Mount St. Helens Eruption and Volcanic Hazards

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) On May 18, 1980, which Cascades volcano blew its top with the largest eruption in North America in recorded history? A) Mt. Shasta, CA B) Kilauea, HI C) Mt. Rainier, WA D) Mt. Garibaldi, B.C. E) Mt. St. Helens, WA 1) 2) Which statement about the May, 1980, eruption of Mount St. Helens is false? A) the initial and most powerful explosive event was preceded by a massive landslide B) mudflows (lahars) accompanied the major eruptive events going 10's of kilometres C) during the eruptive period, the mountain peak was substantially built up by new lava flows and pyroclastic debris D) plumes of ash rose high into the stratosphere during the major eruptive events 2) 3) What was the approximate volume of rock and ash ejected by the last violent eruption of Mt. St. Helens? A) 1 km3 B) 400 m3 C) 18,000 km3 D) 400 km3 3) 4) What was the maximum distance travelled by erupted materials from the last major eruption of Mt. St. Helens? A) 18,000 m into the Stratosphere B) 400 m down the flank of the volcano C) 29 km down the Toutle River D) around the world for several days E) approximately 1200 km into Alberta and Montana 4) 5) What is the largest immediate volcanic threat to human life and property? A) incandescent lava fountains and lava flows like at Kilauea since 1983 B) proximity on the ground to explosive eruptions like Mt. St. Helens, Pinatubo, and Nevado de Ruiz C) stratospheric ash clouds that pose a hazard to international airline travel D) being encased in plaster like the former victims of Pompeii E) phreatic steam eruptions that melt everything within the cloud 5) 6) Approximately how long has B.C.'s Mt. Garibaldi, in the Canadian part of the Cascades volcanoes, been dormant? A) since the last Ice Age B) since May 1980 C) since 1912 D) since 1967 6) 7) What is the direct control on whether a volcano will erupt violently or quietly send out a few flows? A) the population density B) the duration of the quiet interval since its last violent eruption C) the composition of the magma, its temperature, and dissolved gas content D) what the total volume of the volcano has at the time of eruption 7) 8) Which two factors tend to increase the explosive potential of a magma body beneath a volcano? A) low viscosity; low dissolved gas content B) high viscosity and dissolved gas C) high viscosity; low dissolved gas content D) low silica content, low viscosity 8) 9) In general, which of the following types of magma will be more likely to erupt explosively? A) a very fluid komatiitic magma B) a highly viscous felsic magma C) a relatively low viscosity mafic magma D) an intermediate andesitic magma with a low water content 9) 10) Which one of the following shows the correct order (left to right) of decreasing magma viscosity? A) mafic, andesitic, felsic B) felsic, andesitic, mafic C) mafic, felsic, andesitic D) andesitic, felsic, mafic 10) 11) Other than Mt. St. Helens, which of the Cascades volcanoes are currently considered to pose the greatest risk for explosive eruptions? A) Mt. Cayley, Mt. Meager, Mt. Garibaldi, and Salal B) Mt. Adams, Crater Lake, Mt. Jefferson, and Three Sisters C) Glacier Peak, Goat Rocks, Newberry, and Medicine Lake D) Mt. Baker, Mt, Ranier, Mt. Hood, Mt. Shasta, and Mt. Lassen 11) 12) Which magma association with the volcanic landform is least likely or incorrect. A) composite cones - andesitic B) volcanic plateaus and shields - felsic C) glassy volcanic domes - felsic D) cinder cones - mafic 12) 13) At the same temperature, why are magmas with high silica contents more viscous? A) Because high viscosity magma will flow more readily and rhyolites flow the farthest. B) They are more linked together in chains and nets that are strong enough to resist flow. C) The magmas with high silica content are also richer in iron and too dense to flow. D) Any magma with more than 50% silica content is too sticky to flow. 13) 14) Which one of the following statements is not true? A) Melting temperatures of silicate rocks are lowered by small amounts of water. B) When magma reaches the surface, its dissolved gas content increases. C) Melting temperatures of silicate rocks increase with increased pressure. D) Mafic magmas in general have higher temperatures than felsic magmas. 