Deck 4: Up From the Inferno: Magma and Igneous Rocks

Question 1

Why is the outer core the only layer in Earth that is molten?

A)The pressure decreases within Earth, thus allowing iron to melt.
B)The pressure increases within Earth, thus allowing iron to melt.
C)The temperature is high enough but pressure low enough to melt iron.
D)The temperature is high enough but pressure low enough to melt olivine.

Answer 1

C

Question 2

In Bowen's discontinuous reaction series, the first mineral to crystallize out of a mafic melt is __________ .

A)olivine
B)plagioclase
C)pyroxene
D)quartz

Answer 2

A

Question 3

The mantle is composed entirely of __________ .

A)felsic rock
B)ultramafic rock
C)mafic rock
D)intermediate rock

Answer 3

B

Question 4

Volatiles are substances that __________ .

A)crystallize most rapidly out of a melt
B)remain molten even after lava is erupted at the surface
C)melt immediately upon contact with a hot body of magma
D)are gases at surface temperature and pressure

Question 5

Despite the fact that the temperatures within Earth are hot enough to melt rock, Earth is mostly solid. Why do the rocks within Earth NOT melt?

A)The pressure is too high.
B)The pressure is too low.
C)There is not enough water.
D)They are not in contact with air.

Question 6

Important volatiles in magmas include __________ .

A)mafic minerals, such as olivine
B)potassium and aluminum
C)water and carbon dioxide
D)silicon and iron

Question 7

All things equal, a magma will have __________ viscosity than a lava.

A)the same
B)fractional
C)lower
D)higher

Question 8

The analogy in which hot fudge is injected into ice cream, thereby causing the ice cream to melt, is associated with which cause of melting?

A)melting due to a decrease in pressure
B)melting due to an addition of volatiles
C)melting due to heat transfer from rising magma
D)melting due to an increase in pressure

Question 9

Viscosity of a magma does NOT depend on __________ .

A)temperature
B)volatile content
C)silica content
D)volumeof the magma

Question 10

The interior of Earth consists almost entirely of __________ rock.

A)solid
B)molten
C)sedimentary
D)felsic

Question 11

The extremely high __________ within Earth prevents rock from melting.

A)temperature
B)pressure
C)silica content
D)water content

Question 12

Which of the following processes is unlikely to result in magma formation within the Earth?

A)decompression (a drop in pressure)
B)addition of volatiles
C)transfer of heat from adjacent magma or very hot rocks
D)loss of volatiles to the atmosphere

Question 13

Viscosity controls how __________ .

A)hot the fluid is
B)fast a rock will melt
C)quickly the fluid cools
D)fast a fluid flows

Question 14

The composition of magma will _________ when it erupts and turns into lava.

A)remain the same
B)become more felsic
C)become more mafic
D)have more silica

Question 15

Given the solidus and liquidus curves below, which location represents material that is partially melted?

A)a
B)b
C)c
D)d

Question 16

Decompression melting occurs at both __________ and __________ .

A)mid-ocean ridges; hotspots
B)mid-ocean ridges; trenches
C)subduction zones; hotspots
D)subduction zones; mid-ocean ridges

Question 17

__________ melting occurs at subduction zones because the down-going plate __________ .

A)Heat transfer; is extremely hot
B)Heat transfer; creates abundant friction
C)Flux; contains abundant water
D)Decompression; rises toward the surface

Question 18

The difference between magma and lava is that __________ .

A)magma cools more rapidly than lava
B)magma is found at the surface, whereas lava is found below the surface
C)magma is found beneath the surface, whereas lava is found at the surface
D)There is no difference; the two terms mean the same thing.

Question 19

If a body of magma undergoes fractional crystallization, the first rock that crystallizes from the magma will be __________ .

A)identical in chemical composition to the magma
B)more mafic than the magma
C)more felsic than the magma
D)The composition of the rock is not predictable.

Question 20

Which type of magma has the greatest silica content?

A)felsic
B)intermediate
C)mafic
D)ultramafic

Question 21

Which of the following is not considered a type of pyroclastic debris?

A)lapilli
B)blocks
C)ash
D)pahoehoe

Question 22

Felsic igneous rocks typically __________ .

A)contain more iron and magnesium than intermediate rocks
B)are lighter in color than mafic rocks
C)are darker in color than mafic rocks
D)are found in oceanic crust

Question 23

In general, if a body of igneous (source) rock is subjected to partial melting, the magma that is produced is expected to be __________ .

A)identical in chemical composition to the source rock
B)more mafic than the source rock
C)more felsic than the source rock
D)The melt composition is not predictable.

Question 24

Compared with mafic igneous rocks, all felsic igneous rocks __________ .

A)cool and solidify more quickly
B)cool and solidify more slowly
C)solidify at higher temperatures
D)solidify at lower temperatures

Question 25

A sill is a(n) __________ .

A)tabular intrusion that lies parallel to surrounding layers of sedimentary rock
B)cooled layer of an ancient lava flow
C)intrusion formed within the magma chamber of a volcano
D)tabular intrusion that cuts across preexisting layers

Question 26

Granite, a course-grained, felsic intrusive igneous rock is most similar in mineral composition to __________ , which is a fine-grained, felsic extrusive equivalent.

A)andesite
B)basalt
C)gabbro
D)rhyolite

Question 27

Ash, and larger fragments of pumice are all examples of __________ .

A)intrusive igneous rocks
B)hot spots
C)volatiles
D)pyroclastic debris

Question 28

Magma tends to __________ .

