IM Interview: Supereruptions & Supervolcanoes

The scoop: Earth's history is riddled with super-eruptions that very likely had major impacts on the evolution of life, not to mention the survival of humanity. Supereruption researcher Michael Ort of Northern Arizona University chatted with me about what makes an eruption super, where the volcanoes are that cause all this trouble, and the likelihood of one popping off any time soon.

[9:07:38 AM] Larry O'Hanlon: Hi Michael!

[9:08:12 AM] Michael Ort: Okay, now is this working?

[9:08:40 AM] Larry O'Hanlon: Appears to be. Your in the PHX airport, right?

[9:09:19 AM] Michael Ort: Yep. Got up at 4:30 to catch the plane to PHX and now sitting here waiting for a flight to Seattle, and then down to Eugene.

[9:10:06 AM] Larry O'Hanlon: Long day of travel. It's like that going any place from Albuquerque too. Rather indirect.

[9:10:50 AM] Michael Ort: There must be a little delay in the transmission of messages. SO how do we go about this interview?

[9:11:00 AM] Larry O'Hanlon: What's in Eugene? Some equipment you want to use?

[9:11:11 AM] Larry O'Hanlon: Sorry, crossed messages. We just type back and forth to each other

[9:13:29 AM] Michael Ort: Yeah. We have a project on Quilotoa in Ecuador, a volcano that erupted about 800 years ago and wiped out pretty much all of central Ecuador. When the Incas arrived, it was still in bad shape, and so the devastation of central Ecuador presented an obstacle to communication between the northern capital, Quito, and the main capital, Cuzco. This trip will be to analyze melt inclusions in the crystals to see what the water pressure is. This can tell us the minimum depth at which they formed. Preliminary results suggest it was pretty deep - 6 km or deeper.

[9:14:32 AM] Larry O'Hanlon: Wow. That's a great subject of research! Nice to have that human civilization aspect of it.

[9:14:54 AM] Larry O'Hanlon: Now this was a "super eruption" right?

[9:16:42 AM] Michael Ort: Not by most people's definitions. This was perhaps 15-20 km3 total. Most people would define supereruptions as being a few hundred km3 or bigger. This was still a very big deal if you were in central Ecuador, though! The supereruptions of the Andes are in the central and southern volcanic zones.

[9:18:05 AM] Larry O'Hanlon: That's an area with quite a lot of calderas, is it not? Pretty pockmarked and elevated part of the planet.

[9:19:15 AM] Michael Ort: The central volcanic zone is packed with calderas, spread over a broad area N-S and E-W, whereas the southern volcanic zone is narrower E-W, so the calderas form more of a long line instead of a 'field'.

[9:20:07 AM] Larry O'Hanlon: And just how is a caldera different, more potentially eruptive, than something like Mount St. Helens [MSH]?

[9:23:32 AM] Michael Ort: There are two working definitions of caldera, unfortunately. The first, and simplest, is that a crater is <1 km diameter and a caldera is bigger. By that definition, MSH is a caldera too. This bothered a number of volcanologists after the 1980 eruption because most also believed that a caldera has to involve collapse. By this, we mean that the surface rocks collapse into the space made by the magma that erupted and left the underlying magma body. So the second definition is that a caldera is a big (>1 km minimum) depression formed by collapse. The problem with THIS definition is that it can be hard to figure out if there was collapse. In the end, though, with really big eruptions, the caldera is a normal result.

As to being potentially eruptive, MSH is actually more frequently active than the vast majority of calderas, but its eruptions are smaller when they occur.

[9:25:41 AM] Larry O'Hanlon: So these, and eruptions like them, are the largest Earth experiences, in terms of the amount of magma that comes out of the ground? Is that right?

[9:29:47 AM] Michael Ort: Well, maybe we can say they are tied for that honor. Supereruptions range in size up to somewhere around 3000-3500 km3 magma, which probably erupted in the period of weeks to a month or so. These eruptions produce pyroclastic material (pyroclasts = hot chunks) and send the material up into the stratosphere and also send it off laterally for tens to hundreds of km. The other really big kind of eruption are the flood basalts. These erupt enormous quantities of basalt lava flows. Columbia Plateau was a relatively small one of these eruption series. These produce lava flows that travel for hundreds of km and both types of eruptions release enormous amounts of gases that may change Earth's atmosphere significantly.

[9:31:21 AM] Larry O'Hanlon: Ah. So super eruptions, in a popular sense, would be pyroclastic and voluminous.

[9:32:21 AM] Michael Ort: Yeah. That is the poplar definition. The flood basalts are super also, but not supereruptions in the common sense.

[9:33:10 AM] Larry O'Hanlon: So beyond S. America, where are some of the other most super-eruptive regions? Do we even know where they all are?

[9:39:23 AM] Michael Ort: Do you mean Quaternary? I ask because there are a bunch of really cool older ones identified. For example, there was a huge series of supereruptions from volcanoes that stretch from a bit north of the San Juan Mountains in Colorado south through the Mogollon-Datil montains, the Chiracahuas, and then into the Sierra Madre Occidental of Mexico. This series produced perhaps the biggest caldera field ever made. There are late Miocene to Quaternary calderas in central Mexico that produced eruptions that are in the supereruption range. The central Andes, especially the southern part of Bolivia, far NW Argentina, and northern Chile, produced a great series of supereruptions from enormous calderas between 10 and 1 million years ago. A few large calderas in the southern volcanic zone of the Andes produced eruptions that reached the lower end of supereruption size. Toba caldera and a few others in Indonesia produced supereruptions. New Zealand has had a few big eruptions and their volumes get up to supereruption magnitude, although I have to admit I can't remember the exact numbers right now. In the US, Yellowstone, Valles, and Long Valley are the big Quaternary calderas that produced supereruptions.

