Deck 6: Volcanoes: Tectonic Environments and Eruptions

Question 1

How does pahoehoe lava differ from aa lava?

A) Pahoehoe is full of gas holes, and aa is solid lava.
B) Pahoehoe has a ragged top, and aa is smooth on top.
C) Pahoehoe is ropy-looking, and aa is clinkery.
D) Pahoehoe is rhyolite, and aa is basalt.
E) Pahoehoe is basalt, and aa is andesite.

Answer 1

C

Question 2

Eruptions dominated by basalt compositions are found where?

A) along convergent margins involving oceanic and continental crust
B) along divergent boundaries at mid-oceanic ridges
C) over continental hotspots
D) between plates along transform boundaries
E) along convergent margins involving oceanic crust

Answer 2

B

Question 3

What is magma that is forcefully ejected into the atmosphere as particles?

A) lava
B) pahoehoe
C) plutonic
D) pyroclastic
E) lahar

Answer 3

D

Question 4

What two main factors result in more violent eruptions?

A) not too much water and low enough viscosity
B) more water and higher viscosity of the magma
C) higher viscosity and narrow enough vent
D) strong rocks around the vent and more water
E) a large enough volcano with low-viscosity magma

Question 5

If a bulge grows steep enough,it may collapse.Explain how this can trigger an explosive eruption.

A) It removes the cover over the magma, so it can escape.
B) It slices through some of the gas bubbles, making them pop.
C) It doesn't trigger an explosive eruption; it does, however, create a devastating landslide.
D) The friction of the landslide heats that part of the magma, so the dissolved water flashes into steam.
E) It decreases pressure on gases dissolved in the magma, permitting them to expand.

Question 6

If you see a large,steep-sided volcano in the distance,what type of volcano is it and what is the rock composition?

A) a stratovolcano made of andesite lava flows and ash
B) a stratovolcano made of rhyolite lava flows
C) a stratovolcano made of basalt lava flows
D) a shield volcano made of andesite ash
E) a shield volcano made of rhyolite lava flows

Question 7

Which of the two main volcanic gases is heavier than air,collects in low areas,and can asphyxiate people or animals if it is in high concentrations?

A) water vapor
B) hydrogen
C) carbon dioxide
D) ethane
E) helium

Question 8

Which of the following statements about basalt is NOT true?

A) Basalt is at the more fluid end of the spectrum.
B) Basalt, like most dark magmas, has a high amount of silica.
C) Basalt has low viscosity.
D) Basalt has a black/brownish-black color.
E) Basaltic magmas have the highest volatile content.

Question 9

What are the two most abundant gases in magmas?

A) water vapor and oxygen
B) water vapor and carbon dioxide
C) hydrogen and methane
D) methane and helium
E) carbon dioxide and oxygen

Question 10

A rhyolite magma typically erupts in what form?

A) thin, fast-moving lava flows
B) thick, fast-moving lava flows
C) thin, slow-moving ash flows
D) fine ash
E) Rhyolite magma never erupts.

Question 11

If you see an extremely large volcano with very gentle slopes,what kind of a volcano is it and what rock is it likely made of?

A) a stratovolcano made of andesite
B) a stratovolcano made of basalt lava flows
C) a stratovolcano made of rhyolite lava flows
D) a shield volcano made of basalt lava flows
E) a cinder cone made of basalt

Question 12

About how fast can erupting steam travel?

A) up to 4 to 7 km per hour
B) up to about 14 km per hour
C) generally slower than you can run
D) between 400 and 700 km per hour; up to 1,200 km per hour
E) more than 1,600 km per hour

Question 13

A basalt magma typically erupts in what form?

A) pale ash flows
B) pale air-fall ash
C) giant Plinian eruptions that rise 50 km into the atmosphere
D) violent steam-rich surge blasts
E) lava flows

Question 14

Highly explosive magmas are controlled by which of the following?

