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Chapter 5: Tsunami
CHAPTER 6
VOLCANOES: MATERIALS, HAZARDS, AND ERUPTIVE
MECHANISMS
Correct answers are indicated by an asterisk, both in short answer and multiple choice questions.
True or False questions can be easily prepared from multiple choice questions
Web Sites:
http://eos.higp.hawaii.edu/eos/
http://hvo.wr.usgs.gov/
http://interactive2.usgs.gov/learningweb/explorer/topic_hazards_volcanoes.asp
http://lvo.wr.usgs.gov/
http://volcano.und.nodak.edu/
http://volcanoes.usgs.gov
http://volcanoes.usgs.gov/educators.html
http://vulcan.wr.usgs.gov/home.html
http://www.avo.alaska.edu/
http://www.dartmouth.edu/~volcano/
http://www.geo.mtu.edu/volcanoes/
http://www.ig.utexas.edu/research/projects/lips/lips.htm
http://www.soest.hawaii.edu/GG/hcv.html
http://www.volcano.si.edu/
http://www.vsc.washington.edu
Videos:
Video: NOVA - ?Volcano!
Video: NOVA - In the path of a killer volcano
Video: NOVA - ?Return to Mt. St. Helens
Video: National Geographic - In the Shadow of Vesuvius, 1989 (60 min.) Exc. footage of 1944 eruption of
Vesuvius and reconstruction of the events that destroyed Pompeii and Herculaneum.
Video: USGS library spec. collections, MS 955, 345 Middlefield Rd., Menlo Park, CA 94025 (415)3295009.
Video: BBC Horizon Series, 1987, "The Magma Chamber," (50 min.) Osbour Court, Olney
Buckinghamshire, MK 46 4AG United Kingdom. Phone 0234-711198 or 713390. [how studies of
magma at depth aid in the prediction of eruptions]
Video: Gould Media, Inc., Mount Vernon: NY Volcanoes of the United States
Video: Gould Media, Inc., Mount Vernon, NY Mount St. Helens: What Geologists learned
Video: Annenberg/CPB Collection: Earth revealed #13: Volcanism; P.O. Box 1922, Santa Barbara, CA
Video: Geoscience Resources: Eruptive phenomena of Kilauea’s East Zone.
Video: Smithsonian Institution; NHB-119, Washington, DC 20560, Washington, D.C.: Inside Hawaiian
volcanoes
Video: International Association of Volcanology and Chemistry of the Earth’s Interior: Reducing Volcanic
Risk.
Nature: Catastrophe on Sakhalin
References:
Carey, S., H. Sigurdsson, and C. Mandeville, 1992, Fire and water at Krakatau: Earth, v. 1, no. 2. (1983
eruption)
Carey, S., H. Sigurdsson, C. Mandeville, and S. Bronto, 2000, Volcanic hazards from pyroclastic flow
Chapter 5: Tsunami
discharge into the sea: Examples from the 1883 eruption of Krakatau, Indonesia: p. 1-14, in McCoy,
F.W. and G. Heiken, editors, Volcanic hazards and disasters in human antiquity: Geological Society of
America special Paper 345.
Crandell, D.R. and D.R. Nichols, 1989?, Volcanic hazards at Mt. Shasta: U.S. Geol. Survey .
Decker, R. and B. Decker, 1989, Volcanoes: W.H. Freeman and Co., New York, 285 p.
Ewert, J.W. and D.A. Swanson, 1992, Monitoring volcanoes - Techniques and strategies used by the staff
of the Cascades Volcano Observatory, 1980-1990: U.S. Geol. Survey Bull. 1966, 223 p.
Fisher, R.V., G. Heiken, and J.B. Hulen, 1997, Volcanoes, Crucibles of Change: Princeton University
Press, Princeton, N.J., 317 p.
Heliker, C. 1993, Volcanic and seismic hazards on the Island of Hawaii: Bishop Museum Press, Honolulu,
52 p.
Heliker, C., D.A. Swanson, and T.J. Takahashi, 2003, The Pu’u O’o’ Kupaianaha eruption of Kilauea
Volcano, Hawai’i: The first 20 years: U.S. Geological Survey Professional Paper 1676, 206 p.
Jäger, S. and G.F. Wieczorek, 2000, Landslide susceptibility in the Tully Valley area, Finger Lakes Region,
New York: U.S.G.S. Open-file report 94-615, 14 p. on-line version Lipman, P.W. and D.R.
Mullineaux, editors, 1981, The 1980 eruptions of Mount St. Helens, Washington: U.S. Geological
Survey Professional Paper 1250, 844 p.
McGuire, W.J., A.P. Jones, and J. Neuberg, editors, 1996, Volcano instability on the earth and other
planets: Geological Society Special Publication no. 110.
