Stromboli and Etna

Stromboli showed heightened activity during the last days and weeks.

Carls screenshot saved from tinypic

Sunday nights action as seen through a thermo cam.

IngeB found an article on this behavior:
“The stronger eruption intensity of Stromboli has also been subject to an article in Italian webnews. Because of the explosions at its summit, the civil protection organisation has hightened the alert level. http://www.meteoweb.eu/2013/04/non-solo-letna-anche-lo-stromboli-sta-eruttando-con-forti-esplosioni-avviso-di-elevata-criticita-dalla-protezione-civile/200183/ “

Siencia Obsoleta found a wonderfull video of stromboli 17 to 19 april 2013

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Etna:  Here is the report by our EYEWITNESS to make us all turn green with envy.

Schteve: “Mornin` All,

I know you are all dead jealous, but I don`t mind

I left the apartment at a run about 5 minutes after my comment at 17.17… The locals on Via Etnea who were casually going about their Saturday evening business ( posing in their best clothes and eating ice cream) must`ve thought I was crazy ( 6feet6inches of wild eyed English man going full tilt and saying wow over and over…) It was just about dark when I got to Villa Bellini ( a nice park with the best free viewpoint in town.) What can I say, it was just awesome; I couldn`t hear anything, (too much background noise) but what a show…My breathing eventually returned to normal, but my heart carried on pounding throughout. I took pictures until my battery went flat, but nothing really worth sharing (my camera is a little schnap schot job with insufficient zoom.) Lizzie came and met me after her snooze and we adjourned for cocktails and the second half on the roof terrace of the Palace Hotel…

Somehow I have got around Sod`s Law for once, we are off for 5 days in Palermo tomorrow and I was fully expecting Etna to go boom then…

I have some ash from the paroxysm of 20th April but I will pick up some more from this’n if I get chance…
“

The next passage is a repost from yesterdays addition to the Sunday post. We wont test today so we need a new post.

Etna Paroxysm # 13 (?) 2013 summary as seen from the point of view of the VC crowd:

Quite some of us had been noticing that the tremmor rose higher and higher over the last few days and quite some, including Carl, had expected /hoped for it to happen a night earlier. We also may have an Eye-witness very close to the action this time. Schteve is spending his holidays in Sicily. We are hoping he watched it and will give us a report when he returns.

The last few paroxysms have been different to those last year. Last year the tremor rose within a very short period of time, an hour or hours at maximum, and then Etna went BOOM, to go back to slumber a few hours later. This year it is different. The tremmor contiually rises over a period of days, during this uprise, lava is already been splashed out occasionally. Incandescent glow is visible on the cams and so people do watch cameras for 1 or 2 days expecting the real action to appear any minute. But Etna is in no hurry and fooled us for at least a day this time. After the show seems to be over it is not. Lavaflows can still be seen and they last for up to 3 days.

With the last 4 or 5 paroxysms the fountain grew bigger and bigger. Each time the media and THE expert Dr Boris B announced afterwards: the event was stronger than the one before. (though yesterdays eruption column is said to be 500 meters, it was almost twice as high with paroxysm #12 2013)

Because of Etna´s different behavior, people here start coming up with new names for the events: Paroxysmal, and other words were suggested. (help me here, I forgot)

Whenever a VC crowd is on the watch and it is also Sheepy Dalek time, people start funny discussions.

Can you see a face in this pic? Or is it a rabbit to you? The “face” ( or the rabbit? ) even got a name: Rudolph!
Carls offical Party Over pic:

A lava flow which seems to emerge not from the top crater but from a side fissure was still visible on the Lave cam which was also seen by Granyia. http://tinypic.com/view.php?pic=xm67t5&s=5

I can only quote Renato Rio: “It was great “paroxysming” together.“

Now that was our POV. Here comes the media, the expert and Youtube:

IngeB found this: “In this Italian webnews they say the paroxysm seems to be bigger than the last ones. The noise of explosions is so intensive that the window glass is rattling. This noise can even be heard in Taormina. Wind is from S/SW and the ash cloud directed to Messina and the Calabrian coast.“ http://www.meteoweb.eu/2013/04/forte-eruzione-delletna-con-forti-boati-avvertiti-fino-a-taormina/200229/

