Placeholder Image

字幕列表 影片播放

  • Thanks to Brilliant for supporting this whole week of SciShow!

  • Go to Brilliant.org/SciShow to learn more.

  • [ ♪INTRO ]

  • You've probably heard of supervolcanoes.

  • They're like normal volcanoes, exceptyou knowmore volcano.

  • You've probably also heard that some of themlike Yellowstoneare ticking

  • time bombs ready to go off at any moment and wreak havoc on civilization as we know it.

  • This idea pops up in lots of scary news headlines and thrilling action movies, and let's be

  • honest, with the wordsuperin the name, it's just a matter of time before the Avengers

  • have to fight one somehow.

  • And yet, despite all the hype, the one group of people who aren't particularly worried

  • about these volcanoes are the scientists who study them.

  • The truth is that supervolcanoes are real and they can cause unbelievable devastation,

  • but they're not really something we have to worry about.

  • One of the tools geologists use for measuring volcanic eruptions is the awesomely-named Volcanic Explosivity Index.

  • This is a scale that categorizes volcanoes by how much tephra they spew outtephra

  • being the solid rock in the eruption, from big volcanic bombs to very fine ash.

  • Like the earthquake Richter scale, the magnitudes are logarithmic, so every step up in number

  • represents a ten-fold increase in volume of erupted rock.

  • The 1980 eruption of Mount St. Helenswhich was the most destructive volcanic event in

  • the history of the United Stateswas a 5 on the VEI scale because it released around

  • 1.3 cubic kilometers of tephra.

  • On the other hand, the eruptions of Kilauea in Hawai'i tend to have a VEI magnitude of 0.

  • This is because while the volcano produces a lot of semifluid rock, or lava, it doesn't

  • spit up a lot of solid stuff.

  • That's not to say that Kilauea isn't dangerous, it's just isn't very explosive.

  • The highest an eruption can score on the explosivity index is magnitude 8.

  • It's reserved for volcanoes that release at least 1000 cubic kilometers of tephra in a single eruption.

  • That's 1 trillion cubic meters of rock and ashenough to fill 4 million olympic-sized swimming pools.

  • These have sometimes been called super-eruptions, so the volcanoes that can produce them have

  • come to be called supervolcanoes, though the term initially came from pop culture, not the scientific literature.

  • Supervolcanoes aren't common, but there are several around today.

  • If you go visit one, though, don't expect to see a tall ominous mountain.

  • Instead, look for an enormous pit.

  • You see, after a volcano erupts, the ground will sometimes collapse into the now-empty magma chamber.

  • This creates a bowl-shaped depression called a caldera.

  • And supervolcano calderas are so big they're almost hard to spot.

  • A visitor to beautiful Lake Toba on the island of Sumatra might not even realize that the

  • 100-kilometer-long lake is actually a flooded caldera.

  • It was created in the aftermath of a super-eruption that occurred around 74,000 years ago.

  • Of course, perhaps the most famous supervolcano in the world sits beneath Yellowstone National

  • Park in northwest Wyoming.

  • A large section of the park is taken up by the Yellowstone caldera, which is roughly

  • 72 kilometers long and 48 kilometers wide.

  • Deep below the park, the magma chambers of the supervolcano are still very much active,

  • and it shows on the surface.

  • Yellowstone is famous for its hot springs, geysers, and other hydrothermal features which

  • are created when water is superheated underground by the volcano's magma.

  • But while the volcano may still be hot, the last time it actually super-erupted was around

  • 640,000 years ago.

  • Humans as a species didn't even exist then, and we wouldn't for another 300,000 years or so.

  • Geologists can track ancient volcanic eruptions by studying the petrified layers of ash or

  • lava they leave behind.

  • The rock record of the United States holds evidence of 3 major Yellowstone eruptions,

  • 2 of which were super-eruptions.

  • The first one occurred 2.1 million years ago, and was one of the largest known volcanic

  • eruptions in history, covering more than half of the United States in an estimated 2,450

  • cubic kilometers of tephra.

  • The more recent Yellowstone super-eruption of 640,000 years ago was quite a bit smaller,

  • producing about 1,000 cubic kilometers of material.

  • It's the one that created the caldera you can go visit today.

  • And worldwide, the most recent known super-eruption was that of Taupō in New Zealand which exploded

  • a mere 27,000 years ago.

  • Super-eruptions may be devastating, but they're not frequent.

  • Based on past eruptions, geologists have estimated they occur every 17,000 to 45,000 years, or so.

