シャドーイング練習: The Biggest Eruptions That Changed Earth Forever - 動画で英語スピーキングを学ぶ

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The Earth is a gigantic ball of semi-molten rock with a heart of iron as hot as the surface of the Sun.
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Titanic amounts of heat left over from its birth
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and the radioactive decay of trillions of tons of radioactive elements find no escape but up.
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Currents of rock spanning thousands of kilometers carry this energy to the surface.
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Earth's crust is the only thing in their way.
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It feels solid to us, but it's only a fragile barrier, an appleskin around a flaming behemoth.
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True apocalypses can break through and unleash eruptions tens of times more powerful than all of our nuclear weapons combined,
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subjecting the climate to centuries worth of change in a single year, while drowning continents in toxic ash and gases.
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Supervolcanoes.
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How big can they get?
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And will they put an end to humanity?
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Volcanoes There are many types of volcanoes from towering mountains to lava domes,
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but they have two main sources The first is at the boundaries between tectonic plates the pieces of the crust
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that cover the earth like a giant jigsaw puzzle There are seven major tectonic plates and dozens of smaller ones, drifting against each other at up to 15 centimeters per year.
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This sounds slow, but on geological timescales, it is a titanic struggle over who gets to stay on the surface.
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The winning plate crumples into a new mountain range, while the loser is shoved underneath into an ocean of hot rock at 1,300 degrees Celsius.
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The asthenosphere.
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The temperature here is enough to melt rock into a liquid, but the insane pressures of all that mass keep it a superheated solid.
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Tectonic plates are usually in contact with water for thousands of years and absorb some of it.
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When they're submerged into the hot underworld, this water triggers chemical transformations that allow tiny portions to melt into magma.
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Liquid magma is less dense than solid rock, so it rises to the surface in furious bubbles that accumulate in sponge-like reservoirs right under the crust.
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If enough magma accumulates, it becomes powerful enough to pierce through the crust, which we experience as volcanoes.
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This happens under the winning plate, like a revenge attack by the loser before it's erased forever.
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The second main source of volcanoes are thought to be mantle plumes.
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These are columns of abnormally hot rock that rise all the way from the planet's core mantle boundary to the surface.
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Much less is known about them, but in a way, it's as if the Earth's mantle has weather patterns and mantle plumes are a little like hot air, rising to form storm clouds.
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Storms hundreds of millions of years old, made of rock circulating at a rate of a few millimeters per month.
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They don't care about the motion of tectonic plates, so they can break the crust to create volcanoes in the middle of nowhere
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that stubbornly stay active as the crust shifts around them.
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The volcanic boom meter.
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Scientists love to put big booms on a scale
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and came up with a logarithmic scale that measures the volume ejected during an eruption.
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The volcanic explosivity index or VEI.
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Simply put, it starts really small and gets very big very quickly.
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A VEI-2 eruption would fill 400 full Olympic swimming pools with lava.
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We have around 10 of these per year.
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At VEI-3, we already see devastating effects, like the eruption of the Semeru volcano in 2021 that destroyed thousands of homes in Indonesia.
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At VEI 5, we see catastrophic amounts of materials, cubic kilometers of debris, equivalent to an entire lake of molten rock blasted into the air.
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Like the 2022 Hunga Tonga Hunga Hapai eruption that sent a shockwave around the globe many times and created ocean-wide tsunamis.
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At a VEI of 6, an eruption can change the world.
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In 1883, the Indonesian island volcano Krakatoa erupted nearly continuously over the course of five months.
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One of those eruptions blew it apart, producing the loudest sound recorded in history.
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Ten trillion times louder than a rocket taking off heard halfway around the world.
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Thirty-meter-high tsunamis swept away nearby populations, and so much gas and ash were released that global temperatures cooled by nearly 0.5 degrees Celsius.
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Red, dusty sunsets followed for many years.
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At VEI-7, we get super-colossal eruptions, millennium-defining events that human civilization has only encountered a handful of times.
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Mount Tambora was a 4,300-meter-high mountain until it exploded in 1815 and released 400 times more energy than the Tsar Bomba.
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140 billion tons of ash and dust were shot halfway to space before smothering the world's skies, turning them a sickly yellow.
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There was no summer the following year, crops died and over 100,000 people perished.
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This is the dreadful potential of volcanic eruptions, with famines across the other side of the world and even centuries-long cold periods being attributed to them.
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Okay, but what's a supervolcano?
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The term supervolcano is a media invention and not a scientific term.
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The main issue with them is that not every eruption from a supervolcano is a super eruption.
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What makes supervolcanoes special is that they've been waiting to erupt for hundreds of thousands of years.
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Pressure builds up in colossal magma reservoirs several kilometers deep until
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it becomes strong enough to lift the rock above it by several meters.
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Rocks crack under the pressure until they finally give way
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and billions of tons of gas and ash blast out at supersonic speed.
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An insane explosion of at least a thousand cubic kilometers that impacts every corner of the globe.
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And yet, that is only a small portion of the magma reservoir.
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Super-eruptions are like a boiling pot of water popping its lid off and spitting a bit off the top.
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Afterwards, the ground collapses into the void left behind, forming a hole called a caldera caldera.
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Under this caldera, pressure starts building again until the volcano gathers enough energy for another supereruption.
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But this could take hundreds of thousands of years.
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It's estimated
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that one of the few volcanoes capable of supereruptions on Earth could cause a catastrophic eruption every 17,000 years on average.
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That would make them far more frequent than comparable asteroid impacts.
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The most recent supereruption is the Oranui eruption 26,500 years ago in New Zealand.
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With the force of dozens of billions of tons of TNT, a Mount Everest-sized pile of explosives,
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a huge portion of the landscape was scooped out and thrown into the atmosphere.
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It left behind a caldera spanning 20 kilometers, and it caused the entire southern hemisphere to undergo a period of abrupt cooling.
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Though among supereruptions, it's a mere firework.
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The Lake Toba eruption of 74,000 years ago was a much more significant turning point in history.
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It released a gargantuan 5,300 cubic kilometers of material, enough to blanket parts of South Asia in 15 centimeters of ash
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and trigger a rapid 4 degrees Celsius drop in global temperatures.
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It's possible that the volcanic winter lasted 10 years, followed by worldwide droughts for centuries.
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Earth's climate might have not recovered for a thousand years.
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The largest volcanic events we know of were not really huge explosions, but floods of millions of cubic kilometers of lava.
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The grand finale were the Siberian traps around 250 million years ago, a continuous release of lava for 2 million years.
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They raised the ocean temperatures to over 40 degrees Celsius, which caused the Permian-Triassic extinction, killing over 90% of all species.
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Earth's surface needed 9 million years to recover.
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These sorts of eruptions don't change the climate, they are the climate.
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But thankfully, we haven't seen anything even remotely close to that scale in many millions of years.
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So, should you be scared of supervolcanoes?
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Definitely not.
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They have been used to frighten many people and are overhyped as an unavoidable apocalypse.
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The most famous one, Yellowstone, will erupt again, but they will be relatively small eruptions.
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Natural disasters for sure, but not enough to devastate the US or come close to ending humanity.
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The chance of a VEI-8 eruption in the next few hundred years is less than 2%, and more importantly, it wouldn't come as a sudden surprise.
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However, less powerful but more frequent eruptions can also do serious damage to our civilizations
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and are in many ways a much greater concern.
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So we must watch for slow changes in magma reservoirs like ground swelling
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and temperature increases to get an early warning that can save the lives of people living the closest to a volcano.
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And there's time to develop solutions that can remove sulfur and ash from the stratosphere
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to eliminate the root cause of the climate disruption we've seen from previous eruptions. Who knows, maybe we'll even be able to turn this force of destruction
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into an agent for good by exploiting the geothermal energy held in their giant magma reservoirs.
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We've done this work for so many other disasters, and we are already doing things we could only have dreamed about decades ago,
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like sending a probe to perform our first asteroid redirection test.
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With determination, humanity really can solve anything.
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So while deep below us an angry hell is churning and waiting for its moment, you can sleep well tonight.

