Okay, volcanoes are scary as it is, and now you’re telling me that there’s something called…Supervolcanoes?
Well, they are real, but they sound scarier than they are. Supervolcanoes are a complex class of volcanoes that rank 8 on the Volcano Explosivity Index(VEI), the highest value assigned to any of the different kinds of volcanoes. It means that when they super-erupt(there can be smaller eruptions which aren’t supereruptions), they spew out 1000 km3 of tephra(fragmental material produced from a volcanic eruption) into the atmosphere. In comparison, when a traditional volcano erupts, they churn out around 100 km3 of tephra into the air.
The term supervolcano, popularised by a BBC documentary, isn’t really very scientific. The technical term for it is a ‘mega-caldera’. A caldera is a large, hollow depression formed after a massive volcanic eruption. This happens because, after a massive eruption, the volcano has dispensed enough of the magma that had accumulated in its interior to not be able to support the weight of its own volcanic edifice(the mountain that we traditionally associate volcanoes with). It then collapses unto itself to form a caldera. Calderas vary in size from 1-100 km in diameter and can be of quite a few different types like crater-like calderas, shield volcano calderas, and resurgent calderas. Supervolcanoes form resurgent calderas which can be almost 80 km in diameter.
Supervolcanoes go through a life cycle of three major stages
A surge of trapped magma - The first stage in the life cycle of a supervolcano involves a buildup of trapped magma from a hotspot in the interior of the earth’s crust. The hotspot is continuously being fed by magma through a “pipeline” from the earth’s molten interior. As the magma builds up, it creates undue pressure on the ground surface above and causes it to burgeon. The supervolcano Campi Flegrei in Italy caused the ground to rise up by almost 6 ft within a span of 2 years due to the rapidly accumulating magma in its interior.
The second stage in a supervolcano’s life cycle is the stuff of our nightmares. When the magma build up reaches a critical mass, the volcano erupts with all its might, churning out almost a 1000 cubic kilometers of magma into the earth’s atmosphere.
The most recent supervolcano eruption was that of Taupo in New Zealand which erupted around 26,000 years ago. It had a VEI of 8 and sent around 1100 cubic kilometers of tephra into the atmosphere.
Remember when I said that supervolcanoes sound scarier than they are? It’s because on average(it varies a lot), a supervolcano erupts once in 100,000 years. After a supereruption, the volcano collapses into itself forming a large caldera. The ground gradually cools down and rainfall fills up the depression to gradually form a lake. Years pass by and eventually, animals begin to reclaim the area around the caldera giving rise to an entire ecosystem of animals, and natural geothermal features in the lake begin to attract tourists from all around the world, all unaware of the monster that lay asleep right beneath their feet.
In the movie 2012, there is a scene that depicts a cataclysmic eruption of the Yellowstone mega-caldera in the Yellowstone National Park in Wyoming, US. In reality, the Yellowstone caldera is in resurgence with its last supereruption occurring almost 640,000 years ago. With an average time lag of 700,000 years between its supereruptions, the Yellowstone caldera is not overdue for an eruption for at least a while from now.
A supereruption, as stated above, is very rare. But when they do happen, they cause catastrophic damages to the earth and its atmosphere. The unimaginable volume of volcanic ash that a supereruption spews out into the atmosphere causes long-lasting climate changes, often resulting in the inception of a short ice-age. It can also cause complete extinction of species. However, on the flip side, they also help substantially cool off the earth, recycle minerals from the earth’s interior, form fertile new soils, and also create entirely new lands. We could say that it is nature’s own refresh button, one of many.