The Biggest Eruptions That Changed Earth Forever

The Earth is a gigantic ball of semi-molten rock with a heart of iron as hot as the surface of the Sun. Titanic amounts of heat left over from its birth and the radioactive decay of trillions of tons of radioactive elements find no escape but up. Currents of rock spanning thousands of kilometers carry this energy to the surface. Earth's crust is the only thing in their way; it feels solid to us, but it's only a fragile barrier, an apple skin around the claiming Behemoth.

True apocalypses can break through and unleash eruptions tens of times more powerful than all of our nuclear weapons combined, subjecting the climate to centuries worth of change in a single year while drowning continents in toxic ash and gases. Supervolcanoes: how big can they get, and will they put an end to humanity?

Volcanoes—there are many types of volcanoes, from towering mountains to lava domes—but they have two main sources. The first is at the boundaries between tectonic plates, the pieces of the crust 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 cm per year. This sounds slow, but on geological time scales, it is a titanic struggle over who gets to stay on the surface.

The winning plate crumbles into a new mountain range, while the loser is shoved underneath into an ocean of hot rock at 1300°C—the asthenosphere. The temperature here is enough to melt rock into a liquid, but the insane pressures of all that mass keep it a superheated solid. Tectonic plates are usually in contact with water for thousands of years and absorb some of it when they're submerged into the hot underworld.

This water triggers chemical transformations that allow tiny portions to melt into magma. 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. If enough magma accumulates, it becomes powerful enough to pierce through the crust, which we experience as volcanoes. This happens under the winning plate, like a revenge attack by the loser before it's erased forever.

The second main source of volcanoes is thought to be mantle plumes. These are columns of abnormally hot rock that rise all the way from the planet's core-mantle boundary to the surface. 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.

Storms hundreds of millions of years old, made of rocks circulating at a rate of a few millimeters per month, they don't care about the motion of tectonic plates, so they can break the crust to create volcanoes in the middle of nowhere that stubbornly stay active as the crust shifts around them.

The volcanic boom meter—scientists love to put big booms on a scale and came up with a logarithmic scale that measures the volume ejected during an eruption: the Volcanic Explosivity Index or VEI. Simply put, it starts really small and gets very big very quickly. A VEI 2 eruption would fill 400 full Olympic swimming pools with lava. We have around 10 of these per year.

At VEI 3, we already see devastating effects, like the eruption of the Samaru volcano in 2021 that destroyed thousands of homes in Indonesia. 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, like the 2022 Hunga Tonga Hunga Ha'apai eruption that sent a shockwave around the globe many times and created ocean-wide tsunamis.

At a VEI of 6, an eruption can change the world. In 1883, the Indonesian island volcano Krakatoa erupted nearly continuously over the course of 5 months. One of those eruptions blew it apart, producing the loudest sound recorded in history—10 trillion times louder than a rocket taking off—heard halfway around the world. Thirty meters high tsunamis swept away nearby populations, and so much gas and ash were released that global temperatures cooled by nearly 0.5°C. Red, dusty sunsets followed for many years.

At VEI 7, we get super colossal eruptions—millennium-defining events that human civilization has only encountered a handful of times. Mount Tambora was a 4,300 m high mountain until it exploded in 1815 and released 400 times more energy than the atomic bomb. One hundred and forty billion tons of ash and dust were shot halfway to space before smothering the world’s skies, turning them a sickly yellow. There was no summer the following year; crops died, and over 100,000 people perished.

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. Okay, but what's a supervolcano? The term "supervolcano" is a media invention and not a scientific term. The main issue with them is that not every eruption from a supervolcano is a super eruption.

What makes supervolcanoes special is that they've been waiting to erupt for hundreds of thousands of years. Pressure builds up in colossal magma reservoirs several kilometers deep until it becomes strong enough to lift the rock above it by several meters. Rocks crack under the pressure until they finally give way, and billions of tons of gas and ash blast out at supersonic speed—an insane explosion of at least 1,000 cubic kilometers that impacts every corner of the globe.

And yet, that is only a small portion of the magma reservoir. Super eruptions are like a boiling pot of water popping its lid off and spitting a bit off the top. Afterwards, the ground collapses into the void left behind, forming a hole called a caldera. Under this caldera, pressure starts building again until the volcano gathers enough energy for another super eruption.

But this could take hundreds of thousands of years. It's estimated that one of the few volcanoes capable of super eruptions on Earth could cause a catastrophic eruption every 177,000 years on average. That would make them far more frequent than comparable asteroid impacts. The most recent super eruption is the Oruai eruption, 26,500 years ago in New Zealand, with the force of dozens of billions of tons of TNT—a Mount Everest-sized pile of explosives.

A huge portion of the landscape was scooped out and thrown into the atmosphere, left behind a caldera spanning 20 km, and it caused the entire southern hemisphere to undergo a period of abrupt cooling. Though among super eruptions, it's a mere firework. The Lake Toba eruption of 74,000 years ago was a much more significant turning point in history.

It released a gargantuan 5,300 cubic kilometers of material, enough to blanket parts of South Asia in 15 cm of ash and trigger a rapid 4°C drop in global temperatures. It's possible that the volcanic winter lasted 10 years, followed by worldwide droughts for centuries. Earth's climate might have not recovered for a thousand years.

The largest volcanic events we know of were not really huge explosions but floods of millions of cubic kilometers of lava—the grand finale with the Siberian Traps around 250 million years ago—a continuous release of lava for 2 million years. They raised the ocean temperatures to over 40°C, which caused the Permian-Triassic extinction, killing over 90% of all species. Earth's surface needed 9 million years to recover.

These sorts of eruptions don't change the climate; they are the climate. But thankfully, we haven't seen anything even remotely close to that scale in many millions of years. So, should you be scared of supervolcanoes? Definitely not. They've been used to frighten many people and are overhyped as an unavoidable apocalypse.

The most famous one, Yellowstone, will erupt again, but they will be relatively small eruptions—natural disasters for sure, but not enough to devastate the US or come close to ending humanity. 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.

However, less powerful but more frequent eruptions can also do serious damage to our civilizations and are, in many ways, a much greater concern. So we must watch for slow changes in magma reservoirs, like ground swelling and temperature increases, to get an early warning that can save the lives of people living the closest to a volcano.

And there's time to develop solutions that can remove sulfur and ash from the stratosphere 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 into an agent for good by exploiting the geothermal energy held in their giant magma reservoirs.

We've done this work for so many other disasters, and we are already doing things we could only have dreamed about decades ago, like sending a probe to perform our first asteroid redirection test. With determination, humanity really can solve anything. So while deep below us, an angry hell is churning and waiting for its moment, you can sleep well tonight.