When glaciers start running 1

What is a jökulhlaup?

At the moment (December 30, 2012), water height and conductivity are again on the rise in Múlakvísl, an outlet river of Mýrdalsjökull glacier, the one covering the famous Katla volcano in the south of Iceland.

Plots from Icelandic Metorological Office (vatnafar)

This could be a sign for again another jökulhlaup in this region, Mýrdalssandur, where the Ringroad bridge was destroyed last year – or maybe not.

But what is a jökulhlaup?

Jökulhlaup is an Icelandic word which comes from „hlaup(ið)“ which means „(the) run“ and „jökull“ meaning „glacier“ – one of many Icelandic composita, as in Icelandic language words are set together like in puzzles. English words describing the phenomenon are “glacier run” or “glacial outlet flood”. (There is also a German expression for it: “Gletscherlauf”.)

For a long time, it has been sort of a puzzle, what is happening to glaciers and their lakes as well as under the many Icelandic glacier caps where volcanoes lie in wait for their next awakening. Because jökulhlaup often happen without any (observable) eruption.

Glacier outlet floods can have a lot of different origins.

There can be some which have nothing to do with volcanic activity, like the famous Lituya Bay run. http://en.wikipedia.org/wiki/Lituya_Bay In this case, a landslide in 1958 caused an enormous tsunami. Dam failures by earthquake or material break down can also be behind this, as was the case sometimes in the Alps.

Some floods can also be initiated by surging glaciers (http://en.wikipedia.org/wiki/Surge_%28glacier%29 ), which may or may not stand in a complicated and not yet clear relationship to volcanic activity.

And now we are approaching the really interesting cases.

There are also some different kinds of jökulhlaup, the real ones, which are in some way or other caused be volcanic activity.

Some of you were a bit disappointed by the last glacier run from a region with two famous ice cauldrons in the southwest of Vatnajökull, which is called the Skaftárkatlar (Skaftá cauldrons) in August 2012 http://www.vedur.is/um-vi/frettir/nr/2520 . It was a really small one, of about 185 m3/sec.

As is to be seen in this film https://contour.com/stories/skaftarkatlar-30-08-2012 the glacier runs normally come from sort of an indentation in the big ice caps that cover in the whole 11% of Iceland. And the runs from this region are produced very regularly, in a rhythm of 1-2 years, mostly in the spring or summer, so that the people down in Kirkjubaejarklaustur almost set their clock in connection to them.

They are caused by a high temperature area, and intrusion under the ice of Vatnajökull, which melts more or less the same amount of ice in the same time span. The water is collected in a bowl shaped lake under the ice and when there is enough of it, breakes the ice barrier in front and runs down through a system of tubes in the ice, which is built up and widened by the water pressure and heat of the water. These are – as we have seen this summer again – small glacier runs, which build up rather fast to a certain maximum and then slowly fade out again, “(…) there are, however, other types of Skaftá floods which have no distinct discharge peak but maintain a strong, stable current for up to 2 weeks before terminating.” (H. Björnsson, 2010, 2).

A similar kind of smaller, but volcanically induced hlaups is also found at the Grímsvötn volcanic system. We saw two of them in the last months ( see: http://www.vedur.is/um-vi/frettir/nr/2583 and http://icelandreview.com/icelandreview/daily_news/?cat_id=28304&ew_0_a_id=369682 .

Björnsson, 2002, p.4: 2 drawings, fig.3

In former times, travellers were always very fearful about traversing the sander plains in front of the big glacier caps in Iceland. And the guides, local men, farmers and eg. Postmen, praised like heroes. The most famous one of these was Hannes Jónsson of Núpsstaðir (1880 – 1968) whose life could be subject of a post of its own.

But, if these floods were so small and predictable, why would that be so?

There is still another kind of glacier run to be reckoned with, and that is the one normally connected with the notion: It is the cataclysmic outlet flood, having its origin in a big volcanic eruption under one of the icecaps, by which an enormous quantity of melting water is produced and after a longer or shorter period of time depending on intensity of eruption and last but not least on water pressure and decline of slope rushes down to the sander planes below taking with it a mixture of sediments, gases and icebergs.

