Chapter 7. Volcano Case Histories: Killer Events Questions

About ______ cubic kilometers of ash were released by Mount St. Helens, and a similar amount of material formed pyroclastic flows.

0.25

Place the following volcanic hazards in order of their deadliness, with the most deadly process at the top and least deadly process at the bottom.

1. Pyroclastic flows 2. Tsunami 3. Lahars 4. Gas 5. Lava flows

Place the events of the eruptive sequence of the 1980 Mount St. Helens in order of their occurrence, with the oldest event at the top and the most recent event at the bottom.

1. Rising 2. The volcanic bulge 3. A drop in pressure on 4. Rapid escape

Mount St. Helens, one of several large volcanoes in the Cascade Range, has experienced a major eruption every ______ years since about 500 B.C.

100 to 200

Pyroclastic falls account for about ______ percent of volcanic deaths.

2

Volcanologists have estimated that about ______ people have died by volcanic activity in the past 500 years.

275,000

Since it was created 2,500 years ago, the longest Mount St. Helens has gone without erupting is ______ years.

500

Which of the following occurred first in the eruptive sequence of Mount St. Helens in 1980?

A magnitude 5.1 earthquake occurred.

Which of the following towns would be affected if the Osceola mudflow were to occur today at Mount Rainier? (Select all that apply.)

Buckley Enumclaw

What is a sector collapse?

Massive slope failure along the flanks of a volcano due to fracture of rotten rock

Which of the following describe the 2010 eruption of Eyjafjallajokull? (Choose all that apply.)

The eruption style changed when glacial meltwater poured into the magma chamber. It stopped European air travel for 6 days.

Why did carbon dioxide build up to such lethal levels in Lake Nyos?

The gas, produced by volcanic outgassing, accumulated in the lower layers of the stratified lake until it reached critical levels.

Many of the most historically recent devastating volcanic eruptions have occurred ______.

along subduction zones

Volcanoes that form ______ are generally all the same age. Volcanoes that form ______ show an orderly progression in their age from young to old.

along subduction zones; above hot spots

The 1985 Nevado del Ruiz eruption was made particularly deadly due to the presence of ______, since the eruption itself was rather minor.

an ice cap at the volcano's peak

The "mega-blister" that developed along the flank of Mount St. Helens in early April was the result of ______.

an increase in magma volume within the volcano

A pyroclastic flow ______. (Select all that apply.)

can move at speeds that exceed 100 m/sec is a mixture of magma, volcanic ash and gas, and air can reach temperatures of 350o C

The deadly gas that killed 1,700 people and 3,000 livestock near Lake Nyos, Cameroon, in 1986 was later identified as ______.

carbon dioxide

The gas _____ ______ was ultimately responsible for the deaths of thousands of villagers near Lake Nyos, Cameroon, in 1986

carbon dioxide

The German physician Paracelsus could have used the incident near Lake Nyos, Cameroon, in 1986 as an example for the principle named after him. This is because ______.

carbon dioxide gas, normally harmless to humans in low doses, was abundant enough at Nyos to kill 1,700 people

Lava domes can produce pyroclastic flows when ______.

chunks of the dome break off and flow downslope

The accompanying diagram shows a pyroclastic flow forming from a(n) ______. (Image shows red arrows pointed towards eruption and landslide)

direct blast

Volcanic hazards fall into one of two groups: ____ hazards, such as lahars and pyroclastic flows, and ______ hazards, such as famine.

direct; indirect

More than 7,000 pyroclastic flows, formed from ______, occurred on Mount Unzen, Japan, between 1991 and 1994.

dome collapse

Even though evacuations had been put into place, 44 people died when a lava _______ on Mount Unzen in Japan collapsed in May 1991 and created a pyroclastic _______.

dome; flow

The _______ alone determines the poison" is a principle that can be applied to the deaths of humans and animals near Lake Nyos from carbon dioxide.

dose

Primary lahars occur ______, whereas secondary lahars occur ______.

during a volcanic eruption; months or years after an eruption

A volcanic eruption, landslide, or ______ may have been responsible for the release of lethal amounts of carbon dioxide gas from Lake Nyos.

earthquake

Mount Mayon in the Philippines is notorious for pyroclastic flows that form from ______, which has caused about 1,500 deaths since 1616.

eruption column collapse

Spreading centers usually start with three arms, but only two tend to spread apart. The third one that does not develop is called a __.

failed rift

A pyroclastic ______ forms when airborne pyroclasts rain down upon the landscape, with particles ranging in size from ash to bombs and blocks.

fall

Volcanic activity created the _____ that is important to the economy of the village of Vestmannaeyjar on the island of Heimaey, near Iceland.

fishing port

Long, linear ___ eruptions composed of low-viscosity, low-volatile lava flows are typical in Iceland.

fissure

Most Icelandic eruptions occur when lava pours out of long fractures, in eruptions known as ______ eruptions.

fissure

Pyroclasts are ______.

fragmented pieces of magma released during volcanic eruptions that create falls, flows, and surges

The heat created by the eruption of Nevado del Ruiz in 1985 melted _____ which then mixed with pyroclastic material to form a deadly lahar.

