Science a GoGo's Home Page Forums General Discussion General Science Discussion Forum Secrets Behind Supervolcano Eruption

Researchers at Rensselaer Polytechnic Institute have discovered what likely triggered the eruption of a "supervolcano" that coated much of the western half of the United States with ash fallout 760,000 years ago. Using a new technique developed at Rensselaer, the team determined that there was a massive injection of hot magma underneath the surface of what is now the Long Valley Caldera in California some time within 100 years of the gigantic volcano's eruption. The findings suggest that this introduction of hot melt led to the immense eruption that formed one of the world's largest volcanic craters or calderas. Click Here .

Interesting, but pessimistic find Daniel.
Ever the optimist, I believe that supervolcanoes will lessen in intensity, eventually die out, as the Earth ages and cools.

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"You will never find a real Human being - even in a mirror." .....Mike Kremer.
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I gather that the heat in the mantle is mostly produced by radioactivity. Anyone have any idea of the half-life?

If you think in geological time scales Mike I too will agree with you. But I'm not expecting anything different to happen in the next 15 or 20 minutes. Or the next 15 or 20 million years.

Ever the optimist. <g>

As I understand geology I wouldn't expect supervolcanoes to diminish in intensity as long as continents keep drifting round the earth. The supervolcanoes are a product of melting of silicates as eroded material is pushed down into subduction zones. The silica-rich material melts first and erupts explosively. The photo in the article looks like what we call pumice, a relatively pure form of silica with many gas hole in it. Erupts as a pyroclastic flow. If one of these ever happens near you don't bother running. NZ has had several of these type of volcanoes but thankfully not since humans have arrived here. As a geologist said when I was working in the field, "if another of these happens we can put the North Island up for tender."

Returning to this again -


I've been able to glean a few details regarding mantle heat. I find it very interesting, but if you have different facts to hand, I'd be interested.

http://www.ieer.org/fctsheet/uranium.html

uranium-234: half life = 245 thousand years, 0.0055% of all uranium.
uranium-235: half life = 704 million years, 0.711% of all uranium.
uranium-238: half life = 4.46 billion years, 99.284% of all uranium.

Uranium 238 decays into thorium 234 (half-life 24.1 days) which then decays into protactinium 234 (half-life 1.17 minutes)

"Elements with short half-lifes, like uranium-235 and potassium-40 (half-life = 1.25 billion years), were important in the early thermal history of the Earth. About 2.5 billion years ago, elements with longer half-lives, like uranium-238, became more important. Heat production was about 4 times greater 4 billion years ago than it is today. Part of that high heat production is from the decay of the elements with short half-lifes. The other part of that heat was from the accretion of the Earth and the formation of the core. Estimates suggests heat production was divided equally between radioactive decay and accretion"

- Steve Mattox, University of North Dakota

It appears that the heat that causes volcanoes is produced almost exclusively by the decay of uranium 238, with a half-life approximately equal to the current age of the Earth. There's a lesser contribution from thorium decay, K40 decay, other isotopes, and possibly from tidal forces.

What it boils down to (I seem to be finding the puns) is that there will be no change in volcanic activity until the decay of isotopes produces insufficient heat to maintain mantle plasticity. At that point, plate tectonics will cease and the magnetic field will be lost *. I don't have a clue when that point will arrive, but I can imagine it might be at least a billion years hence. Does anyone have any more on this?

* That also means that the Van Allen Belt would vanish, does it not?

Without researching it the statements you have made are consistent with my understanding.

True, but the continents are only floating and drifting because they are sitting on a hot plastic magma.
I cannot believe that the majority of the heat in the Earths core comes thru the decay of Uranium etc.?
Surely the hot liquid metallic core of our Earth is a result of our Earths early formation?

All our companion Planets are supposed to have been 'pulled-out' or formed from a hot proto Sun Giant?

There is enough Radio-active material in our crust, since it has been stated that there would not be enough Uranium
to go round were there to be three times as many Atomic Power Stations built, as there are today. Its already getting in short supply.
Could there be substantial quantity of radio-activity within the Earths core? Even if there was, it would be naturally moderated by the various granite rocks, other rocks, and metals, in the same way as we control the output of our Atomic power stations......else we would have been blown to kingdom come by now? The fact that we havnt, nor have we detected any really hot radio-active spots within our core, must mean that any radio-activity must be well separated and well mixed within our metallic core.
I'd rather bet there is not enough to keep this Earths core molten.
Also remember that all Lead found upon Earth was once Uranuim 235 ....and there is not enough of that.... .to supply all the lead-acid batterys that might be wanted to go in Cars and Trucks of the future, at the pace we are building them today. The Chinese have already overtaken the USA in vehicle output.

