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Transcript
An earthquake occurs in city A. Recordings on a seismograph in city B show only the presence of P-waves. City A and B are on opposite sides of Earth-180' apart. What does this information allow you to infer about the structure of Earth's interior? How does the composition of the oceanic crust compare with the composition of the continen- tal crust? (1) The oceanic crust is mainly limestone, while the continental crust is mainly sandstone. (2) The oceanic crust is mainly limestone, while the continental crust is mainly granitic. (3) The oceanic crust is mainly basaltic, while the continental crust is mainly sandstone. (4) The oceanic crust is mainly basaltic, while the continental crust is mainly granitic. 37. As one travels from an ocean shore to the interior of a continent, the thickness of Earth's crust generally 1 2 The overall density of Earth is approximately 5.5 9/cm3. The average density of Earth's crust is between 2.5 gy'cmtand 3.0 g/cm3. What does this suggest about the density of Earth's core? The composition of some meteorites supports the inference that Eartht core is composed of (1) aluminum and calcium (2) iron and nickel (3) silicon and oxygen (4) magnesium and potassium 41. The temperature of rock located 1000 kilometers below Earth's surface is approximately 1 2 00 3 decreases increases remains the same How does thickness and density of the continental crust compare to that of the oceanic crust? (1) The continental crust is thicker and less dense than the oceanic crust. (2) The continental crust is thicker and denser than the oceanic crust. (3) The continental crust is thinner and less dense than the oceanic crust. (4) The continental crust is thinner and denser than the oceanic crust. 1000° C 2600° C 3300° C 4300° C Plate tbctonics People have always wondered about the origin of continents, mountain ranges, volcanoes, earthquakes, and the multitudes of other features and events. In the past, many legends, religious beliefs, and scientific theories have tried to explain Earth's features and events. Sone of the older Start Here scientific theories include cooling and contraction of Earth, expansion of Earth, and continental drift. None of these earlier theories seems satisfactory for most of the scientific community today. Since the 1960s many new discoveries from the studies of ocean drilling, Earth's magnetism, satellite observations, and detailed analysis of rocks and fossils have led to the plate tectonic theory. This theory has done for the earth sciences what evolution and genetics have done for the biological sciences. It has provided a unifying model to explain most, if not all, major features and events of Earth's lithosphere. The Plate Tectonic Theory The basic concept of the plate tectonic theory is that Earth's lithosphere is broken up into sections or pieces called plates-also called lithospheri< plates and tectonic plates-and their movement and interaction produce major changes in Earth's surface. ln this book the term "plates" will mostly be used. These plates move about Earth's surface at a rate of a few centimeters per year (approximately the rate of fingemail growth). These plates can also move up and down-usually at rates of only millimeters per year--due to uplifting and sinking. The plates can move around and up and down because they are floating on the asthenosphere-a plastic-like layer of the mantle' Topic 12: Earths Dynamic crust and lnterior 259 Refer to Figure 12-12 and the Tectonic Plates rnap in the Earth Science familiar with the names and locations of the various plates. You will observe that the plates usually don't follow continent or ocean boundaries. Note that the North Arnerican plate includes parts of Asia and North America; the Pacific, Arctic, and the Atlantic Oceans; and Greenland and part of Iceland. Westernmost Reference Tables to become ‐ ■shOull be understOod that l ‐ lthe contiⅢ ents dOnt d“ ‐ ft or m●ve on their o嘲 叫 they move as ther assoclated PlateS move.Contine,鑢 : dnft was a term used before‐ 。