Lómagnúpur and the Skeiðarársandur with outlet glacier Skeiðarárjökull in the background. Image from Wikimedia Commons.

In case of an eruption in the Grímsvötn region – Gjálp 1996 was a fissure system which is part of it – , the subglacial lake in the caldera below the mountain Grímsfjall fills, and in filling takes on the form of a sort of subglacial balloon. When a certain limit is reached, the water pressure is high enough and the ice barrier in front of it is broken, and the water rushes downhill. At the beginning through tunnels in the ice, but if the water discharge surmounts a certain limit, the water lifts first the barrier and then the whole glacier and rushes downhill in sort of a big subglacial wave with the glacier riding onto it. And down in the valley, the water spills out in a lot of bigger and smaller outlets at the snout of the glacier and more or less covers the plain in front. (Björnsson, 2010) The jökulhlaup connected to the Gjálp eruption in 1996 produced no less than 55.000 m3/sec at its peak covering all of Skeiðarársandur. (M.T. Gudmundsson, etal. (2004).

Wikimedia Commons

Drangajökull, Langjökull, Hofsjökull, Vatnajökull, Eyjafjallajökull and Mýrdalsjökull

When I started researching this, I was surprised to find out that not only had the “usual suspects” Vatnajökull and Mýrdalsjökull produced bigger and smaller jökulhlaup running in all directions, but that smaller ones were known from virtually all 5 big Icelandic ice caps, i.e. also Drangajökull (most probably not volcanic, because it is situated outside of the active rift zone), Hofsjökull and Langjökull. (O. Sigurdsson, 2005) And two years ago, we could observe how the outlet glacier Gígjökull from Eyjafjallajökull covered a small glacier lake with debris during some jökulhlaup. http://en.vedur.is/hydrology/articles/nr/2097

The phenomenon is of course not limited to Iceland, but is possible in all parts of the world with glacier covered volcanoes like Alaska or the Andes in South America.

And there have also been famous floods in the distant past, i.e. the Pleistocene, like the Lake Missoula floods which carved out the Columbia River Gorge in the USA, the Altai floods in Siberia, even one in Germany (Münsterland) and then there is the case of Jökulsárgljúfur in Iceland. Some of them are thought to have involved such an enormous quantity of water that the one of 1996 in Iceland is really dwarfed by comparison. But we’ll speak more about these in later posts.

Disclaimer: I am no specialist, just an interested layman.
IngeB

Literature:

⁃ Subglacial lakes and jökulhlaups in Iceland, by H. Björnsson (2002)
⁃ Understanding jökulhlaup, from tale to theory, by H. Björnsson (2010)
⁃ Jökulhlaupannáll 1989-2004, by O. Sigurdsson, etal. (2005) (in Icelandic)
⁃ The 1996 eruption at Gjálp, Vatnajökull ice cap, Iceland: efficiency
of heat transfer, ice deformation and subglacial water pressure, by Magnús T. Gudmundsson, Freysteinn Sigmundsson, etal. (2004)

The (ash) history of Iceland, in my backyard – Part II

In part I we found the main bands of a excavation here in SW Iceland:

- dark band of Veidivötn 1477
- double white layer band of Hekla from 1341 (or Öraefajökull 1362) and Hekla 1104
- dark band of Vatnaöldur 870 (called the “Settlement Ash”).
- thick white layer of Hekla 3 (around 1000 BC), one of largest eruptions in Iceland.

But there are many minor layers besides the obvious ones. We will get to them now.

FIGURE 1, Below the 870 settlement ash layer, there is one unknown grey and well visible band. There is also a possible eruption of Grimsvötn and Hekla, and then we find the major Hekla 3 band. Below that, we find a thick dark band, probably from Katla, around 2200 BC, and before that we probably have the ash from the Grimsnes eruptions (dating 3500 BC). Photograph by Irpsit, all rights belonging to him, used by permission.