Sorry guys, I prefer to believe our heat came about by the formation of a molten Earth, PLUS its keeping its internal heat quite hot due to its internal dynamo, and our 24 hr spin.
Our strong Magnetic field, plus its occasional reversals, dosnt come from radioactive decay. We are lucky to have a good self-sustaining metallic dynamo, as do the other planets.

Now the Moon dosnt have a magnetic field (its tiny and fixed) Its supposed to be approx the same age as the Earth, and cold.
So there can't be much radio-activity up there?
Even more to the point, Venus similar in size to Earth, dos'nt have a magnetic field at all, very odd.


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"You will never find a real Human being - even in a mirror." .....Mike Kremer.
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Mike wrote:
"I cannot believe that the majority of the heat in the Earths core comes thru the decay of Uranium etc.? Surely the hot liquid metallic core of our Earth is a result of our Earths early formation?"

I don't believe that is what was written. I think the statement was that most of the heat currently being produced is from U238.

[/quote] Mike Kremer wrote:
"I cannot believe that the majority of the heat in the Earths core comes thru the decay of Uranium etc.? Surely the hot liquid metallic core of our Earth is a result of our Earths early formation?"
[/quote]
Daniel wrote
I don't believe that is what was written. I think the statement was that most of the heat currently being produced is from U238. [/quote]
Mike Kremer wrote;
Huh? Must have missed that
Where does it say that " most of the heat currently being produced is from U238?"

Mike: "Now the Moon dosnt have a magnetic field (its tiny and fixed) Its supposed to be approx the same age as the Earth, and cold.
So there can't be much radio-activity up there?"

I didn't say that radioactivity was the direct cause of the magnetic field. The magnetic field arises as a result of convection of molten iron within the outer liquid core, along with a coriolis effect caused by Earth's rotation. I know, that's not what I said either, but make allowances, it's a long time since I went to school! Fortunately for me, that wasn't my main point.

What I'm really trying to get at is: are there any estimates of how long it will be before the mantle cools sufficiently to stop convecting, thus ending tectonic plate motion and volcanic activity? According to the articles I've found so far, the main source of heat is, in fact, decay of radioactive isotopes. I'll keep looking, and i'll post any good links.

While the scientifically mainstream explanation for these temperature gradients is that the heat is simply left over from the planet's initial formation, a theory espoused by J. Marvin Herndon states that fast breeder nuclear reactor type reactions occur in the core of Earth.

http://en.wikipedia.org/wiki/Earth_core#core

Yes, that's given to account for the temperature of the core, but it doesn't account for the mantle temperature.

I emphasise that I'm talking about the mantle heat, here, not the core heat. Mantle heat, convection, tectonics and volcanic activity. Ignore my misleading gaffe about the magnetic field, which is, of course, connected with liquid core.
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http://earth.leeds.ac.uk/~eargah/Conv.html

?The [mantle] heat is generated by the radioactive decay of natural elements like uranium.?

Greg Houseman
Institute of Geophysics and Tectonics
School of Earth and Environment
University of Leeds
Leeds, LS2 9JT
UK
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OK, Mike, sorry about this piecemeal post, but I just found time to go through your comments properly...

"I cannot believe that the majority of the heat in the Earths core comes thru the decay of Uranium etc.?"

- No, I don't think it's a signicant factor in the core, only in the mantle'

"it has been stated that there would not be enough Uranium to go round were there to be three times as many Atomic Power Stations built, as there are today. Its already getting in short supply."

- That may well be, but the uranium that counts is in the mantle, not the crust

"Also remember that all Lead found upon Earth was once Uranuim 235 ....and there is not enough of that.... .to supply all the lead-acid batterys that might be wanted to go in Cars and Trucks of the future, at the pace we are building them today. The Chinese have already overtaken the USA in vehicle output."

- Yes, there's not much uranium 235 in the crust. It has a shorter half-life than uranium 238 (below), and it's the latter that's providing the mantle heat (together with other isotopes)

uranium-235: half life = 704 million years, 0.711% of all uranium.
uranium-238: half life = 4.46 billion years, 99.284% of all uranium.

- Bear in mind, also, that in the process of accretion, the heavier elements would have tended to sink toward the core, with relatively small amounts remaining in the crust. One good example is iridium, very rare in the crust, except where it arrived after the crust had solidified (google 'KT Boundary Event').

"All our companion Planets are supposed to have been 'pulled-out' or formed from a hot proto Sun Giant?"

- Not quite. The theory is that when the sun condensed from a cloud of dust and gas, there remained a sufficient amount in the shape of a disc in orbit around it to form the planets. This happened gradually by accretion. The accretion process left the Earth in a molten state that allowed most of the heavy elements to sink toward, or into, the core.

"Our strong Magnetic field, plus its occasional reversals, dosnt come from radioactive decay. We are lucky to have a good self-sustaining metallic dynamo"

- Absolutely, excuse my gaffe!

Over to you.