  • But those numbers are just an average, not a prediction.

  • Volcanoes don't operate on precise cycles.

  • That's just not how they work.

  • The forces that lead to an eruption don't build at a constant rate.

  • So there isn't a volcano on Earth that's “overduefor an eruption of any kind,

  • let alone a super-eruption.

  • And while that lack of clock-like activity means we can't predict exactly when a supervolcano

  • will erupt, if Yellowstone was about to, volcanologists would know because it's the best-studied

  • supervolcano around.

  • It's what's called a hotspot volcano.

  • These happen when a particularly hot region of the Earth's mantle melts a lot of nearby

  • rock into magma, which then rises toward the surface.

  • Over the last several million years, the North American continental plate has been sliding

  • slowly to the west, while the mantle hotspot has stayed relatively still.

  • This has created a line of volcanoes stretching from the west coast of North America to Yellowstone's

  • current home in Wyoming.

  • In the future, as the crust continues to move, Yellowstone will be pulled away from the hotspot,

  • and perhaps a new volcanic center will form farther to the east.

  • But for the time being, Yellowstone is still very much an active volcano.

  • It's fueled by a pair of enormous underground magma chambers, the size of which we only

  • came to appreciate in 2015 when a study explored Yellowstone's nether regions using a technique

  • called seismic tomography.

  • It's like a CT-scan, except using earthquake tremors instead of X-rays.

  • Earthquakes create seismic waves, and because these waves travel differently through different

  • materialssuch as molten rock versus cooler solid rockscientists can examine earthquake

  • data to image what's going on underground.

  • The study was the first to visualize both partially-molten magma chambers beneath Yellowstone,

  • together comprising more than 50,000 cubic kilometers in volume.

  • Now, a magma chamber isn't just a big tub of glowing goo.

  • It's a region of hot crust where some of the pore space between the rock is taken up by molten magma.

  • In these particular magma chambers, the researchers estimated that between 5 and 15% of the rock is liquidy.

  • And these magma chambers are the main sources of Yellowstone's volcanic activityactivity

  • which, by the way, includes a lot more than just the occasional super-eruption.

  • Over the last several hundred thousand years, Yellowstone has produced around 80 non-explosive

  • eruptions of lava, the last one occurring around 70,000 years ago.

  • And even more common than that are steam explosions.

  • At least 26 have happened during the 126 years that scientists have been monitoring the region.

  • Super-eruptions, by comparison, are extremely rare, in part because it takes exceptional

  • circumstances to set them off.

  • Standard volcanoes tend to blow because magma flows into the volcano's interior, increasing

  • the pressure like air flowing into a balloon until it pops.

  • But this mechanism isn't likely to cause a super-eruption, since the magma chamb ers

  • of supervolcanoes tend to be larger and have hotter, more flexible walls.

  • As new magma flows in, the chambers can simply expand.

  • So two 2014 studies concluded that super-eruptions are instead caused by a high level of magma buoyancy.

  • See, magma is hotter and less dense than solid rock, so buried magma naturally tends to rise if it can.

  • Imagine you've forced an inflated beach ball underwater in a pool.

  • The air is much less dense than the water, so if you let the ball go, it launches quickly

  • up and through the surface.

  • Using computer models and laboratory simulations, the two studies concluded that super-eruptions

  • happen much the same way.

  • Once enough magma builds up, the crust can't hold it in any more, and it erupts.

  • And geologists don't think this is likely to happen anytime soon.

  • For one thing, magma chambers typically need to be at least 50% molten before they can

  • erupt, and as I mentioned, Yellowstone's are 15% molten at best.

  • Besides, if a super-eruption were about to happen, the changing underground conditions

  • would create noticable changes on the surface as well.

  • Sure, it's tempting to read about a big earthquake or the changing geyser patterns

  • at Yellowstone and wonder if the end is nigh, but it's important to remember that that

  • kind of thing is part of the volcano's normal activity.

  • Yellowstone experiences between 1,000 and 3,000 earthquakes each year, most of which

  • are too small for people to notice.

  • Also, those geysers have always been dynamic features.

  • And the ground continually rises and falls as things underneath shift about.

  • So all of that seemingly dramatic activity isn't a sign of impending doomit's a Tuesday.

  • If a super-eruption were building, earthquakes would be far more frequent, more intense,

  • and more concentrated in particular areas.

  • And we would see similar striking changes to patterns of geyser activity and ground movement.

  • There may even be chemical clues of an impending major eruption in Yellowstone or other supervolcanoes.

