Eifel Volcanic Field II

Recently Nathan took you on a comfortable journey into the Eifel volcanic field. But what is the origin of this intraplate volcanism and where will the journey go?

About 400 million years ago during the Devonian, the Age of Fish, when only plants and insects roamed the land, Laurussia and Gondwana converged into the supercontinent of Pangaea forming the European Variscan Belt. It includes vast mountain ranges stretching from Portugal to Turkey. The Rhenish Massif in central Europe is one of the outcrops of this period, others are the Massif Central in France or the Bohemian Massif in Czech Republic and Poland.

The Rhenish Massif is mainly made of highly folded sedimentary metamorphic rocks, mostly slates, hence the name “Rheinisches Schiefergebirge” or “Rhenish Slate Range”.

Geological map of the Rhenish Massif. Author Jo Weber (Wikimedia Commons)

When the Age of the Mammals dawned and Africa started to collide with Eurasia, a whole lot of volcanic activity started north of the rising Alps. This belt was termed European Cenozoic Volcanic Province by Meyer and Foulger. In the Alpine forelands extensional rift systems developed with the Rhine graben as a prominent feature. Volcanic activity of that period can be found in France (Massif Central), Germany (High Eifel, Westerwald, Vogelsberg, Rhön), The Czech Republic (Eger graben) and Poland (Lower Silesia).

Figure 1 from Meyer and Foulger http://www.mantleplumes.org/Europe.html

The ductile and tough shale and slate bedrock of the Rhenish Massif presumably was incompatible with extensional rifting. Instead the region acted as a hinge between shear rifting along the Upper Rhine Graben and extensional rifting at the Lower Rhine Basin (Illies et al. 1981).

Tectonic situation in central Europe (from this thesis, modified from Illies and Fuchs, 1983)

The Eifel volcanic field is situated west of the Rhine river near Koblenz in the center of the Rhenish Massif. Fluvial deposits prove that this area was uplifted up to 300 m since the Pliocene epoch 5 million years ago and that the uplift had accelerated during the last 800,000 years with maximal elevation around the Eifel volcanic field. Since then the Rhine river and its tributaries were forced to cut deep valleys through the Rhenish Massif, flowing past Hunsrück and Taunus, Eifel and Westerwald, Ardennes and Süder Uplands.

Uplift in the Rhenish Massif, from Meyer and Stets (2002)

The most recent volcanic activity in the West and East Eifel volcanic fields coincides with this uplift which amounts to 0.35 mm per year on average. The dome building may be a combination of widespread uplift of the so-called Rhenish Shield due to horizontal deformation from Alpine orogeny (Illies et al., 1979 and 1981; Meyer and Stets, 2002) and more locally by uplift due to the Eifel mantle plume (Schmincke, 2007).

To study the deep structures of the Eifel region the Eifel Plume project temporarily deployed a large network of seismic stations in 1997. A shear wave velocity model suggested a 100 km wide low-velocity structure extending down at least 400 km into the upper mantle which could indicate an area of increased temperature and partial melting. It remains debated whether this anomaly caused the Eifel volcanism. Other volcanic areas of the European Cenozoic Volcanic Province lack clear evidence of deep mantle plumes and the spacial distribution and timing of eruptive phases is not consistent with movement of the European plate over a fixed hot spot.

Alternative models could be a magma source derived from previous Alpine subduction or local decompression melting from passive rifting caused by tectonic deformation of the crust. Notably, the Mohorovičić discontinuity (Moho) is only 30 km deep below the Eifel while under the Alps it goes down to about 50 km which could give rise to some mantle turbulence and convection.

South-North section of the Moho beneath Europe between 6 and 9° longitude. Depth is highly exaggerated (Image by chryphia). Data from www.seismo.helsinki.fi/mohomap/

There is an overwhelming amount of literature about the recent quaternary activity of the 300+ volcanoes in the Eifel, sadly most of it paywalled or even without online access, because published in books or exotic German journals. So the following is taken from secondary literature. The eruptive history was e.g. summarized by Schmincke in Mantle Plumes (2007), Schmitt et al. (2010) (see Fig. 1 here for a map of geological map of the East Eifel volcanic field) and is nicely illustrated in this German blog post.