mm● │“ e口 ance● ‐ 口ate │こ tectonic theOry ConthF由 : i drtt means the continents lbythemselves att m"ng llrOund Eartht so:u sttrface F● ●re 12‐ 12 and訥 IInfered 詢 輛 On of Farthヽ Lndmmes l鰈 棚 Mヽ 世 show that the continents @ Califomia and Mexico are part of the Pacific plate. Most plates have continental and oceanic crust at their tops. A small number of plates are oceanic-that is, they have only oceanic crust at their tops, like the Nazca and Philippine plates. At least three times, if not more, most of the large landmasses (continents and larger islands) have come together, forming supercontinents. Figure L2-12 shows how the supercontinent Rodinia formed approximately million years ago and how the continents have split and formed since then. Note that diagrams G and H indicate the projected positions of landmasses in the future, based on the rates and directions the plates are moving in now. 800 The Three Types of Plate Boundaries As the plates move, they interact in three ways-they can separate, collide, and slide by each other. Most of the major events involving Earth's crustsuch as mountain building, earthquakes, and volcanic eruptions-occur at the boundaries where the plates interact. Each of the three types of plate boundaries has its own set of unique events and features, which are illustrated in Figure 12-13. Divergent Plate Boundaries Where two plates separate, or diverge, the boundary is called a divergent plate boundary. At these locations the plates move apart and magma rises from below to fill in the separation, resulting in igneous intrusions and extrusions, such as lava flows and volcanoes. (See Figure 12-138.) This divergence is sometimes called sea-floor spreading. This magma and resulting lava form igneous rock that creates new crust and lithosphere, which are then split and divided in two by the divergence. The rnagma that forms in these regions is the result of divergence that lowers the confining pressure and melts rocks of the lower lithosphere and asthenosphere. The divergence also results in rnany earthquakes, most of which are shallow in depth. If the divergence is within the continental crust, the result is a continental rift valley of mountains created by faulting and much volcanic activity. (See Figure 12-13A.) When the divergence is within oceanic crust, the faulting and volcanic activity result in a mid-ocean ridge, a mountain range at the bottom of the ocean that is composed mostly of volcanoes and lava flows. The mid-ocean ridges often have a central depression, or rift valley, as shown in Figure 12-138. Convergent Plate Boundaries When two plates collide, or converge, the result is a convelgent plate boundary. Much of the dramatic events and features of Earth's crust are created at these convergent boundaries. There are three varieties of convergent plate boundaries: o both plates with 260 fopic 12: Earth's Dynamic Crust and lnterior oceanic crust on top Earth around 70o millibnt years ago as superontlnont Rodlnl6 br.aking up, it Eanh around 550 million year after the brlak up ot a 5upercontlnont. Earth arcund 135 millions yeart ago a5 Pangea continues Earth around 250 million y€ar! ago when 3uper@ntinent Pangsa is iust beginning to break up. to breal up. Earth arcund 10o million yea6 ago with furthcr br€ak up Earth at prtsent of Pangoa, Earth 100 mlllion years in future uring prefenlday plate motions ar a guide. l{ote bigger Atlantic Ocean and how Africa hae split and collld€d with Eu.ope. Using present-day plat€ motionr as a gulde, ln apprcximately million years, Ea.th may be clore to .nother 251, sup€nco lnent Flgur. 12.12. change3 ln pogltlons of Errth! landma$€r trom t(x, mllllon yea6 ago to 250 million yarrt into the frnura be<auie of plate t€ctonlct ' Topic t2: Earths Dynamic Crust and lnterior 261 Key B I I E I n r Sediments and sedimentary Stripes of ocean crust with normal and reversed polarity Asthenosphere Oceanic crust Continental crust Lithosphere Earthquake foci --.