Deck 9: Volcanoes and Other Igneous Activity

Question 1

Which type of basaltic lava flow has its surface covered with sharp-edged,angular blocks and rubble?

A)scoria
B)pahoehoe
C)pillow lava
D)aa

Answer 1

D

Question 2

In 1980,________ was the first Cascade Range volcano to erupt since Mt.Lassen in 1915-16.

A)Mt.Rainier
B)Mt.Shasta
C)Kilauea
D)Mt.St.Helens

Answer 2

D

Question 3

Which statement about the May,1980,eruption of Mount St.Helens is false?

A)During the eruptive period,the mountain peak was substantially built up by new lava flows and pyroclastic debris.
B)Plumes of ash rose high into the atmosphere during the major eruptive events.
C)Mudflows accompanied the major eruptive events.
D)The most powerful explosive event was preceded by a massive landslide.

Answer 3

A

Question 4

________ is the major dissolved volatile constituent in both magmas and volcanic gases.

A)Water
B)Carbon monoxide
C)Hydrogen chloride
D)Methane

Question 5

________ magma is the most abundant type of magma erupted on Earth.

A)Basaltic
B)Granitic
C)Andesitic
D)Pegmatitic

Question 6

As magma approaches the surface,water contributes to the explosive potential of the eruption because ________.

A)water has a large heat capacity,which allow it to keep the magma hot enough to explode
B)water dissociates to hydrogen and oxygen at high temperatures but reacts violently at decreasing pressures to produce explosive eruptions
C)water has a lower density in its solid phase than its liquid phase which makes it explode when pressure decreases
D)water dissolved in magma flashes to steam as pressure decreases,and the volume increase leads to an explosive potential

Question 7

Which of the following factors help determine whether a volcanic eruption will be violent or relatively quiescent?

A)amount of dissolved gas in the magma
B)temperature of the magma
C)composition of the magma
D)all of these

Question 8

________ tend to increase the explosive potential of a magma body beneath a volcano.

A)High viscosity and dissolved gas
B)High viscosity and low dissolved gas content
C)Low silica content and low viscosity
D)Low viscosity and low dissolved gas content

Question 9

Which one of the following shows the correct order (left to right)of decreasing magma viscosity?

A)rhyolite,andesite,basalt
B)andesite,rhyolite,basalt
C)basalt,rhyolite,andesite
D)basalt,andesite,rhyolite

Question 10

Which one of the following statements concerning volcanic blocks and bombs is true?

A)Blocks are broken fragments of solid rocks; bombs have smaller sizes than lapilli.
B)Bombs are guided to Earth by laser beams; blocks fall anywhere.
C)Bombs are ejected as magma lumps; blocks are ejected as solid fragments.
D)Bombs and blocks are both smaller than lapilli and cinders.

Question 11

What type of volcanic material is indicative of eruption under water?

A)AA flows
B)Pyroclastic flows
C)Pillow lavas
D)Pahoehoe flows
E)Lava aprons

Question 12

Which magma type would generally have the lowest viscosity?

A)basalt
B)andesite
C)dacite
D)rhyolite

Question 13

Volcanic bombs originate ________.

A)as laser-guided,granite blocks launched from a supersonic jet
B)as blocks of volcanic rock ejected from an erupting volcanic crater
C)as erupted magma blobs that partly congeal before falling to the ground
D)as ash particles that join together in the eruptive plume and fall as cobble-sized objects

Question 14

Considering the history of Mt.St.Helens and Kilauea volcanoes and your knowledge of volcano types in different tectonic settings,if you had to live on a volcano,which of the following would you choose if safety was your only concern?

A)Mt.Spurr in the Aleutian volcanic arc
B)Mt Fujiyama in the Japanese island arc
C)Mt.Rainier in the Cascades just north of Mt.St.Helens
D)Mauna Loa in Hawaii,on the Big Island of Hawaii near Kilauea

Question 15

Volcano A erupts rocks with SiO2 content ranging from 49% to 52% whereas volcano B,100km away,erupts materials with SiO2 content of 62-68%.Which statement best characterizes these two volcanos?