In summary, there seem to have been at least four main eruptive phases:

700,000 to 450,000 years before present: the main bulk of monogenetic volcanoes, small cinder cones and short lava flows erupted in the West Eifel and late some in the East Eifel. Their lava contained leucite (potassium rich) basalts, poor in SiO₂, indicating an upper mantle source.

The West Eifel then fell dormant for several hundred thousand years.

430,000 to 360,000 years before present: In the East Eifel the Rieden complex (“Riedener Kessel”) west of the Laacher See had its most productive episode sputtering out several cubic km of lava in larger cinder cones and kilometer long phonolithic lava flows out of a 4 km diameter caldera system.

215,000 to 190,000 years before present: In the East Eifel the Wehr volcano (“Wehrer Kessel”, a 2 km diameter depression) west of the Laacher See and many large scoria cones in the Neuwieder tectonic basin erupted several cubic km of dense rock equivalent. The lava was highly differentiated phonolitic and rich in SiO₂, indicating that country rock had been partially melted. During this time the first Maars were blasted out of the West Eifel volcanic field.

100,000 to 10,000 years before present: the West Eifel field was peppered with Maars still erupting the original lava, the last one to be the Ulmener Maar. Simultaneously, a new kind of lava, basanites, poor in potassium, hence leucite free, presumably from the asthenosphere, created large cinder cones and lava flows sometimes right next to the Maars (e.g. Meerfelder Maar next to the Mosenberg).

In the East Eifel only the Laacher See erupted 12,900 years ago, without doubt the most powerful eruption of all time in the Eifel probably equalling the total output of the West Eifel volcanic field. The Laacher See erupted more than 6 cubic km of magma within days, with an at least 25 km high eruptive column spreading tephra from Italy to Sweden. The magma is thought to have differentiated over several thousand, possibly tens of thousands of years, showing zonation from mafic to evolved phonolite and carbonatite. Pyroclastic flows temporarily built a dam in the Rhine river which eventually broke unleashing torrential floods, illustrated here (in German). Finally the emptied magma chamber collapsed leaving this recreational lake.

The “Loch Lochy” of Germany, the Laacher See. Image by USEBlackbird (Wikimedia Commons)

So the Eifel volcanism occurred in tens to hundred thousand years periods intermitted by hundred thousand years of dormancy. There was a general trend of eruptions starting in the NW progressing to the SE. Eruptions became increasingly voluminous and explosive with time and there was a shift of lava from an upper mantle source to partially melted crust.

Today the Eifel volcanism is dormant. As already featured in Nathan´s post abundant CO₂ emission is a sign that the Eifel volcanic field is not extinct. But also seismically the region is active. Earthquakes during the past 36 years are almost exclusively confined to the upper 15 km. There is no indication of magmatic origin so far. The highest earthquake density is east of the Laacher See and west of the Neuwieder basin along the Ochtendunger fault zone on a NW to SE axis, aligned to the general tectonic setting in the Rhenish Massif.

Recent earthquakes (Sep 2012 to Jan 2013, green, enlarged) and earthquakes dating back 36 years recorded by the seismic station Bensberg, University of Cologne. Image by chryphia.

And here a 3D plot:

Since 1975 up until January 2013 over 1180 local earthquakes were reported by the seismic station Bensberg (University of Cologne) with some increased frequency in the last years.

