TECTONICS The Earth in Motion · Mount St. Helens, Washington Lassen Peak, ... Lamington, Papua New...
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Mt. Kosciuszko 2228(7310 ft) Mt. Everest (29035 ft)8850 El'brus (18510 ft)5642 Kilimanjaro 5895(19340 ft) Cerro Aconcagua 6959(22831 ft) Vinson Massif (16067 ft)4897 Mt. McKinley (Denali) (20320 ft)6194 R I N G O F F I R E R I N G O F F I R E R I N G O F F I R E R I N G O F F I R E R I N G O F F I R E R I N G O F F I R E R I D G E A T L A N T I C M I D - M I D - A T L A N T I C R I D G E E A S T P A C I F I C R I S E R I D G E M I D - M I D - A T L A N T I C R I D G E E A S T P A C I F I C R I S E A T L A N T I C PACIFIC PLATE PACIFIC PLATE CAPRICORN PLATE COCOS PLATE AUSTRALIAN PLATE NASCA PLATE EURASIAN PLATE JUAN DE FUCA PLATE SOUTH AMERICAN PLATE ARABIAN PLATE SOMALI PLATE NORTH AMERICAN PLATE A N T A R C T I C P L A T E NUBIA PLATE PHILIPPINE PLATE INDIAN PLATE CARIBBEAN PLATE SCOTIA PLATE AFRICAN PLATE PACIFIC PLATE PACIFIC PLATE ARABIAN PLATE CAPRICORN PLATE JUAN DE FUCA PLATE SOMALI PLATE AFRICAN PLATE SOUTH AMERICAN PLATE NORTH AMERICAN PLATE EURASIAN PLATE CARIBBEAN PLATE AUSTRALIAN PLATE A N T A R C T I C P L A T E NASCA PLATE NUBIA PLATE INDIAN PLATE PHILIPPINE PLATE COCOS PLATE SCOTIA PLATE Edge of diffuse plate boundary Edge of diffuse plate boundary Location uncertain L o c a ti o n u n c e r t a i n Location uncertai n San Andreas Fault Edge of diffuse plate boundary Edge of diffuse plate boundary Location uncertain L o c a ti o n u n c e r t a i n Location uncertai n San Andreas Fault A R C T I C O C E A N SOUTH PACIFIC OCEAN NORTH PACIFIC OCEAN NORTH ATLANTIC OCEAN SOUTH ATLANTIC OCEAN INDIAN OCEAN NORTH PACIFIC OCEAN L. Superior Great Bear Lake Great Slave Lake Lake Winnipeg L. Huron L. Michigan L. Ontario L. Erie Lake Malawi Lake Tanganyika Lake Victoria Lake Baikal C a s p i a n S e a A m a z o n Aral Sea N i l e M e d i t e r r a n e a n S e a Bering Sea Caribbean Sea Weddell Sea North Sea Barents Sea Black Sea Arabian Sea Sea of Okhotsk Philippine Sea South China Sea Coral Sea Tasman Sea D r a k e Pa s s a ge Bering Strait Gulf of Mexico Hudson Bay Baffin Bay Bay of Bengal Bass Strait Gulf of St. Lawrence R e d S e a A N T A R C T I C A A M E R I C A N O R T H A M E R I C A A F R I C A E U R O P E A S I A A U S T R A L I A S O U T H GREENLAND S A H A R A R O C K Y M O U N T A I N S A N D E S H I M A L A Y A A N D E S U R A L M O U N T A I N S A L P S Hawai‘i Tahiti Cape Horn Cape of Good Hope Kalahari Desert Madagascar Plateau of Tibet G O B I Kamchatka Peninsula Southern Alaska San Francisco, California Loma Prieta, California San Fernando, California Northridge, California Landers, California Guatemala Michoac´an, Mexico Northern Peru Northern Bolivia Southern Chile Messina, Italy El Asnam, Algeria Armenia Erzincan, Turkey Western Iran Northern Iran Quetta, Pakistan Latur, India Yunnan, China Qinghai, China Gansu and Shanxi, China Tangshan, China Fukui, Japan K¯obe, Japan Tokyo, Japan Kuril Islands, Russia Mindanao, Philippines Ízmit, Turkey Gujarat, India Southern Alaska San Francisco, California Loma Prieta, California San Fernando, California Northridge, California Landers, California Guatemala Michoac´an, Mexico Northern Peru Northern Bolivia Southern Chile Messina, Italy El Asnam, Algeria Armenia Erzincan, Turkey Western Iran Northern Iran Quetta, Pakistan Bam, Iran Latur, India Yunnan, China Qinghai, China Gansu and Shanxi, China Tangshan, China Fukui, Japan K¯obe, Japan Tokyo, Japan Kuril Islands, Russia Mindanao, Philippines Ízmit, Turkey Gujarat, India Denali Park Southern Alaska San Francisco, California Loma Prieta, California San Fernando, California Northridge, California Landers, California Guatemala