14) 15) What drives explosive volcanic eruptions? A) andesitic magma's extremely low viscosity B) high pressures from the melting region far beneath the volcano C) expanding superheated volcanic gases D) collapsing eruption columns 15) 16) ________ is a major dissolved volatile constituent in both magmas and volcanic gases. A) water B) methane C) hydrogen chloride D) carbon monoxide 16) 17) What kind of material is most commonly added to the landscape in explosive volcanic eruptions. A) pyroclastics, ash, bombs, and broken rock B) thin fluid mafic flows that can travel 10's of kilometers C) volcanic gases and fumarolic deposits D) volcanic plugs that form inside craters 17) 18) Volcanic bombs originate ________. A) as blocks of volcanic rock ejected from an erupting volcanic crater B) as laser-guided, granite blocks launched from a supersonic jet 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 18) 19) How fast do hot fluid basalt flows typically advance? A) > 30 km/hour B) 10 to 300 m/hour C) > 100 m/second D) < 5 m/hour 19) 20) What are the two varieties of basaltic lava flows? A) bombs, blocks C) aa, pahoehoe 20) B) cinders, pumice D) tuff, breccia 21) Which type of mafic lava flow has a fairly smooth, flow folded, ropy surface? A) pahoehoe B) block and ash flow C) scoria D) aa 21) 22) Which type of mafic flow has a rough, jagged, clinkery surface and advances slowly at speeds less than 50 m/hour? A) pahoehoe B) aa C) block and ash flow D) scoria 22) 23) Which of the following is a major dissolved volatile constituent in both magmas and volcanic gases? A) methane B) carbon monoxide C) hydrogen chloride D) water 23) 24) Which are usually the most abundant gases emitted during mafic volcanism? A) chlorine and sodium B) water and carbon dioxide C) oxygen and nitrogen D) neon and ammonia 24) 25) Which statement is most correct concerning volcanic effects on our atmosphere. A) Pollution of the atmosphere by sulfur compounds contributes significantly to acid rain. B) If it were not for active volcanism there would be no free oxygen in the atmosphere. C) Gases from volcanoes condense to make natural fertilizer, boosting plant growth. D) Active volcanism is responsible for maintaining atmospheric levels of nitrogen. 25) 26) How are volcanic conduits formed? A) the vent is kept clear by continuous eruption and the walls are formed by deposits B) by injecting molten magma up through the volcano to clear a path C) by superheated gases melting a pipe through the older rocks of the volcano D) by erosion from hot gases that carry hard abrasive rocks and ash upwards 26) 27) Volcanic lapilli are particles ________. A) angular rock fragments larger than 64 mm B) of fused flattened silica rich glass shards and stretched out gas bubbles C) also called cinders, the size of small stones, 2 to 64 mm across D) of incandescent lava that attain aerodynamic shapes and weigh up to 200 tons 27) 28) How do volcanic bombs originate? A) as semi-molten magma blobs that get erupted, streamlined, and partly congeal before falling to the ground B) as ash particles that join together in the eruptive plume and fall as cobble-sized objects C) as high temperature residue violently expelled from the melting region, all the way up the volcanic conduit D) as blocks of old shattered volcanic rock ejected from an erupting volcanic crater 28) 29) 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 ejected as magma lumps; blocks are ejected as solid fragments C) bombs and blocks are both smaller than lapilli and cinders D) bombs are guided to Earth by laser beams; blocks fall anywhere 29) 30) Oxidized, reddish, vesicle rich, mafic lapilli that pile up to form cinder cones are called ________. A) scoria B) pumice C) bombs D) blocks 30) 31) What destroyed the city of St. Pierre, Martinique in 1902? A) mafic lava flows B) heavy ashfall C) mudflows D) a nuée ardente 31) 32) What volcanic environment generated both Mt. Pelee and Montserrat? A) the Italian flood basalt province B) the Andes arc C) the Mid- Atlantic Ridge D) the Lesser Antilles arc 32) 33) How far can nueés ardentes travel from their source vents? A) > 100 km B) < 1 km C) > 1000 km 33) D) up to 10 km 34) Which one of the following is built predominantly of pyroclastic materials? A) rhyolite dome B) fissure-related flood basalts C) composite cone or stratovolcano D) basaltic shield volcano 34) 35) Which volcano is a very large, gently sloping mound composed mainly of mafic lava flows? A) cinder cone B) stratospheric C) shield D) composite cone 35) 36) What are massive, gently sloping volcanoes built of successive, mafic lava flows? A) stratospheric B) composite cones C) shield D) cinder cones 36) 37) What volcanoes dominate in the Galapagos, Iceland, and Kenya? A) cinder cones B) shield C) composite cone 37) D) stratospheric 38) Kilauea and Mauna Loa are what kind of volcanoes? A) explosive, rhyolitic volcanoes B) andesitic composite cones C) small, basaltic cinder cones D) basaltic shield volcanoes 38) 39) What is the largest, known volcano in the Solar System? A) Mauna Kea, southern