Chapter 6: Volcanoes And Volcanic Hazards

25 July 2022
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Gas in basaltic magma is the major controlling factor that determines _____
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- what rock types it will form - what landforms it will create
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The existence of a potentially dangerous situation or event is known as a(n) _____, whereas the likelihood and magnitude of its impact on society is known as its _____.
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hazard; risk
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Match the magma type with its gas bubble behavior.
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- Felsic magma = gas bubbles cannot escape easily; high pressures build up in the magma; typically explosive eruptions; magma is high viscosity - Basaltic magma = gas bubbles escape easily; little pressure builds in the magma; typically nonexplosive eruptions; magma is low viscosity
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List the rocks typically found in calderas, from the top downward. Begin with the rocks at the surface and continue to the rocks the farthest below the surface
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1.) volcanic tuff 2.) hard, welded volcanic rock 3.) finely crystalline granite
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Match the volcanic feature with the hazard.
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- Scoria cone: > falling volcanic cinders and bombs > volcanic ash and gases - Lava flow: > burial of roads > bulldozing and crashing of houses and other structures
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Which of the following are erupted by volcanoes?
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- pumice - lava - ash
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The magma feeding Mount Rainier and the other cascade volcanoes results from melting associated within the Cascadia _____ zone, which is an ocean-continent _____ boundary.
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subduction; convergent
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The typical form for a composite volcano is a _____.
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steep-sided cone
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Which of the following are characteristics of actively erupting volcanoes?
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- glowing orange lava flowing downhill - fragments of molten rock blasting into the air - billowing clouds of ash rising into the air
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The potential hazards associated with a volcano can be assessed by studying various characteristics and the history of the volcano. Match the characteristics with what type of information it provides.
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- shape: steep slopes indicate high viscosity, explosive magma; gentle slopes indicate less explosive magma - rock type: chemical analysis determines magma composition and potential for explosiveness - history: the sequence of layers and isotopic dating can indicate the timing and frequency of eruptions
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_____ forming eruptions are the largest and most violent volcanic phenomena.
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caldera-
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rank the following volcanoes in order of increasing average size. Put the smallest volcano on top and proceed to the largest.
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- scoria cone - composite volcano - large shield volcano
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What type of volcano is Mount Rainier?
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composite
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The volcanic hazards associated with a volcano are dependent upon the type of volcano.
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True
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Which of the following commonly precede a volcanic eruption?
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- increased heat flow from the volcano - steam eruption from the volcanic crater - increased gas flow from a volcano
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Match the magma type with the corresponding eruption type.
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- Basaltic magma: fluid lava flows from shield volcanoes; low viscosity - Felsic magma: expolsive eruptions from composite volcanoes; high viscosity
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Gases more easily remain dissolved in liquids at _____ pressures.
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high
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Shield volcanoes are composed primarily of _____ lava flows.
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basaltic
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which of the following accurately describe a scoria cone?
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- composed of a pile of loose, vesicular lava fragments - steep-sided hill - formed from lava fountains
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Decreasing pressure on a liquid that contains dissolved gases will result in _____.
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the formation of gas bubbles
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Put the events leading to the formation of Crater Lake as we see it today. Put the first (earliest) event on top and proceed to the latest.
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1.) massive ash column eruption of a composite volcano empties the magma chamber 2.) overlying volcano collapses into the resulting void 3.) scoria cone forms in the caldera 4.) rain and snowmelt fill the caldera, producing a large and deep lake
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The volcanic rocks associated with domes are felsic to intermediate in composition, and hence are classified as rhyolite and _____.
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andesite
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Match the eruption products with their appropriate magma descriptions.
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- thin lava flows: low-viscosity magmas with relatively low volatile contents - lava domes: high-viscosity magmas with relatively low volatile contents - lava fountains: low-viscosity magmas with relatively high volatile contents - eruption columns: high-viscosity magmas with relatively high volatile contents
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Proximity to certain types of _____ boundaries is the major factor making some places more prone to volcanic hazards than others.
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plate
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Which of the following are responsible for the huge size of flood basalts?
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- large (long and wide) fissures from which the lava spews - multiple eruption events in the same area - low viscosity of the basaltic magma
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_____ volcanoes produced pyroclastic flows that killed tens of thousands of people at Pompeii and St. Pierre
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composite
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Put the events of the 1980 Mount St. Helens eruption in order. Begin with the earliest event on top and proceed to the last.
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1.) earthquake 2.) landslide 3.) lateral blast and eruption column
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Which of the following plate boundaries is least likely to produce composite volcanoes?
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continent-continent convergent boundary with a high mountain range (Himalayas)
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The largest eruption on Earth are floods of _____ magma.
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basaltic
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Which of the following phenomena are monitored to predict volcanic eruptions?
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- heat flow changes - changes in gas output - ground shaking - changes in topography
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Which of the following is not a hazard typically associated with scoria cones?
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fast-moving lava flows
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Which of the following were hazardous effects produced in mainland Europe by the huge 1783 eruption at Lake, Iceland?