Michoac´an, Mexico Northern Peru Northern Bolivia Southern Chile Messina, Italy El Asnam, Algeria Armenia Erzincan, Turkey Western Iran Northern Iran Quetta, Pakistan Latur, India Yunnan, China Qinghai, China Gansu and Shanxi, China Tangshan, China Fukui, Japan K¯obe, Japan Tokyo, Japan Kuril Islands, Russia Mindanao, Philippines Ízmit, Turkey Gujarat, India Southern Alaska San Francisco, California Loma Prieta, California San Fernando, California Northridge, California Landers, California Guatemala Michoac´an, Mexico Northern Peru Northern Bolivia Southern Chile Messina, Italy El Asnam, Algeria Armenia Erzincan, Turkey Western Iran Northern Iran Quetta, Pakistan Bam, Iran Latur, India Yunnan, China Qinghai, China Gansu and Shanxi, China Tangshan, China Fukui, Japan K¯obe, Japan Tokyo, Japan Kuril Islands, Russia Mindanao, Philippines Ízmit, Turkey Gujarat, India Denali Park Katmai/Novarupta Mount St. Helens, Washington Lassen Peak, California Soufriere Hills, Montserrat Mt. Pel´ee, Martinique Soufri`ere, St. Vincent El Chich´on, Mexico Paricutín, Mexico Santa María, Guatemala Nevado del Ruiz, Colombia Quizap´u, Chile Cerro Hudson, Chile Surtsey, Iceland Bezymyannaya, Russia Ksudach, Russia Pinatubo, Philippines Taal, Philippines Rabaul Caldera, Papua New Guinea Lamington, Papua New Guinea Merapi, Indonesia Kelut, Indonesia Agung, Indonesia Ruapehu, New Zealand Grímsv¨otn, Iceland Reventador, Ecuador Shiveluch, Russia Katmai/Novarupta Mount St. Helens, Washington Lassen Peak, California Soufriere Hills, Montserrat Mt. Pel´ee, Martinique Soufri`ere, St. Vincent El Chich´on, Mexico Paricutín, Mexico Santa María, Guatemala Nevado del Ruiz, Colombia Quizap´u, Chile Cerro Hudson, Chile Surtsey, Iceland Bezymyannaya, Russia Ksudach, Russia Pinatubo, Philippines Taal, Philippines Rabaul Caldera, Papua New Guinea Lamington, Papua New Guinea Merapi, Indonesia Kelut, Indonesia Agung, Indonesia Ruapehu, New Zealand Grímsv¨otn, Iceland Reventador, Ecuador Shiveluch, Russia Ulawun, Papua New Guinea Katmai/Novarupta Mount St. Helens, Washington Lassen Peak, California Soufriere Hills, Montserrat Mt. Pel´ee, Martinique Soufri`ere, St. Vincent El Chich´on, Mexico Paricutín, Mexico Santa María, Guatemala Nevado del Ruiz, Colombia Quizap´u, Chile Cerro Hudson, Chile Surtsey, Iceland Bezymyannaya, Russia Ksudach, Russia Pinatubo, Philippines Taal, Philippines Rabaul Caldera, Papua New Guinea Lamington, Papua New Guinea Merapi, Indonesia Kelut, Indonesia Agung, Indonesia Ruapehu, New Zealand Grímsv¨otn, Iceland Reventador, Ecuador Shiveluch, Russia Katmai/Novarupta Mount St. Helens, Washington Lassen Peak, California Soufriere Hills, Montserrat Mt. Pel´ee, Martinique Soufri`ere, St. Vincent El Chich´on, Mexico Paricutín, Mexico Santa María, Guatemala Nevado del Ruiz, Colombia Quizap´u, Chile Cerro Hudson, Chile Surtsey, Iceland Bezymyannaya, Russia Ksudach, Russia Pinatubo, Philippines Taal, Philippines Rabaul Caldera, Papua New Guinea Lamington, Papua New Guinea Merapi, Indonesia Kelut, Indonesia Agung, Indonesia Ruapehu, New Zealand Grímsv¨otn, Iceland Reventador, Ecuador Shiveluch, Russia Ulawun, Papua New Guinea Kodiak- Bowie Cobb Raton Guadalupe- Baja Yellowstone Hawaii- Emperor Samoa Tahiti- Society Gambier Austral- Cooks Easter Louisville Juan Fern´andez Gal´apagos Trindade St. Helena Walvis Ridge Bouvet Crozet Kerguelen R´eunion Comoros East Africa Afar Tibesti Uplift Cape Verde New England Bermuda Azores Iceland Caroline East Australia Tasmantid Kodiak- Bowie Cobb Raton Guadalupe- Baja Yellowstone Hawaii- Emperor Samoa Tahiti- Society Gambier Austral- Cooks Easter Louisville Juan Fern´andez Gal´apagos Trindade St. Helena Walvis Ridge Bouvet Crozet Kerguelen R´eunion Comoros East Africa Afar Tibesti Uplift Cape Verde