From Yale University and the University of British Columbia, an important step forward in being able to forecast explosive volcanic events.
Before the explosion — volcano’s warning tremors explained
New Haven, Ct. – No matter their size or shape, explosive volcanoes produce tremors at similar frequencies for minutes, days or weeks before they erupt. In the Feb. 24 issue of the journal Nature, researchers at Yale University and the University of British Columbia (UBC) describe a model that explains this strange phenomenon – and may help forecast deadly eruptions.
When such volcanoes erupt they can shoot hot ash up to 40 kilometers into the atmosphere and cause devastating destruction when the ash column collapses and spreads as “pyroclastic flows.” Prior to most of these explosive eruptions the volcanoes shake slightly but measurably, and the shaking becomes more dramatic during the eruption itself. This tremor is one of the primary precursors and warnings used by volcanologists for forecasting an eruption.
“Tremor is very mysterious, most notably because it shakes at pretty much the same frequency in almost every explosive volcano, whether it’s in Alaska, the Caribbean, New Zealand, or Central America,” said David Bercovici, professor and chair of the Department of Geology and Geophysics at Yale, and co-author of the research. “That it’s so universal is very weird because volcanoes are so different in size and character. It would be like blowing on five different musical wind instruments and having them all sound the same.”
For minutes to weeks before eruptions, tremors in nearly all volcanoes stay in a narrow band of frequencies from about 0.5 to 2 HZ. Just before and during the eruption, the frequency climbs to a higher pitch, and the range spreads out to between 0.5 and 7 HZ. This similarity in tremors has been hard to explain because each volcano differs in many variables such as physical structure, magma composition or gas content.
The mathematical model developed by Bercovici and his colleague Mark Jellinek at UBC suggests these similarities can be explained by “magma wagging” – or the rattling that occurs from the interaction of rising magma and the foamy jacket of gas that surrounds it. The factors that control this rattling or wagging vary little between volcanoes, which explains why the same tremors occur in very different volcanoes.
“Explosive eruptions are some of the most spectacular and destructive phenomena in nature, and tremor is both a warning of the event and a vital clue about what is going on in the belly of the beast,” Bercovici said. “This model will provide a much-needed framework for understanding the physics of tremors, and this can only help with the prediction and forecasting of destructive eruptions.”
Here’s the UBC Press release (thanks to WUWT reader “clipe”):
Oscillating “plug” of magma causes tremors that forecast volcanic eruptions: UBC research
- The UBC model illustrates how, as the center ‘plug’ of dense magma rises, it simply oscillates, or ‘wags,’ against the cushion of gas bubbles, generating tremors at a consistent range of frequencies observed around the world. Credit: Mark Jellinek, UBC.
University of British Columbia geophysicists are offering a new explanation for seismic tremors accompanying volcanic eruptions that could advance forecasting of explosive eruptions such as recent events at Mount Pinatubo in the Philippines, Chaiten Volcano in Chile, and Mount St. Helens in Washington State.
All explosive volcanic eruptions are preceded and accompanied by tremors that last from hours to weeks, and a remarkably consistent range of tremor frequencies has been observed by scientists before and during volcanic eruptions around the world.
However, the underlying mechanism for these long-lived volcanic earthquakes has never been determined. Most proposed explanations are dependent upon the shape of the volcanic conduit – the ‘vent’ or ‘pipe’ through which lava passes through – or the gas content of the erupting magma, characteristics that vary greatly from volcano to volcano and are impossible to determine during or after volcanic activity.
Published this week in the journal Nature, the new model developed by UBC researchers is based on physical properties that most experts agree are common to all explosive volcanic systems, and applies to all shapes and sizes of volcanoes.
“All volcanoes feature a viscous column of dense magma surrounded by a compressible and permeable sheath of magma, composed mostly of stretched gas bubbles,” says lead author Mark Jellinek, an associate professor in the UBC Department of Earth and Ocean Sciences.
“In our model, we show that as the center ‘plug’ of dense magma rises, it simply oscillates, or ‘wags,’ against the cushion of gas bubbles, generating tremors at the observed frequencies.”
“Forecasters have traditionally seen tremors as an important – if somewhat mysterious – part of a complicated cocktail of observations indicative of an imminent explosive eruption,” says Jellinek, an expert in Geological Fluid Mechanics. “Our model shows that in systems that tend to erupt explosively, the emergence and evolution of the tremor signal before and during an eruption is based on physics that are uniform from one volcano to another.”
“The role of tremors in eruption forecasting has become tricky over the past decade, in part because understanding processes underlying their origin and evolution prior to eruption has been increasingly problematic,” says Jellinek. “Because our model is so universal, it may have significant predictive power for the onset of eruptions that are dangerous to humans.”
The research co-led by Prof. David Bercovici of Yale University and was supported by the Canadian Institute for Advanced Research, the Natural Sciences and Engineering Research Council of Canada, and the U.S. National Science Foundation.