Of course! Do not miss Dr Boris B.´s Flickr report: http://www.flickr.com/photos/etnaboris/

Arjanemm found this: “For those that haven’t seen enough of Etna, try a search in youtube for “etna 27″. You will find dozens of movies shot yesterday.“
A small selection:

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Alans Riddle is still not solved:

Alan C’s Evil Riddle:

My true dusky identity was hidden! My secret lies in my blackness! Confused?
What am I?
Who are my relatives?
Where can I be found?

Clue:

Pay an old Greek a visit! He may let the cat out of the bag!

Spica

Etna’s paroxysm overview

Since the beginning of this year, Inge B. has kept track of all of Etna’s activity this year and has submitted a summary to keep track of all this for everyone. By now, we have seen a dozen of paroxysms and several other instances of activity at various craters, so it is easy to see people get lost there. For that reason, a table has been made by Inge B. (thanks for that!) which I have sort of converted to wordpress-language.

Etna summit craters map. Image by INGV

Bigger eruptions	Date	Summit craters involved	Characteristics of activity
	9-15 Jan 2013	Bocca Nuova (BN)	Vigorous Strombolian eruption after 3 months quiescence at this crater which had had its first magmatic activity after 10 years again in 2011.
	16 Jan 2013	BN	Strombolian activity
	18 Jan 2013	BN	Strombolian Activity
	20 Jan 2013	New SouthEast Crater (NSEC)	Strombolian activity, first magmatic activity after 9 months quiescence at NSEC
	22 Jan 2013	NSEC	Strombolian activity, more intense than the last ones, bombes rose up to 100 m above crater rim
	28-29 Jan 2013	BN   NSEC	Vigorous Strombolian activity, rumbling noises, to be heard in vicinity of craters Weak Strombolian activity; rhythmic degassing with slight ash content. First time since 12 years, simultaneous activity from 2 summit craters
	30 Jan 2013	BN	Intensive Strombolian activity, launching bombs to about 120 m above crater rim
Paroxysm 1	19 Feb 2013	NSEC	Lava fountaining with production of lava flows, pyroclastic flows, lahars and ash cloud
Paroxysm 2	20 Feb 2013	NSEC	Lava fountaining, lava flows, ash
Paroxysm 3	20 Feb 2013	NSEC	Lava fountaining, lava flows, ash. Second paroxysm that day
Paroxysm 4	21 Feb 2013	NSEC	Lava fountaining, lava flows, ash; 4 paroxysms in 48 hours is very rare
Paroxysm 5	23 Feb 2013	NSEC	Lava fountaining, more intense than before, fountains up to 800 m high, lava flows, ash cloud containing scoriae
	27 Feb – 4 Apr 2013	BN   Voragine (VOR)	Strombolian activity, weak lava fountains continuing through 28 Feb 2013 Explosive activity, first activity of VOR since 1999. Strombolian activity in the night before Paroxysm 6. Still ongoing Strombolian activity with stronger explosions in between, small ash emission, volcanic bombs during Paroxysm 7. Weak Strombolian activity still ongoing; after activity ceased at NSEC at Paroxysm 8, strong explosions at VOR. Weak Strombolian activity still ongoing at Paroxysm 9.
Paroxysm 6	28 Feb 2013	NSEC	Lava fountaining; eruptive fissure opened in the saddle between the Southeast Crater and the New Southeast Crater, lava flows; ash plume, scoriae fallout
Paroxysm 7	5-6 Mar 2013	NSEC	Spattering from new fissure in the saddle between the SEC and the NSEC; lava flows then lava fountains up to 800 m high; intense fallout of scoriae in adjacent towns and villages down to Taormina on the Ionian Coast
Paroxysm 8	16-17 Mar 2013	NSEC	Slow increase of Strombolian activity; lava fountains, ash and scoriae fall, rather violent paroxysm with several loud bangs heard in population centers around the volcano, gas rings; lava overflow, up to 800 m high lava fountains, ash plume 2.000 m high, lightening within the plume; downpour of heavy material, volcanic bombs and big scoriae in the summit area; after explosive activity ceased: small collapses and slides of still hot material
Paroxysm 9	3-4 Apr 2013	NSEC	violent paroxysm, only short time lava fountains, but very loud explosions, noise heard tens of kilometers from the craters, opening of new vents on the NSEC, production of small pyroclastic flows in the summit area (summit area declared “off limits” by the authorities after this episode); ash and scoriae fall in adjacent towns and villages
Paroxysm 10	8-14 Apr 2013	NSEC	Long run-up phase beginning on 8. April with loud Vulkanian (?) explosions (heard tens of km away), some rather heavy explosions with ash emission, followed by a period of Strombolian activity of increasing intensity culminating in lava fountaining on April 12, emission of tephra, ash and lapilli as well as lava bombs, less ashfall though than during Paroxysm 9 and the ones in March 2013; lava flow into Valle del Bove; repeated collapse at NSEC, leading to formation of a depression in the cone lava flow from “saddle” between SEC and NSEC in direction of Belvedere activity also from 2 vents at the base of NSEC on the same day; landslide; small pyroclastic flow two days following of declining activity with some production of weak lava flows
Paroxysm 11	18 Apr 2013	NSEC	From 16 April on some explosive activity at NSEC, ash emissions, small Strombolian eruptions, slowly increasing paroxysm with lava fountaining in the morning of 18. April; eruption cloud with ashfall and lapilli dispersion in direction S-SW; big lava flow into Valle del Bove, two smaller ones from the “saddle” between NSEC and SEC in directions N and S weaker Strombolian activity still ongoing since morning of 19 April
Paroxysm 12	20 Apr 2013	NSEC	Violent activity, ramping up quickly. Fountaining up to 1000 m high with column of gas, ash and lapilli and heavy tephra fall on the east flank. Downpoor of lapilli on the highway Catania-Messina near Giarre. Intensity approximately 30% higher than previous paroxysms.

