Apr 13 2011

The Yellowstone Supervolcano

Did you know that there is a supervolcano hiding beneath Yellowstone National Park? I know scientists frequently delight in telling the public all the horrible ways in which we can be killed, massive damage can be done, or even how the entire human civilization can be wiped out. (My friend, Phil Plait, even wrote an entire book dedicated to the topic – Death from the Skies). It’s a good hook for a scientific discussion – we have an instant morbid fascination with the prospect of epic disaster.

The supervolcano, as the name implies, is a really big volcano. In the past the Yellowstone supervolcano has erupted, to devastating effect. And it will erupt again some day. It’s just a matter of time. Supervolcano eruptions can be so big that they have even been blamed for mass extinctions in the past.

Yellowstone is over what geologists call a hotspot – an area where the hot magma of the molten mantle rises close to the surface, collecting in a magma chamber. At Yellowstone this hotspot is what is causing all the hot springs and geysers. This hotspot is actually stationary, but the North America plate is moving to the west-southwest over the hotspot, making it seem as if is moving to the east-northeast – now over the states of Wyoming, Montana, and Idaho.

Scientists have been mapping this hotspot, and recently they have discovered that the magma plume under Yellowstone is probably larger than was previously thought. Prior techniques for measuring the plume used seismic waves. The recent study used electrical conductance – imaging those parts of the rock that contain briny water (which conducts electricity), and is associated with the plume.

It’s not surprising that the two techniques produced different images, since they are looking at different physical properties. The new data suggests, however, that the magma plume is probably larger than the seismic imaging revealed.

This does not necessarily mean that Yellowstone is any more dangerous than we already thought it was. We know of several large eruptions (supereruptions, of course) of Yellowstone – 2.1, 1.3, and 0.64 million years ago. Based upon this pattern, it looks as if we might be due for another big one. Although this could still mean tens of thousands of years from now. Geologists feel that the probability of an eruption in the next few thousand years is actually quite low.

The pattern is probably real, in that pressure slowly builds up in the magma chamber and then is explosively released. There are many smaller eruptions, however, and this releases pressure, making the timing of bigger eruptions more variable. The last such smaller eruption occurred about 70,000 years ago.

Above is a graphic of the eruption debris field of the recent Yellowstone supereruptions. It’s difficult to imagine an eruption of such magnitude. The effects on weather and air quality would of course extend much beyond the debris fields demarcated above. The biggest eruptions also result in what are called caldera – and there are several in relation to Yellowstone. Essentially the magma chamber erupts and quickly empties, causing the overlying land to sink down into the chamber. The Yellowstone Caldera is about 50 miles in diameter.

Caldera result from the most violent eruptions, which occur about once every million years or so. The violent explosions can also result in pyroclastic flows – rapidly movement walls of gas and rock that can move at 450 mph over a wide range. These can occur with normal volcanoes as well, but of course are much larger with supereruptions.

Supervolcanoes are both fascinating and frightening. Even though it would be cool, I of course hope I never get to see such an eruption (at least not on the Earth).

For those interested in more detail, here is a pretty thorough site on the Yellowstone volcano system.

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11 responses so far

11 Responses to “The Yellowstone Supervolcano”

  1. Your Funny Uncleon 13 Apr 2011 at 12:34 pm

    There was a pretty interesting BBC docu-drama about this a few years ago. Not being a vulcanologist I can’t vouch for the accuracy of the science, but it was certainly a pretty scary show.

    http://www.youtube.com/watch?v=WF-RKzqNtz0

  2. bachfiendon 13 Apr 2011 at 5:07 pm

    Donald Prothero considers volcanos in his recent book ‘Catastrophes’ (strongly recommended).

    Devastating as an eruption of a supervolcano may be, he lists the three most likely short-term threats to human survival as:

    Global warming
    Nuclear proliferation with rogue states acquiring nuclear weapons
    Over-population.

    Fortunately, all three are threats that can be dealt with, given the will. Unfortunately, getting the will and motivation for at least two of them seems lacking.

  3. TheBlackCaton 13 Apr 2011 at 5:21 pm

    I was actually in Idaho not too long ago. Much of Idaho’s geography was actually created by the yellowstone supervolcano. The volcano used to be directly under what is now Boise, causing the land to rise and swell. This caused the land to swell, and created the largest exposed lava field in the world, craters of the moon. It eventually moved on (or rather the NA plate moved on), which cause the land to settle back down. This created the jagged and rugged landscape as well creating a second series of volcanic eruptions from the heat that was produced as the massive are of the crust shifted.

