Generally speaking, the only good supervolcano** is an extinct supervolcano.
Like this one:
More information here
Now these scientists haven’t discover a new volcano. The Indian Peak-Caliente pyroclastic flow (ignimbrite) field is part of the Marysvale Volcanic Field (PDF), which geologists have known about for some time.
The news, I believe, is that the Brigham Young University, Berkeley Geochronology Center and Pacific Northwest National Laboratory geologists were able to trace out a single ash flow field – the Wah Wah Springs eruption – in this extremely complicated geologic setting, identifying a huge eruption of more than 5500 cubic km of material.
That’s bigger than the VEI “9” (on an 8-point scale) La Garita eruption around the same time, 30-35 million years ago. It’s also more than twice the volume of the largest known Yellowstone eruption – Huckleberry Ridge, 2.1 million years ago.
And they claim it happened over a one-week period.
An Ignimbrite Flare-Up
Western North America seems to be an exciting place today, what with the likelihood of massive earthquakes along the San Andreas fault and in the Pacific Northwest, as well as volcanic eruptions like that of Mount St. Helens in 1980.
Actually, though, things have really calmed down there over the ages.
Back in its youth – about halfway between the extinction of the nonavian dinosaurs and the start of the current ice age – the region that’s now western North America, particularly in the southwest, was literally hell on Earth.
…from modern-day Nevada and western Utah into Colorado, Arizona, New Mexico and Mexico, pretty much all the time.
Today the deposits from this period, sometimes called the Mid-Tertiary Ignimbrite Flare-Up, can be thousands of feet thick. The total volume is some 120,000 cubic miles of frozen once-speedy gray death clouds.
Hell on Earth – it’s not an exaggeration.
The scientists who discovered the vast extent of the 30-million-year-old Wah Wah Springs eruption also estimate that the region was rocked by at least 15 supereruptions, and they have found a total of 20 large calderas.
In a paper published this year, they say
This subduction-related ignimbrite flareup is the only one known in the world of its magnitude and … age that is not related to continental breakup.
What Caused the Mid-Tertiary Ignimbrite Flare-Up?
The North American continent actually wasn’t self-destructing then – it was growing.
This was because a formerly huge tectonic plate (called the Farallon plate) was subducting under the west coast (which was in modern-day Utah at the time) and sinking into Earth’s mantle, in the meantime plastering all the island arcs and other bits of land it carried onto North America.
Yes, even the land is an immigrant here.
This is a good and simple animation of the process in plain English.
As you can see there, the material that’s going down into the hot depths melts and some of it rises up a ways inland as a volcano.
This happens all over the world without setting off an ignimbrite flare-up (luckily for humanity). So, what was different about the event in Western North America?
I can’t say for sure because it’s at this point that all the online sources I can find start heading into dense geoscience text and diagrams, all seeming slightly different. In other words, the scientists themselves don’t know exactly what caused such a vast quantity of molten material to reach the surface.
There seems to be agreement on a few things, though.
Chemical analysis shows that up to half the erupted material was derived from Earth’s solid outer crust, i.e., the lithosphere. The rest of the material is very different and came from deeper in the Earth’s mantle. It was either molten or melted as it rose, as mantle rock is wont to do (PDF), especially if a subducting oceanic plate is nearby, bringing a lot of water down with it.
The subduction of the Farallon plate definitely had a lot to do with setting up conditions for the ignimbrite flare-up. My impression is that the geoscientists have problems explaining how so much mantle rock also got in there, and how such huge amounts of the subsequent mixture reached the surface.
As a general member of the public, I have a few questions, too.
- Was there a global winter?
- Did the flare-up have anything to do with the formation of the first permanent ice sheets in Antarctica, which happened a little afterwards?
- Why didn’t this flare-up trigger an extinction event?
The Process of Science
In any event, it happened and then stopped as the Farallon plate sank down deeper. This is good news – hell is not booked for a repeat engagement at that venue.
So here we are. In 2013, a team of scientists made the surprise announcement that over half of the Mid-Tertiary Ignimbrite formed at once in the Wah Wah Springs eruption some 30 million years ago.
That’s a pretty bold claim.
Now the rest of the world’s geoscientists will go over the study and review its results. There will be discussions about it and a lot of back and forth over the coming years. If no one can disprove it, the team’s theory about the Wah Wah Springs eruption will be accepted until a better one comes along.
That’s how science really works.
Media headlines tend to make science news sound like established facts, but what these announcements really mean is that experts have come up with their best explanation for some sort of evidence (in this case, years upon years of fieldwork in the Indian Peak-Caliente caldera complex in Utah and Nevada) and now are asking their peers to decide if it works or if someone out there can come up with a better idea.
One thing is for sure – this team has come up with one of the most awesome explanations ever for one of the most violent episodes in our planet’s long history.
** “Supervolcano” is a controversial term both because it has no scientific meaning and because it’s usually associated with scare headlines in the media for stories that have a tenuous (at best) connection with geological reality. I use it here at the blog because Jacob Lowenstern has defined it informally for “volcanic events in which at least 300 km3 of magma are explosively evacuated from a subsurface magma chamber … and deposited on the countryside as pyroclastic (i.e. fire-fragmental) materials—ash, pumice and rock fragments” – what’s good enough for the Scientist-in-Charge at the Yellowstone Volcano Observatory is plenty good enough for this amateur, too.