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Algol
29th Aug 2010, 20:23
Volcanic eruption in Sumatra - right across the Straits of Melacca from Malaysia. Not too far from Thai airspace either: BBC Asia (http://http://www.bbc.co.uk/news/world-asia-pacific-11123169)

So, will we be seeing flights grounded as in europe during the Icelandic volcano eruption?

Titania
29th Aug 2010, 20:42
Indonesian Welfare Minister (http://berita.liputan6.com/daerah/201008/293703/Pesawat.Menko.Kesra.Terganggu.Letusan.Gunung.Sinabung) was delayed (article in Indonesian, use Google Translation to read). Volcano coordinates: Sinabung 310′12″N 9823′31″E - Volcano reference (http://www.volcano.si.edu/world/volcano.cfm?vnum=0601-08=) at Global Volcanism Program. Spewed sulphur ashes and stones on Friday and erupted with lava early Monday morning (Indo time). First eruption since 1600.

wingview
29th Aug 2010, 20:49
I doubt that very much. In Europe only 1 volcano, in the East lot's of them for many years... Nobody heard of it :}

lomapaseo
30th Aug 2010, 01:39
Where's the smoke high or low altitude ?

Wait for answer and then fly (they probably already know over there)

Biggles78
30th Aug 2010, 02:31
News report just said smoke was rising 1Km (3,280') into the air BUT it is a news report so this may not be accurate.

Sqwak7700
30th Aug 2010, 05:32
I heard that smoke / steam and lava were coming out. I think the Icelandic volcano was spewing ash. This volcano doesn't seem to be putting out any ash.

I think it all comes down to the rock type.

MD80rookie
30th Aug 2010, 06:32
The icelandic volcano was surrounded by ice and snow, that melted and created the ash.

buggaluggs
30th Aug 2010, 07:30
"The icelandic volcano was surrounded by ice and snow, that melted and created the ash."
Actually the ash is created by super compressed gases blasting up through liquid magma, this pulverizes the magma into small particles and blasts them skyward. Depending on the type of magma and size of the particles it's almost the perfect stuff to shagg a jet engine.
Always a pleasant thought as you thunder accross remote volcano strewn parts of the pacific ring of fire in the darkness! :ooh:

Yamagata ken
30th Aug 2010, 10:38
It does depend to a large extent on the rock type. Basalts (eg Hawaii) tend to have a low viscosity and won't store a lot of gas pressure. Andesites (eg Andes) are more viscous, store more pressure and tend to be more explosive. The addition of a significant volume of water flashing to steam (caldera lake, ice sheet) tends to add explosivity and contribute to ash production.

5milesbaby
30th Aug 2010, 12:53
Unfortunately Yamagata Ken, the Icelandic volcano's are basaltic (ocean basin vs ocean basin) so that contradicts your post.

Cubs2jets
30th Aug 2010, 13:06
Quote from CNN:

Some small domestic flights have been deferred because of the volcanic ash, but larger planes have not been affected, since they can simply fly over the ashes, said Bambang Ervan of Indonesia's Ministry of Transportation.

C2j

Yamagata ken
30th Aug 2010, 14:58
Basalt with a glacier over. It does not contradict my post. Volcanos are natural systems, like the weather. Like the weather, there are valid generalisations and local exceptions. Basalt systems are common in areas of crustal extension (Iceland) or hot spots (Hawaii). Andesitic systems are typical of subduction zones (Pacific rim). Within any specific magma chamber there may (or may not) be differentiation leading to eruption of magma of differing composition at different times. Would you like me to go on? I am a geologist.

mad_jock
30th Aug 2010, 15:10
yes please.