- Convection currents @ Figure 12.t3. lyp€s of plate boundaries: (A) Diverging plate boundarie5 Regional metamorphism in the (ontinental crust r€sult in a rift valley. Diverging plate boundades in the ocean result in a mid.ocean ridgb, shallow-depth earthquak€r, igneoui intrusions, extrusions ol lava tlows. vol(anoes, and passive margin basins in a down-warped part of crust. Plate 1 is moving weit and plate 2 is moving east. (c) converging Plate boundades reiult in an oceanic trench, vol<ani( iiland ar<s, igneous int.urions, regional metamorphism, young mountains, and subduction ot o(eani< plate, Earthquake lo<i exi5t at various depths. indicating subductions. plate 1 is moving ea5t and plate 2 i5 moving west. (D) Ttansform plate boundaries rerult in many shallow-focus earthquakes and linle to no igneoua activity. Plate 1 is moving north and plate 2 is moving south, (B) 262 toptc tZ. Eanh's Dynamic Crust and tnterior ・ both plates with coninental crust on toP ・ one plate wi■ l oceanic crust and the o■ er with coninental crust on toP Where hvo plates with ocearuc crust or ocea∬ c and conmtalcrustat their edges converge′ the denser ofthe bvO plates siJG underthe other 礎 :雪 :轟 ヤ 露 場 L麓 ち λ 揚協 礎 l器 雪 ∬ 霊ギ 裾 ]鷺 〇 顎 subducuon of One oceanic Plate under anOther resultin ocean trenches and volcanlcisland arcs The bendhg down ofthe subductt Plate warPs the crust′ ProduChg a long′ steeP′ and narrow depression called an ocean trench.Some ofthese trenches are deeper below sea levelthan the hghest mountams are above sea level The subducthg plate also results in inatta bodies.Some of he magコ a breaks through Earth′ s solid surface and forms a seHes of volcanoes and volcttc islands an isiand arc.The subduchng PrOCeSS also results h a large arnount of earttquake acivity followhg礎 slope ofthe subducing plate i■ to the bottom porions Ofthe lithosPhere. Very decP earthquakes only occur wi■ in subducttg zones The heat and PreSSure of the subduchon causes large areas of crustal rocks to become metamorPhoSed h a processで alled″ reJonal metamorphsm.″ IfJhereis a conttt nearthc hvo conver8脚 ng Plates with oceaic crust′ the crust atthe lnargh ofthe continent may become bent down produchg Cean basn thatis the site of much deposi● on of a」 Ш 量 壼 型 亜 。 sedlrnents(See Figure 12‐ 13C)The Sedh℃ nts come from the erodhg island arcs and the edge ofthe conunents.Many ofthe rocks of eastem New York State fo...led h hstype ofdo― warped bash before he fo...laion ofthe superconhnent Pangea Where a plate、 vith oceajc crust on toP conVerges with a Plate With con■ mental crust on toP′ the denser ocett crust subducts under the conhntallithosPhere.An ocean mnch Off he coast ofa conhnt often forlns from this event The inapa thatfo...ls from the subduclon doesn′ t create an island arc because the contmentis above the region ofrnagma fo...lalon.ヽ hatforms instead are relaively new mountam ranges called ∼ young rnountains.Like the Cascadesin westem Oregon and Wattgton/ these mountam ranges may be mostly volcanlc.They may also be a combhalon of volcaruc′ faulted′ and folded When hvo Plates with continё nts at their edges converge′ the hvo plate edges bunch up togethet causttt a great ttickenhg of■ ℃ crust and hmsPhere hs bunctt uP createsthe nghest Ofyoung mountalrts such as the Himalayas′ where lndia is cOШ dhg with Asia Plate convergence that results in the grow■ ■of young lnountain ranges is called org,圏 嘔y The terIIn is also used to hdicate the jコ ne when mountam 麗 :峨 I]げ 潔 鼻 1服 翻 簾 瀧 雹 ぶ 麗 滉 N蒻 況 甥 肝 and you will note the four orogeies(Gren宙 lle′ Tacoruan′ Acadian′ and ① Alleghaian)that have resulted m mountams h New York State and surrounding regions Transform P:ate Boundaries When hvo plates co■ ide by sliding Past each otheル the boundaヮ is called a transform plate boundary.The drag"g of hu10sPheriC rOcks along the edges of the transfo...lbOunda五 es builds up muCh Potential energy in rocks,this energy is eventua■ y released as k旋 uc Topic 12: EarthS Dynamic Crust and lnterior 263 2 million-year- old volcano Present active volcano Plate position at hot spot 2 million years ago / mechanical energy in the form of earthquakes. The San Andreas fault system in Califomia is an example of a transform plate boundary between the North American and Pacific plates. Driving Forces of Plate Tectonics Plate 1 million yea6 ago Rising magma or rock (stays in same lo(ation) 聰憔濡 蜘… Hawaiian lsland5 Necker (1'l million years) (5m‖ ‖on years) Nihau (7 million years) Oahu (3 million years) 30° S m‖ ‖ on years) Hot spot today on Hawaii FIillrt ll-L. Fot 3pots, ri3ing mrgmr, tnd pl.te is believed that dsing magma from the mantle m€lt5 through the plates of the lit'toiphere. forming movamantr: lt volcano€s at hot spots. As the plate moves, new hot spots and volcanoer form, ai shown in diagram A. The Hawaiian lrlands, Emparcr Ssamount (underwater volcanoes) Trall was cr€ated by movemonts of the Padti( plate over an area ol ridng magma, as rhown in diagram ote how the PacifiG plate may hav€ (hang€d dl]lction some 25 million to 30 million yea6 ago or the rBing hot matqrial changed its location. 