99 Fun Facts About Plate Tectonics

Plate tectonics describes the movement of pieces of which layer of the Earth?

The lithosphere is the cool, rigid shell of crust plus uppermost mantle, and it is broken into plates. They can move only because the hot, semi-solid asthenosphere beneath them slowly flows.

Which sea is an ocean in the making, still widening as the plates on either side pull apart?

The Red Sea. It fills the long, narrow gash that opened when the Arabian Peninsula was torn away from the continent beside it, as new sea floor began to spread between the two.

Which island country sits astride the Mid-Atlantic Ridge, so visitors can walk along the boundary between two plates?

Iceland. Almost all of the ridge lies hidden deep under the ocean, but a hot spot beneath the island is thought to have piled up enough lava to lift this stretch above the waves.

Besides heat left from Earth's formation, what keeps its interior hot enough to drive plate tectonics?

Unstable atoms breaking down. Uranium, thorium and potassium scattered through the rock give off heat as they decay, an estimated half of all the heat that flows out of the planet.

The 2004 Indian Ocean tsunami began when a plate boundary ruptured off the coast of which Indonesian island?

Sumatra. Two plates had been stuck together offshore, storing up strain; when the boundary let go along more than 1,000 km, the seabed sprang up by several metres and shoved the ocean into a tsunami.

Geologists made the case in 2017 for which 'hidden continent', a landmass that lies 94% under the sea?

Zealandia. Its crust was stretched thin as it tore away from a supercontinent in the age of the dinosaurs, so most of it sank, leaving New Zealand and New Caledonia as the largest parts still above the waves.

Which of Jupiter's moons shows signs of ice crustal plates moving and interacting?

Europa. When scientists pieced old Galileo images back together like a jigsaw in 2014, nearly 20,000 square km of icy crust was missing, apparently forced down beneath a neighbouring plate.

Alfred Wegener, the father of continental drift, died in 1930 on a weather expedition to which icy island?

Greenland. Wegener died on the ice cap a day or two after his fiftieth birthday, on his way back from carrying food to stranded colleagues, and never saw his theory accepted.

Why did most geologists reject Wegener's idea of continental drift for decades?

He had no convincing mechanism. The forces Wegener suggested, centrifugal and tidal, were far too weak to push continents through the ocean floor.

What name is given to the single landmass that Alfred Wegener argued today's continents once formed?

Pangaea, from the Greek for 'all' and 'earth'. Wegener himself first called it the 'Urkontinent', German for primal continent, and the name Pangaea first appears in his book's 1920 edition.

In 1969 fossil hunters found Lystrosaurus, a land reptile already known from South Africa, on which other continent?

Antarctica: Lystrosaurus was no swimmer, so its bones in the Transantarctic Mountains meant the frozen continent had once been joined to Africa. A polar veteran called it one of the truly great fossil finds of all time.

Wegener noted that the Scottish Highlands line up with which North American mountain range once the Atlantic is closed up?

The Appalachians. They and the Scottish Highlands are worn-down pieces of one great mountain chain, raised when ancient continents collided and later torn in two as the ocean opened between them.

Arthur Holmes proposed, decades before plate tectonics, that continents are carried along by what?

Mantle convection currents. Holmes pictured hot rock slowly circulating and carrying the continents along like a conveyor belt, and the idea later shaped the theory of seafloor spreading.

Geologist Harry Hess mapped the ocean floor with his ship's echo sounder between battles of which war, years before proposing seafloor spreading?

The Second World War: Hess captained a Navy transport and kept its echo sounder running from one island landing to the next. His profiles revealed flat-topped drowned volcanoes on the sea floor, which he named guyots.

In 1977 scientists diving on a volcanic ridge deep beneath the sea near the Galápagos Islands became the first to see what?

Hydrothermal vents. The geologists went looking for hot springs where new crust forms and, to their amazement, found them crowded with animals nobody had seen before, living without sunlight.

Which mapmaker found a great valley along the crest of the Atlantic's undersea mountains, which Bruce Heezen first dismissed as 'girl talk'?

Marie Tharp. Heezen groaned that her valley 'looks too much like continental drift', then came round when a map of undersea earthquakes lined up neatly inside it.