Sources:
INGV Catania (also for the pictures), reports http://www.ct.ingv.it/en/ (English)
for the 9th paroxysm: http://www.ct.ingv.it/it/component/content/article/11-notizie/news/868
(Italian)
for the 10th paroxysm: http://www.ct.ingv.it/en/component/content/article/11-
notizie/news/875 (English)
for the 11th paroxysm (as per April 20, 2013): http://www.ct.ingv.it/en/ (English) and
http://www.ct.ingv.it/it/component/content/article/11-notizie/news/880 (Italian)

Photo of Paroxysm 10 at the 12th of April 2013. Photo by etnawalk.it

El Nathan

Activity update around the world

Etna has had its ‘paroxysm’ #many. Every eruption is spectacular, but when they are so frequent it gets easier to focus on what is different with every eruption. Bruce Stout and Newby noted that the activity lasted much longer than previously in this series of paroxysms. Why this is, is off course a mystery, but maybe as time progresses we will find out if this is again some kind of new behaviour for Etna. For now, I don’t think many people mind that Etna keeps doing these things, since the eruptions are not much of a nuisance to the people living around it (at least, not more than usual with Etna’s eruptions), but are nice to watch for everyone.

Mr. Behncke of the INGV in Catania has written a nice summary / eyewitness report of the activity, which can be read on his Flickr-photostream. The question is indeed if this longer-lived activity can still be called a paroxysm.

Webcam image of today’s paroxysm. Image by INGV

Inge B. pointed to some images released by the INGV showing the Italian island of Vulcano, which seems to show a bit of unusually strong fumarolic activity.

Eolian island of Vulcano. Image by INGV.

The island is known to be volcanically active in recent history. The last eruption has been recorded in 1888 at the Fossa cone. The cone can be seen in the webcam image above. The Fossa cone has been the main center of activity in the last centuries, and fumarolic activity and gas emissions are ever-present to some degree at the Fossa cone. Sometimes, the activity peaks, like for example in 1985 and 1990, which shows that the town at the bottom of the Fossa cone is still under constant threat.