Is this ‘wagging’ and new word for ‘chugging’? See Lees et al, 2004.
I think a strong case can be made that the infrasound frequencies ( 0.5 to 2 HZ) preceeding volcanic eruptions are electrical in nature, and that an electrical explanation is superior to the mathematical model involving ‘“magma wagging” – or the rattling that occurs from the interaction of rising magma and the foamy jacket of gas that surrounds it.’
Similar signals come from lightning:
Thunderstorms are a source of infrasound as recorded, for example, by the Swedish Infrasound Network:
http://www.umea.irf.se/ume/publications/pdf/agu2006_1043.pdf
The recording equipment covers the frequency range of .5 – 9 Hz.
Of particular note are the differences in the infrasound signals between cloud-to-ground lightning, and intra-cloud lightning. See Fig. 2. Intracloud lightning produces sustained, spectacular infrasound signals of up to 78 seconds. Perhaps these are the differences between positive and negative lightning, but as I do not know for sure, at least it can be observed that the infrasound produced is not explained merely by expanding, rapidly heating air, as we think of thunder.
The power spectrum of thunder in the higher, audible frequencies also differs greatly between types of lightning. Here:
On the Power Spectrum and Mechanism of Thunder
http://europa.agu.org/?uri=/journals/jc/JC076i009p02106.xml&view=article
This abstract says of infrasound from lightning:
“The mechanism of thunder production by a thermally driven expanding channel as described by A. A. Few appears to account for the dominant frequencies observed from many cloud‐to‐ground flashes, but cannot explain the high‐energy low‐frequency peaks of some cloud‐to‐ground and most intracloud discharges.”
I have now shown that the same sound frequencies, .5 – 9 Hz, come from electrical discharge in thunderclouds, and are the signature of different types of lightning, not always produced by shock waves in the air.
Additional examples of infrasound originating from electrical discharges are: sprites, auroras, and bolides. Sprites (image) as a source of these frequencies are not well understood: “The infrasound source corresponds well to the sprite spatial characteristics deduced from camera observations. Questions about generation mechanisms of infrasound from lightning and sprites still remain.”
http://www.agu.org/pubs/crossref/2010/2009JA014700.shtml
So infrasound is a signature of electrical activity in earth’s atmosphere, and should be seriously considered as a source for the tremors from volcanos. Also already noted are the different types of lightning phases at the tops of erupting volcanos which are not well explained by charge separation between moving ash particles.
@_Jim says:
February 23, 2011 at 9:33 pm
Thanks very much Jim. I already caught myself, so therefore the mistake was never made. 😀 Anyways, other lightning observations are made in .5 – 9 Hz infrasound ranges, just not the one I chose.
What can still be highlighted is that there is a lot of electrical activity not well understood accompanying volcanic eruptions. It makes sense to question whether the tremors preceeding eruptions may also be electrical in nature.
http://www.google.com/images?hl=en&source=imghp&q=volcanic+lightning&gbv=2&aq=0&aqi=g10&aql=&oq=volcanic+light
Seem to remember a programme on this a couple of years ago on Channel 4 (UK)
some chap found that all volcanoes produce a undetectable “to human ear” resonance
prior to eruption.Forget what his name was, think he was Italian???
Mycroft, this was well known, but the article describes a new hypothesis for the cause of the resonance.
Zeke, by any chance do you subscribe to the electric sun theory, too? I’m really having a hard time correlating the occurrence of extremely low level sound accompanying lightning and low level sound being conducted through the ground meaning that volcanos are electric.
“Intracloud thunder spectrums show a mean peak value of power at 28 Hz with a mean total acoustic energy of 1.9 × 1013 ergs. Cloud‐to‐ground spectrums show a mean peak value at 50 Hz with a mean total acoustic energy of 6.3 × 1013 ergs.” from your listed source seems to suggest a much higher Hz value than you described. The rest is locked behind paywall.
Here’s where my problem with your line of reasoning comes in. These sounds are heard prior to eruption, BEFORE there is the highly visible discharge of electrical energy which in all of these examples is linked to the infrasound… let me make sure you’re reading my sentence here clearly… the infrasound is linked in all of your material presented to VISIBLE ELECTRICAL DISCHARGES. Whether ash cloud lightning, sprites or cloud to ground lightning… If the volcanos were producing visible lightning prior to eruption, I think that we’d have a much better warning system.
While you’re making a heroic effort to attempt to link these likely unrelated phenomenon, you still haven’t adequately explained how you think that dormant electrical charges in magma produce this regular and demonstrable infrasound waves without the otherwise universal visible electrical discharges…
In fact, not a single link or fact you presented actually makes a case that volcanos are an electrical event, and not a magmatic tectonic event which produces electrical events during the eruptions.