New England Bermuda Azores Iceland Caroline East Australia Tasmantid EQUATOR EQUATOR Divergent (arrow length is proportional to plate motion speed) Convergent Hot spot Divergent boundary Convergent boundary Transform zone Diffuse plate boundary deformation zone Notable earthquake of the 20th century 20th century earthquake greater than 6.5 magnitude Notable volcanic eruption of the 20th century Known volcanic eruption during the past 10,000 years Plate boundary Major tectonic event in the last 100 years Earthquake Plate motion Tectonic feature Volcanic eruption EUROPE NORTH AMERICA SOUTH AMERICA ASIA AUSTRALIA ANTARCTICA AFRICA NORTH ATLANTIC OCEAN SOUTH ATLANTIC OCEAN PACIFIC OCEAN INDIAN OCEAN SOUTH AMERICA NORTH AMERICA AFRICA ASIA EUROPE India AUSTRALIA TETHYS OCEAN ATLANTIC OCEAN PACIFIC OCEAN ANTARCTICA India NORTH AMERICA SOUTH AMERICA AUSTRALIA ANTARCTICA AFRICA PANTHALASSIC OCEAN T E T H Y S O C E A N E UR AS I A China Cimmeria W r a n g e l l i a P A N G A E A Arabia China India Laurentia and Baltica Siberia SOUTH AMERICA AFRICA AUSTRALIA PANTHALASSIC OCEAN ANTARCTICA PALEOTETHYS OCEAN Arabia China Laurentia Siberia Baltica SOUTH AMERICA AFRICA AUSTRALIA PANTHALASSIC OCEAN ANTARCTICA G O N D W A N A Congo China Siberia Baltica SOUTH AMERICA NORTH AMERICA AUSTRALIA PANTHALASSIC OCEAN P A N N O T I A Compare the patterns on this tectonics map with the more general Natural Hazards map seen on the following plate. Natural Hazards | Plate 16 CONNECTIONS After a meteorite impact wiped out the dinosaurs, drifting continental fragments began to collide. Africa pushed into western Eurasia, raising the Alps. India rammed into Asia, creating the Himalayan Plateau and squeezing Southeast Asia aside. Birds and once tiny mammals grew large and evolved in their own ways on the new continents as today’s spectacular mountains began to rise. Cracks across Pangaea spread into rifts and began growing into oceans. The Atlantic opened between Africa and North America as the Pacific shrank. New rifts split North America from Eurasia, and South America tore away from Africa, opening the South Atlantic. To the south, India split away from Africa, with Antarctica and Aus- tralia left alone near the South Pole. Pangaea drifted north, and 225 million years ago the first dinosaurs roamed a world-continent that stretched almost from Pole to Pole and nearly encircled an ocean called Tethys, ancestor of the Mediterranean. The colliding plates slowed their movement, ocean floors sank, and cracks began tearing North America away from Africa. The Pacific’s predecessor, the immense Panthalassic Ocean, surrounded the supercontinent. Some of today’s mountains were formed before continents assumed their present shapes. Laurentia (North America) collided with Baltica (northern Europe) and later with Ava- lonia (Britain and New England). The tremendous pressure of the collisions caused the northern Appalachians and the Caledonian Mountains to rise along the seams of the growing superconti- nent, Pangaea. A chunk of Pannotia broke off and drifted north to the Equator, leaving the continent of Gondwana at the South Pole. The breakaway chunk then split into three parts, which would become North America, northern Europe, and Siberia. Shallow waters became nurseries for the first multicellular animals with exoskele- tons. This fauna diversified rapidly in a burst of evolutionary creativity called the Cambrian explosion. As part of a long, repeating process, a supercontinent called Rodinia began splitting apart 750 million years ago. Ocean basins opened in the growing rifts between the pieces. Some frag- ments collided, pushing up mountains where glaciers grew and spread across the globe, twice even cover- ing the Equator. In time the