The Vulcanian town of Volcano Porto at the base of the Fossa cone. Image by INGV.

The island of Vulcano is off course most famous for being the place that gave volcanoes their name. In Greek and Roman mythology, the god Hephaestus, or Vulcan, was the god of fire and was thought to have its workshop below the Eolian island, leading to the frequent release of fire from the mountains on it. It is also the type locality for one of the 5 main types of magmatic eruptions; Vulcanian activity. This type of activity is characterized by viscous magma, andesitic to dacitic, that frequently erupts explosively and generates volcanic blocks and bombs that rain down on the surroundings. For comparison, Sakurajima is the best example of Vulcanian activity in recent years. The area where the volcanic blocks and bombs rained down during the 1888 eruption on Vulcano is where the town of Volcano Porto is now built, leading to the constant threat mentioned before if Vulcano decides to really wake up and go back to the behaviour the ancient Romans knew it for.

Meanwhile, Tolbachik seems to be re-thinking it’s decision that the eruption has now lasted long enough. Strong seismic activity has been recorded, together with strong gas-steam activity and a big thermal anomaly was seen on satellite images. Estimates of the erupted volume are well above 1 km3, so this number continues to rise for now.

Also, Granyia noted that the Chilean volcano Lascar had seen its alert level raised to Yellow, after reports of small explosions and some ash in steamclouds. Looking at the webcam, it looks like some glowing can be seen. Sernageomin reports (.pdf, in Spanish) that during a helicopter flyover, temperatures above 600 degrees celcius were measured in the crater using a thermal camera, which confirms the reports of glowing at night.

Lascar webcam image. Image by sernageomin.cl

El Nathan

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Post update by Spica:

The Sheepy Dalek bar is open and Alan sent in another Evil Riddle:

I shan’t beat about the bush - a real spiny subject this, but at least you wouldn’t need a tv aerial!

What am I?
What are my special properties?

Good luck and have fun!

Alan C.

The count of Etna paroxysms in February 2013 now stands at 4 (and NTV Riddle)

This screenshot shows the first sight i got when i woke up this morning. Bruce Stout had been watching the event from the time it started and had left comments on VC which made me aware of what is going on. Etna changed its behavior the last days and displayed a 4th paroxysm today early in the morning after being active twice yesterday.

INGV analysed the paroxysms of the 20 in this articles in Italian and English. You can most likely expect a new report on todays events at http://www.ct.ingv.it/ a little later. Dr. Boris Behncke made some comments over at Eruptions where Erik had been writing a post on Etnas behavior too yesterday:

http://www.wired.com/wiredscience/2013/02/etnas-explosive-last-three-days/#comment-806546971

Yesterday someone zoomed in one Radiostudio7 cam and so i could take nice screenshots…

This picture was created out of the best screenshots i got of the Radiostudio7 cam yesterday.

http://www.radiostudio7.it/webcam.asp?web=7&id=7

Claude Grandpey reported live on his blog yesterday.

Check the lower right side of this image. I have not seen that spot before!

I´d like to paste some of the comments into this post to start a discussion:

Bruce noticed that same lava break-out feature has reappeared:
http://i40.photobucket.com/albums/e211/NoEnz/Bildschirmfoto2013-02-21um061250_zpsa0fbc1d1.png but Newby could be assured that no people are in danger because the ava flows down into an uninhabitet valley called Valle del Bove.

Bruce Stout says: February 21, 2013: Good morning, everyone, (yawn), oh look, Etna is at it again (no. 4) instant wake-up call.

Initial thoughts on Etna. A while ago I postulated that the periodicity in Etna’s paroxysms was caused by a steady magma feed into a piston like chamber with a narrow opening to the surface (this piston might be nothing more than the conduit itself). In this case the mechanism would be that magma enters the piston, starts to degass due to drop in pressure and slowly fills the piston until the pressure and volume was high enough to clear out the flimsy plug left by the last event. The built-up pressure in the piston coupled with rising levels of exsolution of gases leads to the fountaining as the piston empties itself. Rinse and repeat.

