Chapter 5

43. Volcanic eruptions release ________, which can block some sunlight from reaching Earth. a. ash c. magma b. gas d. ozone

a. ash

21. Basaltic lavas ________. a. contain less silica than rhyolitic lavas b. contain more silica than rhyolitic lavas c. are more viscous than rhyolitic lavas d. typically contain a greater proportion of trapped volatiles than rhyolitic lavas

a. contain less silica than rhyolitic lavas

13. The lower the viscosity of a lava the more likely it is to produce an ________ eruption. a. effusive c. intrusive b. explosive d. infusive

a. effusive

23. A fast-moving flow consisting of a mixture of water and volcanoclastic debris is termed a ________. a. lahar c. flood basalt b. pyroclastic flow d. hyaloclastite

a. lahar

20. What properties of the source magma lead to the formation of a shield volcano? a. low viscosity and mafic composition b. high viscosity and felsic composition c. any magma composition so long as it contains a large portion of dissolved volatiles d. an intermediate composition magma that encounters seawater in the magma chamber

a. low viscosity and mafic composition

4. The textural term for a basaltic lava flow that has a smooth, ropy appearance is ________. a. pahoehoe c. pumice b. a'a' d. ignimbrite

a. pahoehoe

28. Ash, cinders, and blocks are all types of ________. a. pyroclastic debris c. Pele's hair b. lava flows d. volcanoes

a. pyroclastic debris

34. The average time between eruptions is called a(n) ________. a. repose interval c. forecast b. prediction d. assessment

a. repose interval

38. Volcanoes are considered dormant if they ________. a. still have a magma source but show no signs of impending eruption b. no longer have a magma source and therefore will never erupt again c. have an active magma source and are currently erupting d. have an active magma source but will never erupt again

a. still have a magma source but show no signs of impending eruption

3. Of the three primary forms of subaerial volcanoes, ________ consist of alternating layers of tephra and solidified lava. a. stratovolcanoes c. shield volcanoes b. cinder cones d. fissure volcanoes

a. stratovolcanoes

29. Volcanic bombs are ________. a. volcanic fragments that were ejected while still soft or molten b. explosive bodies of lava with high volatile content c. volcanic fragments that were already solid rock before being ejected during an eruption d. used by geologists to set off small eruptions in volcanoes that are deemed potentially dangerous

a. volcanic fragments that were ejected while still soft or molten

24. Gases that are abundantly emitted by volcanoes include ________. a. water vapor, carbon dioxide, and sulfur dioxide b. oxygen, ozone, and water vapor c. oxygen, hydrogen, and argon d. carbon dioxide, carbon monoxide, and oxygen

a. water vapor, carbon dioxide, and sulfur dioxide

44. Which volcanic eruption nearly wiped humanity off the planet? a. 1991—Mount Pinatubo, Philippines c. 1980—Mount St. Helens, USA b. 75Ka— Toba, Indonesia d. 1815—Mount Tambora, Indonesia

b. 75Ka— Toba, Indonesia

25. In 1902 a famous, deadly pyroclastic flow killed thousands of people on the Caribbean island of ________. a. Puerto Rico c. Aruba b. Martinique d. Jamaica

b. Martinique

42. The famous "year without a summer" occurred due to the eruption of ________. a. Mount St. Helens, Washington c. Kilauea, Hawaii b. Mount Tambora, Indonesia d. Mount Fuji, Japan

b. Mount Tambora, Indonesia

49. A Minoan civilization, postulated to be the fabled "City of Atlantis," was destroyed by the eruption of ________. a. Toba, Indonesia c. Krakatau, Indonesia b. Santorini, Greece d. Mount Fuji, Japan

b. Santorini, Greece

37. Scientists monitor volcanoes to help predict when eruptions will occur. Which of the following is NOT a potential sign to look for when predicting volcanic eruptions? a. changes in earthquake activity b. changes in Earth's magnetic field c. small changes in the shape of the volcano d. increases in gas and steam emissions

b. changes in Earth's magnetic field

40. If a volcano lies along a convergent boundary but has not erupted in over 100,000 years, the volcano is considered ________. a. active c. extinct b. dormant d. dead

b. dormant

1. Nonviolent eruptions characterized by extensive flows of basaltic lava are termed ________. a. pyroclastic c. explosive b. effusive d. plinian

b. effusive

12. Felsic magma tends to form ________ eruptions. a. effusive c. intrusive b. explosive d. infusive

b. explosive

8. Fissure eruptions take place when ________. a. volatiles effervesce prior to lava flow b. groundwater interacts with magma c. basaltic lava clogs the eruptive vent d. lava erupts out of a long crack in the ground forming a curtain of lava

b. groundwater interacts with magma

16. Compared to felsic lavas, mafic lavas have a ________. a. lighter color c. lower density b. lower viscosity d. higher silica content

b. lower viscosity

11. Which of the following is FALSE? Caldera forming eruptions ________. a. can be so explosive that a significant portion of the volcano can be destroyed b. occur when groundwater or seawater enters the magma chamber c. occur due to fractional crystallization of the magma chamber d. produce little to no lava at the surface

b. occur when groundwater or seawater enters the magma chamber

17. Hotspots are produced by mantle plumes that are composed of mafic magma; however, Yellowstone is a hotspot that erupts more explosively because the hotspot ________. a. is hotter and thus melts more rock c. originates at the core-mantle boundary b. rises through the continental crust d. rises through a mid-ocean ridge

b. rises through the continental crust

46. The ash released by explosive volcanic eruptions can also produce ________. a. infertile land c. disruption of magnets b. unusual sunsets d. mutations in livestock

b. unusual sunsets

41. If a volcano was actively releasing a large amount of volcanic gas and then abruptly stopped, what might happen to the volcano in the near future? a. It will become extinct because the magma supply has been rapidly withdrawn. b. It will erupt effusively because the supply of volcanic gas has dissipated. c. It will erupt explosively because the volcanic gases have no way to escape slowly. d. It will erupt effusively because the gases have made the magma less viscous.

c. It will erupt explosively because the volcanic gases have no way to escape slowly.