And purely becuase its quite interesting what you are saying

Yamagata ken
30th Aug 2010, 16:25
I'm not sure how to respond, but thanks Mad Jock. Firstly, this website strips all formatting out so everything comes as one paragraph. I'll try but sorry if this reads like a slab. Secondly, I'm a sedimentologist, and vulcanology only overlaps where things go boom and the rocks fall out from the sky. The physical behaviour of lava depends on the chemistry. Continental crust has the composition of granite/andesite. Pink rock. It is silica-rich and iron deficient, has a low density and high viscosity. Oceanic crust is basalt. Black rock. Basalt is iron-rich, high density and low viscosity. The rheology affects the style of volcanic activity. Hawaii is basaltic. Low viscosity fluid doesn't store gas pressure, and the rivers of lava run to the sea. Mt St Helens is andesitic and the gas pressure built up till it when bang, and the side of the mountain blew off. I'll submit this and try for a new paragraph.

Yamagata ken
30th Aug 2010, 17:13
As I suspected, the PPrune ****eware is concatenating my deathless prose. Moving past generalities, if an ice sheet drops 2-3000 m3 of ice into a basaltic volcano at C1200C, then we are going to see some kind of physical reaction, basalt or not. Very likely a large volume of pulverised rock at high altitude for a few weeks. Conversely, if the andesitic gasses can find an easy way to the surface (typically via a fault), then we get the geological equivalent of a wet fart. This is called a scoria cone. They go snap, crackle pop, create a cone a few hundred metres high, and are common as muck where I live in northern Honshu. If you are interested in eruptions, check out Mt Tambora

Bill Harris
30th Aug 2010, 19:21
Well put, Ken. Not all volcanoes go kaboom.

--Bill

lomapaseo
30th Aug 2010, 20:50
What kind of distribution of events (high altitude spouting above 30k vs much lower oozing) do we get at the following hot spots

North America

Hawaii

Japan

Indonesia

Iceland

Pacific side of South America

My memory seems to be stuck on both Hawaii and Japan being common oozers, while the rest above go Kaboom more often than not

anybody ?

mad_jock
30th Aug 2010, 23:57
then we get the geological equivalent of a wet fart.

Now mate you are talking in lingo that pilots can understand.

Best thing to do is type what you want to say into word. Then copy and paste into a pprune reply window. Then have a look on it on preview then post it.

If you are limited by the medium feel free to post links to suitable websites.

Cheers

MJ

mike-wsm
31st Aug 2010, 01:09
Kaboom. Krakatoa. Bardarbunga.

Yamagata ken
1st Sep 2010, 12:27
Thanks all. I was a bit reluctant to return to this thread, fearing I was in for a serious Modding for my use of Anglo-Saxon. I will try to answer the questions above, prepare/find some diagrams and test out notepad for the formatting. Thanks.

Yamagata ken
1st Sep 2010, 15:56
So we are all dealing with the same terms. Minerals = bricks. Rocks = house. Early in the Earth's history, the less-dense Si-rich minerals differentiated and formed patches of crust floating on the more dense, Fe-rich minerals. The Si-rich minerals have coalesced into the continents, have a bulk composition approaching granite, and cover about 30% of the Earth's surface, The remainder are oceans and floored with basalt. The crust "floats" on the mantle in approximate isostatic equilibrium, with the thicker granite crust C30-50km vs. C6-10km basalt giving us some freeboard. The whole system is flexible, moving up and down with temperature and loading. It also moves laterally. Plate tectonics.

http://a.imageshack.us/img838/1200/tectonicplateboundaries.png (http://img838.imageshack.us/i/tectonicplateboundaries.png/)
Uploaded with ImageShack.us (http://imageshack.us)

This diagram shows most of it. Looking NE, this could be the Pacific. Japan (NW) via Hawaii to South America (SE).

http://a.imageshack.us/img838/1800/pacific1copy.png (http://img838.imageshack.us/i/pacific1copy.png/)
Uploaded with ImageShack.us (http://imageshack.us)

Starting with the divergent plate margin, as the plates move apart basaltic magma rises and solidifies to form oceanic crust. Over time, that crust cools and contracts, and the oceans deepen as it moves away from the spreading ridges. Rarely, the oceanic crust reaches above sea level, as in the case with Iceland. A complication here is the North Pacific divergent margin has been subducted under North America.