A)move upward, away from where it formed
B)move downward, away from where it formed
C)move laterally
D)stay in one place

Question 29

Columnar jointing forms primarily because of __________

A)Contraction and cracking of rock during the cooling process
B)Changes in density of the material as it cools
C)Partial remelting of lava on the surface
D)Fragmentation of the rock due to volatile escape

Question 30

All other factors being equal (i.e., depth, volume, temperature, etc.), which type of igneous intrusion would cool fastest?

A)pluton
B)dike
C)batholith
D)All intrusions cool at the same rate.

Question 31

In the figure provided below, what type of igneous intrusion is the horizontal rock unit indicated by the arrow?

A)dike
B)sill
C)pluton
D)laccolith

Question 32

Bubbles trapped in lava after the molten material are cooled are called __________ .

A)phenocrysts
B)vesicles
C)porphyroblasts
D)pyroclasts

Question 33

A batholith is a(n) __________ .

A)large body of sedimentary rock
B)large body of metamorphic rock
C)large compound igneous intrusion
D)small tabular igneous intrusion

Question 34

Compared with coarse-grained igneous rocks, fine-grained igneous rocks __________ .

A)cool and solidify more quickly
B)cool and solidify more slowly
C)solidify at higher temperatures
D)solidify at lower temperatures

Question 35

Which of the following is NOT a characteristic of obsidian?

A)It is composed of volcanic glass.
B)It exhibits conchoidal fracture.
C)It is typically felsic in composition.
D)It cooled very slowly.

Question 36

An irregular-shaped and bloblike igneous rock body that cooled beneath the surface of Earth is a __________.

A)dike
B)pluton
C)sill
D)laccolith

Question 37

All other factors being equal, if a body of magma becomes more felsic, its viscosity will __________ .

A)increase
B)decrease
C)stay the same
D)Chemical composition has no effect on viscosity.

Question 38

The image below (immediately to the right of the person's head) is an example of a small __________ .

A)sill
B)pluton
C)dike
D)batholith

Question 39

If the volatile content of magma is increased, its viscosity will __________ .

A)increase
B)decrease
C)stay the same
D)Volatile content has no effect on viscosity.

Question 40

An igneous rock with a mixed texture of coarse crystals (phenocrysts) surrounded by fine crystals (groundmass) is termed __________ .

A)porphyritic
B)phaneritic
C)aphanitic
D)vitric

Question 41

What is the fundamental difference between an explosive and an effusive eruption? What variables are important in determining whether a volcano "flows" or "blows"?

Question 42

What are the ways in which geoscientists can monitor volcanoes? Is it possible for scientists to predict eruptions?

Question 43

List the four major magma compositions in order of silica content.

Question 44

Volcanoes that are not currently erupting but have erupted in the last 10,000 years and are likely to erupt again are termed __________ .

A)dormant
B)active
C)extinct
D)suspended

Question 45

Describe the difference between the relative viscosity of felsic versus mafic magma and how this affects the rate of flow of each type.

Question 46

The May 18, 1980, eruption of Mount St. Helens was unique in which way?

A)Lava flows erupted from the base of the volcano.
B)The explosion was initially directed sideways.
C)Large amounts of gases were emitted.
D)The explosion was directed vertically only.

Question 47

What are some of the main volcanic hazards?

Question 48

Compare and contrast a dike and a sill. How are they similar? How are they different?

Question 49

What are the three main types of volcanoes? How is the shape of a volcano related to its eruptive style?

Question 50

Which of the following is not a way in which geologists can monitor a volcano with the goal of making short-term predictions about volcanic activity?

A)earthquakes
B)heat flow
C)radioisotope dating
D)gas emissions

Question 51

An important first step in mitigating volcanic hazards at a volcano is to __________ .

A)compile a hazard assessment map
B)try to divert or stop active volcanic hazards
C)evacuate people at the first sign of trouble
D)measure heat flow in the region

Question 52

Volcanic arcs form along __________ boundaries.

A)transform
B)hot spot
C)convergent
D)divergent

Question 53

Describe the process of decompression melting; be sure to include an example of where this type of melting occurs within Earth.

Question 54

What is a caldera? How is a caldera different from a stratovolcano?

Question 55

Which of the following is most typical of what you would find in a lahar?

A)rock fragments
B)ash and gas
C)water and mud
D)lava

Question 56

Which type of volcano forms from layers of mafic lava erupted in primarily effusive eruptions?

A)cinder cone
B)stratovolcano
C)shield volcano
D)fissure volcano

Question 57

Large igneous provinces involve more than just the formation of large volumes of igneous rock. Which of the following global events has NOT been attributed to large igneous provinces?

A)sea-level rise
B)climate change
C)extinction
D)large outcrops of granite

Question 58

Volcanoes are able to cool global climate in which of the following ways?

A)They release heat during eruptions.
B)Gas emissions reduce the amount of moisture in the atmosphere
C)Aerosols and ash reflect sunlight, causing cooling.
D)There is no evidence that volcanoes can affect climate.

Question 59

__________ form from piles of pyroclastic debris (mainly lapilli) that fountain out of a vent during an effusive eruption.

A)Cinder cones
B)Stratovolcanoes
C)Shield volcanoes
D)Fissure volcanoes

Question 60

Rhyolite and granite are both felsic igneous rocks, although they have different cooling histories and, consequently, different textures. Explain the difference between the two rock types from a cooling perspective and be specific about which igneous texture can be applied to which rock.