ISNS Ch 7
How has life responded to the Mount St. Helens eruption since 1980?
Bacteria have cleaned many of the lakes of volcanic debris. Plants have begun to recolonize barren ground.
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
At which volcanic explosivity index (VEI) do events occur most frequently?
2
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
There are at least ______ active volcanoes in the United States, and it is up to the Volcano Hazards Program to monitor them for signs of potential eruptions and alert the public when volcanic activity changes.
65
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 "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
Sector collapses are the result of the failure of weak or rotten rock, which happens when ______.
hot water and gases thermally decompose the rock
Since most volcanic activity occurs below sea level, ______.
humans cannot directly observe most volcanic activity
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
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.
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
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 ______.
lost consciousness died of asphyxiation
Magma in the Cascade Range is generated by ______.
melting of the mantle wedge during subduction
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
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
Most volcanic activity is not noticed by humans because ______.
the majority of volcanic activity occurs at oceanic spreading centers
Pyroclastic flows derive their energy from three things: ______.
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
What is a sector collapse?
Massive slope failure along the flanks of a volcano due to fracture of rotten rock
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
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: Monitoring seismic waves and ground deformation are surefire methods for predicting impending volcanic eruptions.
False (While it is hoped that seismic waves and ground deformation can be used to reliably predict volcanic eruptions, not enough is currently known about these processes to make them surefire means of volcano prediction.)
True or false: Mount St. Helens erupted without warning in late March 1980.
False (Signs pointed to a potential eruption days beforehand, when dozens of small earthquakes were recorded near the volcano and magma began pushing its way toward the surface)
What is the most common indirect effect that volcanic activity can have on humans?
Famine
The country of _____ is a volcanic plateau built of basaltic lava erupted from a hot spot underlying the Mid-Atlantic Ridge in the North Atlantic Ocean.
Iceland
A scientist determines that "Crystal Volcano" is 5,000 years old. What can that scientist assume about the ages of three other nearby volcanoes?
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.
A massive volcanic eruption 760,000 years ago blew out hundreds of cubic kilometers of magma to create the modern geography of the ______ region.
Long Valley-Mammoth Lakes
One example of a successful advance warning of a volcanic eruption is ______.
Mount Pinatubo in 1991
How does a pyroclastic surge differ from a pyroclastic flow?
Surges have more steam and less pyroclastic material, making them less constrained by topography.
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.
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.
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
The U.S. Geological Survey created the ______ to monitor volcanoes for potential eruptions in volcanically active areas such as California and Yellowstone.
Volcano Hazards Program
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.
A failed rift can occur when __.
a rift fails to open up enough to form a spreading center
One of the first signs of renewed volcanic activity of Mount St. Helens in March 1980 was ______.
a series of magnitude 3 earthquakes
Iceland's origins are very apparent when observing its geography, since ______.
a third of its surface is covered in volcanoes
Volcanic tsunami can be generated by a number of volcanic activities, including ______.
caldera collapse into the sea travel of lahars into the sea undersea eruptions
A pyroclastic flow ______.
can reach temperatures of 350o C is a mixture of magma, volcanic ash and gas, and air can move at speeds that exceed 100 m/sec
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
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
More than 7,000 pyroclastic flows, formed from ______, occurred on Mount Unzen, Japan, between 1991 and 1994.
dome collapse
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
The Long Valley-Mammoth Lakes area in California ______.
experienced a major eruption 760,000 years ago that influenced its modern geography is an area of abundant crustal melting
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 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 potential hazards of volcanic eruptions are extensive and include ______.
poison gas lahars lava flows tsunamis
The most dangerous volcanic processes are ______.
pyroclastic flows (Pyroclastic flows are responsible for 29% of volcano-related deaths.)
Pyroclasts, the shattered fragments of erupted magma thrown up into the atmosphere during an eruption, are brought back to ground during the formation of ______.
pyroclastic surges pyroclastic falls pyroclastic flows
Some phenomena that may be used to predict volcanic eruptions include ______.
seismic waves gas emissions ground deformation
Continued human development near Mount Shasta could prove disastrous because ______.
several towns are already located within the danger zone for pyroclastic flows the rock record shows previous eruptions of Mount Shasta were much larger than those of Mount St. Helens nearby towns are located in valleys, which are more susceptible to lahar flows
Subduction zone volcanoes affect humans more than any other type of volcanic activity because ______.
they eject material directly into the atmosphere, causing short-term changes in climate the areas around subduction zone volcanoes are often heavily populated
Undersea volcanic eruptions are one culprit in the formation of _____, which are the second most deadly volcanic process.
tsunami OR tsunamis
Without the monitoring and advance warning given for the Mount Pinatubo eruption in 1991, it is estimated that ______.
up to 20,000 people could have died, rather than 300
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
Lahars are produced by a combination of ______.
water loose pyroclasts gravity
