mica, and quartz

C) pyroxene, biotite mica, calcite, quartz, and potassium-rich feldspar

D) quartz, potassium-rich feldspar, pyroxene, biotite mica, and calcite

39) Spreading centers have relatively peaceful eruptions of magma because the ________.

A) SiO2-poor magma is at high temperatures.

B) SiO2-rich magma is at a temperature just above the melting point of quartz.

C) Olivine-poor magma has a high-volatile content.

D) Olivine-rich magma has a high viscosity.

40) ________ melting occurs when a rock melts due to a lowering of pressure.

A) Release

B) Adiabatic

C) Elevation

D) Ascension

E) Decompression

41) Pyroclastic debris is ________.

A) chucks of magma and rocks blown into the air by gas in a volcanic eruption

B) solid pieces of rock contained within, and transported by, lava

C) the SiO2-poor magma that remains as gas escapes lava as it flows

D) the SiO2-rich magma that flows quickly down the side of a volcano

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

43) Decreasing the pressure on hot rock generates most magma. 

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

45) 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.

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

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

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

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

50) No magmas contain dissolved gases.

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

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

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

54) Most volcanism is associated with hot spots. 

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

56) Less than 20 percent of Earth's magma extruded through volcanism occurs at oceanic spreading centers. 

57) 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.

58) At oceanic spreading centers, magmas are rhyolitic in composition.

59) 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.

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.

61) 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.

62) The variations in the composition of magmas govern whether eruptions are peaceful or explosive.

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

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

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

66) 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.

67) 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.

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

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

70) At a depth of 32 km, basaltic rock melts at around 1,400°C but this same rock will melt at only 1,250°C at Earth's surface.  

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

72) Antarctica does not lie above any hot spots.

73) The largest number of hot spots lies beneath Africa.

74) The three most recent catastrophic Yellowstone eruptions occurred at 2.06 million, 1.29 million, and 640,000 years ago.

75) The Volcanic Explosivity Index (VEI) ranges from 1 to 100.

76) If two magmas have the same composition, the hotter of the two magmas will have a lower viscosity.

77) 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.

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

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

80) The most abundant dissolved gas in magmas is H20. 

81) Scoria cones form from repeated eruptions over the course of many decades. 

82) Eruptions in Hawaii are always peaceful.

83) 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.

84) Hot spots occur only under oceanic plates.

85) Hawaiian volcanoes produce andesitic lava.

86) Analysis of global sites of magma extrusion found that hot spots, such as Hawaii, represent ________ of the total magma extrusion.

A) 73%

B) 15%

C) 80%

D) 12%

87) Most basaltic rocks are high in Potassium-rich feldspar and muscovite mica.

88) Volcanic ________ are big fragments that are liquid when airborne.

A) ash

B) cinders

C) bombs

D) blocks

89) At the end of the Triassic (201 million years ago), flood basalts occurred during the opening of the Atlantic Ocean.

90) Crater Lake in Oregon is which type of caldera?

A) formed from the summit of a shield volcano

B) formed from the summit of a stratovolcano

C) formed from a giant continental caldera

D) it is not a caldera at all