Ruminarian II – Tolbachik

Some of you may have noticed that I haven’t been doing a large number of plots. In part, this is because digging into a large set of data takes a bit of motivation and patience… and a bit-o-time. KarenZ, dfm, and chryphia have picked up the mantle on animated plots, and have each brought their skills using their programs of choice and produced some truly outstanding animated graphics. This has allowed me to focus on learning and reading… sometimes getting it wrong, sometimes getting it right… or at least pretty close to right.

So… let’s ruminate.

Tolbachik is a fissure vent eruption. It wasn’t until this evening that I realized that my initial ideas about what happened were somewhat wrong. Rather than a sill forming (horizontal magma emplacement) which then fed to an upper sill via a dike (vertical magma emplacement), what happened appears to have been the pressure in already emplaced magma fracturing the rock and continuing along the path that it had been working on for several years.

Back in 1975, this system erupted in “The Great Tolbachik Fissure Eruption,” and according to the Smithsonian’s GVP site, placed 1.2 km³ of magma on the surface. For reference, that’s about 8% of what Lakagigar (Laki) did in 1783-85… and at about 11% of the rate. 2.26 x 10^06 m³/day verses Laki’s 2.02x 10^7 m³/day. Either way, it is still phenomenal. Mt St Helen’s did about 1 km³ in it’s flank collapse and lateral blast, but that was a different sort of critter. Tolbachik (and Laki) both do “Flood Basalts” though Tolbachik is a bit anemic in that regard.

However, it is cool to look at and ponder. Here is a combination EO-1 ALI image overlaid in Google Earth, with features aligned so that everything is in proper context draped over the surface.

“Dmitry Melnikov” over at Dr Erik Klemetti’s Eruptions forum spotted the EOS image.

As noted earlier, I had the sequence a bit off in how I was looking at it. (I’m not an expert so I’m allowed to mess up, right?) Poking around at the various links that show up in the threads, one gave us a bit of fine grained data… well, a lot more than we had. Doing a bit of data juggling, I located the data for the plot used in “Northern group of Volcanoes” It plots out like this;

Here you can clearly see the upper and lower sill/chamber and what probably is the connecting dike. It wasn’t until dfm did a close in animated plot that I noticed that the upper region seemed to initiate the events, and then the upper and lower regions pretty much quaked in unison.

Another thing that got my attention as I was poking around at it… was that the brunt of the quakes were no where near where the eruption was at. Maybe a few connectors from the main quake region, but that was about it. This probably is a manifestation of the feed system. (remember, “Bob” didn’t really have a lot of activity from the believed “chamber” to the Jacuzzi… which seemed to be seismically quiet until after the fact)

Juggling programs… (Excel to DivaGis to Google Earth) gives us this:

Notice anything interesting? Yup. Those two pancakes are directly under the main volcanoes. Roughly a line from Gora Bolshaya Udina to Mount Ostry Tolbachik. Had the dynamics been different, this could have been a main edifice eruption of Tolbachik. Even the seeming “connector dike” is directly under the SouthEastern summit. That pretty much means its actually connected with the vent. The magma just found an easier way out. (again, a lot like “Bob” where the main swarm of activity was pretty much under Tanganasoga but the eruption was over next to La Restinga)

Poking around the net… you find that Pay to Play paper sites can really piss you off. One of the most notorious is Springer… but Springer does have something quite neat. A few “freebie” papers that you and I (un-funded armatures) can get our hands on. One of them is: “Determining magma flow in sills, dykes and laccoliths and their implications for sill emplacement mechanisms” Thomson (2006). Here is the search link for it since direct links don’t work with that site:

http://link.springer.com/search?query=Determining+magma+flow+in+sills

In this paper, the author notes that sills tend to be concave upwards. That means that the propagating ends tend to point more and more towards the surface. A combination of forces can drive this, Forced Deformation, or Faulting. Page 197 of the parent publication (or just go to page 15 of the PDF) and you get a really nice visual example of what he is getting at. It’s entirely possible that something like this is what drove that finger of magma moving southward to turn up and broach the surface. (the tendency of this area to rift probably had a lot to do with it also)

Another thing to consider (speaking of tendencies) is that this entire region is made up of teranes that have been slammed into the Okhotsk plate (sort of a subsidiary of the North American Plate in some renderings) You all remember terranes right? Assemblages of crust material that have a common geologic origin and tend to move as a group. In this case, slivers of island chains squashed into the plate, slivers of oceanic spreading center remnants (the central valley region), an ancient volcanic arc (western side of Kamchatka), and … get this, parts of the Hawaiian hotspot’s activity. (up around Shiveluch where the Emperor Seamounts are periodically gobbled up by the current subduction zone)

Yeah… a lot of stuff going on in Kamchatka.

