Chapter 7. Volcano Case Histories: Killer Events
About ______ cubic kilometers of ash were released by Mount St. Helens, and a similar amount of material formed pyroclastic flows.
0.25
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
At which volcanic explosivity index (VEI) do events occur most frequently?
2
Pyroclastic falls account for about ______ percent of volcanic deaths.
2
Approximately how many of the buildings in Goma, Zaire, were destroyed by a lava flow in January 2002?
25%
Volcanologists have estimated that about ______ people have died by volcanic activity in the past 500 years.
275,000
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
How does DNA analysis tie human evolution to the Toba eruption that occurred 74,000 years ago?
DNA analysis shows that humans experienced a major population crash about the same time as the eruption.
What has been done to prevent another lethal buildup of carbon dioxide in Lake Nyos?
Degassing pipes have been installed to allow carbon dioxide to exit the lake when pressure builds up.
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
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
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.
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
What is a sector collapse?
Massive slope failure along the flanks of a volcano due to fracture of rotten rock
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
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.
Pyroclastic flows Tsunami Lahars Gas Lava flows
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.
Rainier
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.
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.
Rising magma began to reshape Mount St. Helens, setting off a series of earthquakes. The volcanic bulge on Mount St. Helens collapsed, generating an avalanche. A drop in pressure on the side of Mount St. Helens created a pyroclastic flow. Rapid escape of volcanic gases blew magma upward, generating a Plinian eruption phase on Mount St. Helens.
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
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.
Why have degassing pipes been installed in Lake Nyos in Cameroon?
To allow high-pressure gas to escape, preventing the CO2 from building to dangerous levels
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 volcano
Match of the following volcanic eruptions to the correct Volcanic Explosivity Index (VEI) level.
Yellowstone - 8 Tambora - 7 St. Helens - 5 Nevado del Ruiz - 3 Pinatubo - 6
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
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
Volcanic tsunami can be generated by a number of volcanic activities, including ______. (Select all that apply.)
caldera collapse into the sea travel of lahars into the sea undersea eruptions
A pyroclastic flow ______. (Select all that apply.)
can reach temperatures of 350o C can move at speeds that exceed 100 m/sec is a mixture of magma, volcanic ash and gas, and air
The gas was ultimately responsible for the deaths of thousands of villagers near Lake Nyos, Cameroon, in 1986.
carbon dioxide
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 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
Volcanic hazards fall into one of two groups: hazards, such as lahars and pyroclastic flows, and hazards, such as famine.
direct indirect
The accompanying diagram shows a pyroclastic flow forming from a(n) ______.
direct blast
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
More than 7,000 pyroclastic flows, formed from ______, occurred on Mount Unzen, Japan, between 1991 and 1994.
dome collapse
"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.
earthquakes
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
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
Lahars are produced by a combination of ______. (Select all that apply.)
gravity loose pyroclasts water
The Nyiragongo lava flow was especially deadly because it ______.
had an unusually low viscosity, allowing it to move quickly
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
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
The potential hazards of volcanic eruptions are extensive and include ______. (Select all that apply.)
lahars lava flows poison gas tsunamis
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
Less than 1% of volcano-related deaths are caused by ______ because they move very slowly.
lava flows
The city of Goma, Zaire, was devastated in 2002 when _______.
lava flows spilled into the city, destroying 25% of the buildings
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
Nyiragongo produced low-viscosity lava flows during its 1977 eruption, which was caused by ______.
low SiO2 content
Lava flows are rarely responsible for many volcano-related deaths because they ______.
move too slowly
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
Continued human development near Mount Shasta could prove disastrous because ______. (Select all that apply.)
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 several towns are already located within the danger zone for pyroclastic flows
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 ______.
overspilling of the crater rim
The release of carbon dioxide from Lake Nyos mirrors an earlier event at Lake Monoun in 1984. Scientists think that this earlier event was probably due to ______.
overturning of lake-water layers during the rainy season
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
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
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 flows pyroclastic falls pyroclastic surges
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
Carbon dioxide became trapped in Lake Nyos because the lake is ______.
stratified into layers
During pyroclastic the flow is more dilute, less-dense and fast moving and there is more steam and less pyroclastic material. During pyroclastic a large fraction of the material is pyroclastic and the movement is largely controlled by topography.
surge flow
The greatest lava eruption in the historic record is ______.
the Laki fissure event in 1783
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
Pyroclastic flows derive their energy from three things: ______. (Select all that apply.)
the volcanic eruption gas expansion within the flow gravity
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
Undersea volcanic eruptions are one culprit in the formation of , which are the second most deadly volcanic process.
tsunami or tsunamis
During the Lassen Peak eruption in 1915, ______. (Select all that apply.)
very viscous magma broke off in huge chunks as it couldn't flow over the crater rim a pyroclastic flow formed when the north slope of the volcano split massive lahars were formed as melting snow combined with rocky debris
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) the growth of important agricultural plants was slowed a famine killed about 10,000 people
