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.

Accepted Answer

The outer core is the only layer in Earth that is molten because the temperature is high enough to melt iron, but the pressure is not too high to prevent melting. The pressure increases as you move towards the center of the Earth, which causes the inner core to solidify despite its high temperature. The temperature in the mantle is also high enough to melt some minerals, but the pressure is too high for any significant melting to occur.

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

Accepted Answer

In Bowen's discontinuous reaction series, the first mineral to crystallize out of a mafic melt is olivine. This is because olivine has the highest melting point among the minerals in the series and is the most stable under high-temperature conditions.

Question 3

The mantle is composed entirely of __________ .
A)felsic rock
B)ultramafic rock
C)mafic rock
D)intermediate rock

Accepted Answer

The mantle is composed of ultramafic rock, which is made up mostly of the minerals olivine and pyroxene.

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

Accepted Answer

Volatiles are substances that have a low boiling point and are gases at surface temperature and pressure. Examples include water vapor, carbon dioxide, and sulfur dioxide.

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.

Accepted Answer

The pressure within Earth is high enough to overcome the high temperatures and keep the rocks solid. This is because pressure increases the melting point of rocks.

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

Accepted Answer

Important volatiles in magmas include water and carbon dioxide, which can affect the viscosity and explosivity of volcanic eruptions. Mafic minerals like olivine and metallic elements like silicon and iron are not classified as volatiles. Potassium and aluminum are not commonly considered as significant volatiles in magmas.

Question 7

All things equal, a magma will have __________ viscosity than a lava.
A)the same
B)fractional
C)lower
D)higher

Accepted Answer

The answer of All things equal, a magma will have...

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

Accepted Answer

The analogy describes heat transfer, where the hot fudge (heat) causes the ice cream (solid) to melt, similar to how rising magma transfers heat to surrounding rocks, causing them to melt.

Question 9

Viscosity of a magma does NOT depend on __________ .
A)temperature
B)volatile content
C)silica content
D)volumeof the magma

Accepted Answer

Viscosity of a magma depends on temperature, volatile content, and silica content, but not on the volume of the magma.

Question 10

The interior of Earth consists almost entirely of __________ rock.
A)solid
B)molten
C)sedimentary
D)felsic

Accepted Answer

The interior of Earth is divided into three layers: the crust, the mantle, and the core. The crust is the outermost layer and is made up of solid, rocky material. The mantle is the thickest layer and consists of solid but more ductile rock. The core is divided into a liquid outer core and a solid inner core, both composed mainly of iron and nickel. While there is some molten material in the mantle and core, the bulk of the Earth's interior is believed to be solid. Therefore, the best answer is A) solid rock.

Question 11

The extremely high __________ within Earth prevents rock from melting.
A)temperature
B)pressure
C)silica content
D)water content

Accepted Answer

The high pressure within Earth prevents rock from melting. This pressure is caused by the weight of the overlying rock and is higher at greater depths within the Earth.

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

Accepted Answer

Loss of volatiles to the atmosphere would not result in magma formation within the Earth as it involves the removal of gases from existing magma or rocks, rather than the creation of new magma. The other three processes (decompression, addition of volatiles, and transfer of heat) can all contribute to the formation of magma within the Earth.

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

Accepted Answer

Viscosity is a measure of how resistant a fluid is to flow. The higher the viscosity, the slower a fluid will flow. Therefore, viscosity controls how 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

Accepted Answer

The composition of magma, which includes the relative proportions of silica, oxygen, and different minerals, will remain the same when it erupts and turns into lava. However, the proportions of crystals and gases may change during the process.

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

Accepted Answer

The answer of Given the solidus and liquidus curves below,...

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

Accepted Answer

Decompression melting occurs at mid-ocean ridges where rising magma from the mantle encounters lower pressure and begins to melt. It also occurs at hotspots where plumes of hot mantle rise towards the surface and undergo decompression melting.

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

Accepted Answer

Flux melting occurs at subduction zones because the down-going plate contains abundant water.

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.

Accepted Answer

Magma is molten rock found beneath the Earth's surface, while lava is the molten rock that erupts and flows on the Earth's surface. Therefore, magma is found beneath the surface, whereas lava is found at the surface.

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.

Accepted Answer

Fractional crystallization is the process in which a magma cools and minerals crystallize out of it in a systematic order. The first minerals to crystallize are typically the ones with the highest melting points, which are usually more mafic than the magma. As these minerals are removed from the magma, the remaining magma becomes more felsic in composition. Therefore, the first rock that crystallizes from the magma will be more mafic than the magma.

Question 20

Which type of magma has the greatest silica content?
A)felsic
B)intermediate
C)mafic
D)ultramafic

Accepted Answer

Felsic magma has the greatest silica content, usually greater than 65%. This high silica content makes felsic magma more viscous and thick, leading to explosive volcanic eruptions.

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

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

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

The mantle is composed entirely of __________ .

Volatiles are substances that __________ .

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?

Important volatiles in magmas include __________ .

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

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?

Viscosity of a magma does NOT depend on __________ .

The interior of Earth consists almost entirely of __________ rock.

The extremely high __________ within Earth prevents rock from melting.

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

Viscosity controls how __________ .

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

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

Decompression melting occurs at both and .

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

The difference between magma and lava is that __________ .

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

Which type of magma has the greatest silica content?