  4. Woodyon 13 Apr 2011 at 6:24 pm

    My wife and I travelled to Yellowstone for our anniversary a few years ago and had a great time. I hope to go back with our kids when they are old enough as it one of those places where the opportunities to share in the wonders of natural science are spectacular. What kid wouldn’t find geysers, boiling lakes, wolves, elk and bison cool?

  5. eeanon 13 Apr 2011 at 7:13 pm

    would solve global warming for our lifetime at least!

  6. Synoecaon 13 Apr 2011 at 8:35 pm

    you were supposed to debunk super-volcanoes.

  7. kloxon 14 Apr 2011 at 9:11 am

    I think a future mile-stone of humanity will be the ability to defuse volcanoes. Has there been intelligent discussion/publications about this? You hear the meteor impact plans all the time, but so far I haven’t found anything legitimate for volcanoes.

  8. daedalus2uon 15 Apr 2011 at 12:47 pm

    klox, I am not aware of anything either. It would be a lot harder than deflecting an asteroid and would likely take a lot longer. You would need to modify the crust enough such that the mantle plume wouldn’t be able to produce a hole in it or put a hole in the crust and maintain that hole such that the excess pressure and magma is drained away safely and without interfering with your hole.

    Another way might be to inject a dense solid that would melt and then the hot liquid would flow down and carry the heat down. Injecting metallic iron might work, but you would need many km3. That approach might not work because the heat isn’t really going any where, and the falling iron dissipates heat too. At sufficient depth the iron would freeze again, releasing its heat of fusion which would rise right back to where you don’t want it.

    I think the only way to do it would be with an actively cooled hole where the flow of magma through the hole is actively controlled. The only active control mechanism I can think of is to control the viscosity by injection of a viscosity control agent, water would reduce the viscosity, sand would increase it. You could also modulate the density by injecting iron. You would also need the capability of heating the inside of your tube electrically if it got too cold by accident.

    In the last 2.1 million years, Yellowstone has released some 4,310 km3 of magma, or about 2 km3 per thousand years or about 2 million m3 per year. Or about 5,600 m3 per day. With a 1 m2 cross section, that would imply a velocity of 0.06 m/s. 1 m2 is likely too small to easily keep open.

    Your cooled hole would have to go pretty deep, probably at least 10 km and you would have to cool your hole to where steel still has pretty good long term strength, no hotter than 200 C. You would have to circulate liquids to do that, you would probably choose a liquid metal with a density around that of the magma so the hydrostatic pressure doesn’t get very high. The pressure at the bottom of a 10 km hole is about 30,000 to 40,000 psi in magma, in water about half that. In other words you need 15,000 psi to drive water to the bottom of your tube to inject it into magma. A better fluid to use would be a magnitite slurry with a density close to that of magma. They make such things to use for coal cleaning, so the coal (density ~ 1.3) floats and the shale (density ~2.2) sinks.

    If you made the hole cooling/support system neutrally buoyant, it wouldn’t have to support vertical loads. But then you have to balance the density of the fluid inside with the weight and the shear loads and also with the weight of solidified magma on the outside. Doing all of that and keeping the magma inside your tube hot enough to remain fluid and at the right density as it expands from 40,000 psi would be tricky.

    You would probably used staged cooling on the outside of your tube so that some of the heat is removed at high temperature, 500 C or so in order to use that heat to generate the power to run it.

    I don’t think that humans would be able to allocate the resources to deal with such a thing in time to actually do it. They can’t with AGW and that is going to happen with virtual certainty. This would have a much longer time frame and with much less certainty than AGW and the worst effects would be local. People a thousand miles away would feel they could avoid the local effects even if they couldn’t.

  9. Paideumaon 15 Apr 2011 at 3:02 pm

    Another fun post!

    A couple thoughts…

    (1) You mention “the hot magma of the molten mantle”, which kinda makes it sound like the mantle is all molten (liquid). I point this out because I’ve encountered many people who do believe that. It’s my understanding that the current consensus holds the mantle to be generally solid. I am not a geologist, though, so I could be totally off base.

    (2) In doing a few minutes of informal research inspired by your post, I encountered two hypotheses that attempt to explain hotspots. The first “plume” hypothesis states that the molten material (magma) rises through the mantle up from the mantle-outer core boundary (the outer core being liquid) due to convection currents in the magma. This means the mantle really would be hotter and liquid underneath these hotspots.

    The second “plate” hypothesis states that molten material is generated in the crust by its partial melting (specifically melting of the minerals with the lower melting points) due to areas of higher friction, pressure, etc. resulting from plate tectonics. This means that the mantle would not be hotter or liquid underneath these hotspots.

