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What is a super volcano?



As the name implies, a super volcano is an extremely large volcano capable of blasting more than 1,000 cubic kilometers (240 cubic kilometers) of sediment. There are six known super volcanoes and twelve known super eruptions.

What is a super volcano?

If we want to see what makes a super volcano, we first have to understand what a volcano is – and what makes it super.

The Earth's internal structure is layered in three spherical shells: an outer solid crust (everything we see and go), a viscous mantle, an outer core that is much less viscous than the mantle (often considered liquid) ) and a solid inner core. A volcano is a rupture in the crust that allows the material from the asthenosphere to reach the surface in the form of lava, volcanic ash and gases.

One can imagine volcanoes as vents, through which melted rock escapes to the surface. 19659005] Most volcanoes appear because the earth's crust is broken into rigid plates called tectonic plates. These plates "float" on a hotter, softer layer in their coat. When the pressure of gases in the molten rock becomes too great, an eruption occurs, but to do so, a volcano must first collect magma in a magma chamber.

A magma chamber, like a cauldron of molten rock under great pressure, gradually shatters the other surrounding rocks as it tries to reach the surface to release its pressure. These magma chambers lie deep inside the earth, usually about 1-10 km deep.

A representation of the magma chamber of Yellowstone. Yellowstone is a well-known super volcano. Image via NPS

When an eruption occurs and material is ejected from the magma chambers, they sometimes form features called caldera: large circular or oval depressions more than 0.6 miles (0.6 km) in diameter. Calderas appear because the magma supports the weight above it, and when the magma is expelled through the volcano, the whole thing can collapse under its own weight. For this reason, calderas can resemble craters.

But sometimes the magma can not penetrate to the surface, so it collects in the magma chamber and builds up the pressure. As the magma pool gets bigger and bigger, the chamber grows and reaches ungodly pressure – and when it breaks out, it's a huge eruption; you could say a super eruption.

That's right: Supervulcans form when they collect enough magma and pressure for a gigantic explosion. From a formal point of view, geologists classify supervolcanoes with a "VEI" of 8. The Volcano Explosion Index (VEI) is a relative measure of the volcanic eruption volatility developed by researchers from the United States Geological Survey. The largest possible VEI value is 8 – so a super volcano is the largest possible volcano.

VEI and Ejecta Volume Correlation – note that the VEI is a logarithmic scale, which means that each degree of magnitude is ten times larger than the previous one. Tephra is the material that results from a volcanic eruption, regardless of composition or fragment size.

Study Volcanoes

Geologists are even able to study even extremely old eruptions ten million years ago. Supervulcan eruptions send ejecta all over the world and release massive amounts of debris – a thick layer around the volcano, which thins out further and further from the volcano. These deposits can be physically and chemically dated and analyzed and provide a lot of information about the first outbreak.

What are the super volcanoes?

Luckily, there are not that many super volcanoes on Earth. It is not clear how many super-eruptions there were in Earth's history (we'll use that term, though it's not entirely correct). Some studies have found evidence of 60 super eruptions, while others have reported 47 such events, the most recent of which was the eruption of the New Zealand Taupo volcano 26,500 years ago. The Oruanui outbreak was a very unusual eruption with a complex interplay between output and pyroclastic flows that covered New Zealand's North Island with Ignimbrit (a type of hardened tuff) to a depth of 200 meters (660 ft). The same volcanic area caused two more outbreaks, 340,000 and 1,080,000 years ago, respectively.

Another famous eruption is Lake Toba, which occurred 74,000 years ago (it is quite unusual to have two outbreaks in such a fast geological sequence). The eruption of Toba led to a volcanic winter (a decline in global temperatures due to volcanic ash and sulfuric acid and water droplets that darken the sun) with a worldwide temperature drop of 3-5 ° C (5.4-9.0 ° F) and higher latitudes up to to 15 ° C (27 ° F). This had catastrophic consequences for the wildlife of the planet – including the early humans. He killed most of the then living people and caused a population bottleneck in Central East Africa and India, which continues to influence the genetic makeup of the human world population.