pieces reunited to cover the center of a new polar supercontinent, Pannotia. Seafloor Spreading Adjacent oceanic plates slowly diverge at the rate of a few centimeters a year. Along these boundaries—such as the Mid-Atlantic Ridge and the East Pacific Rise—molten rock (magma) pours forth to form new crust (lithosphere). Subduction When two massive plates col- lide, the older, colder, denser one—often the oceanic plate meeting a continental plate—takes a dive. Pulled into the interior of the Earth, it heats up and is reabsorbed into the mantle. Water rising from the subducting plate causes rock above it to melt, causing a volcanic eruption. accretion As ocean plates advance on continental edges or island arcs and slide under them, seamounts on the ocean floor are skimmed off and pile up in submarine trenches. The buildup can fuse with continental plates, as most geologists agree was the case with Alaska and much of western North America. colliSion When continental plates meet, the resulting forces can build impres- sive mountain ranges. Earth’s highest landforms—the Himalaya and adjacent Tibetan plateaus— were born when the Indian plate rammed into the Eurasian plate 50 million years ago. faulting Boundaries at which plates slip alongside each other are called transform faults. An example is California’s San Andreas fault, which accommodates the stresses between the North American and Pacific plates. Large and sudden displacements—strike-slip movements—can create high- magnitude earthquakes. hot SpotS A column of magma rising from deep in the mantle, a hot spot is a thermal plume that literally burns a hole in Earth’s rocky crust. The result? Volcanoes, geysers, and new islands. Eruptions occur at plate boundaries, such as in Iceland and the Galápagos, as well as within plates, such as the volcanoes of Hawai‘i and the geysers of Yellowstone. 50 million yearS ago 100 million yearS ago 200 million yearS ag0 300 million yearS ago 500 million yearS ago 600 million yearS ago ViSualiZing tectonic proceSSeS a fluctuating earth e scale of the thing is otherworldly—a jagged range of outsize mountain peaks, towering three kilometers (two miles) above the abyssal plains and stretching shoulder to vertiginous shoulder along more than 64,380 kilometers (40,000 miles) of seafloor. e global mid-ocean ridge system is by far the grandest geological feature of our planet, snaking into every major ocean basin, and yet it was almost entirely unknown until the 1950s. Early seafloor maps, such as those first printed in National Geographic, revealed a hidden world. ey also helped change fundamentally the way we see our planet, by providing crucial early proof for perhaps the most important geological break- through of the past century. e theory of plate tectonics, popularly known as continental drift, holds that rather than being a stable, planetary skin, the continents are more like rafts constantly adrift upon a bed of molten rock. e ocean ridges are the engines of continental drift, the seams along which new seafloor is formed by cooling magma that rises from below, before spreading outward to push the continents slowly but surely around the Earth’s surface. e results range from immediately spectacular events such as volcanoes, earthquakes, and geysers to the slow-motion uplift of mountain chains and vol- canic islands. Over hundreds of millions of years, new ocean crust is formed along the mid-ocean ridges and old ocean crust is recycled along sub- duction zones, as the continents are shifted and resorted across the face of the Earth. 15 15 TECTONICS The Earth in Motion Tectonics.indd 1-2 5/18/10 10:49:00 AM
Transcript of TECTONICS The Earth in Motion · Mount St. Helens, Washington Lassen Peak, ... Lamington, Papua New...