Hot spots are an exception. They are believed to be the product of anomalous asthenoshere activity, essentially fixed in place as the crust moves over it. Thus we get the linear chain of the Hawaiian Islands, with a kink where the crust changed direction.

Both of the above are basaltic: there is no source for the magma other than recycled oceanic crust or ferruginous lithosphere/asthenosphere. There is also no source for water, and the magma tends to have low viscosity and a low volatile content.

Convergent plate margins are more complex. The classic model is the Japan archipelogo, where subduction has forced a sliver of continental crust to break off from Asia (back arc spreading). Subducted (hydrated) oceanic basalt essentially melts its way up through the granite (also wet), giving a much more variable rheology as well as plenty of gas/steam. The magma works its way up until the confining pressure is less than the internal pressure, then it comes to the surface as an eruption. Most continental volcanos spend most of the time smoking, popping, banging, extruding and sleeping. They bulge and move, then relax as the pressure is released. It is these convergent margin strato-volcanos (eg. Fuji) to compound volcanos (Yellowstone) that produce the really big bangs.
As for what it means to pilots/aviation, check the next two scans from one of my grad texts. Look at the volumes and altitudes.

http://a.imageshack.us/img838/9620/volcano001.png (http://img838.imageshack.us/i/volcano001.png/)
Uploaded with ImageShack.us (http://imageshack.us)

http://a.imageshack.us/img838/1200/volcano003.png (http://img838.imageshack.us/i/volcano003.png/)
Uploaded with ImageShack.us (http://imageshack.us)

lomapaseo
North America, Japan, Indonesia and Pacific side of South America (essentially the Pacific rim) are all convergent plate margins and prone to explosive volcanism. Iceland is divergent, and Hawaii a hot spot. This is where I put on my natural science tinfoil hat and say the models are robust, but there are always exceptions depending on the individual event. The Pacific rim and Med are problematic, the Atlantic and Indian Oceans less so. But add water, and anything can happen. Ref the diagrams above, and phreatic means wet, and plinian was first described by Pliny. I blame the Greeks.

lomapaseo
1st Sep 2010, 17:40
..... Ken ...


North America, Japan, Indonesia and Pacific side of South America (essentially the Pacific rim) are all convergent plate margins and prone to explosive volcanism. Iceland is divergent, and Hawaii a hot spot. This is where I put on my natural science tinfoil hat and say the models are robust, but there are always exceptions depending on the individual event. The Pacific rim and Med are problematic, the Atlantic and Indian Oceans less so. But add water, and anything can happen. Ref the diagrams above, and phreatic means wet, and plinian was first described by Pliny. I blame the Greeks.




I'm not sure how my tried and true quote function is going to work on your text windows now that you are using other than the normal website posting protocol.

Thanks for the info but I need it translated into pilot-speak

The sketch of the plume heights was helpful but I will never be comfortable remembering the umpronounceable names :)


Yes I can accept some predictions as being problematic based on combinations of sources of water etc.

My memory can not reacall in the last 200 years much variation in plume heights above 20k for the Japan and Hawaii erruptions. Thus I never have considered them much of a threat to high altitudes overflights.

On the other hand my memory is that almost all of the erruptions in Alaska and Indonesia put up very high altitude fine ash.

The latest erruption in Indonesia seems to be the rare (for this region) low altitude type.

My only memory of Icelandic erruptions are of the high altitude type
is this to be expected as common for this region?

I do realize that being problematic does allow for some variation, but that's why my original question was aimed more at 200 year history of numerous regional erruptions.





http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/statusicon/user_online.gif http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/report.gif (http://www.pprune.org/report.php?p=5906595) [/quote]

mike-wsm
1st Sep 2010, 21:03
The wiki article on volcanos (http://en.wikipedia.org/wiki/Volcano) contains some more easily digestible classifications.