Both Redewnur, and Mr Bigg have made excellent points

But I am not going to push my point ie That the Earth's heat is a
result of its initial hot gas formation, as is our Sun and our
accompaning Planets. But I am going to go back a few Billion years.
Both your points are excellent, and after some thought, I must
conceed that yes, radioactive fission does ADD to the heat of our
Earths core. Note I have underlined ADD, since an interesting
thought is--just how much heat from fissionable materials is bei
ADDED to our core.
One could start a new discussion with regard as to what might have been the original heat ratio inputs to our Earth, 4.5 Billion years ago when it was first formed?(* see note below)

Two Billion years ago, our Earth had solidified, but with a lot of fast plate movement, due to it having a substantially hotter
interior than today. In addition the ADDED heat from radioactivity
was higher in the core then * ...than today. Its a chicken and egg problem, where did the MAJORITY of our Earths heat come from, say 3 Billion years ago?

Modern Uranium mining statistics state that---in every Uranium mine so far discovered, (the biggest is in Gabon, Africa)....that of the three Radioactive isotopes of Uranium 234,235,and 238, it is Uranium 235 that is mined, because its 235 that sustains a nuclear chain reaction, once it is CONCENTRATED.
Very very interestingly the mining engineers and scientists state, "that--All Uranium 235 atoms, make up 0.720 percent of the total, WHEREVER its found, anywhere in the Earths crust, on the Moon and even in Meteorites!!!!"

Scientist state that even the most massive concentracion of mined ore was compressed and piled up, it could never become a Nuclear reactor, because the Uranium 235 concentration, at less than 1%, is just too low.

Apparently the Gabon Uranium deposits were formed 1.8 Billion years ago....then the natural concentration of Uranium was 3%. However when the Earth was first formed some 4.6 Billion years ago, this figure rose to over 20%, a level at which today, would be considered 'weapons usable'!!

So I don't think we will ever be able to say with certainty exactly what provided the latent heat of the earth's core, all those billions of years ago.
Purer Uranium ores must have gravitated to the Earths core, being a heavy metal, but thankfully i would suppose, we wont blow up, since
ravity, iron ore and other metals must be moderating the radioactive fission, and keeping it in check.

In spite of everything our heat IS lessening, as is I suppose
techtonic movement and volcanoes, both will be a thing of the past a Million years on? Which is what started this discussion.

*notes
Various and varied.> Gabon,Bangombe uranium mine, and others.
> Xenon gas measurements (a uranium fission product)
> Conference at Libreville Gabon, by George A Cowan, in 1975
> Alex P. Meshik (Russian) studying Xenon and other noble gases
brought back by the Genesis spacecraft.
> Olga Pravdivtseva, also the 'Hohenburg Spectrometer'

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"You will never find a real Human being - even in a mirror." .....Mike Kremer.

Mike wrote:
"in every Uranium mine so far discovered, (the biggest is in Gabon, Africa)....that of the three Radioactive isotopes of Uranium 234,235,and 238, it is Uranium 235 that is mined, because its 235 that sustains a nuclear chain reaction, once it is CONCENTRATED.
Very very interestingly the mining engineers and scientists state, "that--All Uranium 235 atoms, make up 0.720 percent of the total, WHEREVER its found, anywhere in the Earths crust, on the Moon and even in Meteorites!!!!"

This is not actually correct in several respects. Picky respects but, I think, important ones.

First one does not mine U235 ... one mine's Uranium and then must separate by, for example, centrifuging Uranium Hexafluoride, the various isotopes.

Second there are places where the concentration of U235 is not 0.720 percent. These are locations where the uranium concentration was high enough, and the U235 concentration back when the earth was young, high enough, for a natural fission reactor to form.

Here's a link:
http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml

When one is considering the initial heating of the earth there are many factors. There is heat produced by gravitational compression and collision, heat from radioactivity, heat from chemical reactions (which may be significant), and clearly heat from nuclear fission. But one might also consider that some heat may too have been provided by the environment in which the planet formed ... both our current star and other stars that may have been part of the process.

How else to explain this:
http://www.meteorobs.org/maillist/msg23330.html
http://www.psrd.hawaii.edu/Nov99/PurpleSalt.html

So we weren't starting at zero.

Mike, you said: "In spite of everything our heat IS lessening, as is I suppose techtonic movement and volcanoes, both will be a thing of the past a Million years on? Which is what started this discussion"

My guess would still be perhaps a billion or more years rather than a million, based on the 4.5 billion year half life of uranium 238. That means that by the time the sun becomes a red giant, the heat being generated in the mantle would still be almost 50% of that at present! A mere million years from now, the heat generated by that radioactive decay would be almost unchanged. I'm sticking with the radioactive decay asssertion on the grounds that it comes from an expert in the subject (see above), and I haven't found anything from an authority in the field that contradicts that. As a matter of further interest in the subject, have you seen DA's new topic: Source of icy moon's heat.