Vesuvius has had tremors during the past 50 years. So far it has been lacking the eruption, thank goodness. Last eruption was 1947, but that was effusive not explosive, and has been well monitored since then. It is overdue an explosive eruption by many decades the last being the one that destroyed Pompaii. Perhaps Vesuvius is the exception that proves the rule.
“Sorry! False alarm. It was only a giraffe humming.”
Mycroft – is Bernard Chouet who you’re thinking of? This BBC Horizon programme from first 2002 transmission,
http://www.bbc.co.uk/science/horizon/2001/volcanohelltrans.shtml
retold the story of the deaths in 1993 of several volcanologists in a team led by Stanley Williams, who together with John Stix decided to go with their own standard way of predicting eruptions, measurement of gases, rather than with then recently discovered meaning of the not up to then understood B line among the A lines on seismographs, interpreted by Bernard Chouet, the long period event.
Narrator: But Chouet could see something in them that no one else could see.
Bernard Chouet: It stared you in the face. Wow, this is obviously different. Embedded in the record among all these A-type earthquakes were classic looking quasi-monochromatic harmonic signatures, beautiful textbook examples.
[For more scientific skullduggery about the event: http://www.nytimes.com/books/01/04/15/reviews/010415.15weinert.html
And she makes the charge that Williams, who had been focused on using gas emissions, not seismic activity, as a key predictor of eruptions, later appropriated Chouet’s work in the name of scientific progress.
Is this why it took me a while to find that programme? I’d seen a repeat on one of the discovery type channels a year or two ago, but articles don’t mention Chouet’s role in this – he appears to have been written out of the story and the predictive power of this downplayed, wiki on Galeras an example.
And back to the programme, the tragedy as told by the people involved:
Narrator: The two methods seemed to contradict each other. Gas measurements suggested Galeras was quiet. The long period events spelt danger. The night before the field trip Williams met with other scientists at their hotel to talk through the options: to go into the crater or not.
John Stix: We were faced with a dilemma in a sense. Here was an active volcano, but a very quiet active volcano. Where were we going?
Narrator: They talked about the long period events. Some expressed reservations about going into the crater when these signals were appearing.
Fernando Gil: We were concerned by these long period events and what had happened when we’d seen them before.
Narrator: But Williams and Stix were not seismologists and Chouet’s long period events were still relatively untested.
John Stix: There was a concern, but we didn’t really understand what those events were, were telling, were telling us.
Narrator: The one scientist who could have helped was missing. Bernard Chouet had been unable to come to Colombia. Both Williams and Stix decided to rely on the science they knew. Gas levels were low, a clear sign, they believed, that Galeras presented no immediate danger..
So, what exactly are they saying about the “wagging”? I didn’t understand the article.
Myrrh.
Think that was the programme? (hate getting old) thanks for the link
from the days when the BBC still aired good science programmes!!
Cheers Mycroft
Re electric volc. There is an annular “atmosphere” of bubbles around the cylinder of magma in the throat. This may act like a leyden jar. The magma in these explosive types is loaded with alkali metal ions in solution – I dont think it’s a stretch to imagine an alkali battery effect.charging and discharging in the pumice “capacitor”. I’m with you Zeke. I always distrust linear thinking.
So they now have a hypothesis. Per my ‘Websters’ – that is ‘A theory that explains a set of facts and can be tested by further investigation.’
So set up your monitors on some subject mountains and prove the hypothesis.
JoeH
Many animals do react on ultrasonic sounds, and tries often to escape. Some domestic animals like cats, dogs and horses are known to act very nervous and confused, as they don’t know what’s happening.
Confirmation that Bernard Chouet was right and yet another scientific consensus was wrong.
http://www.bbc.co.uk/science/horizon/2001/volcanohell.shtml
While were touching on alternative explanations, everyone is familiar with the chugging of plumbing (cavitation) which is caused by cold boiling in pipes due to irregularities in the pipe (bad soldering, mineral deposits in the pipe, etc) resulting in a pressure drop at the irregularity. Let us look at the explosive volcano and how it works: As a granitic magma crystallizes in a magma chamber at depth, a residual fluid builds up at the top of the chamber (the cupola) consisting of superheated water (a granite magma has about 5% water in it) and other volatiles, alkalis, alumina, silica, etc. The pressure continues to rise and causes some doming and fracture reactivation as the pressure surpasses the lithostatic pressure of the overlying rock. When the fracture open up, the pressure in the chamber drops allowing the superheated water to boil. This huge volume of steam blows everything out and the lava (loaded with bouyant air bubbles and driven by this expansion of volume races up the throat. As it goes, the boiling continues in the lava and causes an annular cylinder of pumice to develop as the gas escapes to the cooler contact rock in the throat. After the eruption is finished, things begin to freeze up again and the the magma chamber far below with its now lowered pressure continues to crystallize and a new cycle begins to rebuild the pressure again. This goes on until the granite has completely crytalized and the volcano then becomes dormant.