Yamagata ken
1st Sep 2010, 23:18
lomapaseo

I understand you are after something more specific to aviation. I'll have a look round to see if I can find some more appropriate material when I get back from work. I suspect that may be a problem as I doubt very much whether anyone has done much air sampling type work. Geologists have only measured what they can see in the air or find on the ground.

I think the Met office came in for some unfair stick over the Iceland fiasco this spring for using their general circulation model, so at least we have recognised the problem and moved to the "more work needs to be done" stage. That means holding out the hand for research funds, so don't hold your breath.

The only credible sources for this type of information will be NASA and the USGS, so I'll check there and see if they've done anything specific. As before, it's not my speciality, but at least I speak the lingo.

I put those diagrams up to show the potential scale of eruptions. Sorry about the technical names, they aren't important. The earlier eruption scales have been inferred from ash deposits on the ground, essentially the visible plume. That doesn't help much with the invisible plume.

I've switched from Firefox to IE, which seems to accept basic formatting.

lomapaseo
2nd Sep 2010, 03:39
I put those diagrams up to show the potential scale of eruptions. Sorry about the technical names, they aren't important. The earlier eruption scales have been inferred from ash deposits on the ground, essentially the visible plume. That doesn't help much with the invisible plume.


Thanks for your consideration..

Yes, most of us do like some direct education in this aviation forum by virtue of talking and asking from the experience among us.

So bear with us as we are often ignorant about what we ought to know vs what we want to know or think we know :)

Yamagata ken
2nd Sep 2010, 06:09
Thanks mike-wsm. That wiki article is excellent :ok:

My memory can not reacall in the last 200 years much variation in plume heights above 20k for the Japan and Hawaii erruptions. Thus I never have considered them much of a threat to high altitudes overflights.

On the other hand my memory is that almost all of the erruptions in Alaska and Indonesia put up very high altitude fine ash.

Hawaii is unlikely to be problematic. In Japan we have some minor eruptions at present, but I'm not aware of anything significant over the past 2 centuries. Alaska and Indonesia are both currently very active compared with Japan, but this may be a statistical anomaly as the sample period is very short. I'll look into it further.

My only memory of Icelandic erruptions are of the high altitude type is this to be expected as common for this region?

Iceland is anomalous because Eyjafjallajokull was subglacial, and the Surtsey eruption was submarine. The ash plumes were not related to the style of eruption, but the circumstances.

I've had a look around and found a couple of short papers summarising some of the issues which have come to light this year.

http://www.citiesonvolcanoes6.com/imagenes/COV6-Ash-Forum-Summary.pdf

Keeping an Eye on Volcanic Ash GRSS | IEEE | Geoscience & Remote Sensing Society (http://www.grss-ieee.org/keeping-an-eye-on-volcanic-ash/)

The science community has been a bit caught out because current generation satellites aren't really optimised for volcanic ash monitoring. Also the computer models are based on the presence/absence of ash, and are rather conservative. Industry hasn't helped because we don't know what an acceptable upper limit of ash concentration should be. That makes it impossible to model.

Anyway, minds are being concentrated, and I'll ferret out some historical data.

mad_jock
2nd Sep 2010, 07:59
Your a star Ken

lomapaseo
2nd Sep 2010, 15:12
Thanks Ken for the references above, they at least focus us on the association with safety in flying after an eruption.

Somewhere in all this we need to work out a synergistic balance between the scientists in volcanology, weather, detection and the impact on aircraft systems and engines.. Each specialist knows their field but rarely fully understands its relationship to the other fields.

mike-wsm
2nd Sep 2010, 21:13
I just counted twenty small quakes in the Bardarbunga region of Iceland, which seems a little above average. Bardarbunga (http://en.wikipedia.org/wiki/B%C3%A1r%C3%B0arbunga) is a Stratovolcano, like Krakatoa (http://en.wikipedia.org/wiki/Krakatoa), which went Kaboom (http://en.wikipedia.org/wiki/Kaboom) in a big way as recently as 1883. There was plenty of warning of Krakatoa's eruption, with several years of quakes before the final cataclysmic explosion that reverberated several times round the globe. Hopefully Bardarbunga will be equally considerate in giving fair notice of his intentions.

mad_jock
2nd Sep 2010, 22:34
Ken whats your views of the volcano thats linked with the one that went off in Iceland?