8. While most scientists accept the major part of the plate tectonic theory, there is still much debate about what makes the plates move. The most accepted theory is that mantle convection cu(rents drag or push the plates apart at places where plates diverge. The exact location of these convection currents is hotly debated. The energy source for these convection currents is the heat of Earth's interior, which causes hotteg, less dense parts of the mantle to rise under diverging plates. Gravity pulls down the cooler, more dense regions of the mantle, causing falling convection currents in subduction areas. (See Figures 12-11 and 12-13 for illustrations of convection in the mantle.) Hot Spots One major aspect of lithosphere and crust that is difficult to explain by the conventional plate tectonic theory concems major regions of volcanic activity in the interior parts of plates away from plate boundaries. These regions are called hot spots. Examples include the big island of Hawaii, the region around Yellowstone National Park in Wyoming and Montana, and maybe even the Adirondack Mountains of New York State. See the hot spots on Tectonic Plates in the Earth Science (D Reference Tables. Scientists have proposed that hot spots occur where rising material frorn the lower mantle remains stationary for millions of years. When a plate moves over the ;fi i3,Hff :"n'ffi1l*il"fl;:,,lffi ' *ilr,'#::?"'#il;['ff; can build volcanoes and lava flows and push up regions of the crust to form mountains. Because the plate keeps moving over the rising materials, a series of volcanic mountains form for thousands of miles. These trails of hot-spot featurcs can be used to infer past movements of the plates that moved over the hot spots. See Figure 12-14 to help you understand rising materials and hot spots. Effects of Plate Tectonics fhe rnovements of the plates for 3 to 4 billion years in the past and for untold millions of years in the future has had and will continue to have many effects on Earth and its inhabitants. Many of these effects are described in the sections that follow 254 Topic t Z: farth's Dynamic Crust and tnterior Appe.rrance 01 (ontrnents The outlincs of the present-dav continents appear to fit together like the preces of a jigsan puzzlc because supercontinent Pangea split apart starting approximatelv 225 million years ago, and a ferv pieces have rejoinecl one another. Tlris can be seen in Figure 12-12 and in the Inferrt'd Positions of Earth's Landmasses section oiihc Geologic History of Nerv York in the Earll Sci'rtcr' Rr'[ ri trcc' Inhle'. .! ol Landmasses Similarities in minerals, rocks, fossils, age, and structure features of mountain ranges are found at places where the continents and other landmasses mav have fitted k)gcther in the past. These similar feature s on different landmasses indicate a commonality in age and origin. Todav the continents are separated, and their respective life forms are often greatlv ditTercnt. The variation in life forms on the different land areas is a result of evolution. Hor.vevet fossil eviclence short's that in the past manv prlants and trnimals, such as thc Clttssopteris fossils of Figure 12-15, n'ere the samc throughout the world. Such a rvide distribution of the same plants and animals probably cor-rld not have Features Digging6u*"An interestinq theory related to hot spots is that the impact of an asteroid or comet on Earth could cause weak spots in the crust and mantle, allowing material to rise and causing hot-spot regions. It has even been suggested that these asteroid- or comet-created areas of rising materials could cause the plates to begin moving by cracking the Iithosphere and starting the rise of convection at new divergent plate boundaries. occurred unless the continents n ere connected. Figure 12-15 shows somc oi the now,separated locations that have rocks, rnincrals, fossils, and