Did you notice the erupting Supervolcano?

This idylic scene is from Lake Tondano situated within the 20 by 30km Tondano Caldera.

Some volcanoes just can’t catch a break. Imagine for a little while that you are a bona fidé supervolcano. You are the largest of your type on the planet, you are highly active, and by gosh you have shown what you are capable of. In a perfect world your 20 by 30 caldera explosion should have put the world into awe, and the 1 000 cubic kilometer of DRE you ejected in the form of pumicious tuff covers an entire sub-continent. Yepp, you really did reach the small highly exclusive club of VEI-8 volcanoes. You smirk at your little sibling Monte Sommas antics with Vesuvius. Your Vesuvius event left a 3.5 by 5 km God honest caldera on its own. To top it off you have a huge underground reservoir of liquid acid that would seriously alter the planets weather if you felt like discharging it. You are also perfectly located to have a maximum kill ratio. So, you wake up and stretch your arms and start a double eruption from two different sub-volcanoes just to celebrate the new day. You have your largest eruption in recorded history. Then you look around to see the fearful faces of the residents as they offer up motorcycles in your name, you expect volcanologists doing somersaults as they play lip banjo, and literally thousands of blog pages glorifying your power and shear awesomeness. What do you find? Yawning people and a cockerel trying to wake up a pig sty. You find that for being an erupting supervolcano you are a massive PR failure. One single small earthquake at Yellowstone outperforms you in publicity.

Tondano

Compund satellite image/map of the Tondano area courtesy of JPL.

The quarternary volcano of Tondano in northern Sulawesi (Indonesia) had its massive caldera event about 2.5 to 2 million years ago. Technically it is a somma type volcano, complete with the remnants of Pangalombian, a former stratovolcano that disappeared in a Vesuvian VEI-7 total caldera event.

Parts of the Pangalombian caldera were later covered by the now dormant Tompaso volcano that ejected large amounts of basaltic andesites in a long series of VEI-6 eruptions.

Todays Tondano is known for having acidic maar eruptions inside the caldera, a couple of mud volcano events during recorded history and no less than 4 active volcanoes, Lokon-Empung, Mahawu, Sempu and Soputan. Quite often Lokon-Empung and Soputan have tandem eruptions.

Lokon-Empung

Lokon-Empung is a double coned strato-volcano located at the northern rim of Tondano. Lokon is a flat topped probably dormant volcano that no longer exhibits a crater on top and Empung is a historically active volcano that last erupted 1775. From 1829 onwards the site of no less than 25 eruptions has been Tompaluan, a smaller double crater situated in the saddle pass between Empung and Lokon. It has erupted since 2011 in tandem eruption with Soputan. The tandem eruption before that occurred on the 13^th of May in 2000.

The current ongoing eruption is slowly working its way to becoming a VEI-3 eruption. But it has so far mainly been consisting of small explosive ash eruptions so it takes time to reach that level.

Soputan

This small stratovolcano is located on the southern rim of the Tondano caldera. It is part of trending line of ring dyke vents that formed in consequent eruptions ending with the formation of Soputan stratovolcano. It normally erupts from either the flanking vent of Aeseput or through the unusually large summit crater that pretty much has the same width as the top of the stratovolcano. This is of course a sign of a very young volcano with a highly potent vent system.

The current eruption consists of ejections of small to moderate explosive ash plumes. The ash columns according to the Darwin VAAC have been up towards 12.1km, with several slightly smaller columns reaching 9km height during the last few weeks. Smaller explosive ash plumes have been pretty much ongoing for the last 3 months now. This eruption is quickly ramping up to becoming a VEI-4, and is as such the largest sub-aerial eruption since Grimsvötn 2011 and that is without even counting in Lokon-Empung into the picture.

The system

As any volcano capable of a large caldera event Tondano has a large and intricate internal plumbing. It is believed that there is a very large reformed magma chamber at depth. As pressure increases in that magma chamber when new hot magma arrives it is believed that the magma either goes up into the caldera as emplacements, and that those sometimes cause maar explosions or reheats the very active thermal fields contained within the caldera. Or that the magma is pushed up into smaller sub-chambers under the active rim volcanoes. When that happens eruptions normally follows very rapidly. A sign of the rim volcanoes being systemically interconnected somehow is that Soputan and Lokon-Empung on many occasions has had eruption interspaced with mere hours.

As any Somma volcano the Tondano caldera is highly intricate and complex, and still it is surprisingly badly researched. The only good material is an Icelandic funded study on the possibility for hydrothermal energy plants in the region. Yepp, the Icelanders are going international with their knowhow.

Why it won’t happen

Image by Andreas / AFP – Getty Images. This image shows how relatively close the volcano is to villages, the height of the ash column and at the same time that the base of the ash column is equally wide to the width of the top of the volcano of Soputan.