Now, if this is correct, why the sudden increase in the frequency of these paroxysms? Two possibilities come to mind: Faster rate of magma feed from below or a smaller piston.
Working in favor of the latter, is that the volumes of these paroxysms seem to be smaller than the previous series (though I am flying on the seat of my pants on this one, just guessing from the videos/webcams). It is most likely a combination of both faster feed and a smaller piston volume in the upper conduit. If higher feed, we might see a flank eruption at some stage which Boris once said often follows such series of paroxysms.
Just some random thoughts put here for discussion…
February 21, 2013 at 05:04

Well, bang goes that theory… this paroxysm is back to the old levels:
http://i40.photobucket.com/albums/e211/NoEnz/Bildschirmfoto2013-02-21um055948_zps359e23dd.png

Webcams are offering some very atmospheric shots as the wind is blowing the cloud towards the cam, obscuring the vent:
http://i40.photobucket.com/albums/e211/NoEnz/Bildschirmfoto2013-02-21um052759_zpsa67f8318.png

Spica: Ok the tremor is down again. The event seems to be over.
Bruce took a screenshot of the tremor being at 121 i saw it at 123 and when you check the graph now it shows that is was never as high as with the first paroxysm on the 19th. Can anyone explain this to me, this is not the first time i saw this behavior of the tremor graphs and i never understood it.

Boris mentioned on eruptions that it is not the first time Etna shows many paroxysm. In 2000 it started paroxysms in January and till late August the count ran up to 66 ! of those explosive events. I am bringing the webcam list over again so you have a chance to watch the show on your own.
Etna webcams:

• INGV Etna cams. From this link you can also find the Tremor and Seimology of Etna, cams and more on Stromboli and the Aelion islands.
• Collection of Etnacams by Etnatrekking.
• Etna Guide cam
• Etna Web cam
• Radiostudio 7 cams
• Live cams with Sound, Etnawalk, does not work in all browsers.
• Over 60! webcams of Sicily. Not all of them pointing at Etna
• The Hotel Corsano at Etna has a nice list of cam.
• Lave Cam
• Several Etna webcams, thermalcam and tremorgraph,  all on one page, by volcanodiscovery.com
• Etnaweb cams
• http://www.volcano-webcams.com/

One more screenshot for all who missed the show!

taken from the Lave cam: http://www.lave-volcans.eu/webcams_etna.php?numero=2

Name those Volcanoes Riddle

4 volcanoes 4 points

No 1 – Does it serve as a warning beacon for ocean going ships? Its nickname includes the name of an ocean. SOLVED
No 2 – This volcanic island’s artifacts/treasures, specifically A & A,  can be found in both the B M and the L. A & A are the names of ancient statues. SOLVED
No 3 – Here the salty craters hold a current ‘known’ subaerial world record. SOLVED
No 4 – During a warm, summer month in 2012 its summit displayed an historic ‘first’. Icelandic volcano. SOLVED

Spica

The Decade Volcano Programme

Fig.1 The dead of Herculaneum, burnt to death by 800-centigree hot pyroclastic flows from Vesuvius AD 79 (O Louis Mazzatenta, National Geographic)

The volcanic eruptions of Mount St Helens in 1980 and Nevado del Ruiz in 1985 made the general public aware of the dangers of co-existing with a large and potentially lethal volcano. It doesn’t take much imagination to see the possibilities of a lateral St Helens-type blast on a population of a great city as unaware of the hazard as the unfortunate citizens of Armero, Colombia. Blasts from the past such as Vesuvius 79 AD eruption that obliterated the large Roman cities of Pompei and Herculaneum or the 1902 eruption of Mount Pelée on Martinique, that completely destroyed the town of St Pierre, leaving only two survivors out of a population of some 22,000, served to reinforce the message. With human populations world-wide soaring, it is inevitable that humans will settle closer to potentially active volcanoes in ever-increasing densities. As a result, more human beings than ever are at risk from volcanic eruptions.

