What is a Super Volcano

The Earth is so much bigger than us—it’s hard to get a sense of its scale.  A good example of this is the difficulty in picturing the volcanic caldera in Yellowstone National Park that underlies all the geysers and hot springs there.  Public perceptions of it range from the reasoned reports of geoscientists at the Yellowstone Volcano Observatory all the way to sensationalism in some parts of the media that can be pretty scary sometimes.

Are we all going to die at any moment from a Yellowstone eruption?  Do we have to be rocket scientists to understand the situation?  Just what is a super volcano, anyway?

♦ Definition of a super volcano

The United States Geological Survey (USGS) doesn’t actually define the term “super volcano,” as it has no scientific meaning, but they do state that it “implies a volcanic center that has had an eruption of magnitude 8 on the Volcano Explosivity Index (VEI), meaning the measured deposits for that eruption is [sic] greater than 1,000 cubic kilometers (240 cubic miles).”

The Volcano Explosivity Index is a strange thing, for it classifies some eruptions as “gentle.”  To most of us, any volcanic eruption is violent, even in Hawaii, but geologists see these events a little differently.  To them, the beautiful spectacle of an eruption like those at Stromboli, in Italy, is “gentle,” and they classify such things as a VEI 1.

The eruption of Eyjafjallajökull in Iceland from March to May 2010 was considered a VEI 4, with a volume greater than 0.1 cubic kilometer.  Considering the impact that had on airlines and on millions of people, VEI 4 eruptions would seem to be pretty bad, but the 1980 eruption of Mount St. Helens was 10 times more powerful, a VEI 5 on this logarithmic scale.  It ejected over one cubic kilometer of ash, pumice, and rock, causing 57 fatalities.

The 1883 eruption of Krakatoa, a VEI 6 eruption that ejected more than 10 cubic kilometers (2.4 cubic miles) of material, was 10 times more powerful than Mount St. Helen’s 1980 eruption, and 100 times more powerful than the one in Iceland in 2010.  Now try to imagine something 100 times bigger than Krakatoa in 1883:  that is a VEI 8…super-sized, indeed!

♦ Calderas

Super eruptions, or those on the more powerful end of the scale, can be found in caldera volcanoes.

Yellowstone Caldera is one of over 80 caldera volcanoes that are known worldwide.  Almost half of them have erupted during recorded history (but not Yellowstone).  A few of those eruptions have been quite large, like the VEI 6 eruption at Novarupta, Alaska, the largest known eruption of the 20th century.

“Caldera,” like the word “cauldron,” implies heat; both words come from “caldarium,” the name ancient Romans gave to the room with a hot bath in it.  Today, a caldera volcano is one that erupts so much magma, it collapses in on itself, leaving a generally circular depression that is much wider than the eruptive vent.

Crater Lake is a caldera that was left after a volcano, known today as Mount Mazama, literally blew its top in a VEI 7 eruption some 7,000 years ago.  Volcanism went on intermittently afterwards, and the last eruption at Crater Lake Caldera happened 800-900 years ago; it left a small dome underneath the waters east of Wizard Island.

The largest confirmed caldera-forming event known on Earth occurred over 27 million years ago.  This was the Fish Canyon eruption from an ancient caldera in what is now Colorado.

Yellowstone has had three caldera-forming eruptions, some 2 million, 1.2 million (the third largest one known), and 0.6 million years ago.  Its most recent volcanic eruption was much smaller, however, and happened some 70,000 years ago, when thick, gooey lava flowed out over the land, forming the Pitchstone Plateau.  Steam-powered eruptions, known as phreatic eruptions, happen there, too, with the most recent one occurring around 1350 B.C.

♦ The Yellowstone “Super Volcano”

A more accurate name for a super volcano might be a caldera volcano, as these have presented the most powerful eruptions known.  Yellowstone Caldera certainly qualifies for the “super” tag, but with so many caldera volcanoes around, how did it end up at the center of a media storm?  A big factor may be its location in the world’s first truly national park, one of the most beautiful and well publicized parks in the world today.

In a 2005 article in “Geotimes,” Jake Lowenstern, the scientist-in-charge at Yellowstone Volcano Observatory, described a combination of events that also certainly contributed to the focusing of attention on Yellowstone.  These included the formation of the Yellowstone Volcano Observatory at around the same time that the BBC did an episode on the park’s volcanism. Next, while more scientific study was yielding new discoveries, such as a thermal feature under Yellowstone Lake, a large earthquake in Alaska led to changes in several of the park’s hydrothermal features, causing public concern.  Then the joint BBC-Discovery Channel movie, “Supervolcano,” came out.  It was a fictional drama about what would happen today if one of the volcano’s biggest eruptions repeated itself.  The culmination of all these events are described in the article as “explosions in the newspaper” and “cataclysms on the Internet.”

Today, the Yellowstone Volcano Observatory Web site offers the most complete and accessible information, for scientists and lay people alike, on the current state of knowledge of the volcano and its status, which right now is “normal,” with aviation code “green.”  Intensive monitoring goes on continuously for many different types of signals, any of which could indicate another eruption is on the way and how big it might be.  The news is this:  Yellowstone Caldera sleeps today underneath a blanket of beautiful rock formations, thermal features, and dramatic natural vistas.

♦ “Don’t it always seem to go…”

Not too long ago, in the Okataina volcanic complex of New Zealand, there used to be hot springs and volcanic terraces even more beautiful than those at Yellowstone.  They arose from Lake Rotomahana, and people came from all over the world to see them, even though they were located in a very out-of-the-way section of the back country.  Then, early on June 10, 1886, the volcano that was providing the heat for that natural wonder exploded in a VEI 5 eruption, killing over a hundred people.  The beautiful landscape was devastated and the lake and terraces were gone, most probably forever.

Still, we can’t forget their beauty.  An expedition was mounted recently to excavate through all the volcanic deposits, in the hope that the beautiful terraces did survive the blast.

The volcano that powers all the hydrothermal features of Yellowstone National Park today, and built its hills and valleys, is one of the greatest natural wonders of the world, not least because it is a “super volcano” and a quiet one just now that can be admired and explored cautiously.  This will change, and we will adapt to that change, but we will never be able to bring back the beautiful features that exist today.

The springs and terraces and geysers of Yellowstone National Park are so fleeting on the background of geological time.  Let us enjoy them to the fullest, and without fear, while we can.


Jake Lowenstern, “Geotimes,” June 2005:  “Truth, fiction and everything in between at Yellowstone.”  Retrieved January 28, 2011, from http://www.agiweb.org/geotimes/june05/feature_supervolcano.html

United States Geologic Survey.  “Questions About Super Volcanoes.”  Retrieved January 28, 2011, from http://volcanoes.usgs.gov/yvo/about/faq/faqsupervolcano.php

Wikipedia.  “Volcanic Explosivity Index.”  Retrieved January 28, 2011, from http://en.wikipedia.org/wiki/Volcanic_Explosivity_Index

National Geophysical Data Center.

John Seach.  The largest volcano eruptions.  Retrieved January 31, 2011, from http://www.volcanolive.com/large.html

Volcanism Blog.  “Saturday volcano art:  Charles Blomfield, ‘Rotomahana after the eruption (1887)’”  Retrieved January 31, 2011, from http://volcanism.wordpress.com/2009/03/14/saturday-volcano-art-charles-blomfield-rotomahana-after-the-eruption-1887/