Earthquake data from the seismic station Bensberg from 1975 to 2013 (between 5.21 and 5.472° lat and 7.25 and 7.65° lon, as in 3D plot). Image by chryphia

Helium and other noble gases that are found in high concentrations around the Laacher See are indicators of the volcanic origin of the Mofettas. Helium isotope 4 (⁴He) is naturally formed in earth´s crust. Another rare Helium isotope, Helium 3 (³He), is produced by fission and bombardement with high-energy cosmic rays, so what we find on earth was created before our solar system formed. In the atmosphere it escapes into space. Looking at the ³He to ⁴He ratio in volcanic gases relative to the ratio in earth´s atmosphere (Ra) gives a clue about the source of the magma. If it´s of deep origin, it still should contain relatively high ³He. The ³He/⁴He ratio measured from Mofettas from the Laacher See is 5.5 Ra, indicating an upper mantle source, but it is less than measured at mid oceanic ridges (8 Ra), thus there is mixing with ⁴He from the crust.

So there we are today. Was this the end of it for the next 100,000 years? As long as the Brubbel squirts and the earth rumbles occasionally we can´t be sure of it. Maybe the ants will tell us one day.

And just in case: a list of webcams

chryphia

Many thanks to Nathan for discussion and support!

Ruminerian V – Get your coffee, you’re gonna need it.

One of the reasons I do this, is because as I was growing up, having an interest in things Geophysical/Astrophysical, there was always a search for the “wow” factor. Not everyone’s “wow” sense is geared the same… and in some cases, the scale of stuff that people are familiar with has a lot to say about how they perceive the “wowness” of it. Grabbing that meaningful nugget of data, or of a concept that totally re-vamps your experience level is way cool. It changes your world in incremental steps… or at least how you look at it.

The difficult thing is finding usable data to ruminate on, or to have some esoteric thought wrapped up in equally esoteric language. (see “e-folding” from the last Ruminerian) It’s not that people are intentionally obtuse with the language or ideas, it’s that there is a lot of technical jargon that develops out of any technical field. (How many of you know that a “gyraline modulator” is?) This post, and the others that I have written, are geared towards the person who seeks to find out more.

This, is more.

Before I continue, a bit about SO2. SO2, Sulfur Dioxide, is a volcanic gas. It reacts with water to form H2SO4, also known as sulfuric acid. Take away the water and you get sulfate, SO4. The reaction in the atmosphere goes something like this:

SO2 1 OH 1 3H2O ═> H2SO4 (1) 1 HO2

In Ruminerian IV, I ended on a pretty interesting graphic. (well, I thought it was)

It is derived from “Stratospheric Loading of Sulfur from Explosive Volcanic Eruptions” Bluth et al (1997). This plot shows the e-folding times for SO2 to sulfate conversation, and then for sulfate removal from the stratosphere.

Where this particular model fails horribly, is in how it treats the SO2 input. It assumes one sizable lump of SO2 injected to the stratosphere. Odds are that many volcanic eruptions are not going to be just one quick blast of SO2 and the show is over. For the sake of modeling influx to the stratosphere, you can probably get away with it… but you have to always be aware that this ideal treatment is going to be incomplete. Another line of thinking is that an established vertical plume can eventually propel the gases past the tropopause if it persists long enough and has enough strength.

Revising that plot and looking at the peaks in it and the narrative that went along with it, moderate sized SO2 releases have a sulfate peak about 2.07 months after the event. In winter (for whatever hemisphere) this conversion rate can be slowed by up to 20% (Bluth et al 1997) giving a peak at about 2.27 months. (30 day months). For large eruptions the curves yield 2.78 months and 2.99 months (winter).

Okay, a lot of stuff about … something. But why?

Sulfate is an aerosol. “a suspension of fine solid particles or liquid droplets in a gas.” Smoke from a fire is an aerosol. Clouds and fog are aerosols. That brown crud drifting off of the iron pellet plant in Bahrain is an aerosol. That massive black cloud that spurted out of the stacks on a steam powered Cruiser in Mayport Florida, that then settled on the Quarterdeck of the spiffy new Gas Turbine powered Cruiser moored on the other pier… that was an aerosol. (trashed a lot of summer white uniforms as the partially burnt diesel precipitated out) Even that gunky haze that you can see over New York from 30 km at sea is an aerosol (the same for LA by the way). Fine particles suspended in a gas.