[9:41:25 AM] Larry O'Hanlon: I'm thinking in terms of what we know throughout Earth's history. How common these big eruptions are. It's almost like they serve as a reminder how little time we've been around (i.e., we have not experienced one of them).

[9:43:51 AM] Michael Ort: Well, that is not actually true. The work I have seen on the spreading and development of humans and our genes suggests that humans had made it into India and perhaps Indonesia at the time of the great Youngest Toba Tuff [YTT] eruption 70,000 years ago. There is a genetic bottleneck then, according to some studies, that may be related to a major die off of humans. The YTT was a HUGE eruption (3000 km3) and may have created something like a global winter for a few years.

But yes, we haven't seen many. The Maoris arrived in NZ just a few centuries after the Taupo Ignimbrite eruption (a bit small for a supereruption, but still big) and probably encountered a landscape still in recovery.

[9:44:43 AM] Larry O'Hanlon: Oh yes. I've heard about that.

[9:46:04 AM] Michael Ort: You can see the YTT story on a number of human genetics sites. I can find you one if you want - this one is interesting http://www.bradshawfoundation.com/journey/

[9:46:47 AM] Larry O'Hanlon: I recall it was called on to explain the low diversity of the human genome, as if we came from a small population of survivors. Thanks for the link!

[9:49:21 AM] Michael Ort: Yeah. Either that or we really aren't mutants! I think the big thing about supereruptions is that they are global in scope. That is what distinguishes them from more normal eruptions. They affect the Earth's atmosphere by sending huge amounts of gases and ash into the stratosphere, which is above the troposphere (where weather is). By getting it up so high, the gases, aerosols, etc. stay in the stratosphere for years and affect the climate for a long time. SO, you don't have to be close to a supereruption to have it affect you.

[9:50:47 AM] Larry O'Hanlon: That's a good way of drawing the line. By the effect.

[9:53:01 AM] Michael Ort: Yes, but even that is a little wishywashy. The good-sized Pinatubo eruption sent enough sulfur into the stratosphere to cause a noticeable cooling (something like half a degree) for the next couple of years. It was around 5 km3 - nowhere near a supereruption. The thing with supereruptions is that they magnify all the aspects we normally see from eruptions, and now we are trying to find out if there are positive feedbacks that then create new effects.

[9:53:32 AM] Larry O'Hanlon: Ahah. Got it. Are there any places you'd bet are next in line for a super eruption?

[9:56:58 AM] Michael Ort: Oh goodness. Hard to say with any certainty. We know that there are a bunch of active large calderas around the world, so they could go, but, because no one has ever measured the leadup to a supereruption, we have no real idea what that will look like. Will we see really large amounts of up-doming in advance? What will seismicity look like? Gas releases should be enormous, but can we recognize them? Remember that, in order to erupt hundreds or thousands of km3 magma, it will take some time, perhaps centuries or more, to assemble the magma into one connected, near-surface body. Will we recognize this process?

[9:58:29 AM] Michael Ort: That said, in the US, I would say Yellowstone and perhaps Long Valley are the best candidates. Rabaul in New Guinea is another active one. Perhaps Taupo in NZ. Campi Flegrei in Italy has produced 100 km3 eruptions, so a larger eruption is not out of the question. But in all cases, these are unlikely in our lifetime, and perhaps in our species' lifetime.

[10:00:10 AM] Larry O'Hanlon: sorry. Had to let the carpet cleaners in Well, that's nice to know. Nothing for folks to worry about. Last question: What do you think is more likely: a super eruption or a meteor impact?

[10:07:59 AM] Michael Ort: Okay, we are looking at a frequency rate of a 300 km3 eruption every 100,000 years or so. I am trying to come up with a frequency for meteor impacts that are of a similar order of magnitude. A 1-km diameter object hits Earth about every million years. That would have a bigger effect than the 300 km3 eruption, probably, but has 1/10 the frequency. 100 meter diameter objects hit every 10,000 years and are probably a little less damaging. So, a rough guess is that the chances are pretty similar.

[10:09:13 AM] Larry O'Hanlon: I just had to ask, because the impact folks seem to sometimes use the threat risk as a way to loosen up funding. ;)

[10:11:37 AM] Michael Ort: It IS a risk, but humans have a hard time evaluating this sort of risk. We have a higher chance of dying by being hit by a car than from a meteor, but we feel like we have some control over the car accident, and we are more familiar with that risk (and the fact that we have not YET been hit by it).

[10:13:07 AM] Larry O'Hanlon: So true. That adds to the fascination of this stuff -- the human element is so huge. Well, looks like our time is up. Thanks for your time and willingness. FYI, You may be hearing from Michael Reilly, our geoscience writer. He may want to do a news story about your work. Cheers!

[10:14:19 AM] Michael Ort: See you later! I hope the carpets are clean. Do NOT EVER lift the carpets up and look at what is underneath. You will never lay on the carpet again.

[10:23:25 AM] Larry O'Hanlon: thnx! gotta rip them out for good one of these days.

Article posted September 21, 2009.

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