An unknown metalic grey layer

Above the Hekla 3 layer, there is an unknown layer. It has a strange shiny metalic gray color. This is an unknown eruption estimated between 500 AC and 500 BC. Many eruptions happened at that time, not only from Hekla and Katla, but also an eruption at Torfajökull at 150 AC, Hengill at 80 BC (which is only 20km to the west), and also in Vatnafjöll. I don’t think this ash came from Katla or Hekla, unless they erupted a different ash. This type of shiny metalic ash color is notoriously different from every other ash I have seen in Iceland. But I have seen similar shiny lava rocks in Iceland, in a few places, but I can’t remember where. Until then I cannot make a guess about the identity of this layer.

There also seems to be a brown band between the Hekla 3 and the unknown grey layer. It is probably an undated eruption of Grimsvötn, which usually has this color of ash (around 100-500 BC). There is also a light colored band (just above Hekla 3), and that is probably an eruption of Hekla (around 500-1000 BC).

Below the Hekla 3 layer, there are several bands, shown in Fig.2. We first find a thin band of orange material (at 53cm), then a very large band of dark ash (starting at 56cm), and then another broad band of orange material at around 65cm. There is a thin white layer between both broad bands of dark and orange material (not visible in Fig.2).

FIGURE 2. Below Hekla 3, there is a lot of bands to be found, upon close look. But especially notorious is one dark band around 2000 BC (56 cm deep), possibly from Katla (its something really thick), and also a double band around 5000 BC (75cm deep). Photograph by Irpsit, all rights belonging to him, used by permission.

Around 1500-2000 BC: Torfajökull and Katla?

The first thin orange band is estimated at around 1500 BC. The most likely candidate is the eruption of Torfajökull around 1200 BC, because it tend to erupt such colorful rhyolite ash. The broad grey band is estimated around 2200 BC. Most likely it was one strong eruption from Katla (tephra N4 or N2). What is was, it was big, because this is a thick layer. However around this time, we also had records of an eruptions at Langjökull, dated as ~2050 BC, which was actually nearby, only 40km north (it’s closer than Hekla), in a small shield volcano named Lambahraun. If the eruption started explosively, then its ash might have reached here, but officially there is no known ash from the Langjökull volcanoes and I also don’t expect that even a nearby shield volcano would deposit such a major amount of ash. So we stay with Katla.

Hekla 4 and Grimsnes eruptions (2300 to 4200 BC)

The thin white band is probably the eruption of Hekla4, around 2300 BC, which was a very large eruption. The broad orange material is almost likely from nearby Grimsnes volcano, that erupted several times circa 3500 to 4200 BC. I am actually inside Grimsnes volcanic region; its monogenic cones are just 5-8 km away. During the Grimsnes eruptions, there was some local ash fall. The volcano is just composed of crater rows, with one major explosion crater and the other cones being a deep red. It’s no wonder that the layers from Grimsnes eruptions are of a similar color.

FIGURE 3. Grimsnes volcano, located only 5km away. Its the smallest active volcanic system in Iceland, producing crater rows every few thousand years. It produces plenty of iron-red rock material. In the picture, we see Seydisholar volcanic cone, with Búrfell pleistocene volcano in the background (this is another Búrfell; and behind it lies Hengill to one side and Langjökull to the other) Photograph by Irpsit, all rights belonging to him, used by permission.

Hekla 5 and Botnahraun/Laki, or Holmsá fires eruptions, or Thjorsáhhraun (5000-6000 BC)?

At around 75cm deep (estimated at 5000 BC) we find what looks like a double layer: white material above and a deep dark brown below. It is easy to assign this white material to Hekla5 (another large Hekla eruption at 5050 BC). The brown material underneath is unknown, but likely Grimsvötn. Possibly the Botnahraun/Laki eruption. Alternatively it might also correspond to another big eruption at this time: the Holmsá fires, another Eldgjá-like fissure that opened to the east of Katla. And still it might also be the Thjorsáhraun lava from Bardarbunga/Veidivötn, around 6600 BC. That lava actually travelled some 200km from Veidivötn towards the southwest, passing only cross 5km east from this location. That is the largest lava field on Earth since the ice age.

