Deck 5: Volcanic Eruptions and Landforms

Question 1

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.

Answer 1

D

Question 2

When magma cools so quickly that crystallization cannot take place it produces ________.

A) aa lava
B) granite
C) metamorphic rock
D) obsidian
E) pahoehoe

Answer 2

D

Question 3

The presence of water ________ the melting point of rock.

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

Answer 3

B

Question 4

Spreading centres 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
E) none of the choices are correct

Question 5

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

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

Question 6

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 7

Why does the magma from some volcanoes flow smoothly and relatively peacefully,while the magma from other volcanoes blasts forth violently?

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 plate tectonic setting
D) All of these are correct
E) None of these are correct

Question 8

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

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

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

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
E) none of the choices are correct

Question 11

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 12

In magma the most abundant dissolved 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 13

Volcanic material which has a lower density than water is called __________.

A) Obsidian
B) Plinian rock
C) Pyroclastic bomb
D) Pumice
E) Volcanic glass

Question 14

Molten rock released at the Earth's surface is called _______________.

A) magma
B) plutonic
C) granite
D) lava

Question 15

The most peaceful eruptions are _______________.

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

Question 16

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 17

Hawaiian volcanoes capable of eruption include ___________________.

A) Kilaueau on the island of Hawaii
B) any of the five volcanoes that make up the island of Hawaii
C) the growing but still sub-sea volcano of Loihi
D) all of these are correct

Question 18

Which of the following statements about shield volcanoes is true?

A) They are found in shield areas of the Earth e.g.the Canadian Shield.
B) They develop from violently explosive eruptions.
C) They form from basaltic magma.
D) They produce massive amounts of pyroclastics.

Question 19

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

A) the percentage of SiO₂
B) the viscosity
C) temperature
D) all of the choices are correct

Question 20

Scoria cones are built mainly from ________ type eruptions.

A) ultra-Plinian
B) strombolian
C) icelandic
D) plinian
E) none of these are correct

Question 21

The origin of the holes on this rock surface from Hawaii is:

A) rainfall impact during solidification.
B) microbiological action,that is,microbes decompose organic material which is incorporated into solids.
C) gas that escaped during lava solidification.
D) all of these.
E) unknown,the rock could come from another planet.

Question 22

_________ 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) None of these are correct.

Question 23

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

Question 24

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

Question 25

__________ eruptions are the most violent types of explosive eruptions.

A) Strombolian
B) Vulcanian
C) Plinian
D) Ultra-Plinian
E) None of these are correct

Question 26

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

Question 27

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 28

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

Question 29

Spreading centres are ideal locations for peaceful volcanism because:

A) they sit above the high-temperature asthenosphere.
B) the asthenosphere has low percentages of SiO₂.
C) the oceanic plate pulls apart,allowing hot asthenosphere rock to rise.
D) the magma is low-viscosity basalt that allows gases to escape easily.
E) all of these.

Question 30

Some of Earth's most beautiful mountains are __________,including Mt.Kilimanjaro in Tanzania,Mt.and Mt.Fuji in Japan.

A) stratovolcanoes
B) cinder cones
C) shield volcanoes
D) calderas

Question 31

This figure shows the facade of the church of Paricutin,engulfed in a field of lava flows.Based on the texture of this basaltic lava,we can determine that it is __________.

A) aa
B) tephra
C) pillow
D) pahoehoe

Question 32

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 33

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 any of these times

Question 34

In this figure,A represents a __________ and B represents a ___________ type of volcanic eruption.

A) Strombolian;Vulcanian
B) Icelandic;Plinian
C) Hawaiian;Vulcanian
D) Plinian;Icelandic
E) Hawaiian;Icelandic

Question 35

__________ 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 36

Which of the following best describes the common pattern of a major eruption sequence?

A) An Hawwian precursor,a Plinian main event and a magma plug conclusion.
B) A Vulcanian precursor,a Plinian main event and a lava dome conclusion.
C) A Plinian precursor,a Strombolian main event and a lava dome conclusion.
D) An Ultra-Plinian precursor,a Strombolian main event and a magma plug conclusion.

Question 37

Magma at depth does not contain gas bubbles because ______.

A) of the lower pressure
B) of the higher pressure
C) of the low density of gas bubbles
D) no dissolved gasses are detected
E) of the high magma density

Question 38

The major characteristics of rhyolitic magma are:

A) low temperature of magma,lower viscosity,and higher water content.
B) high temperature of magma,lower viscosity,and higher water content.
C) low temperature of magma,higher viscosity,and higher water content.
D) low temperature of magma,lower viscosity,and lower water content.
E) high temperature of magma,higher viscosity,and higher water content.

Question 39

The factors evaluated in volcanic explosivity index (VEI)include:

A) population density.
B) volume of lahars.
C) duration of continuous blast.
D) pyroclastic flow.
E) volume of gas released.

Question 40

____________ in the Aegean Sea underwent an explosive series of eruptions around 1,628 B.C.E.that buried the Bronze Age city of Akrotiri on Thera to depths of 70 metres.

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

Question 41

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

Question 42

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 43

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

Question 44

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

Question 45

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

Question 46

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

Question 47

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 48

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

Question 49

The most abundant dissolved gas in magmas is water.

Question 50

At oceanic spreading centres,magmas are rhyolitic in composition.

Question 51

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

Question 52

At a depth of 32 kilometres,basaltic rock melts at around 1430°C but this same rock will melt at only 1250°C at the Earth's surface.

Question 53

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.

Question 54

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 55

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

Question 56

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 57

No magmas contain dissolved gases.

Question 58

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 59

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

Question 60

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

Question 61

Icelandic-type eruptions only occur in Iceland.

Question 62

Most of the rocks that melt to form magma do so because heat is added,not because the pressure on it decreases.

Question 63

Flood basalts are the largest volcanic events known on Earth.

Question 64

When basaltic magma reaches the continental surface its composition never changes.

Question 65

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

Question 66

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

Question 67

In the last 200 years,three catastrophic eruptions have occurred at Yellowstone at about 100 years ago,50 years,and last year.

Question 68

Hawaiian volcanoes produce andesitic lava.

Question 69

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

Question 70

There is a linear relationship between the Volcanic Explosivity Index and fatalities.