A)Both volcanos are shield type volcanos that are characterized by quiescent eruptions.
B)Both volcanos are violent,explosive volcanos that spread ash continent wide.
C)Volcano A is likely to be a supervolcano with violent eruptions,whereas volcano B is probably a shield volcano with quiescent eruptions.
D)Volcano A is probably a shield volcano with typically quiescent eruptions,whereas Volcano B is likely a stratovolcano characterized by violent,explosive eruptions.

Question 16

In the movie "Volcano" basaltic lava flows are shown running down flat streets at speeds faster than humans could run.From your knowledge of magma viscosity,is this realistic?

A)Yes,the viscosity of basalt magma is similar to water so it would flow at comparable rates.
B)No,the viscosity of basaltic magma is much higher than water,and thus,would flow much slower than water.
C)No,the viscosity of basaltic magma is much higher than water,and thus,would flow much faster than water.
D)There is no way of knowing because basaltic magmas can have viscosities similar to water or higher depending on temperature and fluids,and thus there isn't enough information.

Question 17

Which of the following is not considered pyroclastic debris?

A)ash
B)cinders
C)bombs
D)pahoehoe

Question 18

Why does magma viscosity vary with silica content?

A)Increasing silica increases a tendency for silica bonds to link up in networks,acting like a polymerization of the magma.
B)Increasing silica content lowers the melting temperature and since increasing the temperature of a magma decreases viscosity increasing silica content increases viscosity.
C)Increasing silica content increases the amount of water a magma can dissolve and water decreases magma viscosity,so increasing silica content decreases magma viscosity.
D)There is no correlation between silica content and magma viscosity.

Question 19

________ are usually the most abundant gases emitted during basaltic volcanism.

A)Chlorine and sodium
B)Neon and ammonia
C)Oxygen and nitrogen
D)Water and carbon dioxide

Question 20

Which type of basaltic lava flow has a fairly smooth,unfragmented,ropy surface?

A)aa
B)pegmatitic
C)pahoehoe
D)scoria

Question 21

The rock pumice often floats yet the density of the rock is greater than water.Why does it float?

A)Pumice is a pyroclastic rock derived from rhyolite glass,and rhyolite glass has a lower density than water.
B)Pumice is a pyroclastic rock comprised largely of open voids formed by gases released when the magma solidified as froth-like material.
C)Pumice is a rock made of rhyolite glass that erupts into water,which traps water in voids and makes the material less dense than water.
D)Pumice is another name for dacite,a low-density rock that floats in water.

Question 22

Which one of the following statements concerning cinder cones is false?

A)They are small volcanoes with fairly steep sides.
B)They are built mostly or entirely during one eruptive cycle.
C)The cinders and other pyroclastic particles are consolidated into welded tuff.
D)The cinders most commonly are basaltic.

Question 23

Mount Pelée on the island of Martinique killed thousands of people in ________.

A)a pyroclastic flow,also called a Nuée Ardent
B)a caldera collapse
C)an ash fall that smothered the people living there
D)a cinder cone eruption

Question 24

Where are the most active volcanoes in the world?

A)Washington State,in the United States
B)Mexico
C)Italy
D)Hawaii

Question 25

The famous destruction of the Roman city of Pompeii was produced by ________.

A)a large cinder cone burying the city in tephra
B)a composite volcano erupted lava that buried the city,fossilizing people who were overridden by the fast moving flows
C)a volcanic mudflow from Mt.Vesuvius that buried the people and the city
D)a pyroclastic eruption from a composite volcano that buried the city in ash and smothered the people living there

Question 26

Shield volcanos form from what type of magma?

A)high viscosity aa basalt magmas
B)low viscosity rhyolite magmas
C)low viscosity basalt magmas
D)high viscosity rhyolite magmas

Question 27

Mount Pelée on Martinique is an example of a ________.

A)shield volcano
B)cinder cone
C)lava dome
D)composite volcano

Question 28

The slopes of most cinder cones are usually about 30 degrees because ________.