In some way form or fashion, they all act upon light that is traveling through them. Reflection, scattering, refraction, absorption. You name it. If the particles are quite small, the effects are generally in the category or Rayleigh scattering. That’s what makes those vivid sunsets or the sky blue. If they are about the size of the light’s wavelength, you get Mie scattering. That’s the effect that makes the clouds appear white.

Now I deviate. As I was growing up, I used to listen to the radio. At night I could pull in stations from hundreds of miles away… during the day time, only the closer stations would show up. I had a great uncle who was into Ham radio, and he took a partial interest in my fascination with all things electric. He gave me a copy of an ARRL handbook. I never got a ham license, but I learned everything in that book… and then some. (I wound up specializing in Electronic Warfare in the military). That late night effect that allowed me to hear stations far away, is caused by ionized layers of the atmosphere.. specifically, the ionosphere.

There are three principle layers involved, the D layer which is strongest during the day, mainly absorbs radio waves. Above that, the E layer, present during the day, acts to reflect radio waves. And above that, the F layer. It’s always present, and in the day time it tends to split into the F1 and F2 layers. This is the one that causes most of your long haul radio intercepts late at night. In CB jargon, its called “skip” because that is what the signal is doing… bouncing off of the ionosphere, back to Earth, and could bounce a second time repeating the process. (no, this is not the Van Allen radiation belts, that is something totally different) “Anomalous propagation” (the real term) can occur due to a number of causes… the sun is the main driver, but meteor showers can energize the various layers also.

This rather busy plot gives you an idea of where everything is at. Note that the vertical scale is logarithmic. Just for reference, I’ve place a few altitude events and items in there for reference… such as Felix Baumgartner’s leap altitude, and the record holder prior to that, Joseph Kittinger. Also noted are high and low altitude of the ISS, and the elevation that Mt Pinatubo erupted to during it’s strongest phase.

Now for something totally new to me. Christian Junge, Atmospheric research pioneer, released a paper in 1961 announcing he discovery of the stratospheric aerosol layer. This region is the area where the nitty gritty happens with respect to volcanoes and the climate. I have spent a few days tracking down good info on the location and the make up of the Junge layer plus some of what goes on there.

It resides at about 17 to 30 km in altitude, depending on conditions. This layer is where sulfate occurs when it forms. How dense it is depends on a number of factors… one of the strongest factors is volcanic activity. A volcano can load this layer quite quickly, and as you saw from the e-fold plot, the material can stick around for a while. One interesting thing that I found out was that the Junge layer can occur at distinct elevation nodes. During heavy volcanic activity, there can be an upper and lower node. Eventually it all settles to that lower range over a period of several months.

Yet another interesting thing about it, is that it is usually there… whether the volcanoes are running or not. There is always a background level of sulfate. This is where it gets pretty wild.

At one time, it was thought that SO2 in the atmosphere (troposphere) could drift up and cause this persistent layer. With the way SO2 plagued Los Angeles, you can bet your bottom dollar that some people were chomping at the bit to blame modern society. Many of us have sat around the Café or over at Eruptions or Jon’s Blog oogleing the OMI or TOMS SO2 vertical column data. Some of the plumes we have seen are valid volcanic events, many are not. Beijing almost always has a plume drifting out over the Pacific, one plume that was seen was slap dab in the middle of nowhere… until we found an industrial facility in the Northern reaches of Russia. (Siberian Traps fans were enthralled at possible implications) Of course Europe and The US are producers… even with the emissions standards. Couple those with the bona-fide plumes we have seen, Tolbachik, Grímsvötn (for some reason a huge plume formed over Iceland two weeks after the eruption), Puyehue-Cordón Caulle … you would think that there would be a huge effect in the Sulfate formation.

It’s not gonna happen. At least not from SO2. (Note, Grímsvötn easily punched the tropopause with it’s eruption, I’m referring to the later plume.)