hemisphere, Mars B) Mount Olympus, Greece, Earth C) Mauna Loa, Hawaii, Earth D) Olympus Mons, Mars 39) 40) What volcanoes have the highest elevations? A) stratospheric C) composite cones 40) B) cinder cones D) shield 41) What are small basaltic cones built during one, short, eruptive episode? A) composite cones B) stratospheric C) shield volcanoes D) cinder cones 41) 42) Which of the following statements concerning cinder cones is false? A) They are small volcanoes with fairly steep sides but large central craters. B) The cinders most commonly are basaltic. C) They are built mostly or entirely during one eruptive cycle. D) The cinders and other pyroclastic particles are consolidated into welded tuff. E) They are often asymmetric with the higher rim in the downwind direction. 42) 43) How quickly are volcanoes like Paricutin in Mexico; Sunset Crater in Arizona, or Nazco Cone in central B.C. built? A) in a single eruptive cycle lasting about a year or more B) in several eruptive cycles over 10's of thousands of years C) in a single eruption within a few days D) in a single eruption within a few hours 43) 44) The 1943-44 eruption of Paricutin in Mexico was characterized by which one of the following sets of volcanic phenomena? A) welded-tuff deposition; caldera formation B) mudflows; explosive ash eruptions C) pyroclastic eruptions; nuée ardente flows D) cinder cone building; mafic aa lava 44) 45) Which kind of eruptive activity is most likely to be highly explosive? A) eruptions of big, continental margin, composite cones B) fissure eruptions feeding lava to flood basalt accumulations C) lava flows from a large shield volcano on an oceanic island 45) 46) What are large, fairly steep-sided cones composed of lavas and pyroclastic layers? A) stratospheric B) shield C) cinder cones D) composite cones 46) 47) What type are the volcanoes of the Cascades and Alaska's Aleutian Islands? A) composite cones B) stratospheric C) cinder cones D) shield 47) 48) What kind of volcano is Mount St. Helens? A) a basaltic cinder cone C) a small, welded tuff cone 48) B) an explosive composite cone D) a basaltic shield volcano SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. For the following items, please choose from one of the following answers. A. shield volcanoes B. composite/stratovolcanoes C. cinder cones 49) ________ massive, gently sloping volcanoes built of successive, basaltic lava flows 49) 50) ________ large, fairly steep-sided cones composed of lavas and pyroclastic layers 50) 51) ________ small basaltic cones built during one, short, eruptive episode 51) 52) ________ the volcanoes of southwestern Alaska and the Aleutian Islands 52) 53) ________ the big volcanoes of Hawaii 53) MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 54) The average composition of rocks composing a large composite cone is similar to which magma? A) felsic B) mafic C) andesitic D) ultramafic 54) 55) Gas rich andesitic magmas generate composite cones made up of ________. A) abundant basalt dykes and thick accumulations of low viscosity flows B) conical shaped lava flows C) multiple overlapping rhyolite domes rimming a central caldera D) abundant coarse pyroclastics and short, thick, viscous lava flows 55) 56) Which correctly describes the size and thickness variation in pyroclastics relative to the composite cone they came from? A) size increases and the deposits get thicker away from the vent B) size and thickness both decrease uniformly away from the central vent C) size increases then decreases with distance but deposits are the same thickness D) size decreases but deposits thicken downslope then thin with distance 56) 57) What natural disaster contributed to the disappearance of the Minoan civilization and gave rise to the legend of "The Lost Island of Atlantis" mentioned in Plato's writings? A) it washed away in a giant tsunami about 79 A.D. B) it was buried by thick ash deposits from Mt. Vesuvius in 79 B.C. C) it was obliterated by volcanic dust storms from North Africa in the sixth century A.D. D) it was buried by thick ash deposits from the volcanic eruption of Santorini about 1600 B.C. and sank as the caldera beneath the island collapsed. 