A)the loose materials ejected from the cone form slopes at the angle of repose
B)cinder cones are mostly basalt and basalt is too weak to maintain a slope greater than 30 degrees
C)they are composites of loose material and lava and the viscosity of the lava requires the slopes to form at about 30 degrees
D)The statement is false; most cinder cones have slopes less than 10 degrees because of the low viscosity of basalt lava flows.

Question 29

Mt.St.Helens in the U.S.and Mt.Fujiyama in Japan are examples of ________.

A)cinder cones
B)shield volcanos
C)composite volcanos
D)calderas

Question 30

A geologist working in an area finds gravels with gentle dips of about 5 degrees.She finds a large outcrop where these gravels are overlain by tephra with prominent layers that dip 35-40 degrees.What is the history of this area?

A)Basalt flows formed after a series of gravels were deposited,covering the local terrain,and built a shield volcano.
B)After the gravel was deposited,a large composite cone was built on the area.
C)Before the gravel was deposited,a cinder cone formed in this area.
D)After the gravel was deposited,a cinder cone formed in the area.

Question 31

A geologist is working in an area of old volcanic rocks exposed by erosion.He finds a large rock outcrop that contains flat lying gravels in the base of the outcrop.These gravels are overlain by basalt that forms a series of layers representing flows.The uppermost basalt lava flows have a dip of about 10 degrees to the west.What does this outcrop record?

A)Basalt flows formed above a series of gravels,filling a river valley.
B)Basalt flows formed after gravels were deposited,covered the local terrain,and built a shield volcano with dips of about 10 degrees.
C)Gravels were initially deposited in a river valley and a cinder cone was erupted,damming the valley,before a cinder cone formed.
D)You can't tell anything about the history of this region from this outcrop.

Question 32

The average composition of rocks comprising a large composite cone or stratovolcano is similar to a(n)________ magma.

A)basaltic
B)ultramafic
C)andesitic
D)rhyolitic

Question 33

Which of the following volcano types are short lived volcanos that last a few days to months and then shut down?

A)shield volcano
B)cinder cone
C)lava dome
D)composite volcano

Question 34

Cinder cones ________.

A)have very steep slopes
B)are usually less than 300 meters (1000 feet)high
C)consist largely of pyroclastics
D)all of these

Question 35

Pillow lavas are ________.

A)basaltic magmas erupted on the seafloor as magma blobs from an explosive,submarine eruption
B)basaltic lava tubes erupted on the seafloor in volcanic piles analogous to toothpaste extruded from a tube
C)andesitic bombs erupted from a cinder cone that accumulate as pillow-like masses around the cone
D)rhyolite glasses that develop a banding that resembles a pillow case with internal snowflake obsidian that looks like feathers

Question 36

Kilauea is an example of a ________.

A)shield volcano
B)cinder cone
C)lava dome
D)volcanic neck

Question 37

Paricutin is an example of a ________.

A)shield volcano
B)cinder cone
C)lava dome
D)composite volcano

Question 38

A rock outcrop exposes a layer of obsidian overlain by volcanic ash and a layer with fragments of lapilli.What rock composition and eruptive type fits this description?

A)basalt erupted from a cinder cone
B)basalt flows and interbedded andesite deposited on a shield volcano
C)andesite and basalt erupted from a stratovolcano
D)rhyolite erupted in violent pyroclastic eruptions

Question 39

A volcanic deposit comprised of red to black lapilli-sized pyroclastic material associated with pahoehoe lava flows was probably deposited on ________.

A)a large composite volcano
B)a shield volcano
C)a cinder cone
D)a satellite shield volcano on a rhyolitic caldera

Question 40

The steep,upper slopes of composite volcanoes are generally produced by ________.

A)large landslides
B)high-viscosity,low-volume silicic magmas that are erupted from the summit
C)satellite or parasitic cones that push up the top of the volcano to steep slopes
D)tilting of the summit by intrusion of high-viscosity magma directly below the summit

Question 41

Mount Pelee on the Island of Martinique erupted in the early 20th century.Why is this eruption famous?