SO2 is a highly reactive gas. As you can see from that plot that it only takes about two and half months for it to react out to below about 10% of what was emitted. (and that’s at the stratospheres rates, it’s probably faster in the tropopause where water vapor is quite abundant) SO2 just does not have the staying power to wind up in the stratosphere due to riding the air currents. In fact, some researchers have studied the SO2 concentration vs altitude and come up with something like this:

Don’t be fooled by that really high correlation coefficient. That’s just how well the curve fit an averaged set of multiple curves generated from the data in Meixner (1984). Think of it as a general guideline and nothing more. What is important is that SO2 trails off quite rapidly with height. It just doesn’t have the staying power.

Before I press on I would like to make mention that the Atmosphere is a highly complex dynamic system. We know a few things about it, such as large scale circulation patterns, but with as much as we do know, you can bet your bottom dollar there is just as much if not more, that is not known. Here is a tidbit that most people don’t know.

Notice the red up arrows. These are the regions where low pressure systems dominate. As air rises, the surrounding air flows inward to fill the space. Where the blue down arrows are at, high pressure systems dominate. Overall horizontal circulation of the individual lows and highs is driven by the Coriolis effect … which is due to residual angular momentum from where the air is coming from. In the Northern hemisphere, Lows rotate clockwise, highs counter clockwise (as viewed from the top). In the Southern Hemisphere, the reverse applies.

Across the world, there are regions that have what are known as “semi-permanent” features… the Icelandic Low is one, another is the Bermuda/Azores high (depending on where it happens to be at) There is no hard and fast rule about what latitude something is going to be at, this is just a generalized rendition of where the boundary regions are at.
Notice that not only is the tropopause usually low over Iceland… the general circulation pattern is lofting air to the tropopause. This also applies to the Kamchatka peninsula which is also not too far south of the Polar cell boundary. (The same for the Aleutian island volcanoes)

Now we move on to the reason for the post… (hell of a lead in eh?)
Two of the more significant volcanic eruption styles… are the massive VEI-6+ explosive eruptions… and the not so explosive VEI-6+ flood basalt events. Of the two, one would think that the huge lava flow events wouldn’t have much of an opportunity to loft stuff above the tropopause. We have already seen that SO2 doesn’t have much staying power, and tends to be scavenged out pretty quickly in the area where most of the water vapor is at… down here in our little realm of existence in the troposphere.

Yet there is a way that massive flood basalts can easily contribute to the Stratospheric Aerosol Layer (another name commonly used for the Junge layer.)

It comes in the form of a little molecule called Carbonyl Sulfide. OCS.
Carbonyl Sulfide can be considered as an intermediate between CO2 (carbon dioxide) and CS2 (carbon disulfide). It has a really long persistence in the troposphere… accounting for up to 80% of the sulfur gases present. I’ve seen residence times ranging from 4 years, to 7.1 to 11 years. Basically, it doesn’t like to react. This gives it time to wander throughout the different atmospheric flows and become well distributed. And a really interesting thing happens when it is hit with ultraviolet light of about 200 to 270 angstroms. (UV-C). The bonds begin to break and it dissociates. Once it does that it forms CO2 and S2… the S2 then reacting with the H2O and OH radicals forming H2SO4… the sulfate.

Hello aerosol haze.

Okay… we have a mechanism not involving SO2 that can make sulfate. Some of the largest sources are the oceans, fossil fuel usage, even the making of concrete. (via a catalytic reaction). In general, the background level of the aerosol is not that big of a deal unless something radically increases the amount there… like an large explosive volcano. Or, a really big flood basalt event. (Eldga, Skaftar, Krafla, Þjórsá lava or any of the huge flow fields that pop up in Iceland from time to time)
Remember, OCS is ultra stable in the troposphere, but once it gets to the stratosphere where the UV-C can get at it, hello Aerosol Haze.

Enjoy!
GEOLURKING

This article has gone through about 4 revisions before I actually wrote it. I hope you were able to read it without dozing off. If you did, it’s no big deal. I doze off reading what I think is really interesting stuff from time to time.