One way, possibly, to estimate when another eruption might occur would be to measure the volume of material ejected. This may give an idea how long it might take to repressure the the top of the magma chamber – especially if these ejection volumes had been measured previously. Anyway, a little vulcanology for the readers.
Oops one other thing! This is not a great analogy with cavitation – the boiling in the lava comes from a different cause but the effect could be similar with bubbles forming – maybe when we take the cork out of champagne we have infrasound in the 0.5 – 5 range. Anyone want to invite me over for champagne and I will see what I can do to measure this.
“For minutes to weeks before eruptions”
Minutes of warning isn’t going to be much use.
There are other ways of measuring magma, most usefully by measuring the deformation of the volcano itself, which inflates as the magma chamber fills.
This being a non-exact science, that’s why volcanologists issue level warmings so that civil authorities can execute plans and avoid unnecessary and expensive early evacuations.
Volcanoes are dangerous and incredibly useful at the same time. Witness the way the people who live around Etna treat warnings and move in plenty of time.
Another possibility that involves “wagging”.
Since the foamy jacket can act as a spring and the dense plug acts as a mass, the spring-mass composite will have a resonant frequency. Of course the frequency will be dependent on the density of the foam and plug and the ratio of foam/plug material.
As the magma ascends and descends the “Tube” it may for a vortex causing the plug to move in a spiral path with the period of the oscillation equal to the natural frequency of the spring-mass system.
Or maybe not…
I suggest a modal analysis using triaxial accelerometers located in at least three equally spaced locations around the vent. See if the motion is (roughly)linear or (mostly)orbital.
*warnings
Perhaps sensors could be set up on known active, known dormant and presumed dormant volcanos and followed. Apparently some folks are concerned that the Banks Peninsula volcanos (near Christchurch, NZ) are moving out of dormancy/ presumed extinction and this might be a good place to test the sound-wave hypothesis.
And where? Here is a link to current worldwide activity
http://www.volcano.si.edu/reports/usgs/index.cfm
NovaReason says:
February 24, 2011 at 12:59 am
Thank you for your considered response. You say it appears as if there is an “heroic” effort here on my part to link unrelated phenomena in order to say that volcanos are electrical in nature. But before anyone starts nodding, I think it is necessary to remind you of the perplexity of the situation:
“Tremor is very mysterious, most notably because it shakes at pretty much the same frequency in almost every explosive volcano, whether it’s in Alaska, the Caribbean, New Zealand, or Central America,” said David Bercovici, professor and chair of the Department of Geology and Geophysics at Yale, and co-author of the research. “That it’s so universal is very weird because volcanoes are so different in size and character. It would be like blowing on five different musical wind instruments and having them all sound the same.”
In this case, what is mysterious is the universal fit of the .5 – 2 Hz frequencies to volcanos all over the world, of every structure and type.
I have offered a simpler alternative to the “magma wagging” in the article. That also is arguably an heroic effort to get a model to fit every type of volcano, by your standards. I provided the research to show that .5 – 7 Hz does accompany electrical discharge activity, although it is not a well known fact and it is not known why. Sprites, you noticed, are in the upper atmosphere where the air is so thin it is not likely at all to be giving off infrasound as thunder.
Then I point out that there is an excess, unexplained, mysterious amount of electrical discharging surrounding volcanic activity during the eruption. I have not closed the case, you are correct. I am simply opening it to another possibility. I have shown that this frequency does not require any particular morphology of diapirs or magma tubes, or an imagined universal formation of “foamy gas jackets” around a stiff magma column; it could alternatively be an underground electric current. .5 – 2 Hz every time? Electricity.
Zeke the Sneak is right. There is plenty of electrical activity in erupting volcanoes.
All of these could be easily straightened out; a four channel oscilloscope coupled to the appropriate sensors e.g. acoustical (air coupled low frequency vibrations), Geophone (low frequency physical vibrations of the earth), electrical measurements of the low or static electric field using electrometers (1), RF detectors (simply wire the output of an AM-band or LW receiver to a scope channel to record lightning discharge activity) .
Multi-channel Data acquisition PCI-based cards can be employed in a PC to log this data for later analysis and determine what occurred first, although some allowance for the medium’s velocity of transmission must be allowed (air vs ‘ether’ vs solid earth) …
(1) http://en.wikipedia.org/wiki/Electrometer
.
Zeke, you said the frequencies for electrical activity were VLF (3 kHz to 30 kHz). Are there also VVLF radio waves associated with volcanic activity? The frequency range .5 to 7 Hz is well below the VLF spectrum.
The seismographic sensors are EMF sheilded and for them to sense electrical voltages from the soil or atmosphere would require high voltage phenomenon like lightening etc…