Mt. Kosciuszko2228(7310 ft)
Mt. Everest(29035 ft)8850
El'brus(18510 ft)5642
Kilimanjaro5895(19340 ft)
Cerro Aconcagua6959(22831 ft)
Vinson Massif(16067 ft)4897
Mt. McKinley(Denali)
(20320 ft)6194
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L. Superior
Great BearLake
Great SlaveLake
LakeWinnipeg
L. Huron
L. Michigan L. Ontario
L. Erie
LakeMalawi
LakeTanganyika
LakeVictoria
LakeBaikal
Caspian Sea
A m a z o n
AralSea
Ni le
Me d i t e r r a n e a n S e a
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C a r i b b e a nS e a
WeddellSea
NorthSea
BarentsSea
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Philippine SeaSouth
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HudsonBay
BaffinBay
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G O B I
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Southern Alaska
San Francisco, CaliforniaLoma Prieta, California
San Fernando, CaliforniaNorthridge, California
Landers, California
GuatemalaMichoac´an,
Mexico
Northern Peru
Northern Bolivia
Southern Chile
Messina, Italy
El Asnam, Algeria
Armenia
Erzincan, Turkey
WesternIran
Northern Iran
Quetta, Pakistan
Latur, India
Yunnan, China
Qinghai, ChinaGansu and Shanxi, China
Tangshan, ChinaFukui, Japan
K¯obe, JapanTokyo, Japan
Kuril Islands, Russia
Mindanao, Philippines
Ízmit, Turkey
Gujarat, India
Southern Alaska
San Francisco, CaliforniaLoma Prieta, California
San Fernando, CaliforniaNorthridge, California
Landers, California
GuatemalaMichoac´an,
Mexico
Northern Peru
Northern Bolivia
Southern Chile
Messina, Italy
El Asnam, Algeria
Armenia
Erzincan, Turkey
WesternIran
Northern Iran
Quetta, PakistanBam, Iran
Latur, India
Yunnan, China
Qinghai, ChinaGansu and Shanxi, China
Tangshan, ChinaFukui, Japan
K¯obe, JapanTokyo, Japan
Kuril Islands, Russia
Mindanao, Philippines
Ízmit, Turkey
Gujarat, India
Denali ParkSouthern Alaska
San Francisco, CaliforniaLoma Prieta, California
San Fernando, CaliforniaNorthridge, California
Landers, California
GuatemalaMichoac´an,
Mexico
Northern Peru
Northern Bolivia
Southern Chile
Messina, Italy
El Asnam, Algeria
Armenia
Erzincan, Turkey
WesternIran
Northern Iran
Quetta, Pakistan
Latur, India
Yunnan, China
Qinghai, ChinaGansu and Shanxi, China
Tangshan, ChinaFukui, Japan
K¯obe, JapanTokyo, Japan
Kuril Islands, Russia
Mindanao, Philippines
Ízmit, Turkey
Gujarat, India
Southern Alaska
San Francisco, CaliforniaLoma Prieta, California
San Fernando, CaliforniaNorthridge, California
Landers, California
GuatemalaMichoac´an,
Mexico
Northern Peru
Northern Bolivia
Southern Chile
Messina, Italy
El Asnam, Algeria
Armenia
Erzincan, Turkey
WesternIran
Northern Iran
Quetta, PakistanBam, Iran
Latur, India
Yunnan, China
Qinghai, ChinaGansu and Shanxi, China
Tangshan, ChinaFukui, Japan
K¯obe, JapanTokyo, Japan
Kuril Islands, Russia
Mindanao, Philippines
Ízmit, Turkey
Gujarat, India
Denali ParkKatmai/Novarupta
Mount St. Helens, Washington
Lassen Peak, California
Soufriere Hills, MontserratMt. Pel´ee, Martinique
Soufri`ere, St. Vincent
El Chich´on, Mexico
Paricutín, Mexico
Santa María, Guatemala
Nevado del Ruiz, Colombia
Quizap´u, Chile
Cerro Hudson, Chile
Surtsey, Iceland Bezymyannaya, Russia
Ksudach, Russia
Pinatubo, PhilippinesTaal, Philippines
Rabaul Caldera, Papua New Guinea
Lamington,Papua New Guinea
Merapi, Indonesia
Kelut, Indonesia Agung, Indonesia
Ruapehu,New Zealand
Grímsv¨otn, Iceland
Reventador, Ecuador
Shiveluch, RussiaKatmai/Novarupta
Mount St. Helens, Washington
Lassen Peak, California
Soufriere Hills, MontserratMt. Pel´ee, Martinique
Soufri`ere, St. Vincent
El Chich´on, Mexico
Paricutín, Mexico
Santa María, Guatemala
Nevado del Ruiz, Colombia
Quizap´u, Chile
Cerro Hudson, Chile
Surtsey, Iceland Bezymyannaya, Russia
Ksudach, Russia
Pinatubo, PhilippinesTaal, Philippines
Rabaul Caldera, Papua New Guinea
Lamington,Papua New Guinea
Merapi, Indonesia