Note: The energy in a photon packet (or wave packet depending on how you look at it) is determined by it’s wavelength. The shorter the wavelength, the more energy per packet. 200 and 270 angstroms are the wavelengths that OCS best dissociated at when exposed to it. I don’t know why, but the ratio of the length of the two bonds is pretty close to the ratio of the differences in those two wavelengths. It’s about 1731 times the length of the bond in both cases. Why? I don’t know. I just found it interesting.

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As noted there were about four iterations of this post before I actually wrote it. Here is some stuff didn’t make it in, but deserves to be mentioned. (well, since I already did the plots for it)

Stepping back from Carbonyl Sulfide… and back to Sulfur Dioxide and the usual way that volcanoes can affect the Junge layer. NASA GISS has a few models they play with. One is a compilation of the “Stratospheric Aerosol Optical Thickness” (What they have against Christian Junge is beyond me, the Junge layer is where most of this stuff is at.) One of the data products is something called the “Tau Line” and represents the average thickness at 550 nm. (that’s pretty much in the middle of “green” light at 520–570 nm.)

http://data.giss.nasa.gov/modelforce/strataer/

For those of you who are chomping at the bit over the Roaring 40′s, nothing really shows up, but they have some nice graphic of sulfate blooms and spreads for various volcanoes over the years. They also have that tau line data set.

First, let’s look at some of the more recent party poppers.

This is a plot of the Tau Line (Aerosol Optical Depth) in relation to a few volcanoes that have gone off recently. Notice that the hemisphere that received the brunt of the sulfate load depends on what volcano erupted.

Also notice that the shape of the curve pretty much follows the decay rate. The lag time between the eruption and the sulfate peak is noted. For the most part, it follows the growth and decay curves at the beginning of the post. Personally, I thought that was pretty neat.

So.. how do they compare to some known atmosphere shakers? Volcanoes such as El Chichón or Pinatubo?

El Chichón, at 17.36°N, had most of it’s effect in the Northern Hemisphere. According to Wikipedia, the Mauna Loa observatory registered a larger drop in Solar radiation transmittance than Pinatubo. However, Pinatubo (15.14°N) had a longer duration of it’s drop. It also had better coupling to both hemispheres. It also had 4.8 times the output of bulk tephra (using GVP Data).

Comparing them with those diminutive spikes over at the right hand side of the plot… those are the ones shown in the previous plot.

How is that for perspective?

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Analyses and visualizations used in this [study/paper/presentation] were produced with the Giovanni online data system, developed and maintained by the NASA GES DISC. (Specifically, the tropopause elevation data)

http://disc.sci.gsfc.nasa.gov/giovanni/overview/index.html#maincontent

“Stratospheric Loading of Sulfur from Explosive Volcanic Eruptions” Bluth et al (1997)

http://www.geo.mtu.edu/~raman/papers/BluthJG.pdf

“The role of carbonyl sulphide as a source of stratospheric sulphate aerosol and its impact on climate” Brühl et al (2012)

http://www.atmos-chem-phys.net/12/1239/2012/acp-12-1239-2012.html

“The Vertical Sulfur Dioxide Distribution at the Tropopause Level” Meixner (1984)

http://link.springer.com/article/10.1007%2FBF00114130?LI=true#page-1

“A ThreeDimensional Global Model Study of Carbonyl Sulfide in the Troposphere and the Lower Stratosphere” Kjellström (1998)

http://link.springer.com/article/10.1023%2FA%3A1005976511096?LI=true#page-1

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

A brief update on El Hierro

This image from the tourist bureau gives quite a good perspective on the island of El Hierro and La Restinga. One just need to lift the eyes to see the volcanic edifices looming over the villcage.

As the smoke starts to clear at El Hierro we get a much more detailed picture of what is happening. As data has poured in we can now deduce a few things.