With this in mind, the HYPERLINK “http://en.wikipedia.org/wiki/International_Association_of_Volcanology_and_Chemistry_of_the_Earth%27s_Interior” \o “International Association of Volcanology and Chemistry of the Earth’s Interior”  (IAVCEI) set out to identify volcanoes that had a history of large, potentially destructive eruptions and were located close to high-density populations. As the project was initiated as part of the United Nations-sponsored International Decade for Natural Disaster Reduction, hence the name Decade Volcano, it was hoped that the United Nations would fund the programme the aims of which was to identify the major strengths and weaknesses of current hazard management and contingency plans at each volcano, and how to address the weaknesses identified.

Fig. 2 The UN General Assembly. It was ultimately here support for the Decade Volcano programme must be obtained, not at some faculty. (Marty Lederhandler, Associated Press)

It must be realised that in a highly politicised world, decisions are rarely based on scientific grounds, but on what is politically feasible. Hence the volcanoes chosen had to have a broad appeal, geopolitical as well as demographic, to the representative body that was to grant the funding. But in order to achieve at least a semblance to a scientifically motivated choice, the volcanoes chosen had to threaten tens of thousands of people with at least two of the following volcanic hazards – lava dome collapse, pyroclastic flows, lava flows, lahars, tephra fall or volcanic edifice instability. Furthermore, the volcano had to have been recently geologically active. As a sop to the UN representatives, who in turn would have to have the sanction of their masters at home, any volcano chosen had to be politically and physically accessible for study and there must also be local support for the work.

In the end, the UN did not undertake to support the programme, and funding had to be obtained elsewhere. Where there is a national body responsible for volcanologic research and monitoring such as in the USA, Italy, Mexico or Colombia, this organisation has assumed responsibility for the volcano or volcanoes that naturally fall under their aegis. The European Union supports research and monitoring at European volcanoes whereas some of its member countries, France and Germany, have undertaken to support the work of Indonesian authorities at the same time giving French and German volcanologists access to research at active volcanoes.

Fig. 3 Koryaksky volcano overlooking Petropavlovsk’s 180,000 inhabitants (Wikimedia)

The 16 volcanoes given status as Decade Volcanoes, with the (main) human habitations threatened given in brackets, are:

USA – Mount Rainier (Seattle, Washington) and Mauna Loa (Hawaii)
Japan – Sakurajima in the Aira caldera (Kagoshima and Kirishima) and Unsen (Unsen and Nagasaki)
Russia – Avachinsky and Koryaksky (Petropavlovsk, Kamchatka)
Italy – Vesuvius (Naples) and Etna (Catania)
Greece – Santorini, a.k.a. Thera (Aegean Islands)
Spain – Teide (Canaries, holiday paradise of Europe)
Mexico – Colima (Colima, Manzanillo)
Colombia – Galeras (Pasto)
Phillipines – Taal (Manilla)
Guatemala – Santa Maria/Santiaguito (Quezaltenango)
Indonesia, Java – Merapi (Yogyakarta)
Democratic Republic of Congo – Nyiragongo (Goma)
Papau New Guinea – Ulawun (???)

While no one doubts that given a possible or hypothetical worst-case scenario, these volcanoes pose a serious threat to nearby human settlements, it’s quite obvious that politics has been a main factor in their selection as Decade Volcanoes. The financially and politically influential USA, Russia and Japan have each been assigned two with four to the equally politically and economically influential Europe, while the large Hispanic contingent of nations accounts for no less than five of the sixteen.

Nevertheless, it is a start and a good one too. The programme has led to a better understanding of the volcanic hazards and in one case, at Etna in 1992, measures were taken on the advice of IAVCEI (International Association of Volcanology and Chemistry of the Earth’s Interior) that eventually prevented a lava flow from reaching a town. Scientists and civil protection authorities have learnt to cooperate as with the very nasty eruption of Merapi in 2010, without which the death toll would undoubtedly have been much higher. Awareness of volcanic hazards from volcanoes not on the list has been heightened as well. A summary of the advances and achievements brought by the first ten years of the programme can be found at “http://www.sveurop.org/gb/articles/articles/decade.htm”  Directly below, followers of this blog may be surprised, or not as the case may be, to learn that our old friend Nemesio M. Pérez compiled the final report of the IAVCEI meeting in Teneriffe, 2010.

