Ch. 4 - Volcanism + Igneous Rocks

Important volatiles in magmas include __________ .

Water and carbon dioxide

Volcanic arcs form along __________ boundaries.

b. Convergent

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

b. Decrease (lower concentration of silica)

Volatiles are substances that __________ .

Are gases at surface temperature and pressure

The mantle is composed entirely of __________

Mafic rock

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

Olivine

The extremely high __________ within Earth prevents rock from melting.

Pressure

The interior of Earth consists almost entirely of __________ rock.

Solid

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?

The pressure is too high.

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

The temperature is high enough but pressure low enough to melt iron.

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

a. ??The same?? (viscosity depends on temperature and silica content, so if they're equal they SHOULD be the same)

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

a. Cinder Cones

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

a. Compile a hazard assessment map

Columnar jointing forms primarily because of __________

a. Contraction and cracking of rock during the cooling process

Which type of magma has the greatest silica content?

a. Felsic

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

a. Increase

Decompression melting occurs at both ______and ____.

a. Mid-ocean ridges; hotspots

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

a. Porphyritic

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

a. Remain the same

A sill is a(n) __________ .

a. Tabular intrusion that lies parallel to surrounding layers of sedimentary rock

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

a. cool and solidify more quickly

Magma tends to __________ .

a. move upward, away from where it formed

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

b. Flux; contains abundant water

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?

b. Radioisotope dating

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

b. Shield volcano

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

b. The explosion was initially directed sideways.

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

b. Water and mud

Felsic igneous rocks typically __________ .

b. are lighter in color than mafic rocks

A batholith is a(n) __________ .

b. large compound igneous intrusion

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

b. more mafic than the magma (the MAGMA is more FELSIC)

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

c. Active

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

c. Aerosols and ash reflect sunlight, causing cooling.

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

c. C

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

c. Dike

The difference between magma and lava is that ____.

c. Magma is found beneath the surface, whereas lava is found at the surface

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?

c. Melting due to heat transfer from rising magma

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

c. More felsic than the source rock

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

c. Pluton

What type of igneous intrusion is horizontal? (test will have a picture)

c. Sill

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

c. vesicles

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?

d. ??Large outcrops of granite

Viscosity controls how __________ .

d. Fast a fluid flows

Which of the following is NOT a characteristic of obsidian?

d. It cooled very slowly (Volcanic glass cools super fast!)

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

d. Loss of volatiles to the atmosphere

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

d. Pahoehoe

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

d. Pyroclastic debris

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

d. Rhyolite

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

d. Solidify at lower temperatures

Viscosity of a magma does NOT depend on __________ .

d. Volume of the magma