Chapter 6: Volcanoes: Materials, Hazards, and Eruptive Mechanisms

Chapter 6: Volcanoes: Materials, Hazards, and Eruptive Mechanisms

CHAPTER 7

VOLCANOES: TYPES, BEHAVIOR, AND RISKS

Web Sites:

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)329-5009.

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 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 7: End of Chapter Answers

1. What products of a volcano can kill large numbers of people long after the eruption has ceased?

* mudflows

2. If a mudflow is heading down valley toward you, what is the best way to survive?

* climb the valley side to be above the flow

3. What is the driving force behind the explosive activity of a cinder cone? Where does it come from?

* Water in the ground boils to steam. Expanding steam blows basalt cinders out of thevent.

4. On a huge shield volcano such as Mauna Loa, what is the main type of eruptive site? Where on the volcano is (or are) such a site (or sites)?

* rift zones along the crests of three radial ridges

5. Yellowstone Park has two huge calderas, each more than 20 km across. How do such calderas form?

* a large mass of molten granite magma approaches the Earth’s surface. The rocks above that magma chamber sag into the magma, leaving the depression.

6. How can you tell whether a plume rising from a stirring volcano contains new magma that may soon erupt?

* If the plume is dark, it contains rock material. If that material is fresh volcanic glass, that indicates the presence of new magma.

7. If a gigantic flow of flood basalt magma were to erupt, why might that cause a sudden increase in global warming?

* A huge amount of carbon dioxide released from the basalt magma would contribute to global warming.

8. How does rhyolite magma form in the line of arc volcanoes like the Cascades?

* Basalt magma rising from above the subducted slab heats granitic continental crust causing melting to form the rhyolite.

9. Why do the Hawaiian Islands form a chain of volcanoes?

* The lithosphere carrying Hawaii slowly moves over a hotspot feeding basalt magma to the overlying volcano. As the volcano moves past the hotspot, a new volcano forms over the active hotspot.

10. Scientists once believed that if a volcano had not erupted in the last 10,000 to 12,000 years, it was extinct. What evidence is there that this is not really correct? Give at least one example (be specific).

* Some volcanoes erupt after still longer periods of inactivity.

Examples are Mt. Lassen after 27,000 years, Santorini erupts about every 30,000 years, Yellowstone erupts about every 600,000 years.

11. What evidence do scientists use to decide whether a volcano may be getting ready to erupt?

* A steam or ash cloud contains shreds of fresh volcanic glass.

* The flank of the volcano is bulging or tilting.

* Volcanic gases show an increase in emissions of sulfur compounds or the ratio of sulfur to chlorine.

* The surface temperature of the volcano is increasing.

Chapter 7 - Short answer questions

1. If you see an extremely large volcano with very gentle slopes, what kind of volcano is it and what is it likely made of? Be specific.

* a shield volcano of basalt lava flows

2. If you see in the distance, a large, steep-sided volcano, what is it likely made of, both in terms of rock composition and rock formation? What type of volcano is it?

* andesite lava flows and ash; a stratovolcano

3. 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?

* basalt fragments; a cinder cone.

4. Why do stratovolcanoes have steeply sloping sides but shield volcanoes have very gently sloping sides?

* The basalt flows of shield volcanoes have low viscosity so the lava solidifies on a gentle slops; the andesite of stratovolcanoes is much more viscous so it solidifies on a steeper slope.

5. A cinder cone has a single large lava flow. Why and when does it form?

* It forms after eruption of much of the cinder cone has formed. It forms because groundwater that forms steam that drives the explosive eruptions has dried out.

6. What signs suggest that a volcano may be getting ready to erupt?

* numerous small earthquakes, harmonic tremors, steam blasts, small ash eruptions, opening fractures, growth of a bulge, burning methane.