glaciers or ice

Pyroclastic flows derive their energy from three things: ______. (Select all that apply.)

gravity gas expansion within the flow the volcanic eruption

Lahars are produced by a combination of ______. (Select all that apply.)

gravity water loose pyroclasts

Primary lahars were generated during the Nevado del Ruiz eruption in 1985 when ______.

hot pyroclastic debris began melting the volcano's ice cap

Sector collapses are the result of the failure of weak or rotten rock, which happens when ______.

hot water and gases thermally decompose the rock

Pyroclastic flows that formed on Mont Pelée, Martinique, in 1902 were generated by ______.

hot water and magma overspilling the rim of the volcanic crater

The fishing port in the Icelandic town of Vestmannaeyjar is an example of ______.

how volcanic activity can sometimes benefit humans

Famine is one example of how volcanoes can have a(n) ___ effect on humans, by lowering agricultural production and killing livestock that humans depend upon for survival.

indirect

Mount Rainier is considered one of the most dangerous volcanoes in the United States because ______.

it is located near a major metropolitan area and is geologically unstable

A(n) _____ is a mudflow composed of volcanic debris that is fluid when moving but solidifies soon after stopping.

lahar

One major hazard in the area surrounding Mount Rainier is the risk of future deposition of ______, which may occur in the path of previous deposits that are rapidly being developed.

lahars

The 1991 Mount Pinatubo eruption featured massive _____ that were produced when Typhoon Yunya passed over the volcano, dumping heavy rainfall.

lahars

Following the failure of the Mount St. Helens bulge, a series of ____ and debris flows formed from a mix of rock and water derived from melting snow. They continued to form for hours after the eruption began. (Enter only one word per blank.)

lahars or mudflows

A scientific team drills deep down into a magma chamber and recovers samples of the magma. Their analysis finds that it contains very few volatiles and is very viscous. They predict that an eruption of the magma would form a ______.

lava dome

Lassen Peak is a ______.

lava dome that formed from highly viscous magma

One of the most dangerous phases of a volcanic eruption occurs when

less energy is fed into the eruption column, causing it to collapse and sending pyroclastic flows down the flanks of the volcano

After residents of villages near Lake Nyos encountered a gaseous cloud in 1986, they ______. (Select all that apply.)

lost consciousness died of asphyxiation

During the Lassen Peak eruption in 1915, ______. (Select all that apply.)

massive lahars were formed as melting snow combined with rocky debris a pyroclastic flow formed when the north slope of the volcano split very viscous magma broke off in huge chunks as it couldn't flow over the crater rim

Magma in the Cascade Range is generated by ______.

melting of the mantle wedge during subduction

The earthquake activity at Mount St. Helens prior to the eruption was the result of the ______.

movement of magma as it accumulated beneath the volcano's peak

Determining the age of recent volcanic eruptions depends upon the presence of ______ trapped in lahars, volcanic ash fall, or lava flows from previous eruptions.

organic material such as trees

The accompanying diagram shows a pyroclastic flow forming from a(n) ______. (The image shows a single red arrow pointed at landslide)

overspilling of the crater rim

The potential hazards of volcanic eruptions are extensive and include ______. (Select all that apply.)

poison gas lahars tsunamis lava flows

The landslide that occurred on Mount St. Helens just prior to its eruption created a drop in _______ that allowed dissolved gas in magma and groundwater to expand very rapidly and erupt explosively.

pressure

Pyroclasts, the shattered fragments of erupted magma thrown up into the atmosphere during an eruption, are brought back to ground during the formation of ______. (Select all that apply.)

pyroclastic falls pyroclastic surges pyroclastic flows

During the 1980 Mount St. Helens eruption, a ______ was generated by a direct blast traveling more than 150 m/sec and annihilating everything in its path.

pyroclastic flow

The most dangerous volcanic processes are ______.

pyroclastic flows

The pyroclastic flow that killed more than 2,000 people in the coastal province of Katimbang, Sumatra, during the 1883 Krakatau eruption conclusively demonstrated that ______.

pyroclastic flows could travel long distances over water

Continued human development near Mount Shasta could prove disastrous because ______. (Select all that apply.)

several towns are already located within the danger zone for pyroclastic flows nearby towns are located in valleys, which are more susceptible to lahar flows the rock record shows previous eruptions of Mount Shasta were much larger than those of Mount St. Helens

The greatest lava eruption in the historic record is ______.

the Laki fissure event in 1783

Subduction zone volcanoes affect humans more than any other type of volcanic activity because ______. (Select all that apply.)

the areas around subduction zone volcanoes are often heavily populated they eject material directly into the atmosphere, causing short-term changes in climate

The avalanche caused by the collapse of Mount St. Helen's bulge also led to a tremendous blast of magma and groundwater when ______.

the avalanche removed lots of rock from the side of the volcano, dropping pressure enough to release the gaseous magma

About half of the ash produced by Mount St. Helens came from ______, and the other half was the result of ______.

the eruption column; pyroclastic flows

Ultimately, the growing bulge on the side of Mount St. Helens failed because ______.