このレッスンについて

このレッスンでは、地球の火山活動やその影響について学びながら、英語スピーキングのスキルを向上させることを目的としています。特に、火山の爆発やその規模を示すボリュームを表現するために必要なボキャブラリーやフレーズを学びます。英語シャドーイングを通じて、発音を改善し、リスニングスキルを高めることができます。特にこのビデオの速さに合わせて影響力のある表現を身につけることで、スムーズで自信のあるスピーキングを実現しましょう。

重要な語彙とフレーズ

  • 火山 (volcano) - 地球内部のマグマが地表に噴出する地点。
  • 噴火指数 (volcanic explosivity index, VEI) - 噴火の規模を測る指標。
  • マグマ (magma) - 地下で溶けた岩石の液体。
  • テクトニックプレート (tectonic plates) - 地球の表面を構成する板。
  • 超火山 (supervolcano) - 巨大な規模の火山。
  • アスファルト (asthenosphere) - 地球内部で高温・高圧の固体層。
  • 津波 (tsunami) - 地震や火山噴火によって発生する巨大な波。
  • 冷却 (cooling) - 温度が下がること。

練習のためのヒント

このビデオはスピーディーな話し方が特徴ですので、shadow speechを用いてスピーキングの練習をしましょう。最初にビデオを見ながら、話し方や発音を注意深く聴いてください。次に、言葉が発せられるのを待って、その後に自分の声で同じ文を繰り返します。この方法を用いることで、トーンやリズムを真似ることができ、自然な話し方の習得に役立ちます。IELTS スピーキング対策としても、この手法は非常に効果的です。ポイントは、すぐに繰り返すのではなく、少し遅れて付いていくことです。これがシャドーイングの鍵であり、あなたのスピーキングスキルを一段と引き上げてくれるでしょう。

シャドーイングとは？英語上達に効果的な理由

シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。