For those who dream dark dreams about enormously destructive eruptions Tondano is a bad bet. Why? Tondano has it all really, large magmatic influx, steady inflation, a large central chamber, active volcanism. Pretty much everything that it should need for a VEI-8 eruption. Except for 3 small things, it does not any longer have the amount of water necessary to drive an eruption like that. As many of you know water is a large part of large caldera events. When Tondano went massively caldera it was situated pretty much at ocean level, so as the final large eruption (probably a large VEI-7) happened and the top of the caldera slumped inwards the ocean roared in and what is probably the largest steam explosion happened. Think of it as hundreds of Krakatau eruptions happening at the same time, and you have the picture. As time has passed the land has been lifted due to tectonic uplift.

Second thing is that the magma before the massive caldera event was highly crystallized rhyolites. After the eruption the magmas have been predominantly alkali basalt-andesites.

And the third reason is that Tondano is very well vented as long as the rim volcanoes are connected to the central magma chamber. As soon as the pressure gets above a certain level the magma squirts into the sub-chambers and the volcano on top erupts.

To put it simply, Tondano is a champagne bottle with 5 bottlenecks. The cork is well fastened on top of the actual central chamber, so it cannot erupt that way. Then it has one volcano with the cork slammed back fairly well (Sempu), but that is not fully dormant. One that has the cork put lightly back on (Mahawu) and two bottlenecks that haven’t seen a cork for hundreds of years.

Basically, the pressure is almost constantly being released by Lokon-Empung and Soputan, and if that is not enough Mahawu erupts too. Last time Mahawu erupted with another of the volcanoes it was Lokon-Empung in 1958. Currently even if pressure got really high the only thing that would happen is that all 4 volcanoes would go off.

The only risk for anything really interesting happening would be if one or two of the vents got blocked off. Even then no caldera event would happen, but the likelihood of a Vesuvius event would increase a lot. Currently the candidates for that is either Lokon-Empung or Soputan. Soputan seems to have a very wide bore caliber vent so it could probably release the pressure without exploding from the face of the planet. But Lokon-Empung has evolved quite a lot more, and as it has grown older the vent has narrowed down considerably. If Lokon-Empung was subjected to high pressure it would probably not be able to handle the stress and subsequently go off with a VEI-6+. This is though not likely at current geological timescale.

The only real risk is that a magmatic emplacement will happen in, or around the large reservoir of sulphuric acid (water with a ph of 2). I think anybody can imagine how un-nice a maar event, or even worse, a phreatic explosion, would be if it happened to cubic kilometers of liquid acid. First of all it would make northern Sulawesi uninhabitable and kill off large portions of all life there. And a phreatic explosion would severely hamper the world weather for quite some time. Not a nice thought is it, an acid caldera event. I would decidedly not want to be around if that happens.

Tondano today

Lokon-Empung belching out a 3km ash column.

For being a highly active volcanic region with at best medium risk of fatalities the volcano is surprisingly badly monitored and highly under-studied. Almost all I have written is from one study alone, and that was produced by Orkustöfnun as a part of the geothermal engineering program. Interestingly that report predates the recent article in Nature about a new tectonic plate forming next to Sulawesi. You can clearly see the rift fault in one of the maps in the PDF. Nature seem to have done a bad background check on their paper before publication.

In reality if we look beyond the doom and gloom prophecies of a large caldera event volcano the risk is the bad monitoring. The area is heavily populated and an unexpected VEI-4 eruption at a flanking vent, or lahars, or pyroclastic flows will kill people, potentially a lot of people.

A thought

When a volcano of this size erupts and the world’s volcanologists, volcano-bloggers, and generally the large number of volcano aficionados yawn and continue to look at other less interesting volcanoes that is not even erupting, then something is a bit wrong. I happily admit that it took me almost a week before I actually got around researching the volcano. Then my jaw dropped and I started doing somersaults while playing lip banjo. It is just the sad truth that there are more well known supervolcanoes in the predominantly white western world that steal all the attention.

While we sit and moan about there being no interesting eruption we did not even reflect as we read that two more volcanoes in Indonesia erupted simultaneously 30km from each other. The only comments about it was that people rode their motorcycles inside an ash cloud to get to and from work (Lokon-Empung), and that a rooster cackled at a video of Soputan barfing up a 9km ash column. Then we went back to looking at out Katlas, Heklas, and the rest of the non-erupting volcanoes. Indonesian volcanoes could do with a good PR-Agency.

CARL

http://www.os.is/gogn/unu-gtp-report/UNU-GTP-2010-03.pdf

What’s going on at Katla? Part III

Image from Wikimedia. Aerial picture of Katla.