Rhodes, J.M. and J.P. Lockwood, editors, 1995, Mauna Loa Revealed: Structure, composition, history, and
hazards: American Geophysical Union, Geophysical Monograph, v. 92, 348 p.
Scarpa, R. and R.I. Tilling, eds., 1996, Monitoring and mitigation of volcano hazards: Springer-Verlag,
N.Y., 862 p.
Scott, K.M., J.W. Vallance, and P.T. Pringle, 1995, Sedimentology, behavior, and hazards of debris flows
at Mount Rainier, Washington: U.S. Geol. Survey Prof. Paper 1547.
Sigurdsson, H. 1990, Assessment of the atmospheric impact of volcanic eruptions, in Global catastrophes
in Earth History, An interdisciplinary conference on impacts, volcanism, and mass mortality, V.L.
Sharpton and P.D. Ward, editors: Geological Society of America Special Paper 247.
Tilling, R.I., 1989, Volcanic hazards - International Geological Congress, 28th, Short Course in Geology:
Vol. 1, American Geophysical Union, Washington, DC.
CHAPTER 6 - End of Chapter Answers
1. What factors influence the violence or style of an eruption?
* amount of water (more water, more violent eruptions)
* viscosity of the magma (higher viscosity, more violent eruptions)
(or composition of magma - e.g. rhyolite more violent than basalt)
2. What properties of basalt magma control its eruptive behavior?
* low water content
a. low viscosity
3. What properties of rhyolite magma control its eruptive behavior?
* high water content
* high viscosity
4. What drives an explosive eruption?
* steam
5. How does pahoehoe lava differ from aa lava?
Chapter 5: Tsunami
* pahoehoe is ropy-looking; aa is clinkery
6. How fast do red hot basalt flows typically move?
* less than 1 meter per second (about that of a brisk walk)
7. How much ash on a roof would generally cause it to collapse?
* about 20 cm
8. Which is more dangerous to a person—an ash fall or an ash flow? Why?
* an ash flow. Falling ash is cool or cold. An ash flow would incinerate the person; it is
extremely hot and suffocating
9. Why is erupting volcanic ash dangerous to jet aircraft flying at an altitude of 8 to 10
kilometers (30,000 feet)?
* The ash gets into the engine and the engine heat melts it. It coats the inside of the
engine and can stop it, causing the plane to crash.
10. What causes a big bulge to slowly grow on the flank of an active Cascades volcano?
* It grows because rising magma is pushing it up
11. If you visit Mount St. Helens, Washington, you will see thousands of trees lying on
the ground, all parallel to one another. Explain how they got that way.
* The intense lateral blast at the beginning of the eruption blew them all down with their
tops pointing away from the site of the blast.
12. If an ash flow approaches you from across a kilometer-wide lake, are you likely to be
safe or not? Explain why.
* Not safe. Ash flows can cross much wider bodies of water.
13. What characteristics of an old ash-fall tuff will permit you to distinguish it from an
old ash-flow tuff?
* an ash-flow tuff is not thinly layered and pumice fragments in it generally become
coarser upward. Its lower part is commonly cross-bedded. It forms thicker deposits in
valleys and its lower part may show lenses of black obsidian.
14. Which of the hazards of erupting volcanoes kill more people than anything else? Why
are they so dangerous?
* mudflows. They flow down valleys where people live. They flow at high speed and are
as dense as wet concrete.
15. What can happen to heat, pressure, and water content to melt rock and create magma?
* add heat, decrease pressure (dry), or add water to cause melting.
Chapter 6 - Short answer questions
Chapter 5: Tsunami
1. About how fast can ash flows travel?
* more than 160 km per hour; up to 200 km per hour
2. What are the main distinctions between basalt and rhyolite? Complete the following
table:
basalt
rhyolite
b. color:
*black or dark
white or pale
colors
c. silica percent:
*50 %
70 %
d. most abundant gas:
*carbon dioxide
water (or steam)
e. viscosity (relative):
*low
high
f. how explosive (relative): *not very
very
3. A basalt magma typically erupts in what form?
* lava flows
4. A rhyolite magma typically erupts in what form?
* ash (ash fall or ash flow)
5. What are the two most-abundant gases in magmas?
* Water vapor and carbon dioxide
6. Which common volcanic gases are poisonous? Name two.
* carbon dioxide in high concentrations
* sulfur oxides (or hydrogen sulfide)
7. Which of those two gases is heavier than air, collects in low areas, and can asphyxiate
people or animals if it is in high concentrations?
* carbon dioxide
8. What two main influences on a water-bearing basaltic magma can cause water to
separate from a magma to drive an eruption?