The magnetometers that first charted the seafloor's magnetism in the 1950s were adapted from wartime aircraft gear built to find what?

Submarines. Detectors built to hunt them from the air were towed behind survey ships instead, where they picked up odd magnetic variations across the ocean floor that nobody had expected.

Vine, Matthews and Morley realised in 1963 that the seafloor's magnetic stripes are a recording of what?

Earth's magnetic field flipping. New crust freezes in the direction of the field as it cools and then moves aside for the next batch, so the ocean floor works like a tape recording of every flip.

In 1963 Canadian geophysicist J. Tuzo Wilson explained which island chain as a plate drifting over a fixed 'hot spot'?

Hawaii. Wilson reasoned that each island was built over the same stationary plume of heat and then carried away, which is why the islands grow steadily older and more eroded toward the northwest.

Which continent drifts north about 7 cm a year, enough to leave its official map coordinates 1.5 metres out by 2016?

Australia. Global coordinates stay put while the ground moves, so the country's 1994 map grid slipped steadily out of step, and a new grid had to be drawn up with every point shifted north to catch up.

Which landmass was once an island far south of the Equator before drifting north to collide with Asia?

India. It crossed thousands of kilometres of ocean before striking Asia, and the collision is still going on: the mountain wall raised along the join is being pushed higher today.

A 2011 earthquake off which country is calculated to have shortened Earth's day by about 1.8 millionths of a second?

Japan. When the plate boundary off its north-east coast slipped, enough rock shifted, by NASA's calculations, to make the planet spin a touch faster, and to nudge the axis Earth's mass is balanced on by more than 10 cm.

Which force is most widely thought to be the greatest driver of plate motion?

Slab pull. The cold, dense edge of a plate sinks under its own weight and drags the rest of the plate after it, while the push from the ridges is thought to add less.

Which technology lets geologists measure plates creeping a few centimetres a year?

GPS. Receivers fixed to the ground on different plates have their positions measured again and again, to within a fraction of a millimetre a year, so geologists can watch the two sides of a fault creep past each other.

Which two continents' matching coastlines were noticed as early as 1596?

South America and Africa. The mapmaker Abraham Ortelius suggested in 1596 that the Americas had been torn away from the Old World by earthquakes and floods, three centuries before Wegener made the case.

What do 'sima' and 'sial', old textbook names for oceanic and continental crust, stand for?

Silicon-magnesium and silicon-aluminium. The names were coined in German from the elements' first letters, and the difference matters: magnesium-rich ocean crust is the denser of the two, so it lies low enough for the sea to cover it.

Which US national park sits above a hot spot that has left a trail of older volcanic craters across Idaho?

Yellowstone. The plume of heat stays put while North America slides south-west across it, so a 500-mile trail of old craters runs back through southern Idaho, with the park at the young end.

What do geologists call slabs of ancient ocean floor now found stranded high and dry on the continents?

Ophiolites. Named from the Greek for snake, after their scaly green rock, they let geologists walk through a slice of deep ocean crust and the mantle beneath it without getting their feet wet.

The Mid-Atlantic Ridge is an example of which boundary type?

Divergent. The plates move apart along the ridge and new crust wells up to fill the gap, at about 2.5 cm a year, which has been enough to widen the Atlantic from a narrow inlet into an ocean.

The San Andreas Fault in California is the classic example of which boundary type?

Transform. The two plates slide sideways past each other at about the rate fingernails grow, so Los Angeles, west of the fault, is slowly heading north and will one day sit beside San Francisco.

Curving chains of volcanic islands such as the Aleutians and Marianas form at which kind of boundary?

Ocean-to-ocean subduction zones. Lava piles up on the sea floor above the diving plate until volcanoes break the surface, strung out in a curve because they follow the line of the deep trench beside them.

Why is neither plate subducted when two continents collide, as with the Himalayas?

They have similar densities. Neither slab of light continental rock will sink beneath the other, so the crust between them crumples and piles skyward instead, and the range is still rising as the squeeze goes on.

The summit of which mountain is made of limestone that formed on an ancient sea floor, complete with fossil sea creatures?