A)It was the first caldera forming eruption observed by modern scientists.
B)It produced a major lateral blast that leveled a city,killing many people.
C)It was a small cinder cone on an island that erupted in a sugar cane field.
D)The volcano produced a pyroclastic flow that swept down the mountain,killing thousands of people.

Question 42

Which of the following is not an accurate statement about the melting process in the earth's interior?

A)Melting of rocks is incomplete with partial melts extracted as magma and solid residues left behind.
B)Water dramatically lowers the melting temperature of silicate rocks,and addition of water commonly contributes to production of magma.
C)Upwelling flow in the earth's interior brings higher temperature rocks toward the surface and contributes to decompression melting.
D)The earth's lower mantle is entirely molten and heat from this zone produces partial melting in the upper mantle,which produces the diverse volcanic rocks we see at the earth's surface.

Question 43

A ________ is an intrusive,igneous rock body that is tabular and concordant.

A)laccolith
B)dike
C)pluton
D)sill

Question 44

Pyroclastic flows move ________.

A)very rapidly,too fast to outrun on foot
B)as gravity flows similar to snow avalanches
C)as a dense cloud that contains hot magma particles suspended in hot gases and moves rapidly downhill
D)all of the above
E)none of the above

Question 45

Which of the following is emplaced over millions of years to form a composite intrusive complex?

A)dike
B)sill
C)laccolith
D)batholith

Question 46

A ________ is the largest discordant body of intrusive,igneous rock.

A)lopolith
B)laccolith
C)pluton
D)batholith

Question 47

The Columbia Plateau in the northwestern United States is an excellent example of ________.

A)silica-rich lava flows
B)pyroclastic flow deposits
C)flood basalts
D)an eroded shield volcano

Question 48

Which of the following is a tabular intrusive body with subparallel intrusive contacts?

A)dike
B)laccolith
C)stock
D)columnar joints

Question 49

The largest percentage of total magma production on earth occurs at what plate tectonic setting?

A)hot spots like Hawaii
B)convergent plate margins
C)transform plate margins
D)spreading ridges

Question 50

Which of the following best describes Shiprock,a famous volcanic feature in New Mexico?

A)a very recently active,basaltic cinder cone
B)an extinct,highly symmetrical,composite volcanic cone
C)the eroded remains of a volcanic pipe and radiating dikes
D)an extinct,massive,rhyolitic shield volcano

Question 51

What volcanic events formed Crater Lake,Oregon? When did they take place?

A)A powerful explosion blew away the top of a stratovolcano 10 million years ago.
B)The crater of a large,extinct cinder cone filled with water 5 million years ago.
C)Landslides and volcanic mudflows dammed the Mazama River 500 years ago.
D)Caldera collapse followed major ash and pyroclastic-flow eruptions 6000 years ago.

Question 52

Mt.Rainier in Washington State is often thought to be the most hazardous volcano in the lower 48 states of the United States because ________.

A)it is close enough to Seattle and Tacoma,Washington that these cities could be destroyed in a pyroclastic flow
B)the volcano is close enough to Seattle and Tacoma,Washington that a large explosive eruption could bury the cities in a large rock avalanche similar to the Mt.St.Helens eruption
C)large amounts of glacial ice on the mountain could be melted by even a small eruption,potentially generating dangerous lahars that would travel rapidly down river valleys to heavily populated areas
D)The statement is false; the volcano poses little hazard to humans except for the few who live close to the volcano.

Question 53

Which of the following best describes melting of the mantle at subduction zones that leads to island arc volcanos?

A)Heat is carried downward with the subducting plate and melts the mantle above the downgoing plate.
B)Water released from the subducting plate decreases the melting temperature in the mantle above the downgoing plate to generate magmas from the overlying mantle wedge.
C)The subducting plate is heated as it is carried to depth and the subducted oceanic crust melts.
D)The subducted plate subsides into the mantle and allows magma from the lower mantle magma ocean to rise toward the surface.

Question 54

A ________ is a near surface,intrusive igneous rock body that results from local inflation of a horizontal sill.

A)batholith
B)dike
C)laccolith
D)volcanic neck

Question 55

Calderas range in size from less than 1km to tens of kilometers across.What do they all have in common?