An incomplete map of super volcanoes around the world. Red is VEI 8 and Orange is VEI 7.

The most famous super volcano is, without a doubt, the Yellowstone.

The Yellowstone Super Volcano

Unlike most volcanoes that emerge on the border of tectonic plates, Yellowstone (in Idaho, USA) is a hotspot. Hotspots are bags of unusually hot magma. It is assumed that these hotspots are powered by the underlying jacket. Interestingly, their position is not affected by plate tectonics – as the plates move, the hotspot stays in the same place because it is under the crust. This can create a so-called hotspot trail that leads to the illusion that the hotspot is moving – in fact, it is the surface of the earth moving across the hotspot. There are many scientific debates about the nature and development of hotspots, but let's go back to Yellowstone, right?

Do you remember, as we said, that hotspots can leave their mark? That's exactly what the Yellowstone hotspot did. There are not one but several calderas (including the Island Park Caldera, the Henry Fork Caldera and the Caldera of Bruneau-Jarbidge). The current hotspot is located below the Yellowstone Caldera.

The Calderas of Yellowstone. Picture credits: NPS

The largest eruption in the Yellowstone occurred 2.1 million years ago and had a volume of 2,450 cubic kilometers. However, it had several minor eruptions. The volcanic activity in Yellowstone seems to happen periodically – there was an outbreak 1.3 million years ago and an outbreak about 630,000 years ago. Much smaller eruptions (not super eruptions) happened 2270 years ago.

What would happen if Yellowstone erupted

A super-eruption of Yellowstone would have catastrophic consequences. The outbreak itself (the local lava and ejected rocks) would fade compared to what would happen on a larger scale. First, it could bury states like Wyoming, Montana, Idaho, and Colorado in three feet of volcanic ash that kills plants, animals, and insects alike. Electrical systems would be destroyed, houses would be crushed, and much of the US would be badly damaged.

But perhaps worse, the ashes would spread like a blanket around the world, enveloping the earth and reflecting back the sunlight, a volcanic winter. Temperatures could drop a few degrees, the harvest would fail and the famine is likely to spread around the world. This situation would take several years before finally normalizing.

Luckily that's unlikely.

A Yellowstone outbreak would be a catastrophic scenario. Luckily that will probably not happen. Picture credits: NPS.

Should we be worried?

Not really. Studies have shown that super eruptions are extremely rare – due to volcanic activity over the past 13.5 million years, a 1% probability of outbreaks of this magnitude over the next 460-7,200 years. Statistically, there are 1.4 million surges of volcano per million years, which means there is at least a 75% chance of a VEI 8 outbreak during this period.

La Garita Caldera is a large volcanic caldera in the volcanic area of ​​San Juan. It took place about 28 million years ago and is one of the largest known volcanic eruptions in the history of our planet. Picture via Wikipedia

While these eruptions can be extremely damaging, they are so rare that the time-averaged effect is really not that great . But here's the thing: VEI 7 eruptions occur much more frequently (10-100 times), which means that on average we should be more concerned about these VEI 7 eruptions than the supervolcano outbreaks.

The year without summer

Mount Tambora had an outbreak of VEI 7 in 1815, which led to 1816 "The Year without summer "

Supervulkans are among the most impressive features of our planet, capable of godless eruptions that would mess up the entire planet. But as so often, it's not the big sword that threatens, but the thousand smaller cuts.

Bonus: A Super-Super-Volcano

Interestingly, a 2004 study reported a VEI-9 outbreak, in charge of the Fish Canyon Tuff

Wait a minute – I thought you said VEI 8 was the maximum possible eruption?

Well, yes, but scientists found evidence of an eruption with a mass of> 10 16 kg and a magnitude of 9.2. So while VEI 8 is technically the largest classification, the Fiscany Canyon tuff eruption was more than 10 times larger than it would be necessary to classify it as a super volcano.

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