A) high magnesium content and high water
B) high silica content and high water
C) low silica content and high water
D) high silica content and low water
E) high iron content and low water

Question 15

Why do shield volcanoes have very gently sloping sides?

A) Their andesite composition produces huge ash flows that spread over a large area.
B) Their andesite and rhyolite have low viscosity because of their water content, and spread over a low slope.
C) Their basalt flows have low viscosity, so the lava solidifies as gentle slopes.
D) Their basalt ash spreads out widely in the strong winds over the open ocean.
E) Their basalt magmas blow out violently from all of their pent up steam.

Question 16

If you see in the distance a small,steep,smooth-sided volcano,what type of volcano is it and what is it likely made of?

A) a stratovolcano made of andesite lava flows and ash
B) a stratovolcano made of rhyolite lava flows
C) a stratovolcano made of basalt lava flows
D) a shield volcano made of andesite ash
E) a cinder cone made of basalt fragments

Question 17

What can cause water to separate from a water-bearing basaltic magma to drive an eruption?

A) Injection of dry rhyolite magma into the basalt magma chamber from below can cause water to separate.
B) A decrease in pressure as the magma rises can cause water to separate.
C) Water streaming up into the magma chamber from the Earth's mantle can cause this.
D) Once water gets into a basalt magma, it can't separate.
E) Basalt magmas only erupt as lava flows; water is irrelevant.

Question 18

Which of the following statements about volatiles is true?

A) Carbon dioxide is the most abundant gas in volcanoes.
B) Magmas that contain little water erupt violently.
C) Water content determines the violence of a volcanic eruption.
D) Water exposed to high temperatures of magma becomes a solid.
E) Basaltic magmas have the highest volatile content.

Question 19

What causes a big bulge to slowly grow on the flank of an active Cascades volcano?

A) Thick lava flows pile up around the vent.
B) A huge gas bubble released from the magma inflates it.
C) The magma reacts with snow on the volcano, causing magma inflation.
D) The hot magma melts older ash, causing it to expand.
E) Rising magma is pushing it up.

Question 20

Which of the following locations five kilometers from the crater of a volcano would likely be safe from a large pyroclastic flow,if any?

A) far side of a steep-sided, 100-meter-high hill
B) far side of a five-kilometer-wide lake
C) behind a large tree with an 80-centimeter-diameter (2½ feet) trunk
D) None of the locations are safe: ash flows can flow over large hills, can cross large expanses of water, and can fell very large trees.
E) All of the locations are safe: ash flows cannot flow over large hills, cannot cross large expanses of water, and cannot topple very large trees.

Question 21

How does lava differ from magma?

Question 22

If a bulge grows steep enough,it may collapse.Explain how this can trigger an explosive eruption.

Question 23

List the styles of explosive eruptions,and give a brief explanation of two of them.

Question 24

What are the two most abundant gases in magmas?

Question 25

What are the main distinctions between basalt and rhyolite? Compare them based on color,silica content,relative viscosity,relative explosiveness,and the most abundant gas in each.

Question 26

Why do landslides sometimes trigger explosive eruptions?

Question 27

What two main factors dictate that an erupting magma will be explosive?

Question 28

What two main influences on a water-bearing basaltic magma can cause water to separate from a magma to drive an eruption?

Question 29

What property(s)of magma determine the magnitude of an eruption?

Question 30

About how far can a pyroclastic flow travel?

Question 31

Why were the predictions and mitigation of the hazards for the eruption at Mount Pinatubo so successful? What types of strategies did authorities use to evacuate people?

Question 32

If you had to choose between enduring a Strombolian eruption and a Vulcanian eruption,which would you choose and why?

Question 33

A large,steep-sided volcano is likely made of what composition of rock? In what form was the rock erupted? What type of volcano is it?

Question 34

List and describe the types of tectonic environments where volcanic eruptions take place.

Question 35

Which common volcanic gases are poisonous? Name two.