* decrease in pressure
* crystallization
9. What two main factors dictate that an erupting magma will be explosive?
* high water content, high viscosity
10. If the bulge grows steep enough it may collapse. Explain how this can trigger an
explosive eruption?
* Collapse of the bulge decreases pressure on gases dissolved in the magma. That
permits them to separate from the magma, expand rapidly, and drive the explosive
Chapter 5: Tsunami
eruption.
11. Sketch a simple diagram to show controls over the hazard distance from a volcano
for an ash flow. Label the diagram completely.
*
gas thrust
zone
sloping
energy line
tops
this hill
stops at
this hill
12. If an ash flow approaches you from the opposite side of a large hill, are you likely to
be safe or not? Explain why.
* If the hill is high enough and far enough from the volcano you may be safe because the
flow tends to flow down valleys. If the hill is not so high or is closer to the volcano
you are not safe since their momentum can carry them over the top.
13. An extremely large volcano with very gentle slopes is likely to be what kind of
volcano and is likely made of what kind of rock? Be specific.
* a shield volcano of basalt lava flows
14. A large, steep-sided volcano is it likely made of what composition of rock? In what
form was the rock erupted? What type of volcano is it?
* andesite lava flows and ash; a stratovolcano
15. A small, steep, smooth-sided volcano is likely to be what type of volcano? What is it
likely made of?
* basalt fragments; a cinder cone.
16. Why do landslides sometimes trigger explosive eruptions?
* Removal of load by landsliding, decreases pressure on gases in the magma and permit
Chapter 5: Tsunami
them to expand explosively.
17. How does lava differ from magma?
* Lava is magma that erupts onto the Earth’s surface.
18. Why might a landslide trigger a volcanic eruption?
* it would remove load from the magma chamber to permit gas to bubble out of a magma
and explode.
19. What danger signs might indicate that a volcano may be preparing to erupt?
* numerous small earthquakes, harmonic tremors, steam blasts, small ash eruptions,
opening fractures, growth of a bulge, burning methane.
Chapter 6 - Multiple choice questions:
1. 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.
2. What properties of basalt magma control its eruptive behavior?
a.
low water and large magma volume
b.
high water and low magma volume.
c.
* low water content and low viscosity
d.
low water and high viscosity
e.
high water and low viscosity
3. What properties of rhyolite magma control its eruptive behavior?
a.
* high water content and high viscosity
b.
low water and large magma volume
c.
high water and low magma volume.
d.
low water content and low viscosity
e.
low water and high viscosity
4. 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, aa is smooth on top
c.
* pahoehoe is ropy-looking; aa is clinkery
d.
pahoehoe is rhyolite and aa is basalt
e.
pahoehoe is basalt and aa is andesite
Chapter 5: Tsunami
5. How fast do red-hot basalt flows typically move?
a.
about 5 meters per hour.
b.
about 5 centimeters per minute
c.
* less than 1 meter per second
d.
10 meters per second
e.
10 kilometers per minute
6. What is the smallest amount of volcanic ash on a roof would commonly cause it to
collapse?
a.
no amount of ash would cause collapse; it is too light to be a problem.
b.
more than about 3 cm
c.
* more than about 20 cm
d.
more than 2 meters
e.
more than 20 meters
7. Why is erupting volcanic ash dangerous to jet aircraft flying at an altitude of 8 to
10 kilometers (30,000 feet)?
a.
ash coats the surface of the wings making the plane too heavy to fly
b.
ash covers the windshield of the plane so the pilots can’t see where they are going
c.
pieces of ash are rising so fast that they shoot down the plane
d.
*ash gets into the engines, which melt the ash causing the engines to stop
e.
ash can penetrate the aluminum body of the fast-moving plane causing
decompression of the plane and deaths of all on board.
8. What causes a big bulge to slowly grow on the flank of an active Cascades
volcano? it grows because:
a.
thick lava flows pile up around the vent
b.
a huge gas bubble released from the magma is inflating 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
9. Following the May 1980 eruption of Mount St. Helens, Washington, thousands of
trees lay on the ground, all parallel to one another, because:.
a.
* a lateral blast at the beginning of the eruption blew them all down
b.
a big earthquake at the beginning of the eruption shook them down
c.
huge mudflows racing down slope flattened them
d.
a giant landslide from the volcano toppled them
e.
thermal winds during the eruption toppled them.
10. If an ash flow approaches you from across a kilometer-wide lake, are you likely
to be safe or not? Explain why.
Chapter 5: Tsunami
a.
b.
Safe; hot ash slows would chill and stop as soon as they hit cold water
Safe; ash flows move along the ground; they would continue harmlessly
underwater
c.
Safe; hot ash flows would boil the water and that would stop them
d.
Not safe because a fast-moving ash flow would cause a deadly tsunami wave.
e.