First of all GPS figures today confirmed that this is indeed a fourth bolus of magma coming up from the depth.  The first one in July 2011 started the entire hubbub and in the end caused the sub-aquatic eruption south of La Restinga. A second bolus in January that followed the same path revigorated the ongoing eruption briefly, but was too small to keep up the pressure in the volcanic system and the eruption dwindled to a halt. The third bolus is so far the most interesting, during a few days more magma arrived than during the first one that caused the eruption. The magma arrived at the same place as for the first two (around the Tanganasoga volcano), but then it took an entirely new path and created quite a few earthquakes as it moved towards the western point of the Island. The fourth bolus also arrived at Tanganasoga, and immediately started to move south and slightly downwards.

Image by IGN. GPS data points for the uplift, figures are aproximatly 2 days old.

We still have only one set of data points for the GPS, but since it is visible on many of them it is still credible. What is a good test for if there is actual inflation or not is to check for motion in EW and NS directions. A false read normally does not show that.

The earthquake swarm is very vigorous with more then 100 earthquakes per day. The pattern is still continuing with a south and slightly down dipping motion. We will see if the hard tested village of La Restinga will have to suffer both the knowledge and the feeling of magma moving straight down under their feets.

Image by IGN.

We can also rule out any degassing or actual small eruption, what initially looked like harmonic tremor are most likely small earthquakes, there is no clear signal showing harmonic tremor to this date.

Image by IGN. No harmonic tremor showing on the charts now. So, no eruption, or no de-gassing.

There is no way to know if this bolus will cause an eruption or not. The lack of harmonic tremor says that it will at least not happen within the next 24 hours or so. But, for the residents on El Hierro the same advice is always valid, stay on top of the news.

CARL

Salud El Hierro!

The thermal hot spring bath of Balneario Pozo la Salud. Quite likely the new “to be at” spot for Jacuzzi watching.

The volcanic island of El Hierro is really turning into the Little Volcano that Could.

3 earthquakes seem to have changed the ballgame around once more.  First came two deep earthquakes at a new spot at 10.10 in the morning, both of them at the depth of 20 km. 26 minutes later followed a 2.6M at 10 kilometers depth.

Within minutes a sharp increase was noticed in the high frequency tremor. The tremor lacks low frequency components making this a dead giveaway that we are seeing a de-gassing event. What has happened is that a persistent earthquake swarm north of Balneario Pozo La Salud most likely finally cracked through and things started to move up beyond the de-gassing threshold.

Image by IGN. Please notice the lack of tremor at the lower frequencies.

After the 10.36 earthquake the shallower earthquakes pretty much disappeared and we had an onset of a new active deep earthquake swarm. In retrospect it is clear that we most likely caught the arrival of a new bolus of magma arriving from depth. If so it is the fourth time new magma arrives from the depth.

The deep earthquake swarm roughly follows the same pattern as for the previous 3 arrivals. Activity started at 20 kilometers depth at Tanganasoga, and then moved outwards and slowly dipped deeper. Every arrival has taken a slightly different direction; this one is moving into what can only be seen as pristine territory.

Image by IGN. Notice the 10km swarm north of Pozo la Salud, and the arrival of the new magma at 20km around Tanganasoga, this time moving roughly towards La Restinga area with a slow dip downwards. Remember that it never went this way during the Eruption of Bob south of La Restinga.

It is still too early to see anything on the GPS, but it should start to be visible tomorrow.

Question then is where is the de-gassing happening? My guess is that the guests of Balneario Pozo La Salud might have an interesting wake up call. If they are lucky they will have a brand new hot water Jacuzzi out in the ocean. For those who do not know, Pozo La Salud is a thermal spring bath in El Hierro.

CARL

Friday riddle is still unsolved:

I am the stony product of music that make Pavarotti mate a canis canis sheep mixture, I am spawned out of the apothecary.

What am I? And what is my origin? 3 points to be had, 2 for the name of “What am I”, and 1 for the origin. There is also a cunningly hidden bonus point out there…