Fig. 4 The 2334 m high Ulawun stratovolcano, Papau New Guinea (listspress)

But it cannot be claimed that all the Decade Volcanoes represent the 16 volcanic centers most dangerous to human populations, nor that the efforts are directed where they are most needed. Let us look at Ulawun, Papau New Guinea as one example! Ulawun, a 2334 meter high stratovolcano, is the tallest volcano of the Bismarck Archipelago chain and one of the most active volcanoes in Papua New Guinea. According to John Seach, it is composed of lava flows interbedded with tephra and erupts basalt and andesite through Strombolian and Pelean eruptions. Thus the main danger to humans comes from the pyroclastic flows associated with Pelean eruptions, the other Decade criteria met are those of tephra fall and structural failure. John Seach reports that the 1980 eruption resulted in an 18 km high eruption column that devastated some 20 square kilometres and claims that structural collapse could potentially lay waste to an area hundreds of square kilometres. That is an area with a radius of about eight to ten kilometres.

But is Ulawun really such a highly dangerous volcano? First of all, as far as I can tell from maps and satellite images, there are few human habitations within the danger zone. Second, it erupts basalt and andesite, neither of which are associated with particularly devastating eruptions. Basalts erupt effusively as at Hawaii or semi-explosively as at Etna. Andesites predominantly erupt explosively, but rarely result in a high VEI as both volume-wise and explositivity-wise they are small to medium. Third, Ulawun erupts regularly, 34 eruptions over the past hundred years with most assigned a VEI of 1, 2 or 3 with a single VEI 4. While this is impressive and a constant reminder to the locals that theirs is a dangerous volcano, the regular eruptions prevent the build-up of a much larger eruption – and also inhibits the build-up of a large human population on its fertile slopes.
Let’s now move our examining eye some 200 km to the NW of Ulawun! There we find Rabaul, the city of WW II fame fought over by the Japanese and Americans for its superb anchorages. Up until 1994, Rabaul was the provincial capital with a population of some 17,000 inhabitants. On September 19th 1994, the Tavurvur and Vulcan stratovolcanoes erupted simultaneously which destroyed the town as had happened previously in 1937. Fortunately, no more than five people were killed this time against 500 on the previous occasion. Today, the provincial capital has moved to Kokopo, a scant 20 km away, but Rabaul is slowly being rebuilt as happened after its 1937 destruction.

Why is Rabaul then, to borrow a phrase from Carl, such an ill-begotten piece of real estate? The reason for its superb anchorage is that it is a submerged caldera, 8 by 14 km wide. The town is located on the rim of the caldera and there are no less than eight vents of which four are stratovolcanoes such as the already named Tavurvur and Vulcan. Just to make certain of the town’s eventual destruction, the spit of land on which Rabaul is situated is not only the edge of the Rabaul caldera. A scant three kilometres due north lies the equally submerged Tavui caldera, source of the 5100 BC Raluan rhyolitic ignimbrite, an eruption listed as producing 4.0  ±  1.0  x  109 m3 of tephra.

Fig. 6 Map of the Rabaul Caldera (USGS)

No doubt there are other, and better examples of volcanoes that ought to have been Decade Volcanoes instead of some of the obviously less than well-chosen current ones, but it cannot be denied that the project has realised its goals and done so very well indeed! The context of its genesis, well before the advent of the world-wide web with its instantly accessible webcams and monitoring equipment, has to be taken into account as well. In the final analysis, the Decade Volcano programme has to be regarded as being highly successful.

HENRIK

Suggested reading:

HYPERLINKS :

http://upload.wikimedia.org/wikipedia/commons/4/42/WikiReader_Decade_Volcanoes.pdf

http://www.iavcei.org/” http://www.iavcei.org/

http://www.sveurop.org/gb/articles/articles/decade.htm

http://www.geo.mtu.edu/volcanoes/rabaul/rabaul.usgs.html