2. In 79 C.E., the citizens of Pompeii in the Roman Empire were buried by pyroclastic debris derived from an eruption of ________. a. Mount Olympus c. Mount Vesuvius b. Olympus Mons d. Mount St. Helens

c. Mount Vesuvius

50. Volcanoes have provided some positive benefits to humankind and life in general over geologic time. Which of the following is NOT true about volcanoes? a. Volcanic eruptions can enrich soils, making land more fertile. b. Volatiles from volcanoes provided much of our early oceans' water. c. Volcanic eruptions have prevented several mass extinctions by cooling Earth's climate. d. Gases from volcanic eruptions provided much of the content of the early atmosphere.

c. Volcanic eruptions have prevented several mass extinctions by cooling Earth's climate.

26. What was unusual about the 1986 volcano-related disaster near Lake Nyos in Cameroon? a. A volcanic eruption involved a lateral blast of volcanoclastic debris that no one anticipated. b. Pyroclastic flows buried surrounding villages, reminiscent of Pompeii ~1,900 years earlier. c. Volcanically derived carbon dioxide gas bubbled from the lake and suffocated people and animals nearby. d. A slurry of lava and lake water flowed rapidly outward from the lake and buried surrounding villages.

c. Volcanically derived carbon dioxide gas bubbled from the lake and suffocated people and animals nearby.

35. Changes in the shape of a volcano can indicate ________. a. an increase in the heat flow from the magma b. an extinct volcano becoming active c. a magma chamber filling or emptying d. the release of gases from the magma

c. a magma chamber filling or emptying

45. How can volcanic eruptions lower the global temperature on Earth? a. gases block sunlight c. ash blocks sunlight b. gases trap heat d. ash traps heat

c. ash blocks sunlight

14. Felsic magma generally forms in ________. a. the mantle c. continental crust b. mid-ocean ridges d. oceanic crust

c. continental crust

27. The cloud that rises from the vent of an actively erupting volcano is composed of ________. a. smoke from wildfires inside the volcanic crater b. smoke from wildfires on the outer slopes of the volcano that funnel into the crater c. fine volcanoclastic debris (ash) suspended in the air d. a continuous fountain of dark, basaltic lava

c. fine volcanoclastic debris (ash) suspended in the air

5. The Columbia River Plateau is an example of a ________. a. caldera c. flood basalt b. fissure d. hot spot

c. flood basalt

7. The Hawaiian island chain is an example of a(n) ________. a. island volcanic arc c. hotspot island chain b. continental volcanic arc d. stratovolcanic assembly

c. hotspot island chain

30. A mixture of air, hot ash, and pumice lapilli that rushes down the side of a volcano in a scalding avalanche is termed a(n) ________. a. ash fall c. pyroclastic flow b. lahar d. convective plume

c. pyroclastic flow

15. Why is felsic magma much more likely to produce an explosive eruption? a. Felsic magma is at a higher magma temperature, which will force an explosion. b. Felsic magma cools at a lower temperature and thus will still be molten upon eruption. c. Felsic magma has a low viscosity, which will flow easily and erupt at a faster velocity. d. Felsic magma has a high viscosity, which will tend to stick in and clog volcanic conduits.

d. Felsic magma has a high viscosity, which will tend to stick in and clog volcanic conduits.

47. Which of the following volcanic products can decrease global temperatures? a. sulphur dioxide c. carbon monoxide b. mafic magma d. ash and aerosols

d. ash and aerosols

22. Whether an eruption will primarily produce lava flows or pyroclastic debris is NOT influenced by the ________ the source magma. a. viscosity of c. proportion of volatiles within b. composition of d. depth and residence time of

d. depth and residence time of

33. Columnar joints form when ________. a. a lava flow cools very rapidly, causing the flow to shatter in a chaotic pattern b. a lava flow encounters groundwater, which causes the flow to rapidly fracture c. a lava flow erupts under deep water d. during the final stages of cooling, a lava flow contracts, forming tall polygonal fractures

d. during the final stages of cooling, a lava flow contracts, forming tall polygonal fractures

32. Which of the following poses the greatest hazard to human life associated with volcanoes? a. flowing lava c. falling ash b. volcanic gas d. pyroclastic flows

d. pyroclastic flows

36. If magma is fracturing rocks as it moves through the subsurface, there would most likely be an increase in ________. a. recurrence interval c. silica content b. volcanic gas emission d. seismic activity

d. seismic activity

18. Pillow lavas are associated with ________ eruptions. a. subaerial rhyolitic c. submarine rhyolitic b. subaerial basaltic d. submarine basaltic

d. submarine basaltic