mountain structures in common. These similaritics suggest that the lancl areas wcre together when thest'features n'ere formecl, and that these areas have since separated as thc plates moved. As the plates move portiorrs of Earth's surface to ncrv locations, rocks are exposed to different climate conditions. The fincling of rocks near the Earth Today South po e Fi9u7e 12''l!. Changing features ot landmasses due to plate movement3: Many feaiures of Earth'5 landmas5es in rocks more than 250 million years old don't make senge unless the landmas5e5 were in different locations approximately 250 million years ago when the supercontinent Pangea existed. Top. 12 Eanh's Dynam c Crlst and ntet or 265 equator with evidence of glacial erosion and deposition and rocks near the poles with coal deposits of the same ages indicates a climate pattem of hot near the poles and cold near the equator. The probable answer to this dilemma is that plate rnovements have changed the locations of the landmassps. Age and Heat Patterns of Oceanic Rocks As the magma rises and forms basaltic igneous rocks at the mid-ocean ridges, it spreads outwards away from the ridges with divergence. This divergence of the plates is illustraied by dating samples of the oceanic basaltic rocks. The farther the sample is from the center of a rnid-ocean ridge, the older the igneous rock is. The rocks are dated using the methods of radioactive-decay dating. Another similar pattern is indicated from heat flow measurements taken from the basaltic ocean crust. Measurements indicate that heat decreases as distances from the mid-ocean ridges increase. This makes sense because the hottest rocks should be closest to the magma and lava from which they formed. / Magnetic Patterns of Oceanic Basaltic Rocks The divergence of the oceanic lithosphere and crust at mid-ocean ridges is shown by patterns in magnetism of the oceanic-basaltic rocks. The Earth's magnetic poles flip-flop in polarity (north changes to south and south changes to north) in periods of thousands of years in a process called reversal of Earth's magnetic polarity. The Ge"rathに norh pde reasons for these magnetic reversals and the question of whether the magnetic reversals are cyclic or non-cyclic have not been answered. Iiy'hat is known is that Earth's magnetic field has reversed hundreds of times since the magnetic field's origin, probably billions. of years ago. (See Figure 12-16.) / graphic south pole .//// Normal magnetic polarity of today ,'/ ,/ / Geogmphに notth pde \ ヽ \ e \ p 0 Geog'aphic sou/th pole ,"ny.nynry Reversed magnetlc polarity Flgurc tI-16. o.nal and r€veF€d polarity of Eartht mrgnetirm; Eanh! magnetic lield fliFflops from nomal polarity to r€ver5ed polarity in time spans of thougands of yea6. 266 fopt 12: Eanhs Dynamic Crust and tnterior When basaltic rock crystallizes at the mid-ocean ridges, its magnetic minerals are aligned; therefore, they record the particular polarity when the magma and lava solidi$'. Normal polarity is when magnetic north is near the north geographic pole and magnetic south is near the south geographic pole-as is true today. Reversed polarity is when magnetic north is near the south geographic pole and magnetic south is near the north geographic pole. It has been found that there is a pattem of corresponding stripes of basaltic rock on either side of the mid-ocean ridges of normal and reversed polarity. This evidence suggests that the corresponding stripes were formed at similar times, and the sea-floor spreading has separated them during divergence. These stripes are illustrated on Figure 12-13 . Note that these stripes are nbt a visual feature but a pattem only indicated by magnetic instruments used in airplanes or oqeanographic research ships. Other Effects of Plate Tectonics The movement of the plates has had and will continue to have other effects on Earth and its inhabitants: o environmental hazards, such . . . . . as volcanic eruptions, earthquakes, and tsunamis changes in Earth's climate and weather, such as altering the locations of land and ocean areas and creatilrg mountains to change wind pattems changes in the factors that cause our day-to-day weather by changing the dishibution of land and ocean areas and other features, such