Download Skinner Chapter 7

Fall 2000
Lohrengel
Geology 1013 - Earth System Science
Chapter 7 - Study
Instructions:
Read each question carefully before answering. Work at a steady pace, and you should
have ample time to finish.
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1. Volcanic eruptions are rare; normally there is an average of about
one or two eruptions each year.
2. Explosive eruptions happen primarily in volcanoes with basaltic
magma, such as the Hawaiian and Icelandic volcanoes.
3. The principal gas emitted by volcanoes is water vapor.
4. Water vapor and carbon dioxide together make up about half of all
gases emitted from volcanoes.
5. Because of their low viscosities, basaltic lava flows move more
quickly than pyroclastic flows.
6. Violent undersea eruptions can cause tsunamis.
7. A fissure eruption is a type of eruption in which ash and pyroclasts
are ejected from a cone at the summit or along the flanks of a
volcano.
8. A pyroclastic flow is essentially the same as a lava flow.
9. Most magmas are less dense than the solid matter from which they
form.
10. Magma temperatures measured during eruptions range from 1000\C° to
1200\C°C.
11. Some magmas are more viscous than others because of their
a. compositions.
b. temperatures.
c. silica contents.
d. All of these are true.
e. None of these is true.
12. Crater Lake, Oregon, occupies the __________ left by the prehistoric
eruption of Mount Mazama.
a. volcanic neck
b. volcanic vent
c. caldera
d. tephra cone
13. By far the most important tectonic environment for the formation of
explosive volcanoes is
a. subduction zones.
b. divergent (spreading) plate boundaries.
c. transform plate boundaries.
d. intraplate "hot spots."
14. What is the most abundant gas given off by volcanoes?
a. CO 2
b. N 2
c. SO 2
d. H 2O
e. H 2S
15. What is the most abundant gas given off by volcanoes?
a. carbon dioxide
b. sulphur dioxide
c. nitrogen
d. water vapour
16. Stratovolcanoes are composed of
a. breccia and debris.
b. silica-rich lavas.
c. runny basaltic lavas (low viscosity).
d. interlayered tephra and lava flows.
17. Mount St. Helens is a typical
a. tephra cone volcano.
b. stratovolcano.
c. shield volcano.
d. eroded volcanic neck.
e. fissure flow.
18. Which one of the following statements is false?
a. Pyroclastic activity includes ash falls, ash flows, and lava
flows.
b. Most lava flows are slow enough that people can easily move out
of the way as they approach.
c. Volcanoes in the Pacific "ring-of- fire" are generally
characterized by explosive eruptions.
d. Fires and mudflows are two serious secondary effects of volcanic
activity.
19. Shield volcanoes are composed primarily of low viscosity
a. basalt.
b. rhyolite.
c. andesite.
d. granite.
20. Tephra deposits may contain
a. volcanic glass.
b. crystals.
c. fragments of igneous rock.
d. All of these are true.
21. Calderas form by
a. accumulation of thick piles of lava.
b. accumulation of thick piles of tephra.
c. explosion and/or collapse within a volcanic structure.
d. the development of lava domes.
e. extensive fissure flows.
22. A(n) _____________ is an igneous body in which the magma was
intruded parallel to the layering of the country rock, which has
been pushed up to form a mushroom-shaped dome.
a. laccolith
b. sill
c. dyke
d. batholith
23. Magma that flows out onto the surface of the Earth is called
a. a volcanic neck.
b. lava.
c. basalt.
d. tephra.
24. By definition, magma consists of
a. molten rock.
b. molten rock, with or without dissolved gases and suspended
crystals.
c. molten rock, with or without fragments of pyroclastic material.
d. lava.
25. The two common igneous rocks derived from basaltic magma are
a. basalt and granite.
b. basalt and andesite.
c. basalt and gabbro.
d. granite and rhyolite.
26. Which type of magma contains the most silica (SiO 2)?
a. rhyolite
b. andesite
c. basalt
27. By definition, lava is
a. magma.
b. molten rock with or without dissolved gases and suspended
crystals.
c. a type of pyroclastic material.
d. magma that oozes out of a volcano.
28. Tephra is
a. a type of pyroclastic rock.
b. an unconsolidated deposit of pyroclastic material.
c. a type of pyroclastic flow.
d. a type of volcanic rock.
29. The shape of a volcanic structure is due to
a. gravity.
b. the proportions of lava and pyroclastics erupted.
c. the viscosities of the erupted materials.
d. All of these are true.
30. Which one of the following types of intrusive rock bodies is
typically the largest?
a. stock
b. sill
c. batholith
d. dike
31. The three main kinds of magma are ________________, _______________,
and _______________.
32. The two variables that influence the physical properties of magma
the most are _________________ and _________________.
33. Igneous rock may be ___________________, meaning that it formed deep
within the crust, or ___________________, meaning that it formed
at the surface.
34. In general, the higher the temperature, the _______________ the
viscosity of a magma.
35. Basalt and gabbro contain the same minerals but differ in
___________________.
36. A volcano made up of lava flows, with a broad, roughly dome-shaped
formation and an average surface slope of only about 5-10\C° is called
a(n) _________________ volcano.