Everest. Its summit rock holds fragments of trilobites and sea lilies that lived on the floor of a long-vanished sea, then were hoisted nearly nine kilometres into the sky as two continents collided.

What do descending slabs release that makes the mantle above them melt and feed volcanoes?

Water from hydrous minerals. At depth the sinking plate 'sweats' out its water, which lowers the melting point of the hot rock above, so mantle that was solid begins to melt without getting any hotter.

Lava that erupts underwater at the ocean ridges freezes into rounded lobes named after which household item?

Pillows. Cold seawater chills each squirt of lava so quickly that it skins over into a rounded lobe before the next one oozes out, and thick piles of these pillow lavas build up wherever new sea floor is made.

The worldwide seismograph network that mapped Earth's earthquake zones in the 1960s was built mainly to detect what?

Nuclear weapons tests. America would not sign a test ban it had no means of policing, so a global net of seismographs went up to listen for blasts, and geologists got a windfall of precise earthquake data.

Which plate's rim is lined with deep ocean trenches, where it bends and dives back into the mantle?

The Pacific. It is the plate doing the diving at the trenches on its northern and western rim, and the volcanoes and earthquakes set off there form much of the famous Ring of Fire.

Which part of Africa is slowly tearing away from the rest along a chain of valleys, volcanoes and long lakes?

East Africa. The crust there is being stretched until it cracks, and if the pulling goes on for millions of years the sea is expected to flood in and leave the Horn of Africa as a large island.

The most recent supercontinent broke up into which two landmasses?

Laurasia and Gondwana. The northern half became North America and Eurasia, the southern half the rest, and the Tethys sea that opened between them was later squeezed shut, its floor crumpled up into mountain ranges.

Which oceanic plate is diving beneath the west coast of South America, heaving up the Andes as it goes?

The Nazca plate. It slides under the continent along the Peru-Chile trench, and the squeeze both lifts the Andes and sets off strong, destructive earthquakes all the way down the coast.

Which small plate is diving beneath Washington and Oregon, feeding Mount St. Helens and the other Cascade volcanoes?

The Juan de Fuca plate. It is one of the smallest plates on Earth, the leftover of a once-vast plate now mostly swallowed beneath North America, and its locked edge last let go in a giant earthquake in 1700.

One leading explanation for Venus lacking plate tectonics is the absence of what?

Water. On Earth it soaks into the crust and weakens it along the zones where plates break and slide, as if oiling the machinery, while Venus is thought to have boiled its oceans away long ago.

Magnetic striping was detected on which planet by an orbiting spacecraft in 1999?

Mars. The Mars Global Surveyor found stripes in its ancient crust like those on Earth's sea floor, a hint, still debated, that the young planet may once have had moving crust of its own before it froze up.

Plate tectonics is thought to help keep Earth habitable over millions of years by regulating what?

The carbon cycle. Volcanoes leak carbon dioxide out and sinking plates carry carbon-rich rock back down, a slow loop that works like a thermostat and has kept Earth from ending up like Venus.

The Romans named copper after which island, whose mountains are a slab of ocean crust lifted above the sea?

Cyprus. Its copper ore formed on the deep sea floor long before that crust was raised into mountains, so miners there have in effect been digging into an old ocean bed since ancient times.

'Tectonics' comes from 'tekton', Greek for a builder, a root also hidden in which job title?

Architect: from the Greek 'arkhitekton', the chief builder. So the word itself says nothing about motion: it describes how Earth's crust is built, its folds, faults and mountain ranges.

Africa's slow push north into Europe crumpled the crust between them into which mountain range?

The Alps. Africa has been pressing into Europe for tens of millions of years and has not stopped, which is why Italy and Greece are still shaken by earthquakes.

Geologist S. Warren Carey championed continental drift for decades, but thought the continents parted because Earth was doing what?

Expanding. If new sea floor keeps forming and none is destroyed, the globe has to grow; the idea lost out once old sea floor was found to sink back into the Earth at the deep ocean trenches.

Which lake is the deepest on Earth because it fills a rift where a continent is slowly being pulled apart?

Lake Baikal. Its 1.6 km depth is only the top of the crack, which holds some 7 km of mud as well, and geologists read it as the first chapter in how a continent splits and an ocean is born.

