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

Herðubreið – Renewed activity at Askja

Photograph by Zanthia. On the picture one can see Mount Herðubreið. Herðubreið (Broad Sholder) is a tabletop mountain, or in another word, a Thuya.

Yesterday an earthquake swarm started with a 3.4M earthquake at Herðubreið. So far the swarm has had 15 earthquakes above 2M, among those 3 where at Askja proper. This swarm as well as the previous ones at Herðubreið have been to the west of the volcano. And those earthquake swarms have been deemed to be lateral intrusions from Askja.

Image by Icelandic Met Office (IMO). Askja to the left of the green star, the black “circle” above is Frémrinamúr. Kverkfjöll is due south and not showing here.

Image by Icelandic Met Office (IMO).

Only problem here is the 3 earthquakes that happened within Dyngjufjöll (Askja). Having 3 earthquakes above 2M at the same time as a medium sized earthquake swarm takes place rather beggers coincidence. I think when the hubbub of this is over the area will be removed from Kverkfjölls fissure swarm. One should also remember that Kverkfjöll is the smallest volcano on the riftline.

Image by Icelandic Met Office (IMO). There seems to be magmatic components to the earthquake swarm when looking at a higher resolution.

On the other hand, this is as far as known not anywhere near any part of Askjas fissure system. We should remember that. Personally I thought up untill now that Herðubreið itself belonged to the Frémrinamúr volcanic fissure swarm. Apparantly I was as wrong about that as the ones who thought it belonged to Kverkfjöll.

Image by Icelandic Met Office (IMO). The earthquake swarm shows well also at the Dyngjufjöll SIL-station.

So, now we are back to a long dormant volcano that had it’s last eruption before deglaciation. And that put it as having erupted at 6000BC latest (time when the glacier withdrew). How do we know that? Thuyas only form under glaciers that are big enough to contain the erupted lava thusly forming the tell-tale tabletop look of a thuya. So, we are talking about a long dormant volcano here.

Image by University of Iceland and Professor Sigrún Hréinsdottir. Inflation showing at Askja. The inflation at Herðubreið started 2 years before.

If we look at the 12 +2M earthquakes we find that 9 of those are between 2.2 and 7.9 kilometres deep. 2 of them are 1.1km deep, and that is a dummy value when an actuall depth has not been set, then we have the original 3.4M quake that has a suspiciously undeep figure. The current given depth is almost certainly around 5 to 7km and will be revised sooner or later. What does this then tell us? That the figures point towards a magmatic intrusion into an old chamber. Remember, this is my interpretation.

So, back to Herðubreið. What is Herðubreið? In my eyes Herðubreið is starting to look like a volcano on it’s own. One of the reasons is that it started to inflate just to the east before Askja started to inflate. It in fact started inflating and having earthquake swarms to the east before Askja stoped deflating. So, I am actually contemplating that Herðubreið and Askja had a common origin and has been rifted apart by the EISZ part of the MAR over the course of millenia. What I am trying to say is that they might actually share a deep root found in the current EISZ. We could think of them as two non-twins sharing the same womb and umbilical cord.

Untill we have new data from the area this is a bit speculative, but I do not think it is that much way off.

CARL

Earthquakes – What’s the fuzz?

Picture from sandandreas.org Picture shows the perhaps most famous faul line on the planet, the San Andreas Fault. It is the cause of large earthquakes in California.

What is an earthquake?

Perhaps the question should have been; when does an earthquake start? For me as a physicist what we normally perceive as an earthquake is just the boring business end of a rather fascinating process, because the earthquake actually starts far back in time.

What we normally see and feel as an earthquake is nothing else than rock breaking. During a small earthquake it is not a larger piece than what you might find in your back yard, and when it is a large earthquake it can be a breakage running for hundreds of kilometers in a fault-line. To simplify it we say that the amount of energy released is the same as the area of the rock breaking in a fault line. There are other factors of course, but this is not the time for that.

Back to when an earthquake starts. To answer that well we have to understand that there are 3 types of earthquakes (that we need to mind today, there are more types of course).

Tectonic earthquakes

This kind of earthquake is driven by the movement of the continental plates; the motion is rather slow from a human standpoint. The speed of the continental plates is normally ranging from 1 to 5 centimeters per year. This type comes in 3 common subtypes; rifting (Mid Atlantic Rift) is when two plates are being pulled apart, clearly visible as the MAR slowly pulls Iceland apart. The second is subduction earthquakes as one continent plate is pushed down under another. Japan is a good example of this. Then we have shearing rifts, which is when two continental plates are sliding past each other.

In general the rifting earthquakes are the weakest, followed by the medium of shearing rift quakes, and then the subduction earthquakes as the strongest (Japan and Chile). The reason for this being the relative crust thickness, a rift zone has to thin crust to create the largest earthquakes, a shearing quake only affects crustal parts that are rubbing together, and the old crusts that are involved in subduction earthquakes has had the time to grow thick enough.

Math is simple. If the fracture is ten km long in a rift zone with ten km thick average crust, then a full faulting would affect 100 square kilometer. The same for 50 km thick subduction earthquake would be 500 square kilometer. Also we have the fact that the old rock in a subduction zone is generally more brittle and have a longer faulting.

Tingvellir on Iceland, the site of many fault lines after earthquakes. The entire area has sunk down due to all rifts.

Magmatectonic

A magmatectonic earthquake is when magma pushes upwards and releases pent up energy that already exists in a rift, shear or subduction zone. Here the movement of magma works as a trigger mechanism, but is rarely the cause of the earthquake. It works more like the small stone that topples the wagon.