37. Magma temperatures measured during eruptions range from ____________
to ______________.
38. Smooth, ropy- looking lava is called __________________. Rubbly,
rough- looking lava that forms from cooler, higher-viscosity magma is
called _________________.
39. Bubble holes trapped in lava when it solidifies are called
________________.
40. Magma consists of molten rock, often containing ________________
and _______________.
41. Why does gas bubble out of magma when it moves towards the surface?
42. What is the difference between magma and lava?
43. What is the difference between lava and pyroclasts?
44. What is the difference between pyroclasts and tephra?
45. Why is tephra sometimes dangerous long after an eruption has ceased?
46. How are temperature, composition, and viscosity interrelated in
magmas?
47. What is the "Ring of Fire"?
48. Match each description with the name and date of the volcanic event:
i. Mount Pinatubo, 1990
ii. Mont PeleÇ, 1902
iii. Nevado del Ruiz, 1985
iv. Mount St. Helens, 1980
v. Krakatau, 1883
vi. Mount Mazama, ca. 4600 B.C.
____ a. Explosive eruption of island volcano in Indian Ocean;
tsunami killed 36,000
____ b. Lateral blast of Cascades Range volcano in Washington;
killed 62
____ c. Hot, mobile pyroclastic flow from Caribbean volcano; killed
29,000
____ d. Prehistoric eruption blasted out a huge caldera that now
hosts Crater Lake
____ e. Tephra eruption from Philippines volcano destroyed U.S.
airforce base
____ f. Mudflows on Colombian volcano formed when tephra combined
with melting glaciers; killed 20,000
49. How are pyroclastic rocks named?
50. What are the two forms of igneous rock that can form through the
solidification of magma channels underneath a volcano that is no
longer active?
51. Why is the study of volcanoes relevant to Earth system science?
52. What is Bowen's reaction series, and how does it account for the
different types of magmas and rocks that occur in the Earth?
53. What is fractional melting, and how can this process account for the
formation of different magma types?
54. Summarize the main types of hazards associated with volcanic
eruptions.
55. Discuss the relationship between the tectonic cycle and the
locations of different types of volcanoes.
56. Compare and contrast the modes of formation of the three main magma
types: basaltic, andesitic, and volcanic.
57. Describe how rocks are named according to textures and mineral
assemblages.
_____________________________________________
Fall 2000
Lohrengel
Geology 1013 - Earth System Science
Answer Key: Chapter 7 - Study
1. F
2. F
3. T
4. F
5. F
6. T
7. F
8. F
9. T
10. T
11. D
12. C
13. A
14. D
15. D
16. D
17. B
18. A
19. A
20. D
21. C
22. A
23. B
24. B
25. C
26. A
27. D
28. B
29. D
30. C
31. (basaltic...andesitic...rhyolitic) OR (basalt...andesite...rhyolite)
32. (temperature...SiO 2 content) OR (temperature...composition)
33. (intrusive...extrusive) OR (plutonic...volcanic)
34. lower
35. grain size
36. shield
37. (1000\C°C...1200\C°C) OR (1832\C°F to 2192\C°F)
38. pahoehoe...aa
39. vesicles
40. (gases...crystals) OR (dissolved gases...suspended crystals)
41. Pressure controls the amount of gas a magma can dissolve; more gas
is dissolved at high pressure, less at low. Gas dissolved in a
rising magma acts the same way as gas dissolved in soda water. When
a bottle of soda is opened, bubbles form because the pressure inside
the bottle has dropped, allowing gas to come out of solution. Gas
dissolved in an upward- moving magma also comes out of solution and
forms bubbles as the pressure on the magma decreases.
42. Magma is molten rock (along with gases and suspended crystals) that
forms at high temperature under ground. Lava is magma that reaches
the Earth's surface through a volcanic vent.
43. Lava is magma that oozes out of a volcano and pours over the
landscape. Pyroclasts are fragments of solid rock and shattered
pieces of hot magma that are ejected during the course of an
explosive volcanic eruption.
44. Pyroclasts are fragments of solid rock and shattered pieces of hot
magma that are ejected during the course of an explosive volcanic
eruption. Tephra is a deposit of unconsolidated (loose) pyroclasts.
45. Rain or melt water from snow can loosen tephra piled on a steep
volcanic slope and start a deadly mudflow.
46. Magma viscosity depends on temperature and composition, especially
the SiO 2 content. The higher the silica content, the more viscous
the magma. The higher the temperature, the less viscous the magma.
47. The Ring of Fire is a ring of explosive andesitic volcanoes
surrounding the Pacific Ocean rim, parallel to plate subduction
margins.
48. a-v; b- iv; c- ii; d-vi; e- i; f- iii
49. Pyroclastic rocks are named on the basis of clast size. They are
called agglomerates when tephra is bomb-sized, and tuffs when the
pieces are lapilli- or ash-sized. Sometimes the name is modified
according to the composition of the rock, such as "andesitic tuff,"
or the texture, suc h as "welded tuff."
50. A volcanic pipe is a cylindrical conduit of igneous rock below a
volcanic vent. A volcanic neck is a pipe laid bare by erosion. Many
volcanic pipes and necks were channelways through which magma fed
the volcano while it was still active.
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