Geol 155 Chapter 6

Mt. Vesuvius and other volcanoes in the Mediterranean region have formed because of _____________. (pg 161) A) rifting of Africa from Europe B) subduction of the Mediterranean sea floor beneath Europe C) a hot spot D) continent-continent collision between Africa and Europe E) strike-slip fault movement

B) subduction of the Mediterranean sea floor beneath Europe

The production of magma is favored by an increase in ____________ and __________, and a decrease in __________. (pg 152) A) pressure, water content, heat B) pressure, heat, water content C) heat, water content, pressure D) solar heat, water content, pressure E) solar heat, pressure, water content

C) heat, water content, pressure

An explosive and catastrophic volcanic eruption is least likely to occur ________________. (pg 150) A) at a subduction zone such as Japan B) at continental hot spots such as Yellowstone National Park C) in the Hawaiian Islands D) in rift zones within continental crust such as the Rio Grande Rift E) An explosive eruption is equally likely to occur at any of these locations.

C) in the Hawaiian Islands

Mineral growth in magmas at the surface with temperatures around 1000 to 1200C 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.

C. Both of these are correct.

_______ eruptions are the most violent types of explosive eruptions. A. Icelandic-type B. Vulcanian-type C. Plinian-type D. Hawaiian-type E. Pompeiian-type

C. Plinian-type

_______ 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

C. Vulcanian-type

Basaltic magmas rich in Fe, Mg, Ca and poor in SiO2 are generated mostly by the melting of the ____________ and are erupted mostly as _____________. (pg150) A) asthenosphere, pyroclastic debris B) continental crust, pyroclastic debris C) continental crust, lava flows D) asthenosphere, lava flows E) core, lava flows

D) asthenosphere, lava flows

When a volcanic cone collapses into its magma reservoir it forms a ________________. (pg 163) A) shield volcano B) stratovolcano C) scoria cone D) caldera E) fissure eruption

D) caldera

What are the most important factors controlling the creation (not composition) of magma? (pg 152) A) radiation, water content, and oxygen B) water content, heat, and oxygen C) radiation, pressure, and water content D) pressure, heat, and water content E) heat, water content, and silicon

D) pressure, heat, and water content

whether a volcanic eruption is peaceful or explosive depends on _________. (pg 153)

concentration of water in magma

three ways viscosity of magma is changed: (pg 150)

1. Higher temps, lowers viscosity 2. silicon and oxygen(sio2 increase the viscosity 3.increasing content of mineral crystals increases viscosity

In the 1997 movie Dante's Peak, the final eruption of the stratovolcano blasted a huge cloud of ash and dust high into the atmosphere which then collapsed down the flanks of the mountain under the force of gravity. The style of the eruption portrayed would be best interpreted as _______ which created a _______. (pg 160) A) Plinian, pyroclastic flow B) Strombolian, lava flow C) Pelean, lava flow D) Hawaiian, pyroclastic flow E) Plinian, lahar

A) Plinian, pyroclastic flow

Hot spots under the continental lithosphere generally create __________ while those under oceanic lithosphere commonly create __________. (pg 170) A) calderas, shield volcanoes B) shield volcanoes, stratovolcanoes C) cinder cones, stratovolcanoes D) calderas, stratovolcanoes E) cinder cones, shield volcanoes

A) calderas, shield volcanoes

Rhyolitic magmas rich in K, Al, Na, and SiO2 typically are produced by the melting of _____________ and are associated with _____________ eruptions. (pg 150) A) continental crust, highly explosive B) continental crust, peaceful C) mantle, highly explosive D) oceanic crust, peaceful E) oceanic crust, highly explosive

A) continental crust, highly explosive

The most peaceful eruptions are _____________. A. Icelandic type eruptions B. Plinian eruptions C. Strombolian eruptions D. Vulcanian eruptions E. Surtseyan eruptions

A. Icelandic type eruptions

Magma viscosity increases with _______________.(pg 150) A) Increasing temperature, increasing silica (SiO2) content, and increasing crystal content B) Decreasing temperature, increasing silica (SiO2) content, and increasing crystal content C) Decreasing temperature, decreasing silica (SiO2) content, and decreasing crystal content D) Increasing temperature, decreasing silica (SiO2) content, and decreasing crystal content E) Decreasing temperature, increasing silica (SiO2) content, and decreasing crystal content

B) Decreasing temperature, increasing silica (SiO2) content, and increasing crystal content

In order from least explosive to most explosive, eruptions can be described as _________________.(pg 153) A) Plinean, Hawaiian, Icelandic B) Hawaiian, Strombolian, Plinian C) Vulcanian, Icelandic, Strombolian D) Strombolian, Plinian, Vulcanian E) Icelandic, Volcanian, Hawaiian

B) Hawaiian, Strombolian, Plinian

The Earth's outer core is thought to be a highly viscous zone of liquid iron. However, liquid iron never rises from this zone to erupt as molten iron on the surface of the Earth. What is a plausible explanation for this observation? A) The temperature of liquid iron from the core is so low that it crystallizes in the lower mantle. B) The density of iron liquid in the core is higher than the overlying mantle rocks. C) The density of iron liquid in the core is lower than the overlying mantle rocks. D) The density of iron liquid in the core is the same as the overlying mantle rocks. E) Molten iron is too viscous to flow.