Here is an animated GIF I did the other night…. it was noted that this sped up sequence looked a bit like a frying pan fire. Appropriate.

http://volcanocafe.files.wordpress.com/2012/12/tolbachik.gif

Here is a re-tasked webcam where you can grab a peek at the activity from time to time.

http://www.qicknews.de/Webcams/Tolbachik.php

Enjoy!

GEOLURKING

RIDDLE  - Name those Volcanoes

The sovereignty of first was briefly the subject of a ‘blague Francaise’
The second used to have vents (now pits) that share their name with a footballing legend – the name of this volcano means ‘long’ in the local language
The third is the only volcano within the arc of the SS islands chain to have erupted rhyolite pumice – Solved Protector Shoal
The fourth is located approx. 3 kms due west of a small group of  ’sibling’ rocks – Solved Kick ‘em Jenny 
The fifth shares its name with a species of lacertid – this giant wall lizard can only be found on the Island that bears the same name as the volcano

The link is that they are all submarine volcanoes!

One point for each volcano and one point for spotting the link!

The Dead Zone

Updated 13 Sep 2012, see end of article.

In logic, an assumption is a proposition that is taken for granted, as if it were true based upon presupposition without preponderance of the facts. (Wikipedia)

Back around May of this year, Carl asked me to do a series of simulations using KWare’s Heat3D, a program written by Ken Woheltz and the Reagents of the University of California under the sponsorship of the US Governement. It’s a cool little program that allows you to run heat simulations of magma intrusions into rock of varying characteristics. I had been prompted to write an article about one of the more perplexing areas in Iceland (well, to me it is). Not feeling that I was up to the task, I offered to do the supporting graphics if Carl could find someone to write the meat and potatoes of the article. I killed off a weekend working up the plots, but two of the catch points that we ran into were; “What temperature of the intruding magma should we use?” and “What exactly is the geothermal gradient of the region?”

With those two uncertainties, and the bedlam of real life, the post never made it to the forum. Things happen.

Before I go on, I must warn each and every reader here that I am not a seismologist, geologist, or bona-fide expert in the field. I read a lot, have been “studying” geology and physics in some shape form or fashion for about 37 years. I am just an amateur like many of you, so there is ample room for error.

With that out of the way… now we discuss

First, “The Dead Zone” is not an actual named place. It’s just a colloquialism specific to VolcanoCafe. It’s that region of Iceland between Katla/Torfajökull and Bárðarbunga/Grímsvötn. I refer to it as “The Dead Zone” due to the seeming low number of quakes. Historically, and pre-historically, the region is quite active with fissure eruptions. Irpsit and others can give you more definitive dates and names about the area, but I am limited to what I can cobble together from various sources. There are many other features here, but the main ones that I can find data on are Veidivötn, Vatnaoldur, Skaftar, Eldgja and Trollagigar. (spelling as listed in GVP and may be missing some of the diacritical marks) Veidivötn, Vatnaoldur, and Trollagigar are part of the Bárðarbunga system, Eldgja belongs to Katla, and Skaftar belongs to Grímsvötn. (As parts of the parent volcanoes fissure swarms). As you can see from the overview plot, there just are not very many quakes in this region. (Ignore the dot dashed blue line, that was part of the original plot set and is not used here)

Now, why is the Dead Zone dead? Because it is really… really hot. Much more than you would think. When an eruption is completed, magma sits and cools after the eruption is over with. This cooling rate depends on the thermal conductivity of the surrounding rock. For Basalt, the heat capacity is 840 J/kg K. (this is what I used in the simulations), Granite, for comparison is 790 J/kg K. This is in part due to its lower density. How it works… in order to raise the temperature of one kilogram of the material by one Kelvin (same as one degree C), you need 840 Joules of energy (for Basalt). Since we are talking about heat capacity, Water is 4185.5 J/kg K and Ice (at 0°C) is 2090 J/kg , so you can see how water or ice can drastically affect what is going on. This is one of those “gotchas” that can throw this whole scenario off. This area has a high water table and that can seriously affect how accurate the simulations are. Keep that in mind as I continue.