Kelut, Indonesia Agung, Indonesia
Ruapehu,New Zealand
Grímsv¨otn, Iceland
Reventador, Ecuador
Shiveluch, Russia
Ulawun, Papua New Guinea
Katmai/Novarupta
Mount St. Helens, Washington
Lassen Peak, California
Soufriere Hills, MontserratMt. Pel´ee, Martinique
Soufri`ere, St. Vincent
El Chich´on, Mexico
Paricutín, Mexico
Santa María, Guatemala
Nevado del Ruiz, Colombia
Quizap´u, Chile
Cerro Hudson, Chile
Surtsey, Iceland Bezymyannaya, Russia
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Pinatubo, PhilippinesTaal, Philippines
Rabaul Caldera, Papua New Guinea
Lamington,Papua New Guinea
Merapi, Indonesia
Kelut, Indonesia Agung, Indonesia
Ruapehu,New Zealand
Grímsv¨otn, Iceland
Reventador, Ecuador
Shiveluch, RussiaKatmai/Novarupta
Mount St. Helens, Washington
Lassen Peak, California
Soufriere Hills, MontserratMt. Pel´ee, Martinique
Soufri`ere, St. Vincent
El Chich´on, Mexico
Paricutín, Mexico
Santa María, Guatemala
Nevado del Ruiz, Colombia
Quizap´u, Chile
Cerro Hudson, Chile
Surtsey, Iceland Bezymyannaya, Russia
Ksudach, Russia
Pinatubo, PhilippinesTaal, Philippines
Rabaul Caldera, Papua New Guinea
Lamington,Papua New Guinea
Merapi, Indonesia
Kelut, Indonesia Agung, Indonesia
Ruapehu,New Zealand
Grímsv¨otn, Iceland
Reventador, Ecuador
Shiveluch, Russia
Ulawun, Papua New Guinea
Kodiak-Bowie
Cobb
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Yel lowstone
Hawai i-Emperor
Samoa
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Gambier
Austra l-Cooks
Easter
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Tr indade
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Hawai i-Emperor
Samoa
Tahit i-Society
Gambier
Austra l-Cooks
Easter
Louisv i l le
JuanFern ´andez
Gal ´apagos
Tr indade
St . Helena
Walv is Ridge
Bouvet
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Kerguelen
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Comoros
East Afr ica
Afar
Tibest iUpl i f t
CapeVerde
New England
Bermuda
Azores
Ice land
Carol ine
East Austra l ia
Tasmant id
EQUATOR EQUATORDivergent (arrow length is proportional to plate motion speed)
Convergent
Hot spot
Divergent boundaryConvergent boundaryTransform zone
Diffuse plate boundarydeformation zone
Notable earthquakeof the 20th century
20th century earthquakegreater than 6.5 magnitude
Notable volcanic eruptionof the 20th century
Known volcanic eruptionduring the past 10,000 years
Plate boundary Major tectonic event inthe last 100 years
Earthquake
Plate motion
Tectonic feature
Volcanic eruption
EUROPENORTHAMERICA
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SOUTHAMERICA
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AFRICA
ASIAEUROPE
IndiaAUSTRALIA
TETHYSOCEAN
ATLANTICOCEAN
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India
NORTHAMERICA
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LaurentiaSiberia
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SOUTH AMERICANORTH AMERICA
AUSTRALIA
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Compare the patterns on this tectonics map with the more general Natural Hazards map seen on the following plate. Natural Hazards | Plate 16
CONNECTIONS
After a meteorite impact wiped out the dinosaurs, drifting continental fragments began to collide. Africa pushed into western Eurasia, raising the Alps. India rammed into Asia, creating the Himalayan Plateau and
squeezing Southeast Asia aside. Birds and once tiny mammals grew large and evolved in their own ways on the new continents as today’s spectacular mountains began to rise.
Cracks across Pangaea spread into rifts and began growing into oceans. The Atlantic opened between Africa and North America as the Pacific shrank. New rifts split North America from Eurasia, and South America tore
away from Africa, opening the South Atlantic. To the south, India split away from Africa, with Antarctica and Aus-tralia left alone near the South Pole.