Yamagata ken
3rd Sep 2010, 10:35
Firstly, geologists aren't really the right people to consult if you are interested in the impact of volcanoes on aviation. We are good at saying when things happened historically, and why. For the here, now and tomorrow, geophysicists and remote sensing people are the right people to ask. Regardless, I've been pressing on.

The critical measure for aviation is the Volcanic Explositivity Index (VEI), nicely explained in Wikipedia here.

Volcanic Explosivity Index - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Volcanic_Explosivity_Index)

A VEI of 3 or greater should certainly get your attention. VEI 3 gives a plume 3-15km high, and they occur approximately annually. The Smithsonian Institute Global Volcanism Program | Volcanoes of the World (http://www.volcano.si.edu/world/) maintains a database of eruptions over the past 10,000 years. Unfortunately that database doesn't include the VEI, but there is a table of eruptions of VEI of 4 (plume 10-25km) or greater. I've cut the events since 1700 from the table and pasted them into the database, then plotted them on a World map to give an idea of signficant recent activity. Geological databases always annoy physicists because the numbers come from disparate sources and can be very subjective, but you have to start somewhere.

http://a.imageshack.us/img201/473/widescreenmapofearth013.png (http://img201.imageshack.us/i/widescreenmapofearth013.png/)
Uploaded with ImageShack.us (http://imageshack.us)

I have 94 events of VEI 4 or greater in 300 years, excluding multiple events at the same volcano. These include:
Indonesia/PNG 20
Japan/Islands 11
Kurils 7
Kamchatka 5
Aleutians/Alaska 10
Central America 10
Chile 8
Iceland 5

Yamagata ken
3rd Sep 2010, 10:55
mad-jock


Ken whats your views of the volcano thats linked with the one that went off in Iceland?

Iceland is part of the Atlantic mid-ocean ridge which for some reason happens to be at the surface. Possibly there's a thermal anomaly, but I don't know. Normally the ridges are about 3km below sea level and the confining pressure prevents explosive eruptions despite the presence of water. The process is normally one of extrusion, with local boiling, but no sea surface expression. The only indication of MOR activity normally is seismic activity.

I suspect the Eyjafjallajokull eruption would normally have had little effect on European aviation, except for the very atypical wind and weather conditions at the time. I know. I was in the UK at the time building a mega-shed in my brother's back garden. Wearing a T-shirt and getting sunburned in April :ooh:

I'll look at some of the seismic and remote sensing over the weekend.

lomapaseo
3rd Sep 2010, 14:16
Ken

Thanks again for the updated images above

Firstly, geologists aren't really the right people to consult if you are interested in the impact of volcanoes on aviation. We are good at saying when things happened historically, and why. For the here, now and tomorrow, geophysicists and remote sensing people are the right people to ask. Regardless, I've been pressing on.

Yes and we appreciate that. At least we can get some balanced expertise on the different contributions to the aviation side of the problem



A VEI of 3 or greater should certainly get your attention. VEI 3 gives a plume 3-15km high, and they occur approximately annually.

While I will agree that a VEI 3 will get your attention, it seems to be well handled by diversions or overflights and has not been involved in any of the historical aviation incidents involving engines.

I take it that the latest eruption in Indonesia is a VEI 3 or less?

mike-wsm
3rd Sep 2010, 14:40
Iceland is part of the Atlantic mid-ocean ridge which for some reason happens to be at the surface. Possibly there's a thermal anomaly, but I don't know.

See Iceland Plume (http://en.wikipedia.org/wiki/Iceland_plume).

mike-wsm
3rd Sep 2010, 14:50
Ken whats your views of the volcano thats linked with the one that went off in Iceland?