Trying to make sense of complex phenomenae

In the first two instalments, we had a look at Katla as she appears through media and what she has done historically. It is now time to have a look at what’s going on and try to paint a coherent picture of what she actually is, is up to and able to do, but first let us recapitulate what we found previously:

• There is a general interest in Katla because she is and has been regarded as a very dangerous volcano by generations of Icelanders.
• The presentation of Katla in media is skewered by vested interests ranging from scientists who hope to increase their professional and/or public standing, people trying to cash in on the interest generated such as journalists and bloggers, and finally, there are people trying to increase their standing within the subculture of doomsaying and alarmism.
• Katla is a massive but relatively young volcano, located on the MAR, and formed when Iceland was covered by glaciers.
• The records include two large fissure eruptions on the NE flank of Katla; the prehistoric 5 km3 Hólmsá Fires of 5550 BC and ~22 km3 Eldgjá eruption in 934 AD. In historic times, the 1100 years or so that Iceland has been settled, there have been 27 listed eruptions (28 if the inferred minor subglacial 2011 eruption is included), 23 of which have been explosive.
• Of the 23 explosive eruptions, three have been assigned VEI 3, thirteen VEI 4 and four VEI 5.
• The four VEI 5 eruptions are remarkably alike in size at 1.2 – 1.5 km3, which is at the upper end of what Katla probably is able to do but at the very lower end of VEI 5 eruptions.
• Tephrochronology (in some cases complemented by radiocarbon dating) has identified a further 103 eruptions going back ~8,500 years, and in the few cases where a VEI has been assigned, none have been greater than a VEI 4.
• Katla does not possess a caldera-sized magma chamber.
• In order to account for the great number of explosive eruptions which involve more evolved magmas, Katla could have more than a single magma chamber.
• The available evidence suggests that in order to break through the up to 700 meters thick Mýrdalsjökull glacier, an eruption must be at least a substantial VEI 3.
• Direct and (primarily) indirect evidence suggests that smaller eruptions, mainly basaltic VEI 0 – 2 eruptions are severely underrepresented in her eruptive record and ought to exceed the number of observed eruptions.

Fig 1. Mýrdalsjökull showing the main glacier outlets, directions of jökulhlaups and areas affected. E –
Entajökull, S – Sólheimajökull, K – Kötlujökull, M – Markarfljot, Ss – Sólheimasandur, MS – Mýrdalssandur.
Eyjafjallajökull is to the left and the smaller glacier above is Tindfjallajökull (adapted from Google Maps).

The greatest danger from Katla comes from the very quick and extensive melting of the glacier caused by large eruptions which results in destructive jökulhlaups. There are three major outlets from the glacier: Entujökull to the NW that empties into the Markarfljot river and valley north of Eyjafjallajökull, Sólheimajökull to the SSW that empties onto the Sólheimasandur and finally, Kötlujökull to the SE that empties in a great arc east through south onto the Mýrdalssandur. What ought to be prime farmland and in fact once was settled, is nowadays an unsettled wasteland because of the devastating jökulhlaups unleashed by Katla. This is the true reason why Katla is considered to be such a dangerous volcano.

The fact that one often comes across the reference that in the days before the Hringvegur (ring road), “people were afraid to traverse the Sólheima- and Mýrdalssandur because of the frequent jökulhlaups” is another indication that smaller and unrecorded eruptions that cause only minor hlaups are far more frequent than the 40 – 80 years often given as the interval between main, and thus visible, eruptions.

Fig. 2. The foundations of the old bridge across the Múlakvísl river destroyed by the July 9th 2011 jökulhlaup
are visible to the left. The new bridge was laid down a week later. (photo John A Stevenson, GVP website)

Apart from the postulated connection between the Eyjafjallajökull and Katla volcanoes, one question that always crops up is the Goðabunga cryptodome. Many volcanologists maintain that it is a part of the volcanic system of the Katla central volcano. Others, notably Sturkell and his co-workers, claim it is part of the Eyjafjallajökull volcanic system. In order to shed some light on this issue, I asked our own GeoLurking if he could make a plot of all the earthquakes from 1994 up to and including the 2010 Eyjafjallajökull eruption. The results are quite clear and do throw up a surprise:

Fig 3. E-W cross section, view from south, through Eyjafjallajökull, Goðabunga and Katla. Plot by and
courtesy of GeoLurking. The “lines” formed at approximately 5, 3 and 1.1 km at Goðabunga and Katla are most
likely artefacts caused by quakes being assigned a poorly defined depth. The latter, 1.1 km, is the default depth
assigned by the automatic system in case it cannot compute a depth within the predetermined level of certainty and unless they are manually checked, which is not the case of every quake, automatic depth remains uncorrected, hence these artefacts.