    I couldn’t tell from my admittedly quick-’n-dirty research if this is an actual scientific controversy or if the “plate” hypothesis (which I’d never heard of before) was just the ravings of another lunatic with a keyboard and Internet access. Do you have any insights here?

  10. daedalus2uon 15 Apr 2011 at 11:27 pm

    The “hot spot” idea has to be generally correct. There are sources of heat in the mantle (radioisotope decay) and the core (freezing of iron). The heat from those sources has to go somewhere and the only place it can go is to the surface. What ever is in the mantle will get hotter until the heat can escape.

    There is too much heat to be transfered by conduction, so the heat has to be carried by convection. That generally is the plume model, a spot gets hotter due to radioisotope decay until it gets so hot that the heat is carried away by convection.

    That convection has to carry hot stuff up, and then other stuff has to flow down by displacement. The hot stuff flows up due to the differential pressure produced by differential density due to differential temperature.

    The Earth’s crust has a lot of water in it, and water greatly reduces the melting point of silicate melts and greatly increases their fluidity. On Venus, where there is much less water in the crust, the crust is much thicker and stiffer, even though the surface of Venus is much hotter. What happens on Venus is that because the crust is thicker and stiffer, the plumes underneath the crust have to get much hotter in order to generate the pressure gradient to “break through”. Then there is a massive flood of magma. This is like the flood basalts that happened in Siberia and released an estimated 1 to 4 million km3, over a thousand times what the Yellowstone supervolcano released. I suspect that the very large release was related to higher levels of geothermal heat from greater radioactive heat decay than is occurring now.

    The plumes of stuff moving up, cause other areas of stuff to move down. This is the essence of plate tectonics. Plumes move up and create new surface, and surface moves down, and is subducted down. The plumes moving up push surface until it collides with other surface and then one piece has to move down underneath the other piece. This subduction occurs at plate boundaries and the plate that gets moved down becomes hotter, the water and hydrated minerals form silicate melts and the volatile compounds in the subducted regions (water, carbon, sulfur, etc) form the volatiles that reduce the density of magma such that it can come up at volcanoes.

    The “ring of fire” is where surface is being subducted under other plates and where the volatiles are recycled by the volcanoes.

    There can be “hot spots” that are in the middle of a plate, and as the plate moves, the hot spot moves relative to the plate surface. This results in chains of volcanoes such as Hawaii. There is one hot spot, but because the surface moved, several volcanoes have resulted.

    The Yellowstone hot spot is also in the middle of a plate and not at its edge.

  11. RockScion 02 May 2011 at 8:57 am

    I’m a bit late to this I know, and I’m no expert on Yellowstone, but I am a geologist and wanted to point out a couple of things about hotspots.

    As Paideuma suggested, mantle plumes are not predominantly made of magma, and even the upper parts which do contain melt are not close to being 100% molten. The vast majority of the mantle is solid. Most of it, the asthenosphere, is hot enough to flow and convect (the very top part, the lithospheric mantle, is cool and rigid and makes up the tectonic plates). The plume hypothesis says that ‘hotspots’ like Hawaii and Yellowstone are caused by upwelling plumes of hotter material in the mantle, probably originating at the core-mantle boundary. Because the mantle material within the plume is hotter than normal mantle, it can melt at a greater depth and to a greater degree than normal mantle would in the same circumstances. It’s lower density also makes it more buoyant, causing uplift in the overlying plate, thinning it and allowing the hot plume material to rise to shallower depths and melt even more. In some cases, as with the Deccan Traps, the plate was thinned to the point of rifting, producing a huge outpouring of magma.

    Magma chambers on the other hand occur within the crust, and do not form part of the actual mantle plume. Wherever there is melting happening, for whatever reason, the magma is likely to rise up through the crust and collect in a magma chamber (or many magma chambers). As Steve says, where there is a constant supply of magma (like the Yellowstone hotspot), pressure will build up in the chamber and be released by an eruption.

    There is some genuine controversy around the plume hypothesis – it’s not quite my field, but to my knowledge the consensus at the moment is firmly on the side of plumes existing, and that’s the view I hold. The alternative view isn’t quackery though, there are real scientific questions about hotspots that haven’t been satisfactorily settled yet. The wikipedia article on plumes is fine on the basics, but does perhaps overstate the problems with the plume hypothesis.

    Also, if anyone’s googling around for info about plumes, you should be aware that http://www.mantleplumes.org is an anti-plume site, although that’s not immediately clear to a non-specialist. That doesn’t mean it’s wrong, but it is one sided so don’t use it as your only resource!

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