These seem to be the ball-park figures:
Eyjafjallajokull vei=2 to 4 (the one that went off)
Katla vei=3 to 5 (closely linked)
Bardarbunga vei=5 to 7 (nearby)
The vei scale is logarithmic, each unit of vei indicates ten times the ejecta.

Yamagata ken
4th Sep 2010, 03:44
Thanks for that mike-wsm.

Some comments on VEI. It's a scale devised by geologists to categorise events which we can recognise in the rock record, or measure on the ground for recent events. Essentially, the visible part of the plume and the bits that fall out of it. It isn't telling us is anything about low concentration suspended particulates or oxygen-excluding gasses, so it's very much a first approximation. Obviously, it's the invisible parts of the eruption that are the real hazards for aviation: a big cloud of rock in the sky being relatively easily seen and avoided.

I'll look around to see what information is in web-land from geophysics (seismic) and remote sensing. I have a working knowledge of both (tools of trade), but I'm not a specialist. I'm sure many better minds than mine are at work on the problem, and I know the tools work.

Finally, I find it difficult to know how to pitch this. I don't want to appear patronising or superior, or an idiot. I also get things wrong, and appreciate suggestions and corrections.

desert goat
4th Sep 2010, 05:16
then we get the geological equivalent of a wet fart.

Hey Ken- I reckon a few people in my first year geo class would have progressed quicker if we were given a few more explanations like that!:8

mad_jock
4th Sep 2010, 11:11
I don't want to appear patronising or superior, or an idiot

Well personally I don't think your coming across as any of them. So crack on

And I thank you for taking the time to post.

In fact I have browsing the OU geo courses.

Its one of the things which I quite like about this board is that mostly it is very welcoming to outside skill sets. The Air France thread is another example of this with the posters who know alot about ocean currents and surveying providing some cracking posts about how it all works.

Yamagata ken
6th Sep 2010, 05:35
Volcanic seismology

Seismicity has been studied for several centuries, but what we regard as modern instrumentation was first developed in the 1930s. Post WWII seismology was driven by the oil industry, where it is the exploration tool of choice, and the US government establishment of a global network to monitor USSR nuclear testing. The economic and political imperatives for processing huge amounts of data have had a major influence on the devlopment of super computing, and sophisticated analysis techniques. This work has spun off into the science community. As a result, it is relatively cheap and easy to install seismometer arrays to monitor and report volcanic seismic activity in real time. Software to process and model the internal structures and processes is freely available. Seismic monitoring has predictive capability.

Volcanic eruptions are expensive. Monitoring is cheap, effective, happens in real time, and can be automated. All responsible governments do it. The USGS has a lot of excellent material on line.

A glossary here: CVO Website - Earthquakes and Seismicity (http://vulcan.wr.usgs.gov/Glossary/Seismicity/description_earthquakes.html)

An accessable description of monitoring techniques and activities here: Monitoring Volcano Seismicity (http://volcanoes.usgs.gov/activity/methods/seismic/index.php)

Animations here: IRIS - Volcano Monitoring (http://www.iris.edu/hq/programs/education_and_outreach/animations/16)

Benoit http://www.earth-prints.org/bitstream/2122/1630/1/01%20benoit.pdf has compiled data showing a difference between non-eruptive and eruptive activity.

http://a.imageshack.us/img823/8523/volcseis04.png (http://img823.imageshack.us/i/volcseis04.png/)

The USGS comments on magnitude: "Most volcanic-related earthquakes are less than a magnitude 2 or 3 and occur less than 10 km beneath a volcano. The earthquakes tend to occur in swarms consisting of dozens to hundreds of events.", i.e non-eruptive.

Benoit again gives a table of earthquake magnitude associated with eruptions (Column 4).

http://a.imageshack.us/img411/4694/volcseis03.png (http://img411.imageshack.us/i/volcseis03.png/)

So, being mindful of the uncertainties of natural and non-linear systems, geophysical (and geochemical) monitoring are effective tools for the timely forecasting/warning of volcanic events of interest to the aviation community.