B) The density of iron liquid in the core is higher than the overlying mantle rocks.

Eruption of magma at mid-ocean ridge systems occurs mostly by ___________________. (pg 152) A) decompressive melting of the lithosphere B) decompressive melting of the asthenosphere C) decompressive melting of the core D) decompressive melting of the lower mantle E) decompressive melting of the upper crust

B) decompressive melting of the asthenosphere

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.

B. Basaltic eruptions begin from circular fractures surrounding the bulge.

The presence of water ________ the melting point of rock. A. raises B. lowers C. does not change D. may raise or may lower

B. lowers

The three Vs of volcanology are __________________. (pg 157) A. viscosity, volatiles, velocity B. viscosity, volatiles, volume C. viscosity, velocity, volume D. volatiles, volume, variability E. volatiles, velocity, variability

B. viscosity, volatiles, volume

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

B. width compared to its height

Water at depths within a geyser system exists at temperatures above the boiling point at the Earth's surface. Why does the water become steam at more shallow depth and erupt? (pg 156) A) Increase in pressure near the surface. B) Increase in heat near the surface. C) Decrease in pressure near the surface. D) Decrease in heat near the surface. E) Increase in radioactive decay near the surface.

C) Decrease in pressure near the surface.

The main process that causes volcanoes to explode violently is _______________. (pg 152) A) hot convection currents in the asthenosphere that push magma upward B) density differences within the magma that force part of the magma upward C) a decrease in pressure triggering rapid expansion of the gases in a magma D) chemically volatile substances that explode within the volcano vents E) rapid expansion of the solid crystals in a magma with decrease in pressure

C) a decrease in pressure triggering rapid expansion of the gases in a magma

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

C. after the magma chamber is mostly empty

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

C. southwestward

Silicon and oxygen link up to form the silicon-oxygen ______________. A. dihedron B. trihedron C. tetrahedron D. hexahedron E. dodecahedron

C. tetrahedron

Which of the following factors helps determine whether a volcanic eruption will be violent or relatively peaceful? (pg152) A) The ease with which dissolved gas escapes from the magma. B) Temperature of magma. C) Composition of the magma. D) Each of the choices is correct.

D) Each of the choices is correct.

When magma viscosity, volatiles, and volume are all high, a common landform that can result is _______________. (pg 163) A) a shield volcano B) a scoria cone C) a lava dome D) a caldera E) a fissure

D) a caldera

In places such as Mt. Pinatubo, people were evacuated from a large area before the eruption. Yet in Hawaii volcanic eruptions occur frequently, and eruption-viewing has become a major tourist attraction. Why? (pg 146) A) Most of the magma erupted on Hawaii is in the form of lava flows. B) Violent gas-charged eruptions are not common on Hawaii. C) The viscosity of magma erupted on Hawaii is generally very low. D) Hawaii lies over a hot spot where magma comes from melting of the mantle. E) All of the choices are correct.

E) All of the choices are correct.

True or False Oceanic volcanoes are explosive and dangerous, subduction zone volcanoes are peaceful. (pg 145)

False; oceanic volcanoes are peaceful, subduction zone explosive and dangerous.

What are the styles of eruptions. (pg 154)

Icelandic, Hawaiin, Strombolian, Vulcanian, Plinian

Name the different volcanic landforms.

Shield volcanoes, flood basalts, scoria cones, stratovolcanoes, lava domes, calderas

______ _____ ______ are tall and beautiful, volume of magma released is small compared to spreading centers. 7-13% of all magma, down going plate carries oceanic plate rock covered with water saturated sediments into much hotter zone. Presence of water lowers melting point of the rock. (pg144) (volcanic mountains we see at the edges of the continents)

Subduction Zone Volcanoes

True or False: Over 90% of volcanism is associated with the edges of tectonic plates (pg 144)

True

true or false: more than 90% of volcanism is associated with the edges of tectonic plates. most other volcanism occurs above hot spots. (pg44)