Magmatic earthquakes

These are caused by inflow of magma into dykes or magma chambers. The pressure of the magma pushes the rock until it flexes and finally breaks. I will come back to this one.

Age of earthquakes

Here comes what I find to be the interesting part of earthquakes. The age and the processes that make some places able to contain more energy (the last part of which won’t be covered here). I am going to use MAR earthquakes as an example here. As the MAR is spreading with an average of 5cm a year it starts to stretch an area of newly formed crust, our part of the crust is when it starts to stretch 10km thick (just an example). It is rather ductile, so it can take quite a bit of stretching, how much of it we know fairly well.

How do we know it? Well, as an earthquake happens it makes a crack, these cracks normally ranges from 1 to 10 meters or sometimes even more. Our earthquake will give a 5 meter crack. Simple mathematics would give that it would take about a hundred years for our earthquake to form. Problem is just that normally only half of the energy pent up is released in one event. So, it would be more like two hundred years since our earthquake got under way.

The size of our quake will now be determined by the area affected, and effected via the length and depth of the faulting line.

I have here made enormous simplifications, so anybody who wants to explain more in detail in a comment is most welcome to do so.

A magmatectonic earthquakes age is harder to determine, it can be a small amount of magma that hits an old pre-earthquake fault line that is close to faulting. Or it can be a lot of magma hitting a juvenile fault line. The effect will be pretty much the same. With one difference, the first one will most likely not cause an eruption; the second is likely to do so. And, if you have a mature fault line hit by a lot of magma, well that would be your basic Laki eruption.

Magmatic earthquakes are normally fast, anything from a few years, to a few days. In the case of Theistareykjarbunga it took about a year from inflation started to the first earthquake, at El Hierro it took weeks. This is normally governed by the size of the magma chamber, which in Theistareykjarbungas case is huge, compared to El Hierros chambers.

Picture copyright by Magnus Lundgren. Ever been dreaming about diving from one continent to another? Thanks to Magnus stunning picture we can see how it is can be done on Iceland. On one side we see America, on the other Europe. Only in Icelands Thingvellir Fault Zone is it this easy.

Earthquakes and Volcanoes

Magmatic earthquakes are caused solely by pressure from magma and the gases released by the magma. The exception is of course rift zone volcanoes like Krafla. It can either be pressure from below as new magma comes up through the mantle, it can be dyke intrusions, feeder tubes opening up, or inflation of magma chambers, and of course as the vent is opening up as the last stage of an eruption.

Here comes the thing, size does matter. A small 1M earthquake is cracking your average garden stone (well, a large one). A 3M quake is producing a fault that is roughly 100 times larger, and releasing 1000 more times the energy counted in destructive force. I am not going into the math of that here, it is fairly complex. But if someone wants to do it in a comment, please feel free.

So it takes 100 1M earthquakes to fault as large an area as one 3M earthquake, and it takes a thousand of them to crush as much stone (this would be the important number when talking about magma chamber formation). You should think mining blasts here. It is one thing to crack a fault line the length of the detonation on the video below, it is something completely else to blow all that rock to smithereens.

So please, if you see one earthquake of 1M strength, it is not important. If you see a hundred it might be interesting as a sign of something. But to actually have any significance at all, you need a lot more than that. Before a normal eruption you have hundreds or thousands of earthquakes ranging from M1 to M3 or more. And the 1Ms are not even important really. Only exception to this rule that I know of is of course Hekla. That one just needs a few below 1M, and then one around 2M, and then it goes off. But that is the known exception.

And let me reiterate this, I am not a geologist, nor a geophysicist, I am just a normal physicist trying to explain something really hard, and by doing so I have simplified things a lot. If you find that it is too simplified, or simplified so much that it is useless, feel free to compliment and explain further in the comment field. I will only appreciate it.

And once again, small earthquakes are really small, don’t be fooled.

And now over to a huge detonation courtesy of New Boliden Mining AB, I just like big detonations. Sorry, it is probably genetic among Swedes, blame Nobel. 1100 ton explosives used, 2Kton destructive nuclear device equivalent. And now to the real candy, this a 4M earthquake equivalent.

CARL

Earthquakes at Reykjanes Ridge

Photograph by Greg Headley. Reykjanes is quite literaly the spot where you can see how the world is dividing. This out-cropping of the MAR is where the Mid Atlantic Rift comes up out of the ocean.

Six o’clock yesterday (tuesday) a small swarm of earthquakes started at Reykjanes Ridge, it started with a 3.8M at 05.48 in the morning. That quake was followed by a limited number of quakes that trended downwards in strength.

Earlier today (wednesday) the swarm returned and picked up strength and amount of quakes quite considerably.

Image by Icelandic Met Office. The telltale signs of 3M+ earthquakes. The green stars of Iceland.

Image by Icelandic Met Office.

These earthquakes are visible on all SILs in iceland. I have here though chosen to show what it had as effect on the Hekla Borehole strainmeter plot. Look at how it produces first two large spikes, and then a bell-curve as energy increases, and then decreases in the swarm.

Image by Icelandic Met Office. Bell curve of seismic energy.

Reykjanes Ridge is a sub-aquatic volcano as well as a part of the MAR. It has had numerous eruptions, sometimes producing ephemereal islands, and some islands that has stayed above surface.

There are though no sign of this being an eruption, at least yet there is not telltale harmonic tremoring. So, it is most likely a normal tectonic earthquake episode.

Bathymetric map of the Reykjanes Ridge.

Just to put this into perspective. The current swarm of earthquakes at Reykjanes Ridge has during the last couple of hours (as I am writing this) released more energy than Katla has done in the last half a year, and the amount of energy released from the last 3 months of activity at El Hierro, put together. Awesome come to think about it.

CARL