Tectonic plates typically creep along at a few centimetres a year, roughly the pace at which what grows?

Fingernails grow about as fast as the plates part along the Mid-Atlantic Ridge, 1 to 4 cm a year. The speediest plates manage about 16 cm, closer to the rate at which hair grows.

Which sporting event was about to begin when the 1989 Loma Prieta earthquake struck the San Andreas Fault system?

The World Series was moments from Game 3 between two Bay Area baseball teams, so the shaking went out live on national television. Many locals had left work early to watch.

Which river seemed to run backwards during the 1811–12 New Madrid earthquakes, which struck far from any plate boundary?

The Mississippi threw up waves that rolled upstream and temporary waterfalls as the ground heaved, so onlookers believed it had reversed. The shocks hit the middle of a continent, not an edge.

Which sea dried out almost completely about six million years ago, after its only link to the open ocean was sealed?

The Mediterranean was cut off from the Atlantic and evaporated within about a thousand years, leaving salt minerals beneath its floor. It refilled in a rush when the Strait of Gibraltar reopened.

Which famous Scottish lake lies along the Great Glen Fault, where two blocks of crust slid sideways past each other?

Loch Ness fills a trench that Ice Age glaciers gouged out of rock the fault had already weakened. It holds a greater volume than any other Scottish loch.

Which Danish beer brand shares its name with a mid-ocean ridge found by an expedition its foundation funded?

Carlsberg's scientific foundation paid for the Danish research ship Dana to sail round the world in 1928–30, and the undersea ridge the voyage discovered was named in its honour.

Which young English naturalist felt an 1835 earthquake in South America and found mussel beds stranded above the tide?

Charles Darwin read the stranded shellfish as proof the land had just been raised. High in the Andes he went on to find seashells, more evidence of a continent on the rise.

Which American founding father suggested in 1782 that Earth's surface might be a shell floating on a fluid interior?

Benjamin Franklin, better known for his kite and lightning rod, pictured a shell that the moving fluid beneath could break and disorder, some 180 years before plate tectonics.

Which salt lake, its shore the lowest land on Earth, fills a basin torn open between the African and Arabian plates?

The Dead Sea sits in a gap pulled open because the Arabian plate is sliding north faster than its neighbour. The same line of faults made the Sea of Galilee and the Gulf of Aqaba.

Which land bridge, formed about three million years ago, first let animals walk between North and South America?

The Isthmus of Panama set off the Great American Interchange of wildlife between the two continents. By parting two oceans it is also thought to have created the Gulf Stream.

Which belt of earthquakes and eruptions, holding about two-thirds of the world's volcanoes, surrounds the largest ocean?

The Ring of Fire also unleashes about 90% of the world's earthquakes, including most of the largest. It counts between 750 and 915 active or dormant volcanoes, depending on where its limits are drawn.

Which city was devastated in 1906 when the San Andreas Fault ruptured along nearly 300 miles of California?

San Francisco was more than 80% destroyed, much of it by the fires that broke out afterwards and burned for several days. The shaking was felt from Oregon to central Nevada.

Which country was struck in 1960 by the strongest earthquake ever recorded, a rupture about 800 km long?

Chile's Valdivia earthquake reached about magnitude 9.5 and sent tsunamis as far as the Philippines and the Aleutian Islands. It struck where an oceanic plate is forced down beneath the continent.

Which US state was rocked on Good Friday 1964 by the most powerful earthquake ever recorded in North America?

Alaska shook for more than four and a half minutes as the ocean floor jolted farther beneath the coast. Only one earthquake measured anywhere in the world has been stronger.

Which European capital was almost completely destroyed on All Saints' Day 1755 by an earthquake, tsunami and fires?

Lisbon lies near the fault zone running between the Azores and Gibraltar, where the African and Eurasian plates press together under the sea. The tsunami wrecked ports in the Azores as well.

Which country is crossed by the North Anatolian Fault, where big earthquakes since 1939 have struck ever farther west?

Turkey has had seven earthquakes above magnitude 7 along the fault since 1939, each one west of the last. The sequence reached the town of İzmit, with devastating effect, in 1999.