  • A 2018 study examined the history of major volcanic eruptions in the Phlegraean Fields

  • of Italy, and characterized how the composition of magma changed as eruptions approached.

  • Based on that, they concluded that the region is beginning to build to its next major eruption...

  • but that it will probably be tens of thousands of years before it actually blows.

  • And across the board, volcanologists say we'll get years or decades if not centuries of warning

  • before a supervolcano erupts.

  • Still, they're keeping an eye on them just in case.

  • For example, the Yellowstone Volcano Observatory monitors geologic activity all across the park.

  • So you can rest assured that if anything changes, we'll know about it.

  • Right now, the United States Geological Survey says that the chances of a Yellowstone super-eruption

  • happening in the next few thousand years are quoteexceedingly small.”

  • In fact, it's not even a sure thing that Yellowstone will ever have another super-eruption.

  • Thanks to the movement of the crust, the Yellowstone caldera is already slightly to the northeast

  • of the major magma chamber beneath it.

  • Yellowstone might simply be dragged away from its heat source before it gets the chance

  • to blow its top again.

  • So there's really no reason to lose sleep worrying about a super-eruption.

  • But, just for imagination's sakewhat would happen if one of them did go off, say, tomorrow?

  • Well, the eruption could have impacts all over the globe.

  • The region nearest to the supervolcano would experience the absolute worst versions of

  • the standard volcano arsenal, including lava flows, pyroclastic clouds, earthquakes, toxic

  • gases, and more.

  • If Yellowstone went off, for instance, it's unlikely anyone in the park would survive.

  • Meanwhile, most of the rest of the United States would have to worry about ash.

  • Here in Missoula, almost a third of a meter of volcanic ash could rain down, and even

  • places like Orlando and DC could receive a few millimeters of the stuff.

  • Those tiny particles of rock and volcanic glass can clog up engines, damage lungs, and

  • even collapse the roofs of buildings if enough falls.

  • So a Yellowstone super-eruption would cause medical, economic, and structural chaos across the country.

  • And, wherever in the world it happened, a super-eruption would almost certainly mess with global climate.

  • The eruption of Mount Tambora in 1815 pumped so much volcanic ash and gas into the atmosphere

  • that global temperatures dropped about 3 °C the following year.

  • And it only ranked a 7 on the VEI scale.

  • A super-eruption might do the same thing on a larger scale, impacting just about every

  • corner of the globe.

  • But, though there'd be some havoc, it wouldn't be the end of the world.

  • None of Yellowstone's previous eruptions are linked to major extinction events.

  • Neither are the eruptions of any other supervolcanoes, for that matter.

  • We might fear for our own safety because for a long time, scientists have thought the Toba

  • super-eruption 74,000 years ago caused a decline in human populations.

  • But even that has been called into question by more recent archeological data.

  • Regardless, all of this really isn't something we need to worry about today.

  • I can't stress this enough: volcanologists say there's no reason to think any supervolcano

  • is going off anytime soon.

  • Still, researchers will continue to monitor and collect data on supervolcanoes

  • Because, someday in the futurein several thousand years, maybeYellowstone or another

  • supervolcano will start stirring, and future humans will be really glad we spent all this

  • time studying supervolcanoes when it does.

  • Until then, we can leave the doomsday stories to Hollywood.

  • In order to understand and predict volcanic eruptions, volcanologists need serious math

  • chops to understand their data.

  • If you want to brush up on your own math skills, Brilliant.org has a bunch of math-related

  • courses to cultivate your abilities.

  • Not to mention science, engineering, and computer science!

  • Their math courses cover everything from practical applications to the theory of numbers.

  • And of course there's one on statistics, which every researcher needsand it's

  • great for the rest of us, too.

  • Every course is designed to be hands-on, with interactive quizzes and guided problems.

  • Courses are available offline via Brilliant's mobile apps, so even if your train goes into

  • a tunnel, you can keep learning without being interrupted.

  • The first 200 people to sign up at Brilliant.org/SciShow will get 20% off the annual Premium subscription.

  • And by checking it out, you'll be supporting SciShow, too!

  • [ ♪OUTRO ]

Thanks to Brilliant for supporting this whole week of SciShow!

字幕與單字

影片操作 你可以在這邊進行「影片」的調整,以及「字幕」的顯示

B1 中級 美國腔

您无需担心黄石(You Don’t Need to Worry About Yellowstone (or Any Other Supervolcano))

  • 2 1
    joey joey 發佈於 2021 年 05 月 19 日
影片單字