Yamagata ken
6th Sep 2010, 06:26
Sparks (http://www.eps.mcgill.ca/~courses/c186-530/Readings/Thursday,%2013%20September%20-%20overview/Sparks%202003.pdf) has published an excellent paper on forecasting volcanic eruptions. It is fairly technical, but should be understandable to anyone with a reasonable grip on physics. I'll quote from section 2, and recommend reading section 3 "Volcanos as dynamical systems".

"2.1. Seismicity
Seismic monitoring can give real-time data and correlations have been established between magma movements, disruptive phenomena and seismicity. Before eruption, ascending magma has to push rocks apart and this perturbs stress distributions and pore fluid pressures, commonly resulting in fracturing and numerous small-magnitude earthquakes. Earthquakes above background levels are commonly the first warning signs of impending eruption, although an eruption may not happen. Indeed the majority of volcano-tectonic crises do not lead to eruption. Once an eruption starts seismicity provides information on the style of activity and detects changes in the physical system.

Key developments in volcano seismology have been the recognition of different types of earthquake that can be linked to particular volcanic phenomena, and the recognition of long-period signals related to flow of volcanic gases and geothermal fluids. These developments have been augmented by the installation of networks of three-component and broad-band seismometers. The eruption of Mount Redoubt, Alaska (1989^1990) illustrates a success story in seismicforecasting. Here 11 swarms of long-period earthquakes were precursory to explosive eruptions. Warnings were issued for the explosive eruptions of 14 December 1989 and 2 January 1990 based on the characteristics of the swarms (Fig. 1). The forecast was based on two concepts. First the long-period events were interpreted as movement of pressurised fluids along fractures. Second the waxing and waning of the swarm intensity (Fig. 1) was attributed to mechanical weakening of the system before a catastrophic failure and explosive eruption.

http://a.imageshack.us/img28/6296/volcseis01.png (http://img28.imageshack.us/i/volcseis01.png/)

Seismic data have been used to evaluate the materials failure forecast method (FFM). The FFM is based on laws of material failure in which failure time is forecast from the inverse relationship between time and a proxy for strain rate, such as ground deformation or seismic energy release. Retrospective analyses of seismic energy release patterns at Mount St Helens, Mount Redoubt and Mount Pinatubo indicate that the eruptions could have been predicted within a few hours or days using this approach (Fig. 2). Seismologists can distinguish and interpret different types of earthquake signal. Several types of earthquake have been recognised at the Soufrie're Hills Volcano, Montserrat. Volcano-tectonic earthquakes are distinguished from shallow earthquakes that contain long-period components (Fig. 3). The former was prominent in the precursory as magma forcibly created a pathway to the surface. The latter were associated with growth of the lava dome; the occurrence of such earthquakes in November 1999 was used to recognise that dome growth had resumed after 20 months of inactivity. Seismicity in dome-forming eruptions is also associated with rock-falls and pyroclastic flows generated by dome instability. Seismic signals have been used to locate flow pathways and to estimate their speed. The seismic signal of a pyroclastic flow slowly emerges and then decays as the flow moves towards and then past the seismic station. This Doppler effect can be exploited because different stations record peak amplitude and signal duration that are controlled by flow position relative to the station. The signals can be calibrated to flow size and then related to models of flow run-out."

http://a.imageshack.us/img835/5365/volcseis02.png (http://img835.imageshack.us/i/volcseis02.png/)

Yamagata ken
6th Sep 2010, 12:08
mad jock In fact I have browsing the OU geo courses. I have the greatest respect for the OU and their Earth Science courses. I still have and use several OU publications, set texts for my undergraduate course. Several of my peers (mature students like me) qualified for full time university courtesy of their OU studies. As a post-grad, I tutored OU field courses, and was very impressed with their student-centred approach. The OU is good stuff.