Deck 8: Volcanic Activity

Question 1

The number of fatalities from the Mt. Pinatubo eruption was relatively low because

A)the eruption was relatively small
B)few people lived in the vicinity of the volcano
C)the eruption was predicted successfully, and the area was evacuated
D)the eruption, though large, was characterized by extensive lava flows

Answer 1

C

Question 2

Why are most active volcanoes associated with plate tectonic boundaries?

A)Plate tectonic boundaries are created by volcanism.
B)Spreading or sinking plates interact at plate boundaries with other materials to produce magma.
C)Earthquakes at plate boundaries bring large amounts of magma to the surface.
D)In reality, most volcanoes are in the plate interiors rather than at plate boundaries.

Answer 2

B

Question 3

Hundreds of residents near a dormant volcano at Lake Nyos died when

A)a sudden volcanic eruption deposited thick ash over the town
B)an unexpected lahar destroyed the village
C)a dense cloud of volcanic gas was released
D)acid rain from sulfur dioxide emissions caused widespread damage to vegetation

Answer 3

C

Question 4

What is one reason that ash fall is such a significant hazard?

A)The basaltic magma that produces the ash is low in silica.
B)The weight of the ash can cause structural damage to buildings.
C)The pyroclastic flow that deposits the ash is a hot, glowing cloud.
D)The associated lava flows can cover large areas.

Question 5

What is the principal difference between craters and calderas?

A)Calderas are much larger depressions created by collapse of the upper portions of the volcano.
B)Calderas are associated with cinder cones, while craters are associated with shield volcanoes.
C)Craters are created by explosive eruptions, while calderas are not.
D)Craters are associated only with fissure eruptions.

Question 6

Why were the citizens of Heimaey, Iceland, successful in stopping the lava flow that threatened their harbor?

A)They had a ready supply of water with which to chill the lava.
B)The Icelandic air force bombed the lava flows.
C)A giant sea wall was constructed to stop the lava flows.
D)The lava was rhyolitic in composition.

Question 7

Composite volcanoes are typically associated with subduction zones.

Question 8

A shield volcano is typically andesitic in composition.

Question 9

The shape of shield volcanoes is a function of

A)lava viscosity
B)proportion of pyroclastic debris included in the edifice
C)local variations in the tilt of the land surface
D)the explosive nature of the eruptions that produce the shield

Question 10

Why is topographic monitoring sometimes useful in forecasting a volcanic eruption?

A)A volcano sometimes swells as lava moves into the edifice.
B)Volcanic eruption is more likely as an area undergoes tectonic uplift.
C)Seismic activity occurs as the volcano rises.
D)Topographic monitoring reveals the likelihood of lahar generation.

Question 11

Composite volcanoes consist almost completely of lava flows.

Question 12

Why do composite volcanoes consist of alternating lava and pyroclastic layers?

A)Composite cones are created by lava composition alternating between basalt and rhyolite.
B)Composite cones typically are interlayered with lava flows from nearby shield volcanoes.
C)Composite cones are created by a mixture of explosive activity and lava flows.
D)The lavas in composite cones are typically rhyolitic in composition.

Question 13

Volcanic domes form on oceanic plates above hotspots.

Question 14

Viscosity is a primary control on the nature of volcanic activity.

Question 15

A lahar is produced when

A)ash is blown out of a vent and onto the side of the volcano
B)ash and other pyroclastic ejecta become saturated with water
C)a lateral blast spreads ash across a large area
D)a lava flow breaks apart on the steep portion of a composite cone

Question 16

Viscosity of a magma is controlled by

A)the eruptive processes at work
B)the types and amounts of gases dissolved in the magma
C)the water content of the magma
D)temperature and silicon content of the magma

Question 17

Why is the geologic history of a volcano important in hazard prediction?

A)The geologic history helps to determine whether evacuation is necessary.
B)The geologic history reflects the history of subduction beneath a volcano.
C)The geologic history is an important indicator of seismic activity.
D)The geologic history reveals the frequency and style of eruptions.

Question 18

Mid-ocean ridge volcanism produces what type of volcanic rock?

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

Question 19

Composite cones typically are associated with what type of plate tectonic feature?

A)mid-ocean ridge
B)hot spot
C)continental collision zone
D)subduction zone

Question 20

Seismic activity serves as a tool of volcanic forecasting because

A)moving magma causes earthquakes
B)earthquakes and dangerous volcanoes are both associated with subduction zones
C)seismic activity indicates emission of volcanic gases
D)earthquake usually cause the volcanic summit to collapse, setting of an eruption

Question 21

________ is the primary human adjustment to volcanic activity.

Question 22

Volcanic domes typically consist of the rock type ________.

Question 23

Volcanic gas emissions are important because they tell geologists how flammable the gases in the magma are likely to be.

Question 24

Lahars are usually produced by saturation of thick volcanic ash.

Question 25

________ are small volcanoes formed from tephra accumulation near a volcanic vent.

Question 26

The 1991 eruption of Mt. Pinatubo cooled the Earth's climate the following year.

Question 27

Caldera eruptions are very common features of subduction zones.

Question 28

The citizens of Heimaey, Iceland, succeeded in stopping a lava flow from blocking their harbor.

Question 29

________ eruptions are among the most violent and largest known.

Question 30

The Hawaiian islands were formed volcanism associated with a(n) ________.

Question 31

________ are volcanic mudflows.

Question 32

Shield volcanoes typically consist of the rock type ________.

Question 33

Tens of thousands of people were killed in the 1991 Pinatubo eruption because of a lack of prediction of the eruption.

Question 34

The 1980 eruption of Mt. St. Helens produced large lava flows that filled the nearby river valleys.

Question 35

Ash flows are rarely dangerous.

Question 36

Lava flows are the most dangerous of the primary volcanic hazards.

Question 37

________ is a volcanic gas associated with acid rain and vog.

Question 38

The May 18, 1980, eruption of Mt. St. Helens began with a massive ________.

Question 39

________ are dangerous, hot masses of ash and gas that travel down the flanks of a volcano.

Question 40

The eruption of Mt. ________ in 1991 killed several tens of people with pyroclastic flows.

Question 41

At ________, Cameroon, a dense cloud of gas was released from a volcanic crater, flowing down the volcano and killing hundreds of people.

Question 42

________ activity beneath a volcano is an indication of moving magma.