From this cross section, it is quite clear that there is no connection between the Eyjafjallajökull volcanic system and Katla. Eyjafjallajökull has its own, well-defined feeder system from the Moho (first molten layer beneath the Earth’s solid crust) as does Katla, thus they are wholly independent of one another. As can also be seen, albeit not as clearly, Goðabunga too seems to be independent of either Eyjafjallajökull and Katla, the ramifications of which will be the subject of a later post by Carl. Sufficient to say that when we contemplate what Katla herself may be up to, we must differentiate between activity at Goðabunga and activity at Katla. Once we do, we see that while Goðabunga is more or less continuously active, Katla operates in bursts and seems to be most active during summer and autumn when the ice cap is at its, relatively speaking of an up to 700 m thick glacier, thinnest.

Fig 4. Activity post-Eyjafjallajökull. Activity at Eyjafjallajökull is minor and has to do with the system settling down after the end of the eruptive phase. Note that at a depth of 0 to 5 km or so, there seem to be three separate areas of activity at Katla. (Plot by and courtesy of GeoLurking.)

After the Eyjafjallajökull eruption, Katla seems to have entered an active phase with a suspected subglacial eruption on July 9th 2011 and several pits or craters forming on top of the glacier. This activity seems to be localised to three main areas within the caldera:

Fig. 5. Earthquake activity at Katla July 9th 2011, the day of the jökulhlaup and suspected subglacial eruption. Both the 1823 and 1918 eruptions occurred close to but just east of this area. The 1823 eruption occurred close to the easternmost red spot while the 1918 eruption was roughly at the rightmost dark blue spot below it. (IMO)

Fig 6. Earthquake activity at Katla July 17th 2011. (IMO)

Fig. 7. Earthquake activity at Katla July 21st 2011. The 1755 eruption was situated in the same area as the three overlapping orange spots. (IMO)

As can be seen, there are at least three distinct areas of activity inside the caldera with the one associated with the inferred July 9th eruption well to the south. The pits formed in the glacier also align with these three areas, albeit the pits to the northeast seem more drawn out along the caldera wall and not over the center of activity. These three areas seem to tie in with the three areas of activity noted in fig 4 as do the locations of three of Katla’s major eruptions. Thus there is not a single vent, but at least three at surface distances of approximately 5 to 8 km from each other. It is equally likely to judge from Fig 3. and Fig 4. in conjunction, that at great depth, they do have a common source.

I will now present you with my personal view of Katla, but do not be afraid to disagree or draw your own conclusions (within reason please, no Katlatubos here):

Katla is a young volcano and far more active than has previously been thought. Unlike the similarly aged but much less active Eyjafjallajökull, Katla has had more time to develop her system of sills to the point where they are fewer in number than they originally were but have a substantially larger magma-carrying capacity and approach or may have reached the point where they can be considered magma chambers proper. Since cooking evolved magmas takes a long time, usually millennia in the case of cubic kilometre-sized silica-rich magmas and at the very least many centuries for intermediate magmas, it is highly likely that Katla possesses several pockets of magma capable of eruptions ranging from high VEI 3s to small VEI 5s. Not only do the times between such eruptions argue this, their wide spread of location within the caldera does so too.

The most common type of eruption at Katla is the small, subglacial eruption of a few tens of millions of cubic meters of basaltic magmas. These eruptions are not energetic enough to break through the very thick Mýrdalsjökull glacier and the only proofs of their existence are intense earthquake swarms followed by minor jökulhlaups and later observations of deep pits or craters, sometimes water-filled, in the glacier ice. My guesstimate is that there may be many such small eruptions over any given ten-year period, and possibly in the case of a period of high activity, there may even be more than one in a single year. By back-tracking and investigating old accounts over the past few centuries of jökulhlaups in the area not associated with visible eruptions, it ought to be possible to identify many of these minor eruptions.

While a larger “proper” eruption of Katla in the VEI 3 – 5 range cannot be ruled out, I find one unlikely at present as the current activity mostly is in areas already depleted of evolved magmas by geologically speaking very recent major eruptions. Also there is little sign of the uplift required on GPS. If one were to occur, the odds for one towards the upper end of what Katla is able of ought to be better in the Eastern to Northern parts of the caldera.

Finally, what we do see when we look at SIL-stations such as Austmannsbunga, located on the NE caldera rim (not a coincidence, see above), is hydrothermal activity following a period of possibly still ongoing magmatic intrusion and not signs of an imminent, large eruption.

Fig 8. Hydrothermal activity at Katla as shown on the Austmannsbunga SIL (IMO)

I’m sorry to be such a boring old fart, but if this is unsatisfactory, start looking for intense earthquake activity at some 25 – 10 km depth, showing on the IMO map for Mýrdalsjökull as being in the Eastern to Northern part of the caldera, activity that shows a clear upwards trend and spreads when it reaches depths approaching 5 km!

HENRIK