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- reduced summer sunlight - unusually cold winter - crop failures and famine
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Contrast eruption columns with pyroclastic flows by putting the description in the category.
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- Eruption column: > Tephra erupts high into the atmosphere along with large amounts of hot volcanic gases > Ash particles drift back down to Earth hundreds of kilometers or more from the volcano - Pyroclastic flow: > Ash layers are deposited only on and adjacent to the slopes of the volcano > Tephra billows down the slopes of the volcano in ground -hugging flows at speeds of over 100 km/hr
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Which of the following rock types are associated with basaltic volcanoes?
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- nonvesicular basalt - scoria - volcanic bombs - vesicular basalt
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Almost 40,000 people were killed by the 1883 eruption of Krakatau, Indonesia. Krakatau was a _____ that formed a caldera.
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composite volcano
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Which of the following are properties characteristic of calderas?
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- form from collapse of overlying ground into emptied magma chamber - bounded by steep escarpments - large, basin-shaped volcanic depression
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Which of the following is a recognizable characteristic of recent calderas?
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steep-sided, basin-shaped depression
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Which of the following processes contribute to the growth of composite volcanoes?
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- pyroclastic flows - ash column eruptions -eruption of lava flow
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Which of the following are two ways in which volcanic domes grow?
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- thick flows of lava break out and flow down the steep surface of the dome - magma injected into the interior expands and breaks up the overlying cooled lava
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Lava flows are produced by basaltic magmas that contain _____ than those that produce scoria cones.
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less gas
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Which of the following lists the four types of volcanoes shaped like hills and mountains?
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scoria cone, shield, composite, dome
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Which of the following are hypothesized sources of the magma that produce flood eruptions?
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- melted asthenosphere from around the plume in the shallow mantle - melted lithosphere over a mantle plume - plume material from deep in the mantle that melts at shallow depths
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The largest concentration of composite volcanoes on Earth is located along the _____.
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Pacific Ring of Fire
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Which of the following are locations where flood basalts are known to have occurred?
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- india - siberia - oceanic plateaus - brazil
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Which of the following volcanic hazards are posed to the surrounding areas by Mount Rainier?
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- pyroclastic flows - lava flows - mudflows
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Which of the following is not true of basaltic lava flows?
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They pile up in steep, cone-shaped hills
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Put the events of caldera formation in order. Begin with the first event, and end with the last.
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1.) magma erupts as ash column, emptying a shallow magma chamber 2.) overlying material collapses into emptied chamber in a series of fault blocks 3.) ash and other pyroclastics fill the subsiding crater 4.) small rhyolite domes form in caldera
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Which of the following materials commonly are found in composite volcanoes?
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- volcanic tephra - volcanic tuff - andesitic lava flows - lahars and landslide deposits
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Huge circular depressions from which volcanoes erupt are called _____.
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calderas (or crater)
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Which of the following accurately describe most shield volcanoes?
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- broad and gently sloping form - composed of a succession of lava flows
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_____ are common on composite volcanoes because of their abundant clay, loose rocks, moisture, and steep slopes.
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debris flows, landslides, and lahars
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Which of the following best describe a young scoria cone?
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- little soil buildup on slopes - dark, fresh-looking lava - central crater at top of a conical hill
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Volcanic eruptions can produce huge floods by _____.
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melting ice sheets
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Which of the following is not a typical hazard posed to human-made structures by lava flows?
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high winds
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Due to their large size and the volume of erupted gases, which of the following are likely true for flood basalts?
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- highly reflective sulfuric acid droplets in the atmosphere could lead to global cooling' - such eruptions could lead to increased greenhouse warming
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Which of the following are the two main factors controlling volcanic eruption style?
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- magma composition - volatile content of the magma
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Long, thin lava flows are typically produced by _____.
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low-viscosity lavas
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An older scoria cone would have _____ compared to a younger scoria cone.
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more soil and plants
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Which of the following events accompanied the caldera-forming eruption at Santorini, Greece, about 3,500 years ago?
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- huge ash column forms - pyroclastic flows occur - caldera collapse drops island beneath the sea surface - tsunami travels south and hits Crete
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In A.D. eruption at Mount Vesuvius in Italy, which killed about 25,000 people in Pompeii and Herculaneum, consisted mainly of _____ that roared down the slopes of the composite volcano.
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pyroclastic flows
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Which of the following situations would represent the highest level of volcanic hazard to a population?
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- town located along a river drainage directly downhill from a volcano - town located very near to a volcano
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Volcanic vents can take which of the following forms?
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- narrow linear fissures - roughly circular craters
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The most common volcanic rock found in lava flows on composite volcanoes is _____.
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andesite
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According to the fossil record, _____ events have coincided with the approximate times when flood basalts were erupting.
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mass extinction
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Which of the following is not a way in which volcanic domes are commonly destroyed?
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collapse into emptied magma chambers below
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Which of the following techniques are used to monitor changes in the shape of volcanoes that may indicate magma movement and imminent danger of eruption?