True

Over ______ of Earth's magma extruded through volcanism takes place at the oceanic spreading centers. (pg 144) a. 90% b. 80% c. 70% d. 60% e. 50%

b. 80%

Over ______ of Volcanism is associated with the edges of tectonic plates. (pg 144) a. 90% b. 80% c. 70% d. 60% e. 50%

b. 90%

Spreading centers are an ideal location for volcanism because________. (pg 152) 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

d. all of the choices are correct

Melting caused by decrease in pressure. (pg 152)

decompression melting

True or false 100% of the Earth's magma extruded through volcanism takes place at the oceanic spreading centers. (pg144)

false

Over 90% of volcanic activity is associated with ________. (pg144)

plate-tectonic boundaries

Gas blasting into the atmosphere takes along chunks of magma and older rock known as _________.

pyroclastic

The fluidity of a liquid, its internal resistance to flow. Lower ____ the more fluid the behavior. (pg 150)

viscosity

magma contains dissolved gasses held as ______. (pg 150)

volatiles

When magma viscosity and volatiles are low but magma volume is extremely large, a ______________ is likely to result.(pg 159) A) flood basalt eruption B) caldera C) stratovolcano D) scoria cone E) lava dome

A) flood basalt eruption

The occurrence of geysers in Yellowstone National Park is evidence for the presence of what material below the surface? (pg 156) A) melted rock B) radioactive materials C) diamonds D) the asthenosphere E) carbon dioxide

A) melted rock

In the 1997 movie Volcano there is a violent volcanic eruption in Los Angeles. This is not realistic because _________________. A) this area is cut by a strike-slip fault system which typically has no associated volcanic eruptions B) this area is an oceanic-oceanic subduction zone which typically has no associated volcanic eruptions C) this area is an oceanic-continental subduction zone which typically has no associated volcanic eruptions D) this area is a continent-continent collision zone which typically has no associated volcanic eruptions E) this area is hot spot zone which typically has no associated volcanic eruptions

A) this area is cut by a strike-slip fault system which typically has no associated volcanic eruptions

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

A. Pompeii and Herculaneum

_________ 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

A. Stratovolcanoes

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 ______________. (pg 159) A. Tambora, in 1815 B. Krakatau, in 1883 C. Mt. St. Helens in 1980 D. Mt. Pelee in 1902 E. Mt. Vesuvius in 1631

A. Tambora, in 1815

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

A. The subduction of Mediterranean sea floor beneath Europe.

Slow flowing, more viscous basaltic lava commonly has a rough, blocky texture called ________. A. aa B. bb C. cc D. pahoehoe E. poi

A. aa

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

A. stratovolcanoes

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

A. water vapor (H2O)

Three settings where volcanic rocks generally form are ________________. (pg 144) A) subduction zones, continent-continent collision zones, mid-ocean rift systems B) subduction zones, continent-continent collision zones, hot spots C) subduction zones, continent-continent collision zones, continental strike-slip faults zones D) subduction zones, hot spots, mid-ocean rift systems E) subduction zones, continental strike-slip fault zones, mid-ocean rift systems

D) subduction zones, hot spots, mid-ocean rift systems

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

D. All of the choices are correct

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.

D. All of the choices are correct.

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.

D. All of the 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? 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

D. All of these are correct

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

D. Diamond Head, Oahu

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

D. more than 100

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

D. pillow lava

Why is volcanism in subduction zones more explosive than in other volcanic settings? (pg 145) A) Magmas in subduction zones are generally rich in silica. B) Magmas in subduction zones contain more water because of melting of hydrated rocks and minerals. C) Magmas in subduction zones are generally more viscous. D) Magmas in subduction zones tend to become solid at lower temperatures thus increasing their viscosity. E) All of the choices are correct.

E) All of the choices are correct.

The type of magma erupted on the Hawaiian Islands is predominantly basaltic. What type of volcanic landform do you expect to find on the islands? (pg 157& 162)) A) stratovolcanoes B) scoria cones C) shield volcanoes D) lava domes E) Both shield volcanoes and lava domes.

E) Both shield volcanoes and lava domes.

Why do people tend to inhabit areas with high potential for volcanic eruption? A) These areas generally have fertile soils. B) These areas generally have phenomena such as hot springs that attract people. C) The period between major eruptions is generally so long that people become complacent about the dangers. D) These areas typically are beautiful settings. E) Each of the choices is correct.

E) Each of the choices is correct.

Why are rhyolitic magmas generally more explosive than basaltic magmas? (pg 150) A) The lower silica content and higher temperatures of rhyolitic magma allow the gas to escape easily. B) The higher silica content and higher temperatures of rhyolitic magma allow the gas to escape easily. C) The higher silica content and lower temperatures of rhyolitic magma allow the gas to escape easily. D) The higher silica content and higher temperatures of rhyolitic magma make it difficult for the gas to escape. E) The higher silica content and lower temperatures of rhyolitic magma make it difficult for the gas to escape.

E) The higher silica content and lower temperatures of rhyolitic magma make it difficult for the gas to escape.

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.

E. All of these are correct.

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

E. Paricutin