A)They all form by subsidence of the caldera center due to withdrawal of magma from below.
B)They all form in explosive eruptions.
C)They all are formed in rhyolitic volcanos and have associated eruptions of ash flow tuff.
D)They all form from collapse of composite volcanos following explosive eruptions; Crater lake is an example.

Question 56

Most of the active volcanoes on land are located in a belt known as the ________.

A)Ring of Fire
B)Gulf Coast zone
C)Mid-Pacific Ridge
D)Red Sea rift

Question 57

The greatest danger from pyroclastic flows is ________.

A)being incinerated by the hot gas and entrained magma.
B)being smothered by hot gases and ash.
C)being buried in ash.
D)not significant because they move so slowly they can be avoided.

Question 58

Which of the following is not a significant volcanic hazard?

A)injury or death by inhalation of air heavily laden with volcanic ash
B)being overrun by a fast moving basaltic lava flow
C)being caught in a river valley and being overcome by a volcanic mudflow/lahar
D)a tsunami generated by a massive submarine volcanic eruption

Question 59

Which of the following best describes the bedrock in the Sierra Nevada Mountains in California?

A)basalt; dikes
B)gabbro; plutoliths
C)andesite; laccoliths
D)granite; batholiths

Question 60

What type of volcano would be most likely to generate large landslides?

A)shield volcano
B)cinder cone
C)composite volcano
D)caldera

Question 61

In what plate tectonic setting are magmas generated predominantly by fluids fluxing the melting process by decreasing melting temperature?

A)hot spots
B)spreading ridges
C)transform faults
D)convergent plate margins

Question 62

A basaltic volcano is likely to produce an explosive column that would endanger flying aircraft.

Question 63

When magma rises toward the surface,pressure decreases can lead to release of dissolved gases in a magma with a volume increase that can produce an explosion.

Question 64

large,fairly steep-sided cones composed of lavas and pyroclastic layers

Question 65

The higher the viscosity of a magma,the lower the potential for explosive eruptions.

Question 66

the volcanoes of southwestern Alaska and the Aleutian Islands

Question 67

Which type of plate margin is characterized by volcanos that include basalt,andesite,dacite and rhyolite?

A)hot spots
B)spreading ridges
C)transform faults
D)convergent plate margins

Question 68

The recent (geologically)volcanic activity in Yellowstone National Park is ________.

A)related to plate subduction
B)related to a divergent plate boundary
C)related to a transform plate boundary
D)related to intraplate,hot spot volcanism

Question 69

Ash and lapilli are different sized pyroclastic particles.

Question 70

massive,gently sloping volcanoes built of successive,basaltic lava flows

Question 71

The eruptions of the Hawaiian volcanoes may be described as explosive in comparison to the 1980 Mount St.Helens eruption.

Question 72

pahoehoe aa volcanic bomb pillow lava

Question 73

Mt.Vesuvius Mt.Mazama Mount Pelée Kilauea

Question 74

Powerful,explosive,volcanic eruptions can result in climatic cooling for millions of years following the eruption.

Question 75

Most granitic batholiths are generated ________.

A)as intrusions beneath composite volcanos along convergent plate margins
B)where spreading ridges occur beneath continents
C)along transform faults,which accounts for their linear geographic distribution
D)along hot spot chains beneath continents,like a welder cutting through the continent to make a linear belt of intrusive granites

Question 76

Which of the following statements best describes the big Hawaiian volcanoes?

A)They lie directly above a transform plate boundary that cuts deeply into the mantle.
B)They lie directly above an active subduction zone where the Pacific plate is sinking into the mantle.
C)They lie along the crest of the East Pacific Rise,a mid-ocean ridge or spreading center.
D)They are situated in the interior of a large,Pacific plate above a hot spot deep in the mantle.

Question 77

Dissolved gases may comprise up to a few percent by weight of a magma.

Question 78

The viscosities of magmas increase with increasing percentages of silica.

Question 79

-the big volcanoes of Hawaii

Question 80

small basaltic cones built during one short,eruptive episode