Geol 155 chapter 7

Why are pyroclastic flows one of the most dangerous types of hazard associated with volcanic eruptions? (pg 186) A) They can form with little or no warning and move at extremely high velocities. B) They can cover large areas with a dense cloud of ash and dust that can asphyxiate an entire city. C) The temperature of the cloud can be several hundred degrees Centigrade causing fires. D) Each of the choices is correct.

D) Each of the choices is correct.

What causes a pyroclastic flow to move at high velocities? (pg 186) A) Gravitational collapse of an eruption cloud. B) Energy from the eruption. C) Internal turbulence that keeps particles in the air. D) Release of gas from magma particles and heating of surrounding air creating a "popcorn" effect E) all of the choices are correct

E) all of the choices are correct

Mt. Rainier, Washington, is number one on the danger list of many volcanologists because of ____________. (pg 192) A. its great height B. its extensive glacial cap C. its frequent earthquakes D. its active hot-water spring systems, which have weakened the mountain internally

E. All of the choices are correct.

Violent causes of death from volcanic eruptions include _______. (pg 186) a. pyroclastic flows b. tsunami c. lahars d. poison gases

E. all of the choices are correct

True or False Magma at spreading centers is low-temperature, low-viscosity, and basaltic, with easy escape of gases, providing all the factors that promote the peaceful eruption of magma.

False

At which location would you expect relatively peaceful volcanic eruptions? (pg 175)

Iceland

True or False In Icelandic-type eruptions, low viscosity, low-volatile content lava erupts peacefully.

True

True or False Pyroclastic flows can travel across bodies of water.

True

True or False The Pacific Northwest of the United States (Washington and Oregon) has long-term risk for both explosive volcanic eruptions and a moment-magnitude earthquake of around 9.

True

Signs of impending eruption are? (pg 200)

seismic waves, ground deformation, gas measurements

A pyroclastic flow can best be described as _________________. (pg 186)

a flow of gas and hot ash

The violent flank eruption of Mount St. Helens in 1980 was set off by ________. (pg 179)

an earthquake that caused collapse of part of the mountain thus rapidly releasing pressure

Melting of thick caps of snow on volcanoes, such as Mount St. Helens, can generate which of the following hazards? (pg 179)

lahars

The eruption of Mt. Pinatubo in 1991 endangered people, animals, and property because of __________________. A. massive lava flows B. lahars and pyroclastic flows C. acid rain D. pelting lapili E. poisonous gases

lahars and pyroclastic flows

About _____ people have been killed by volcanic action during the past ____ years.

275,000, 500

If you were in an airplane flying over a subduction zone what would you expect to observe on the continent adjacent to the zone?

A chain of steep-sided volcanoes subparallel to the subduction zone

Ways of generating pyroclastic flows include ______________. (pg 186) A. dome collapse as at Mt. Unzen, 1991 B. overspilling of crater rim as at Mont Pelée, 1902-1903 C. directed blast as at Mt. St. Helens, 1980, and Mt. Pinatubo, 1991 D. eruption column collapse at Mt. Mayon

All of the choices are correct.

Lahars can form by all of the following except ________________. (pg 191) A) melting of a snow cap on a volcano B) flow of lava into the ocean C) flow of pyroclastic material into a river D) heavy rainfall during eruption of pyroclastic material E) collapse of a crater lake or dam

B) flow of lava into the ocean

During the 1990's, hundreds of trees were killed at Mammoth Mountain, California, by the diffuse emission of _________ gas. (pg 198)

CO2

What was the gas that caused widespread death of people and animals near Lake Nyos in 1986? (194-196)

Carbon dioxide

Melting of the mantle forms the most common type of magma that is extruded onto the Earth's surface because ______________. A) this type of magma forms at high temperatures which allow it to rise to the surface before crystallizing completely to become solid rock B) this type of magma has low percentages of SiO2 so it has low viscosity which allows it to move more easily to the surface C) this type of magma is generally extruded in rift zones where there are fractures that provide avenues for flow D) all of the choices are correct E) none of the choices are correct

D) all of the choices are correct

Which of the following hazards to humans are related to volcanic eruptions? (pg 186) A) Burial by volcanic-generated mudflows. B) Asphyxiation from volcanic gases. C) Tsunami D) Being struck by pyroclastic debris. E) All of the choices are correct.

E) All of the choices are correct.

True or False In 1973 the town of Vestmannaeyjar on the island of Heimaey (off the coast of Iceland), was devastated by pyroclastic flows which completely filled and closed the town's harbor.

False

True or False Nuee ardente (French for glowing cloud) is another term used to describe a lava flow.

False

In 1883, Edvard Munch created his famous painting the scream after witnessing a blood a red sky over Oslo, Norway, caused by the eruption of ______. (fig 7.1 pg175)

Krakatau volcano, Indonesia

In August 1986, a gigantic volume of carbon dioxide gas belched forth from ____________ and swept down the adjacent valleys asphyxiating 1700 people.