57) 58) Which one of the following best describes volcanism in the Cascade Range of northern California through Washington and its northerly extension as the Garibaldi Belt in SW B.C.? A) related to a mid-ocean ridge system B) related to a mantle plume C) related to deep, transform faults D) related to plate subduction 58) 59) Which best describes a caldera? A) a large depression hundreds of km across full of volcanic deposits B) a collapse pit less than 1 km2 on the summit of a volcano 59) C) a small, steep- sided, volcanic depression bored out by an eruptive plume D) a large circular volcanic depression caused by collapse after a large scale, explosive felsic eruption 60) What volcanic events formed Crater Lake, OR? When did they take place? A) the crater of a large, extinct cinder cone filled with water; 5 million years ago B) caldera collapse followed major ash and pyrodastic-flow eruptions; 7000 years ago C) landslides and volcanic mudflows dammed the Mazama River; 500 years ago D) a powerful explosion blew away the top of a composite cone; 10 million years ago 60) 61) How was Crater Lake, Oregon formed? A) as a remnant of the 'great flood' B) caldera collapse of the top of Mt. Mazama after the eruption 7000 years ago partly emptied the magma chamber C) when sea floor spreading permitted seawater to flood into the newly formed volcanic rift D) a prehistoric eruption of Mt. St. Helens 61) 62) The greatest rate of volcanism and largest accumulations of volcanic deposits are associated with ________. A) rhyolitic lava domes B) ash clouds dispersed in the stratosphere C) giant cinder cones D) flood basalts from fissure eruptions 62) 63) The Columbia Plateau in Washington and Oregon is what type of volcanic feature? A) flood basalt plateau B) a thick stack of welded- luff layers C) a field of large composite cones D) a caldera filled with rhyolite lava flows 63) 64) Which of the following best describes Shiprock, a famous volcanic feature in New Mexico which is sacred to the Navaho? A) a very recently active, basaltic cinder cone B) an extinct, massive, rhyolitic shield volcano C) an extinct, highly symmetrical, composite cone D) an erosionally resistant volcanic neck, remains of a volcanic pipe and radiating dykes 64) 65) Tabular sills and lava flows often have regular geometric grids of vertically oriented, thermal shrinkage cracks called ________. A) honeycomb fractures B) columnar joints C) hot flashes D) arthritic joints 65) 66) Which of the following best describes the composition and form of the typical felsic bedrock in the Coast Ranges of BC or the Sierra Nevada Mountains in California? A) andesite; laccoliths B) granite; batholiths C) basalt; dykes D) gabbro; bysmaliths 66) 67) A ________ is the largest, discordant body of intrusive, igneous rock. A) batholith B) pluton C) laccolith D) lopolith 67) 68) A ________ is an intrusive, igneous rock body that is tabular and concordant. A) sill B) dike C) pluton D) laccolith 68) 69) A ________ is a near surface, intrusive, igneous rock body that results from local inflation of a horizontal sill. A) batholith B) volcanic neck C) dike D) laccolith 69) 70) Xenoliths are likely to be associated with which magmatic process and igneous rock body? A) magmatic differentiation; gabbro sill B) intrusion; granitic batholith C) columnar jointing; lava flow D) flattening; welded ash flow tuffs 70) 71) Which region has the greatest concentration of currently active volcanoes? A) coastal plain of west Africa B) Pacific "Ring of Fire" C) Red Sea area D) Siberia 71) 72) How are the Icelandic volcanoes related to plate tectonics? A) They lie on a subduction zone where two plates are converging. B) They lie on a spreading centre where two plates are converging. C) They lie along a subduction zone where two plates are diverging. D) They lie on a spreading centre where two plates are moving apart. 72) 73) What is the most abundant type of magma erupted at oceanic spreading centres? A) felsic B) mafic C) andesitic D) pyroclastic 73) 74) Which kind of volcanism is typical of mid-ocean ridge systems? A) explosive; felsic, pyroclastic flows B) submarine; mafic lava flows C) subversive fissure eruptions and flood basalts D) explosive; composite cones 74) 75) Which of the following best describes seamounts and islands of the deep ocean basins? A) andesitic pyroclastic rocks submerged when the mountains sank below sea level B) huge granite batholiths intruded beneath the ocean floor C) piles of basaltic lava flows built up from the ocean floor by multiple, summit and flank eruptions D) domed gabbro intrusions and massive, submarine, rhyolitic, pyroclastic cones 75) 76) What is the dominant lava type erupted along mid-ocean ridges? A) mafic B) ultramafic C) felsic 76) D) andesitic 77) Which statement best describes the big Hawaiian volcanoes? A) lie directly above an active subduction zone where the Pacific plate is sinking into the mantle B) lie along the crest of the East Pacific Rise, a mid-ocean ridge or spreading centre C) lie directly above a transform plate boundary that cuts deeply into the mantle D) are situated in the interior of a large, Pacific plate above a mantle plume deep in the mantle 77) 78) What is the correct