Anyway… when a dike intrudes into rock, whether it erupts or not, it starts loosing heat at a rate that can be calculated (provided you have the skill, or a program written by someone with the skill). Heat3D runs through the iterations of how heat migrates into the surrounding rock.
Here is how a single intrusion works out over a few years.

In my original set of graphics, I used a temperature of 1600°C magma due to the runniness of the flows and how far they traveled. My original guess was 1100°C based on a statement that I had seen in a paper, and much discussion occurred between Carl and myself about what would be the sane value to use.

“Time constraints on the origin of large volume basalts derived from O-isotope and trace element mineral zoning and U-series disequilibria in the Laki and Grímsvötn volcanic system” Binderman et al (2006) places the temp in the 1120–1140 °C range based on a “Mg in glass” geothermometer. (calculating diffusion and formation rates vs temp and pressure). Another reference (that I can’t locate at this moment) implies a temperature of 1200°C at 250MPa for one of the clast minerals. 250 MPa is in the 10 km depth range. Still uncertain of what temp to use, I went with the program default of 1250°C.

I used a 10 meter dike width based off of the average of three known dike sizes contained in “Geodetic GPS measurements in south Iceland: Strain accumulation and partitioning in a propagating ridge system” LaFemina et al (2005). This produces a really crappy 95% confidence range of 0.5 to 10.2 meters. (three samples is horrendous, but it’s all I had) Since the size of the plot grid has a direct play in how long the simulations take to run, I used 10 meters in order to get the simulations done in one evening.

Okay… now the actual run. As noted, this is not the original, and for brevity, I focused on only one system, Veidivötn. In case you didn’t know it, Veidivötn is probably the most lively fissure system in the region. It’s responsible for many of the Tungnaárhraun tephra layers. (THc. THd, THe…) GVP places an event there at the following dates: -6650, -4800, -4600, -4550, -4400, -4200, -1200, 150. For each eruption, I placed a 10 meter wide dike and ran the program out until the next intrusion date, which was then added and the process repeated. Another “gotcha” that you should be aware of, the eruptions did not necessarily occur in the same part of the fissure. This simulation assumes that they did. In effect, this skews the region towards being hotter than it might really be (and don’t forget the possible effect of the water that I mentioned previously)
So… here is the final product for what conditions may be like under the Veidivötn fissure. The temperature scale from the previous plot applies here.

Pretty gnarly eh? This is the crux of why I think that you won’t really see many small quakes in this region. Each one of those fissure lines has a heat structure similar to this. The crust is for the most part, plastic and yields to any stress that comes along… until it arrives too quickly for it to give. Then you have the larger quakes and potentially an opening of the fissure if the conditions are right… such as a nearby parent volcano being at or near erupting and having a ready supply of magma to flow down the rift and open it the rest of the way up. Structurally, there isn’t really much there to hold the two sides together. Plate shifts can do it (tectonic), or a parent volcano.

---

From “IAVCEI General Assembly 2008 Conference Field Excursions, Excursion 1: Historical Flood Lava Eruptions The 1783-84 Laki and 934-40 Eldgjá events” August 14-17 2008

“In 1783 the people of south Iceland had enjoyed a favourable spring and were looking forward to summer. However, their destiny was about to change. Weak earthquakes in the Skaftártunga district in mid-May were the first sign of what was to come. The intensity of these earthquakes increased steadily and on 1 June they were strong enough to be felt across the region from Mýrdalur and Öræfi. The earthquake activity escalated up until 8 June when a dark volcanic cloud spread over the district, blanketing the ground with ash (Figure 18a). The Great Laki eruption had begun.”

I’ve worked out the distances to Mýrdalur and Öræfi from the Laki site and applied an Mw to MMI estimate based on a few real world quakes from the USGS catalog in order to get a feel for how the power drops off over distance. Based on the MMI levels at which a quake becomes detectable by an unaided person, the quakes leading into the Laki event were in the Mag 4.5 to 5.0 range.

It’s a bit of a reach, but extending the formulas from “New Empirical Relationships among Magnitude, Rupture Length, Rupture Width, Rupture Area, and Surface Displacement” Wells and Coppersmith (1994) down to Mag 4.5, you get the following numbers.

Mag 4.5 – Surface rupture length 0.5 km, Subsurface rupture length – 1.3 km, Downdip rupture width – 1.7km.
Mag 5.0 – Surface rupture length 1.3 km, Subsurface rupture length – 2.7 km, Downdip rupture width – 2.9 km.