* Not safe. Ash flows can cross much wider bodies of water
11. Which of the following would you not find in an old ash-flow deposit?
a.
pumice fragments in it become larger upward.
b.
It is thicker in the valley bottom than on adjacent ridges
c.
streaks of black obsidian near the base of the deposit.
d.
* thin layers of ash
e.
charred logs
12. Which of the hazards of volcanoes kill more people than anything else?
a.
lava flows
b.
ash flows
c.
ash falls
d.
landslides.
e.
* mudflows
13. If a mudflow is heading down valley toward you, the best way to survive is:
a.
* climb the valley side to be above the flow
b.
run down valley – fast!
c.
if there is a house in the valley, nearby, get inside so the flow will go around you
d.
climb the nearest tree
e.
jump onto a tree floating in the mudflow and ride it down valley until it slows
down.
14. If a gigantic flow of flood basalt magma were to erupt, why might that cause an
increase in global warming?
a.
The high temperature of a giant basalt lava flow would heat up the atmosphere
b.
Basalt magma contains steam at such a high temperature that the steam would
heat the atmosphere
c.
The high temperature of the basalt lava would start widespread fires that would
heat the atmosphere
d.
Radiant heat from the red-hot basalt would heat the molecules in the atmosphere.
e.
* A huge amount of carbon dioxide released from the basalt magma would
contribute to global warming
15. About how fast can ash flows travel?
Chapter 5: Tsunami
a.
b.
c.
d.
e.
up to 1 to 2 km per hour
up to about 16 km per hour
generally slower than you can run
* more than 160 km per hour; up to 200 km per hour
more than 1600 km per hour.
16. 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
17. 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.
18. 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.
19. 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.
20. What can cause water to separate from a water-bearing basaltic magma to drive
an eruption?
a.
injection, into the basalt magma chamber, of dry rhyolite magma from below
b.
* decrease in pressure as the magma rises
c.
water streaming up into the magma chamber from the Earth’s mantle
d.
once water gets into a basalt magma it can’t separate
e.
basalt magmas only erupt as lava flows; water is irrelevant.
21.If the bulge grows steep enough it may collapse. Explain how this can trigger an
explosive eruption?
a.
That removes the cover over the magma so it can escape
Chapter 5: Tsunami
b.
c.
That slices through some of the gas bubbles, making them pop
That 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
flashed into steam.
e.
* That decreases pressure on gases dissolved in the magma, permitting them to
expand
22.If an ash flow approaches you from the opposite side of a large hill, are you likely
to be safe or not?
a.
being behind a hill you are fine; ash flows go down valleys
b.
safe because the ash flow would stop at the hill or go around the sides of it
c.
safe because you can duck and it will go over top of you
d.
* not if you are close to the volcano; fast-moving ash flows can go over nearby
hills
e.
not safe because even well away from the volcano when the ash flow reaches the
top of a hill it picks up speed going down the far side and that takes it to the
top of the next hill, and so on.
23.Which of the following locations five kilometers from the crater of a volcano, if
any, likely would be safe from a large ash flow? Explain why or why not.
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 (2 ½ feet) trunk
d. * None of them: ash flows can flow over large hills ash flows can cross large expanses
of water ash flows can fell very large trees
24.In contrast to an old ash-flow deposit, an old ash-fall tuff do not include which of
the following?
a.
thin layers
b.
layers become coarser-grained towards the base
c.
the ash evenly coats hills and valleys
d.
the ash is never welded to black obsidian
e.
* big pieces of pumice float to the top of a layer.
25.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 of basalt lava flows
Chapter 5: Tsunami
e.
a cinder cone made of basalt
26.If you see in the distance, a large, steep-sided volcano, what type of volcano is it
and what rock composition?
a.
a stratovolcano of andesite lava flows and ash
b.
a stratovolcano of rhyolite lava flows
c.
a stratovolcano of basalt lava flows
d.
a shield volcano of andesite ash
e.
a shield volcano of rhyolite lava flows
27.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 of andesite lava flows and ash
b.
a stratovolcano of rhyolite lava flows
c.
a stratovolcano of basalt lava flows
d.
a shield volcano of andesite ash
e.
* a cinder cone of basalt fragment.
28.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 on a gentle slops
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
29.Which of the following is not a sign suggesting that a stratovolcano may be
getting ready to erupt?
a.
numerous small earthquakes,
b.
harmonic tremors,
c.
growth of a bulge,
d.
burning methane
e.
* a large mudflow a year after a previous explosive eruption.
30.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
31.Magma that is forcefully ejected into the atmosphere as particles is:
a.
* pyroclastic
Chapter 5: Tsunami
b.
c.
d.
lava
pahoehoe
plutonic
32.Eruptions dominated by basalt compositions are found:
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