And now we get even older in time… Seydisholar 7000 BC

Below this point, it starts to get complicate to assign the identity of any layer because of a mud deposit underneath. There is some orange material just above it, which I assume it might have been the eruption of Seydisholar at 7000 BC, from the nearest Grimsnes crater row. That was the largest eruption of the Grimsnes system, with an estimated VEI4. And I am just a few kms from it.

Saksunarvatn ash 8000 BC?

At some points, there is a strange thick dark brown band around this depth, at around 70-80cm (see Fig. 4), which could have been the famous Saksunarvatn ash layer (Grimsvötn, 8000 BC): the largest eruption in Iceland in the Holocene. This ash is widespread recorded in northern Europe, and is used as an important marker dating the beginning of the Boreal period (end of the Young Dryas glaciation). Both the double layer (the 5000-6000 BC, referred before) and this deep dark brown layer, seem to ondulate, with one sometimes appearing over the other, and then exchanging positions. Their age is therefore highly uncertain.

Figure 4. Overall of our soil profile, with major bands identified. We cannot go before 8000 BC, as mud was deposited. Photograph by Irpsit, all rights belonging to him, used by permission.

The tale of a river bed, nearer sea levels, and also the ice age

Below 90cm we mostly find mud. This might have been a time when glaciers were over this region. At the glaciation peak, the ice sheet must have been at least 400m thick here, because of the nearby tuya Ingolfsfjall. However the peak glaciation must have been short, because we find much more shield volcanoes at this region than tuyas. About 5 km north, there is a large moraine, from where most of the time the large glacier terminated. For most of the ice age I was just at outside of the glacier.

The mud might been also caused by nearby Hvitá river (which drains the now distant Langjökull). The excavation is just next to a waterfall-like valley, thay I know it was the path of Hvitá river now 2km east.  Therefore it might been subject to much soil erosion and river deposits sometime before 8000 BC.

In early post-glacial time, the sea level was higher and the coast was actually nearby. There is actually evidende of a coast just 5km south (in the nearby shield volcano Hestfjall). The sea must have been pretty close and again this location was subject to much erosion. Because of all these reasons, we possibly do not have the record for the famous Vedde Ash (Katla 10.000 BC), which is one of the two largest eruptions in Iceland in recent millenia; the other was the Grimsvötn Saksunarvatn ash (both VEI6). In one spot, I did see some white material around 90cm deep, but I am unsure if this was it.

Ancient Lava (from Lyndhalsheidi)

Finally, on the bottom of the excavation, around 1.5m deep, there is a bedrock of lava rock (visible at some spots at lesser depths, such as in Fig.2). They are eroded and rounded (probably by the last glaciation). This is lava from the shield volcano Lyndhalsheidi that is just 8km northwest. Its lava actually flowed where I now stand, but that eruption was on the interglacial before the last glacial, so it was a long ago. However the glaciation continuously exposed and eroded that ancient bedrock.

Layers near the surface

There is no significant ash layer since the 1477 Veidivötn ash. However we can see sometimes faint layers from recent eruptions. One black layer around 5cm is probably the VEI5 Katla 1918. One faint white layer at 8cm is probably Hekla 1845 eruption. And a faint dark layer around 12cm is probably Laki 1783 (but it could have been the eruptions of Katla in 1755 or 1721; not visible in Fig.5).

FIGURE 5. Ash layers from recent eruptions in Iceland. There are not as continuous as the bigger ones, they only appear here and there. One can also see that the main white layer are actually two distinct white bands. The ash of 1477 is also double but because it started as a first eruption of rhyolite pink ash from Torfajökull, followed by basaltic brown ash of Veidivötn later. Photograph by Irpsit, all rights belonging to him, used by permission.

ICELANDIC ASH RECORDED IN GREENLAND

FIGURE 6. Again, an overview of the soil profile, but now using the initial picture form part I, and color enhanced. It’s exciting to contemplate the history of 10.000 years of eruptions in such a small soil wall. Photograph by Irpsit, all rights belonging to him, used by permission.