7. Harmonic tremors recorded on seismographs near volcanoes are generally interpreted as:

* moving magma

8. A volcanic crater is formed by (be specific):

* explosive eruption of volcanic material

9. A volcanic caldera is formed by (be specific):

* collapse of par of a volcano into its erupting magma chamber

Chapter 7 - Multiple choice questions

1. A big bulge sometimes slowly grows on the flank of an active Cascades volcanobecause:

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

2. What is the driving force behind the explosive activity of a cinder cone? Where does it come from?

1. Rhyolite contains water that expands as steam to drive the eruption
2. The rhyolite takes on water as it approaches the surface; it boils driving the eruption.
3. * Water in the ground boils to steam. Expanding steam blows basalt cinders out of thevent
4. Water in the basalt magma expands rapidly as steam to erupt
5. Rain falling on the basalt as it erupts boils to drive the eruption

3. On a huge shield volcano such as Mauna Loa, what is the main type of eruptive site and where on the volcano?

a.the huge collapse caldera at the summit

b.at intersecting fractures at the summit of the volcano.

c.* rift zones along the crests of three radial ridges extending out from the summit

d.near sea level where the magma first reaches the surface

e.near the sea floor because the magma doesn’t have to rise as far

4. Yellowstone Park has two huge calderas, each more than 20 km across. How do such calderas form?

a.When that giant volcano erupts, it blows out the surface rocks to leave the depressions

b.When the basalt magma gets close to the surface it melts the overlying rocks leaving the depressions

c.* a large mass of molten granite magma approaches the Earth’s surface and the rocks above that magma chamber sag into it

d.Coriolis effects on the near-surface magma drag the surface rocks down

e.The rising, rotating magma creates a low-pressure center analogous to the eye of a hurricane.

5. How can you tell whether a plume of ash rising from a volcano contains new magma that may soon erupt?

a.If the plume is white, it is pale rhyolite, and therefore new magma

b.If the rising plume contains solid pieces of rhyolite the volcano may be ready to erupt

c.If the plume is dark and the glass in it is basalt, new magma is rising rapidly, a danger sign

d.* If the plume is dark, it contains rock material. If the rock is fresh volcanic glass, it contains new magma

e.If the plume is accompanied by a rhyolite lava flow, the gas in the magma chamber below is still pent up and ready to blow out.

6. What evidence do scientists not use to decide whether a stratovolcano may be getting ready to erupt?

a.A steam or ash cloud contains shreds of fresh volcanic glass

b.numerous microearthquakes

c.a large bulge growing on the flank of the volcano

d.an increase in sulfur oxide gas emissions from the volcano

e.* They look down the crater to see red-hot molten magma.

7. In the line of arc volcanoes, like the Cascades, over an active subduction zone, where do the three magmas form that erupt at the surface?

a.basalt, andesite, and rhyolite form in the mantle directly below the volcanoes

b.basalt, andesite, and rhyolite magmas form in the lower crust before erupting

c.basalt and peridotite magmas form in the mantle, andesite in the crust

d.basalt forms in the mantle, andesite and rhyolite form from the basalt after it rises into the volcano.

e.* Basalt forms in the mantle, rhyolite in the crust, and andesite by mixing them in the crust

8. An example of a shield volcano is:

1. Mt. Vesuvius
2. Mt. St. Helens
3. Mt. Shasta
4. Mt. Pinatubo
5. * Kilauea

9. An example of a stratovolcano is:

1. Mt. St. Helens, Washington
2. Mt. Vesuvius, Italy
3. Mt. Pinatubo, Philippines
4. Mt. Mazama, Oregon
5. * all of the above

10. Stratovolcanoes erupt the following:

1. ash
2. pyroclastic flows
3. lava flows
4. mudflows
5. * all of the above

11. An example of a cinder cone volcano is:

1. Mt. St. Helens, Washington
2. Mt. Vesuvius, Italy
3. Mt. Mazama, Oregon
4. * Paricutin volcano, Mexico
5. Kilauea volcano, Hawaii

12. Shield volcanoes are composed of:

1. * basalt lava
2. rhyolite ash flow deposits
3. andesite lava
4. alternations of lava and ash
5. a mix of basalt, andesite, and rhyolite

13. A very large volcano with gentle slopes is likely to be a:

1. stratovolcano
2. * shield volcano
3. composite volcano
4. lava dome
5. cinder cone

14. A small volcano with smooth, steep sides is likely to be a:

1. stratovolcano
2. shield volcano
3. composite volcano
4. lava dome
5. * cinder cone

15. Volcanic hotspots erupt large amounts of:

1. basalt only
2. rhyolite only
3. basalt or andesite
4. andesite or rhyolite
5. * basalt or rhyolite