Pangaea drifted north, and 225 million years ago the first dinosaurs roamed a world-continent that stretched almost from Pole to Pole and nearly encircled an ocean called Tethys, ancestor of the Mediterranean. The colliding
plates slowed their movement, ocean floors sank, and cracks began tearing North America away from Africa. The Pacific’s predecessor, the immense Panthalassic Ocean, surrounded the supercontinent.
Some of today’s mountains were formed before continents assumed their present shapes. Laurentia (North America) collided with Baltica (northern Europe) and later with Ava-lonia (Britain and New England). The
tremendous pressure of the collisions caused the northern Appalachians and the Caledonian Mountains to rise along the seams of the growing superconti-nent, Pangaea.
A chunk of Pannotia broke off and drifted north to the Equator, leaving the continent of Gondwana at the South Pole. The breakaway chunk then split into three parts, which would become North America,
northern Europe, and Siberia. Shallow waters became nurseries for the first multicellular animals with exoskele-tons. This fauna diversified rapidly in a burst of evolutionary creativity called the Cambrian explosion.
As part of a long, repeating process, a supercontinent called Rodinia began splitting apart 750 million years ago. Ocean basins opened in the growing rifts between the pieces. Some frag-ments collided, pushing up mountains
where glaciers grew and spread across the globe, twice even cover-ing the Equator. In time the pieces reunited to cover the center of a new polar supercontinent, Pannotia.
Seafloor SpreadingAdjacent oceanic plates slowly diverge at the rate of a few centimeters a year. Along these boundaries—such as the Mid-Atlantic Ridge and the East Pacific Rise—molten rock (magma) pours forth to form new crust (lithosphere).
SubductionWhen two massive plates col-lide, the older, colder, denser one—often the oceanic plate meeting a continental plate—takes a dive. Pulled into the interior of the Earth, it heats up and is reabsorbed into the mantle. Water rising from the subducting plate causes rock above it to melt, causing a volcanic eruption.
accretionAs ocean plates advance on continental edges or island arcs and slide under them, seamounts on the ocean floor are skimmed off and pile up in submarine trenches. The buildup can fuse with continental plates, as most geologists agree was the case with Alaska and much of western North America.
colliSionWhen continental plates meet, the resulting forces can build impres-sive mountain ranges. Earth’s highest landforms—the Himalaya and adjacent Tibetan plateaus—were born when the Indian plate rammed into the Eurasian plate 50 million years ago.
faultingBoundaries at which plates slip alongside each other are called transform faults. An example is California’s San Andreas fault, which accommodates the stresses between the North American and Pacific plates. Large and sudden displacements—strike-slip movements—can create high-magnitude earthquakes.
hot SpotSA column of magma rising from deep in the mantle, a hot spot is a thermal plume that literally burns a hole in Earth’s rocky crust. The result? Volcanoes, geysers, and new islands. Eruptions occur at plate boundaries, such as in Iceland and the Galápagos, as well as within plates, such as the volcanoes of Hawai‘i and the geysers of Yellowstone.
50 million yearS ago100 million yearS ago200 million yearS ag0300 million yearS ago500 million yearS ago600 million yearS ago
ViSualiZing tectonic proceSSeS
a fluctuating earth
The scale of the thing is otherworldly—a jagged range of outsize mountain peaks, towering three kilometers (two miles) above the abyssal plains and stretching shoulder to vertiginous shoulder along more than 64,380 kilometers (40,000 miles) of seafloor. The global mid-ocean ridge system is by far the grandest geological feature of our planet, snaking into every major ocean basin, and yet it was almost entirely unknown until the 1950s.
Early seafloor maps, such as those first printed in National Geographic, revealed a hidden world. They also helped change fundamentally the way we see our planet, by providing crucial early proof for perhaps the most important geological break-through of the past century. The theory of plate tectonics, popularly known as continental drift, holds that rather than being a stable, planetary skin, the continents are more like rafts constantly adrift upon a bed of molten rock. The ocean ridges are the engines of continental drift, the seams along which new seafloor is formed by cooling magma that rises from below, before spreading outward to push the continents slowly but surely around the Earth’s surface. The results range from immediately spectacular events such as volcanoes, earthquakes, and geysers to the slow-motion uplift of mountain chains and vol-canic islands. Over hundreds of millions of years, new ocean crust is formed along the mid-ocean ridges and old ocean crust is recycled along sub-duction zones, as the continents are shifted and resorted across the face of the Earth.
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TECTONICS
The Earth in Motion
Tectonics.indd 1-2 5/18/10 10:49:00 AM