as mountains and large continental regions the rock cycle the major landscape features of Earth-continents, ocean basins, mountains, plains, and plateaus exposing rocks to weathering and erosion that carve the details of the solid Earth surface and form sediments Base your answers to questions 42 through tt8 on the following diagram, The diagram is an earlier tectonicplate model that represents one possible interpretation of the movements of Earth's rock surfaces according to the theory of plate tectonics. According to this interpretation, Earth's lithosphere consists of several large plates that are moving in relationship to one another. The arrows in the diagram show some of this relative motion of the plates. The diagram also shows the age of formation of the igneous rocks that make up the oceanic crust of the northern section of the Pacific plate. Age of rocl6 of Pacitic plate A lurassic B Early Cretaceous C Middle Cretaceous D Late Cretaceous E Eocene 1 According to the Earth Science Reference Tables, during which geologic time period were the continents of North America, South America, and Africa closest together? (3) Triassic Tertiary (4) Ordovician Cretaceous 2 According to the theory of plate teqtonics, the distance between two continents on opposite sides of a mid-oceanic ridge will generally 1 2 3 decrease increase 44. Which statement is best supported by the relative movement shown by the arrows in the diagram? (1) North America and South America are moving toward each other. (2) The lndian-Australian plate is moving away from the Eurasian plate. (3) The African plate and Eurasian plate are moving away from the North American plate. (4) The Antarctic plate is moving away from the North American plate. remain the same Topic 12: Farths Dynamic Crust and lnterior 267 The boundaries between all of these plates are best described as the sites of (l) 53. Evidence of subduction exists at the boundary between the (1) African and South American plates (2) lndian-Australian and Antarctic plates (3) Pacific and Antarctic plates (4) Nazca and South American plates frequent crustal activity (2) deep ocean depths (3) continental boundaries (4) magnetic age pattern Which geologic structure is represented by the double line separating the North American Which of the following cross-sectional diagrams best represents a model for the movement of rock material below the <rust along the midAtlantic ridge? ●●0“ plate from the African and Eurasian plates? thick continental crust thick layers of sediment mid-ocean ridge granitic igneous rock 47. Which provides the best explanation of the mechanism that causes these plates to move “20“ across Earth's surface? 48. convection currents in the mantle faulting of the lithosphere the spin of Earth on its axis prevailing wind belts of the troposphere The age of formation of the igneous rocks A, B, C, D, and E that make up the oceanic crust of the northern half of the Pacific plate suggests that this section of the Pacific plate is generally moving in which direction? (1) from north to south (3) from westto east (2) from 5outh to north (4) from east to west 49. 55. The following drawing represents the ocean floor between North America and Africa. Scientists theorize that Africa and South America were once part of the same large continent. Cite two pieces of evidence that support this theory. 50. Which statement Describe two expected similarities between rock samples found equal distances from and on opposite sides of the Mid-Atlantic Ridge. 52. Which feature is commonly formed at a plate boundary where oceanic crust converges with 1 continental crust? a mid-ocean ridge (3) a transform fault an oceanic trench (4) new oceanic crust 2 268 fopt l2: Eanhb Dynamic crust and tnterior otd -l Young dネ ︱ ︲ 明 0 割﹁ も 51. Which graph best represents the age of the bedrock in the ocean floor along line AB? dネ ︱ ︲ 呵 0 瀾刊 お best supports the concept that continents have shifted position? (1) Basaltic rock is found to be progressively younger at increasing distances from a midocean ridge. (2) Marine fossils are often found in deep-well drill cores. (3) The present continents appear to fit together as pieces of a larger landmass. (4) Areas of shallow-water seas tend to accumulate