Lake Nyos in Cameroon

During the summer of 1783, the greatest lava eruption of historic times poured forth at _________, accompanied by the release of an enormous volume of gases that enshrouded much of northern Europe in a "dry fog" or blue haze rich in SO2 (one of the visible components of today's urban smog). (pg 193) A. Mont Blanc, France B. Vesuvius, Italy C. Stromboli, Italy D. Ararat, Turkey E. Laki, Iceland

Laki, Iceland

Which continental hot spot in the United States has posed the greatest threat in historic times? (Pg 198)

Long Valley caldera

In the United States, there was great concern in the early 1980s when earthquakes were frequent, including harmonic tremor, and four magnitude 6 earthquakes caused damage near this volcanic center. (pg 198)

Long Valley caldera in California

The jokulhaup that occured in 1996 in iceland _______.

Melted part of the ice cap, releasing a flood that at its peak flowed as the second largest river in the world.

On 8 May 1902, a massive eruption of this volcanco killed 30,000 people in the town of St. Pierre. The volcano was _______? (pg190)

Mont Pelee, Martinique

The two most active Cascade Range volcanoes over the past 4000 years are?

Mount St. Helens and Mount Shasta

A genuine success story of advance warning before a large eruption occurred in the Philippines in 1991 before the climactic eruption of _________________. (pg 198)

Mt. Pinatubo

In 1985, this volcano produced a minor eruption that melted part of a glacier near its summit, sending a lahar down its slopes and killing at least 22,000 people: (pg 191) A. Vesuvius, Italy B. Mont Pelée, Martinique C. Mt. Mayon, Philippines D. Nevado Del Ruiz, Colombia E. Popocatepetyl, Mexico

Nevado Del Ruiz, Colombia

True or False The eruption of Nevado del Ruiz in Columbia in 1985 dropped hot pyroclastic debris onto glaciers, resulting in lahars.

True

True or False The most typical icelandic eruptions are fissure eruptions where lava pours out of long fractures (pg 175)

True

True or False The plate-tectonic process responsible for volcanoes in the Pacific Northwest region of North America is identical to the cause of the region's great earthquakes—subduction of the Juan de Fuca plate.

True

True or False The radiocarbon process of documenting major eruption dates for volcanoes in the past 50,000 years or so is the same as that used to work out dates of major prehistoric earthquakes.

True

In 1902, the town of St. Pierre near Mt. Pelee was destroyed and its population of 28,000 killed because of __________. (pg 189-190)

a gaseous flow of incandescent volcanic ash and dust.

Subduction zones are characterized by _______. (pg 177) a. andesitic to rhyolitic volcanic rocks b. steep-sided volcanoes composed of alternating pyroclastic debris and lava flows c. pyroclastic flows and calderas

all of the choices are correct

In August 1986, a gigantic volume of gas belched forth from Lake Nyos in Cameroon and swept down the adjacent valleys asphyxiating 1700 people. The gas was _________. (pg 194) A. sulfur dioxide B. carbon dioxide C. hydrogen sulfide D. carbon monoxide E. super heated H2O

carbon dioxide

Several geologic phenomena are being studied as signs of an impending volcanic eruption. These include seismic waves, ______________, and the release of gases. (pg 200) A. ground deformation B. flash floods C. landslides D. hymenoptra behavior E. unusual animal behavior

ground deformation

When magma is too viscous to flow it can form a sticky blob that blocks the conduit of a volcano and forms a steep-sided feature known as a _______________. (pg 162)

lava dome

Gases that are commonly emitted during volcanic eruptions include all of the following except __________. (pg 175)

nitrogen

The two most frequent causes of death from volcanic eruptions are (pg 186 & 190)

pyroclastic flows and tsunami.

The deadliest processes have been _____, ______, _____, and ______.

pyroclastic flows, tsunami, lahars, and indirect effects leading to famine.

volcano fatalities

pyroclastic flows, tsunami, lahars, and indirect- famine, gas, lava flows

A type of pyroclastic flow having higher steam content and less pyroclastic material. Surges are lower density, more dilute, high velocity, and may flow outward in a radial pattern. (pg 188)

pyroclastic surges

Ring shaped base surges that occur when more steam and less pyroclastic material combine to produce a more dilute, less dense, high-velocity flow (pg188)

pyroclastic surges

A high-temperature, fast-moved cloud of fine volcanic debris, steam, and other gases. (pg 186)

pyrpclastic flow

most of the Earth's explosive volcanoes are located in a zone that encircles the Pacific Ocean called the ring of fire. The types of volcanoes that commonly formin this zone are called _________ that form by the melting of asthenoshpere and lithosphere rocks during _________. (Pg 176)

stratovolcanoes, subduction

Many of the deaths at Mt. St. Helens on May 18, 1980 were related to _________. (pg 188)

the effects of lateral blast

Active volcanoes today in Oregon and Washington, including Mount St. Helens, result from____? (pg 177)

the subduction of the Juan de Fuca plate beneath North America

Lahars created on stratovolcanoes have high destructive energy because _______________. (pg 191)

they are a dense mass of water and rock that flows down steep slopes over thousands of feet of elevation

During the 1986 Lake Nyos eruption the most dangerous areas to be were _______ because the gas was ________. (pg 194- 196)

valleys, more dense than air