environment for the geologically recent, volcanic activity in the Yellowstone National Park area? A) related to plate subduction B) intraplate, mantle plume volcanism C) related to a transform plate boundary D) related to divergent plate boundary 78) 79) Which of the following is associated with deep mantle plumes? A) the very young cinder cones scattered across the southwestern United States B) the volcanoes of Hawaii and the Quaternary activity in Yellowstone National Park C) Mt. St. Helens and other volcanoes of the Cascade Mountains D) Vesuvius and the other volcanoes of Italy 79) 80) The recent (geologically) volcanic activity in Yellowstone National Park is ________. A) related to a divergent plate boundary B) related to plate subduction C) related to intraplate, mantle plume volcanism D) related to a transform plate boundary 80) TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. 81) The eruptions of the Hawaiian volcanoes may be described as explosive in comparison to the 1980 Mount St. Helens eruption. 81) 82) A magma's viscosity and tendency ncy to cause explosive eruptions depends on its composition, temperature and volatile gas content. 82) 83) Basaltic lavas are generally hotter and more viscous than andesitic lavas. 83) 84) In general, mafic magmas are more likely than andesitic to erupt explosively. 84) 85) Mafic magma is more likely to erupt explosively and form pyroclastic deposits than felsic or andesitic magma. 85) 86) The viscosities of magmas increase with increasing percentages of silica. 86) 87) Basaltic volcanoes like Kilauea are typically the most explosive. 87) 88) Aa flows are generally thinner, faster moving and have smoother surfaces than pahoehoe flows. 88) 89) When the molten lava drains away from beneath the hardened surface of a flow it leaves open tunnels called lava tubes. 89) 90) Dissolved gases may compose up to a few percent by weight of a magma. 90) 91) Water and carbon dioxide are the most abundant gases emitted from the mafic magmas of the Hawaiian volcanoes. 91) 92) Powerful, explosive, volcanic eruptions can result in climatic cooling for millions of years following the eruption. 92) 93) Ash and lapilli are different sized pyroclastic particles, smaller and larger than 2 mm respectively. 93) 94) Volcanic bombs are explosive and detonate on impact. 94) 95) A nuee ardente is generated by an erupting basaltic lava fountain. 95) 96) Vents that emit only heated, volcanic gases and water are called fumaroles. 96) 97) In general, cinder cones are much larger than shield volcanoes. 97) 98) Basaltic shield volcanoes comprise the mountains of the Cascade Range. 98) 99) Gas rich andesitic magmas generate composite cones. 99) 100) Most composite cones have a simple eruptive history dominated by one or two events. 100) 101) The shape of Mt. St. Helens after the 1980 eruption was due to a landslide that triggered a lateral blast and an asymmetric eruption. 101) 102) Of the more than 50 volcanoes that have erupted in North America in the past 200 years, most are located in the Alaskan Aleutian Islands. 102) 103) Crater Lake in Oregon actually occupies a caldera, not a crater. 103) 104) Repeated eruptions of relatively fluid lava from fissures (Columbia River Plateau, Deccan Traps) can eventually cause an area to be covered by flood basalts. 104) 105) Domes form from high viscosity felsic magma slowly erupted into a volcanic crater. 105) 106) A volcanic neck is a solidified plug of magma extruded slowly above the rim of the crater. 106) 107) Basalt is the most common magma erupted along oceanic rift systems. 107) 108) The active Hawaiian volcanoes are situated directly above a major boundary between two of the Earth's largest tectonic plates. 108) 109) The partial melting of peridotite in the mantle generates mafic magmas. 109) 110) Magma generation at depth almost always involves partial melting, not complete melting of the source rock. 110) Answer Key 1) E 2) C 3) A 4) D 5) B 6) A 7) C 8) B 9) B 10) B 11) D 12) B 13) B 14) B 15) C 16) A 17) A 18) C 19) B 20) C 21) A 22) B 23) D 24) B 25) A 26) D 27) C 28) A 29) B 30) A 31) D 32) D 33) A 34) C 35) C 36) C 37) C 38) D 39) D 40) C 41) D 42) D 43) A 44) D 45) A 46) D 47) A 48) B 49) A 50) B 51) C 52) B 53) A 54) C 55) D 56) B 57) D 58) D 59) D 60) B 61) B 62) D 63) A 64) D 65) B 66) B 67) A 68) A 69) D 70) B 71) B 72) D 73) B 74) B 75) C 76) A 77) D 78) B 79) B 80) C 81) FALSE 82) TRUE 83) FALSE 84) FALSE 85) FALSE 86) TRUE 87) FALSE 88) FALSE 89) TRUE 90) TRUE 91) TRUE 92) FALSE 93) TRUE 94) FALSE 95) FALSE 96) TRUE 97) FALSE 98) FALSE 99) TRUE 100) FALSE 101) 102) 103) 104) 105) 106) 107) 108) 109) 110) TRUE TRUE TRUE TRUE TRUE FALSE TRUE FALSE TRUE TRUE