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- tiltmeter usage to determine changes in slope - radar imaging to detect small changes in topography - GPS station monitoring
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Which of the following are characteristics typical of volcanic domes? Assume a relatively young dome.
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- often occur in clusters - rubble-covered surface - steep-sided
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The same volcano may produce both explosive and nonexplosive eruptions.
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True
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The higher the gas pressure builds in magma, _____.
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the more explosive an eruption it is likely to produce
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Shield volcanoes have low slopes primarily because _____.
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the low viscosity of basaltic magma allows it to flow downhill for long distances
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Which of the following accurately describe young lava flows?
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- rough upper surface - steep flow fronts
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Select from below the typical components of a composite volcano.
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- mudflow deposits - lava flows - pyroclastic flows
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When lava flows reach the ocean, they _____.
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solidify and add land to an island
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Volcanism culminating in the Yellowstone eruptions of the past 2 million years has produced a set of overlapping calderas that stretch in an arc to the southwest from Yellowstone to southeastern Oregon, suggesting that North America has been riding to the southwest over a _____ for at least the past 12.5 million years.
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hot spot
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Which of the following were warning signs prior to the catostrphic eruption of Mount St. Helens in May 1980?
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- formation of a bulge on its flanks - earthquakes
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Mount Pelรฉe, which killed about 30,000 people with pyroclastic flows in 1902, is a _____ volcano located over a subduction zone.
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composite
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Which of the following is not evidence of recent volcanic activity?
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thick, well-developed soil
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Rhythmic seismic activity tends to _____ volcanic eruptions.
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precede and accompany
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Which of the following are typical hazards associated with scoria cones?
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- toxic volcanic gases - falling cinders and volcanic bombs - volcanic ash
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Volcanic domes form from the accumulation of _____ lava over a volcanic event.
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viscous
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Which of the following are typically erupted from a volcano?
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scalding hot ash, lava, and gases
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_____ eruptions can erupt more than 1,000 cubic kilometers of magma, resulting in the collapse of the overlying ground into a large crater.
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caldera-forming
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A composite cone would be expected to have slopes that are _____ than those of a shield volcano.
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steeper
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Match the eruption style with its description
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Eruption column: Ash particles drift back down to Earth hundreds of kilometers or more from the volcano. Tephra erupts high into the atmosphere along with large amounts of hot volcanic gases. Pyroclastic flow: Ash layers are deposited only on and adjacent to the slopes of the volcano. Tephra billows down the slops of the volcano in ground-hugging flows at speeds of over 100 km/hr
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Volcanic mudflows can be detected remotely by monitoring _____
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characteristic rumbling produced as they rush down valleys
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Lava flowing in _____ in Hawaii can remain hot and fluid for so long that it flows all the way to the ocean.
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lava tubes
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Reduced temperatures and growing seasons in Europe following the 1783 Lake eruption were primarily caused by _____
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blocking of sunlight by volcanic ash and aerosols
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The following is a location in which flood basalts erupted:
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Columbia Plateau
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Which of the following commonly preceded a volcanic eruption?
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Steam eruptions from the volcanic crater Increased gas flow from a volcano Increased heat flow from the volcano
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Which of the following are ways in which volcanic domes are commonly destroyed?
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Collapse of the steep flanks into block and ash flows Internally derived explosions from trapped gas pressure
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Which of the following is not a typical eruption style during the growth of a composite volcano?
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Caldera collapse
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True/False: All hills made of volcanic rocks are volcanoes
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false
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True/False: A typical volcanic eruption is likely to kill millions of people at a time.
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false
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The following events accompanied the 1883 eruption at Krakatau, Indonesia:
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Most of a large island collapses into a caldera Tsunami waves strike ships and nearby coastline Largest and loudest explosion in recorded hisotry occurs HIgh eruption column and pyroclastic flows form
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Which of the following would be evidence that a volcano has been inactive for a long period of time?
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Well-developed soils on volcanic rocks
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Volcanic domes form from the accumulation of ____ lava over a volcanic vent.
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viscous
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When fluid lava erupts onto the surface, it typically produces _____
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lava flows
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The A.D. 79 eruption at Mount Vesuvius in Italy, which killed about 25,000 people in Pompeii and Herculaneum, consisted mainly of _____ that roared down the slopes of the composite volcano.
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pyroclastic flows
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The ways in which lava flows destroy human-made structures:
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Covering roads Burning buildings Crushing/bulldozing buildings
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Magma rising through the crust fractures rocks, producing rhythmic, repeating
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seismic shaking
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Older lava flows tend to have surfaces that are _____ than younger lava flows.
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more subdued and have more soil and plants
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Which of the following are ways in which older calderas typically become harder to recognize?
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Disruption by faulting Burial by younger rocks Erosion
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Flood-basalt eruptions are fed by _____
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long fissures/dikes
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_____ eruptions are among the world's most lethal natural disasters
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Caldera-forming