The Zagros Mountains, crumpled up where the Arabian plate collides with Eurasia, lie mainly in which country?

Iran's main oilfields lie in the Zagros foothills, where the folding and faulting caused by the collision helped to trap petroleum underground.

Which island split from Africa about 180 million years ago, an isolation that left 90% of its wildlife unique?

Madagascar has stood alone since a second split about 90 million years ago, when the landmass it had left Africa with broke away in turn. It ranks among the world's 17 megadiverse countries.

Which university's football stadium sits on the Hayward Fault, which runs under it nearly from goalpost to goalpost?

UC Berkeley built California Memorial Stadium in two halves because of the fault, which drags one side south by about a millimetre a year. Expansion joints in the walls let the halves move.

Which weak, slowly flowing layer of the upper mantle, named from the Greek for 'without strength', carries the plates?

The asthenosphere is almost entirely solid, with less than 0.1% of its rock melted, yet it is hot enough to creep a few centimetres a year across thousands of kilometres.

Which boundary between Earth's crust and mantle is named after the Croatian seismologist who detected it in 1909?

The Mohorovičić discontinuity, or Moho for short, lies 5 to 10 km beneath the sea bed but 20 to 90 km beneath the continents. Earthquake waves abruptly speed up as they cross it.

Which hard, speckled rock is widely distributed throughout the continental crust?

Granite helps build continental crust that is 25 to 70 km thick, several times thicker than the crust under the sea, which is generally less than 10 km.

Which green mineral, cut as the gemstone peridot, makes up more than half of Earth's upper mantle?

Olivine is one of the commonest minerals on the planet by volume, yet it is seldom seen because it weathers quickly once it reaches the surface.

Which geological term for an episode of mountain building comes from the Greek words for 'mountain' and 'creation'?

Orogeny takes place where plates converge: the squeezed edge of a plate crumples and is lifted into one or more mountain ranges, forming a long belt that geologists call an orogen.

What do geologists call the old, stable cores of continents, a name taken from the Greek word for 'strength'?

Cratons have often survived whole cycles of continents merging and splitting. Their rock can be up to 4 billion years old, against 180 million for the oldest sea floor.

Which mountain range between Europe and Asia, among the world's oldest, was raised when two ancient continents collided?

The Urals are the worn-down seam left where a continent called Kazakhstania was welded onto its western neighbour, in a collision that lasted nearly 90 million years.

Which narrow sea opened about five million years ago as a sliver of Mexico was rifted off the North American plate?

The Gulf of California is young for a sea and still growing. The Baja peninsula on its western shore began breaking from the mainland 12 to 15 million years ago, when a spreading ridge cut into the coast.

Which California national park preserves half of an extinct volcano that the San Andreas Fault has carried 200 miles?

Pinnacles is named for the eroded spires of a volcano that erupted 23 million years ago. The fault sliced off its western half and has been hauling it north-west ever since.

Which mountain range was pushed up when the Iberian microcontinent collided with the south-western edge of Europe?

The Pyrenees rose after Iberia had first rifted away from western France, opening the Bay of Biscay in its wake, and then pressed back into the continent farther south.

Which vast ocean surrounded the last supercontinent when all the land was joined?

Panthalassa has lost every scrap of its original floor, swallowed back into the planet around its edges. The largest ocean on today's map is its direct descendant.

Which supercontinent, named from the Russian word for 'motherland', came together about a billion years ago?

Rodinia was itself built from the wreckage of an even older supercontinent. It broke apart again more than 600 million years ago, and its fragments later regrouped once more.

Which name is given to the future supercontinent predicted to form over the North Pole as the Arctic Ocean closes?

Amasia would be built by the merger of Asia and the Americas, which one 2012 study expects within the next 50 to 200 million years.

Which spot in the Mariana Trench, the deepest known point of the sea bed, is named after two British survey ships?

The Challenger Deep lies nearly 11 km down. The first HMS Challenger located it during her voyage of 1872–76, and a second ship of the same name confirmed its record depth in the 1950s.

Which small oceanic plate, named after an island of Costa Rica, dives beneath Central America and feeds its volcanoes?