sediment, which gradually sinks 56, lgneous materials found along mid-ocean ridges contain magnetic particles that show reversal of magnetic orientation. This is evidence that (1) volcanic activity has occurred constantly throughout history (2) Earth's magnetic poles have exchanged their positions (3) igneous materials are always formed beneath oceans (4) Earth's crust does not move Base your answenr to questions 57 thrcugh 51 on the following diagram. The diagram shows the magnetic orientation of igneous rock on the sea floor on the east side of a mid-ocean ridge, The pattern on the west (left) side of the ridge has been omitted. The age of the igneous rock and its distance from the ridge center are shown. Ridge Center I Magnetic minerals in these rock indicate magnetic nonh as it i5 today. 01234 I Magnetic minerals in this rock indiaate magnetic nonh to be where magnetic south is today. 0 Age (millionr ef years) s0 r00 150 Distance (km) 57. Which of the following diagrams best represents 59. Which inference can best be made from the the pattern of magnetic oribntation in the sea diagram? floor on the west (left) side of the ocean ridge? (1) The orientation of Earth's magnetic field (2) has reversed with time. The size of the continents has changed with time. (3) The elevation of sea level has changed with time. (4) The amount of fossil material preserved in the igneous rock has changed with time. ①②00 50. The crustal material on both sides of the ridge indicates that the tectonic plates are diverging converging not moving moving parallel to the ridge 58. According to the diagram. what is the approximate rate of sea-floor spreading? (1) 1 km/million years (2) 2 km/million years (3) 40 km/million years (4) 50 km/million years “ 20“ 61. As the distance from the center of the ridge increases, the age of the rocks decreases increases remainS the same increases and decreases in a cyclic pattern Topic 12: EarthS Dyoamic Crust and lnterior 269 Base your answers to questions 62 through 66 on the following diagrams. Diagram I is a map showing the location and bedrock age of some of the Hawaiian lslands. Diagram ll is a cross section of an area of Earth that illustrates a stationary magma sourre (rising magma and hot spot) and the process that could have formed the islands. N 4 1 1 Kauai 56to38m‖ lion years Oahu 2.5 to 2.2 million years 宵tua6 聰 Southeast Pacincocean Hawaii than L0 million Less 0 50 l` Magma source │ lf each island formed as the tectonic plate moved over the magma source in the mantle, as shown in diagram ll, where would the next volcanic island form? (1) northwest of Kauai (2) northeast of Hawaii (3) southeast of Hawaii (4) between Hawaii and Maui Which of the following graphs best represents the ages of the Hawaiian lslands, comparing them from point A to point B? olヒ A― ① 00 0 Hawaiian lslands is probably thinner and similar in composition thinner and different in composition thicker and similar in composition thicker and different in composition Volcanic activity like that which produced the Hawaiian lslands is usually closely correlated with (l) nearness to the center o{ a large ocean (2) sudden changes in Earth's magnetic field (3) frequent major changes in climate (4) frequent earthquake activity Which of the Hawaiian lslands has the greatest probability of a volcanic eruption? 3 1 4 2 Oahu Maui Hawa11 奎IL ●B A―― ― ―― ‐ B (1) Compared to the continental crust of North America, the oceanic crust in the area of the Kauai lll years 100 150km │ Mantle 曹 │[〕 ≧ 1≧ :≧ A― B (3) 曼lh A― (2) 6フ . B (4) What do mid-ocean ridges and hot spots have in common? (1) They are associated with rising magma. (2) They are always associated with present-day plate boundaries. (3) They commonly are associated with earthquakes of great depth. (4) Neither is associated with plate motions. Which observation provides the strongest evidence for the inference that convection cells exist within Earth's mantle? (1) Sea level has varied in the past. (2) Marine fossils are found at elevations high Stop Here above sea level. (3) Displaced rock strata are usually accompanied by earthquakes and volcanoes. (4) Heat-flow readings vary at different locations in Earth's crust. 27Q toptc l2: Earths Dynamrc Crust and lnterior