THESE ARE ESTIMATES

There is a bit of slop in the formulas, it is an attempt to get a working estimate of the physical manifestations that you would see from a quake. These particular formulas are only considered reliable for events down to Mag 5.2, but they do track well with no oddities in the curves. Below 5.2 the confidence in what the formula says drops off.

From that, it seems that the Mag 4.5 to 5.0 quakes are what is needed to open the system up. They have the right sort of features; the crust itself has likely healed very little from the previous events and should not take a lot of energy to re-open.

All this rumination and reading is one thing… but there is always something missing when you think and talk about these fissure eruptions. That’s the scale of the things. Since none of us were around, we just don’t know or have a frame of reference. All we have are eyewitness accounts. From some of those accounts, we know how long or how tall the fire curtain was, but that’s it. Just numbers in a book. Here, I have scaled an image of a generic fissure eruption and placed a few well known silhouettes in front of it so that you can see just how big these things are.

Enjoy.

GEOLURKING

GL Edit: The silhouetted buildings are;
Empire State Building – 443.2 m, Taipei 101 – 449.2 m, Burj Khalifa – 829.84 m, Sears Tower – 527 m, Petronas Towers – 451.9 m

“GVP” = Smithsonian Institution – Global Volcanism Program

UPDATE:

Irpsit says:
September 12, 2012 at 18:26

From what I know Laki eruption could be observed from almost anywhere in Iceland, in distance. The reports even speak that you could see the fountains from far away, but probably not everywhere in Iceland, as 1km high is not enough for that.

This put me on a search for two of the images that I made for the original article. I was able to pull them from Google archive of my mail.

They are not as stunning as the scaled image, but they are worth pondering. The ruddy maroon rectangle represents the Skaftar (Laki) fire curtain anchored to the surface, as seen from a couple of locations.

Activity in Iceland’s Dead Zone

Photograph by Skúli Thor Magnusson. Stunning view of the Veidivötn Lakes.

The Dead Zone

In the area going from Vatnajökull down to Torfajökull and Myrdalsjökull there is normally almost no seismic activity. This has given the area the not so scientific name of the Dead Zone. It contains the fissure swarms of Bárdarbunga, Grimsvötn and Katla. Grimsvötns fissure swarm is called Laki and Katlas is called Éldgja.

Veidivötn

Bárdarbungas fissure swarm is called Veidivötn, and has had the largest lava-floods on the planet in the last 10 000 years. The largest of those is called the Thjorsahraun putting out an estimated 20 cubic kilometers of lava.

Photograph by Örn Óskarsson. Anybody who wishes to rent a cabin?

Rifting Fissure Eruption

When Katla, Bardarbunga or Grimsvötn has a major and sudden influx of magma from the hotspot, and the fissure swarm of the volcano in question suffers a rifting of the Eastern Icelandic Seismic Zone opening it up. Then what happens is a VEI-6 eruption at the central volcano, and a minimum of 10 cubic kilometers of lava erupts down a minimum of 100km fissure. It is the most destructive type of eruption likely to happen in the northern hemisphere.

The reason of them being that problematic is that it at the same time it releases a lot of ash into the atmosphere, about 100 times the amount from Eyjafjallajökull and also the fissure releases a lot of sulphuric gasses. This phenomenon is called dry fog, and was reported in most of northern Europe and the USA during the eruption of Laki in 1783.

The Laki eruption is the most deadly in European modern history due to the famine that followed. 1783 is also known as the year without summer.

Dead Zone activity of today

Image by IMO. Look at the line running up from Torfajökull/Myrdalsjökull, that is Veidivötn.

During the last 12 hours a series of small (1 to 1,8M) earthquakes happened inside the Dead Zone. They trend from Torfajökulls Landmannalaugar up along the Veidivötn fissure towards Skrokkalda.

What is remarkable that this phenomenon has never been recorded before.

At the same time there where harmonic tremoring in the SIL-station of Skrokkalda, Vatnsfell and also Snaebyli, shown here is the activity at Vatnsfell.

Image by IMO. Vatnsfell SIL-station showing harmonic tremor.

There has also been activity at the Dyngjufjöll, the principal SIL-station of the Bárdarbunga volcanic complex.

http://hraun.vedur.is/ja/oroi/dyn.gif

And here is a webcam of sorts for the Veidivötn area:

http://helgi.dk/?page_id=352

Caveat for the press

Please dear all, it is still far from any possible eruption in the area. At most this is a signal of what can come, nothing more.

CARL