the weak rock was unable to overcome the effects of gravity

Estimating the number of people who have died from volcanic eruptions is difficult because ______.

there is a lack of written historical records for some time intervals and parts of the world

Volcanic tsunami can be generated by a number of volcanic activities, including ______. (Select all that apply.)

travel of lahars into the sea caldera collapse into the sea undersea eruptions

Undersea volcanic eruptions are one culprit in the formation of _______, which are the second most deadly volcanic process.

tsunami or tsunamis

As a result of the 1783 Laki fissure event in Iceland, ______. (Select all that apply.)

volcanic gases killed more than half of the country's livestock (horses, sheep, and cattle) a famine killed about 10,000 people the growth of important agricultural plants was slowed

Partial melting of rock in subduction zones is aided by the addition of ______, which is (are) released by sediments on top of the subducting plate.

water

What is the most common indirect effect that volcanic activity can have on humans?

Famine

What kind of eruption was the 1783 Laki eruption, which produced the most lava by volume of any volcano in recorded history?

Fissure eruption

A scientist determines that "Crystal Volcano" is 5,000 years old. What can that scientist assume about the ages of three other nearby volcanoes? (Select all that apply.)

If the volcanoes were created by subduction, they are likely to be about the same age. If the volcanoes were created by a hot spot, the ages of the other volcanoes depend on the location of Crystal Volcano in the sequence.

What was the result of glacial meltwater pouring into the Eyjafjallajokull magma chamber as it was erupting in 2010?

It caused a Vulcanian eruption that blew pyroclastic material 9 km into the atmosphere.

Imagine that the Kelut Volcano experienced an eruption last year. Recent heavy rainfalls have mixed with pyroclasts to produce a series of devastating lahars. How would a geoscientist classify these lahars?

Secondary lahar

How does a pyroclastic surge differ from a pyroclastic flow?

Surges have more steam and less pyroclastic material, making them less constrained by topography.

The 1816 "Year Without a Summer," during which global temperatures were well below average, was the result of short-term climatic changes caused by the eruption of _______ Volcano

Tambora

According to the map, in which of the urban areas located near Mount Shasta would one most likely be the safest to live during a future eruption?

Edgewood

True or false: A body of water between a village and a volcano will keep the citizens safe from pyroclastic flows.

False

True or false: Mount St. Helens erupted without warning in late March 1980.

False

True or false: The majority of the 117,000 deaths from the Tambora eruption were the direct result of pyroclastic flows and lahars generated by the explosive eruption.

False

True or false: Volcanic outgassing occurs only with erupting volcanoes.

False

An Icelandic farmer wrote the following about the death of some of his livestock: "The animals that wandered around the fields got yellow-colored feet with open wounds, and yellow dots were seen on the skin of the newly shorn sheep, which had died." The farmer was the describing the effects of which volcanic eruption?

Laki

The volcano we call _____ ______ went through a series of eruptions from 1914 to 1917, producing large plumes of ash, lahars, and pyroclastic flows that devastated a large but uninhabited area.

Lassen Peak

How has life responded to the Mount St. Helens eruption since 1980? (Select all that apply.)

Plants have begun to recolonize barren ground. Bacteria have cleaned many of the lakes of volcanic debris.

______________ are one deadly volcanic hazard that can be released by both erupting and nonerupting volcanoes.

Poison gases

Determine whether each of the following statements describes pyroclastic surges or pyroclastic flows.

Pyroclastic flow Movement is largely controlled by topography Pyroclastic surge More dilute, less-dense, fast-moving flow Pyroclastic flow Larger fraction of pyroclastic material Pyroclastic surge Larger fraction of steam

How are the absolute ages of recent volcanic eruptions measured?

Radiocarbon dating is performed on trees or other debris trapped in volcanic ash or lahars.

Mount _____ (shown in the image) is best described as 33.6 cubic miles of structurally weak rock capped by 1 cubic mile of ice, making it inherently unstable.

Rainer

What strange event took place in four villages near Lake Nyos, Cameroon, on 21 August 1986?

Residents were asphyxiated from a gaseous cloud, causing about 1,700 deaths.

During the June 1991 eruption of Mount Pinatubo in the Philippines, secondary lahars may not have formed if it had not been for ______.

Typhoon Yunya, which dumped heavy rains on the area over the erupting

Your friend is interested in visiting Mount St. Helens but wants some ideas as to what activities that they can do while visiting. What could you suggest, based upon your knowledge of the area?

Your friend could go fly fishing for trout in the nearby lakes.

Forty-four people, including journalists and volcanologists, were killed at Mount Unzen on 3 June 1991 from ______.

a pyroclastic flow generated from dome collapse

A failed rift can occur when __.

a rift fails to open up enough to form a spreading center

Twenty-two thousand people were killed in the town of Armero during the Nevado del Ruiz volcanic eruption when ______.

a series of lahars roared down steep-walled canyons and buried the town

One of the first signs of renewed volcanic activity of Mount St. Helens in March 1980 was ______.

a series of magnitude 3 earthquakes