The Cocos plate shows only one scrap of land above the waves, Cocos Island itself, about 550 km off the Costa Rican mainland. Its sinking edge also sets off a belt of earthquakes that reaches into Mexico.

Which region of the American West formed as the crust was stretched and thinned over the past 17 million years?

The Basin and Range spans more than 500 miles, from the eastern scarp of the Sierra Nevada to the Wasatch Fault. Each ridge is a block of crust that tilted along faults as the region pulled apart.

Which natural record in dead coastal cedars let scientists date the Cascadia earthquake to the winter of 1699–1700?

Tree rings showed that 'ghost forests' of red cedar in Oregon and Washington last grew in 1699. The earthquake dropped the coast into the tidal zone, and salt water killed the trees where they stood.

Besides its own continent, the North American plate also carries the eastern corner of which large country?

Russia is split between two plates: the North American plate reaches west as far as the Chersky Range in eastern Siberia, so that region shares a plate with New York.

Which sunken continent did a Victorian zoologist invent to explain fossils found an ocean apart?

Lemuria was proposed in 1864 as a drowned land bridge, to explain why lemur fossils turned up on widely separated shores. Drifting continents later explained the pattern without it.

Which theory, born from surveys of California's 1906 rupture, says strained rocks snap back into shape in an earthquake?

Elastic rebound was worked out by geophysicist Harry Fielding Reid, who studied how the ground had shifted in the 50 years before the fault broke. The stored energy escapes as seismic waves.

Which distant cosmic objects emit the radio signals that let far-apart telescopes track plate motion to the millimetre?

Quasars lie so far away that they make steady reference points. By timing the arrival of their radio waves at antennas on different continents, geodesists can measure how the gaps between them change.

Which ancient oceanic plate, mostly swallowed beneath North America, is credited with raising the Rockies far inland?

The Farallon plate slid under the continent at an unusually shallow angle, so it buckled the crust much farther from the coast than a sinking plate normally does. It is named after islands off California.

What do geologists call crustal fragments that ride in on one plate and are welded onto the edge of another?

Terranes keep a geological history unlike that of the rocks around them, which is why they are often called exotic. The idea grew out of 1970s studies of North America's jumbled western mountains.

Which Caltech seismologist shares with Kiyoo Wadati the name of the sloping earthquake zones that trace sinking plates?

Hugo Benioff and Wadati discovered the zones independently. Their earthquakes reach about 670 km down, which lets seismologists map a descending plate in three dimensions.

Which kind of earthquake, striking where one plate is forced under another, includes every magnitude 9 since 1900?

Megathrust earthquakes build up when friction locks two plates together along an extremely large thrust fault. The strain keeps growing until the fault gives way.

Which principle, from the Greek for 'equal standstill', has Earth's crust floating at a height set by its thickness?

Isostasy explains why high mountains need deep roots: the low-density rock beneath them supplies the buoyancy that holds the peaks above the surrounding land.

Which imaging technique compares earthquake waves recorded around the world to map sunken plates deep inside Earth?

Seismic tomography can pick out a long-vanished plate because the sunken rock is still colder than its surroundings. The remains of one lost plate have been imaged beneath North America.

Which metamorphic rock, made at very high pressure but low temperature, is a telltale sign of a vanished sinking plate?

Blueschist takes its colour from the mineral glaucophane. The cool but deep conditions that create it arise only where a plate descends, and the rock is rare because it must then be carried back up.

The fastest plate convergence measured on Earth, up to 24 cm a year, is at the trench named after which island nation?

Tonga's trench is also the second deepest on the planet. Its lowest point, the Horizon Deep, lies about 10,800 metres beneath the waves.

Which tiny Californian town was wired with instruments for a San Andreas earthquake predicted by 1993 that came in 2004?

Parkfield had been given 90 to 95% odds of a quake by 1993, and the wait ran eleven years over. A bridge there has piers that the creeping fault has shifted more than five feet out of line.

Which Himalayan country was struck in 2015 by the Gorkha earthquake, a sudden upthrust on the plate boundary beneath it?

Nepal sits where one plate is slowly diving beneath Eurasia. The shaking in its capital came in slow, rolling waves, and many rural people were working outdoors at the time, which kept the toll down.