To finish today I read some papers that described which ash layers appeared in Greenland ice cores. We find there the 1362 Öraefajokull, 1104 Hekla, 870 Vatnaöldur ash, Hekla 3 and Hekla 4 eruptions, the very large ash layers of Saksunarvatn/ Grimsvötn (8000 BC) and Vedde / Katla (10000 BC), followed by many ash layers from Katla, Hekla or Grimsvötn, and finally other two very large ash layers: one from Tindfjallajökull Thorsmörk ignimbrite, 53.000 years ago (that was a VEI6+, and possibly even a VEI7). The volcano is still dormant now and right next to Katla and Eyjafjallajökull); the other big eruption was 300.000 years ago, and hypothesized to be from Krafla or Hofsjökull.

After this lenghty post, please feel free to call me a big ash hole.

IRPSIT

Editors note: Do click on the images, then you will see all of the details since they are rather large.

Update by Spica:
Here is the link to part I of the story.

Monte Somma & Vesuvius

Painters rendition of the 79 AD Pompeian eruption of Vesuvius.

The World’s most ill-begotten real estate, Part II

Monte Somma is an old volcano, activity started 400 000 years ago. Over the next 375 000 years a massive strato-volcano was built up at around the same location as todays Vesuvius. The main geological component is guarinite, an epitaxy of hiortdahlite, wöhlerite and låvenite. There is no known record of any caldera forming events during this long period. At the end of the period Monte Somma had an edifice containing four times the rock volume of today’s Vesuvius (calculated conservatively).

The volcanicity in the area is driven by the back-arc subduction zone caused as the African plate slams into the Eurasian plate, and then being pushed under. On the European side melt from the friction of the plates is being released through the Campanian volcanic arc. Other close by members of the volcanic arc is Campi Flegrei and Mount Epomeo (Island of Ischia).

25 000 years ago Monte Somma suffered the Codolan eruption, an ultra-plinian eruption that eradicated almost the entire volcano in a cataclysmic failure of the magmatic chamber. The Codolan ash lies on top of the Campanian Ignimbrite caused by Campi Flegrei 34 000 years ago, making the Codolan eruption the youngest of the cataclysmic events caused by the Campanian arc. The highest remaining point after the eruption is today known as Punta del Nasone (Tip of the Nose), an 1 132 meter high edifice on the caldera rim. The eruption probably had a significant effect on the population size in southern Europe.

Google Earth Image of Vesuvius. On the upper left you can clearly see the caldera wall of Monte Somma with the Tip of the Nose (1132m).

Vesuvius is born

From the ashes of Monte Somma a new volcano started to grow almost immediately. During the first 8 000 years the new volcano had a fairly unevolved magmatic chamber system. As such it could not cause large eruptions, instead it slowly, but steadily built up.

That changed about 17 000 years ago when a cycle started consisting of frequent small to medium eruptions interspersed by Plinian eruption ranging between VEI-5 and VEI-6. To date there has been 8 of these larger events in the current cycle. Calling them large might seem ridiculous compared to the Codolan ultra-plinian event, but one should compare within the cycle. These eruptions are believed to range between 5 and 15 cubic kilometers of ash counted in Dense Rock Equivalent (DRE). Compared to the 0.25 cubic kilometers (DRE) of Eyjafjallajökull these eruptions are rather large.

These larger eruptions take place roughly every 2 000 to 3 000 years. This time interval makes sense if one takes into account that the magmas needs time to fractionalize enough to evolve to the highly explosive magmas involved in these eruptions.

The latest plinian eruption was of course the 79 AD eruptions that eradicated the cities of Herculaneum and Pompeii. I will cover this eruption in a separate article in the series about Neapolitanean volcanicity. This eruption is the reason we call these eruptions plinian. The reason for that being the historian Pliny the Younger (Plinius), writing down the quintessential record of the eruption.

The plinian eruption before that was the Avellino eruption (Pomici d´Avellino) that took place 3 800 years ago. Archaeologists have noticed that this eruption had a large effect on the regional Bronze Age population.

After the 79 AD eruption Vesuvius has had numerous small to medium sized eruptions ranging from VEI-1 up to VEI-5. Some of these have been notoriously ashy. The 472 and 1631 eruptions yielded ash that travelled as far as Constantinople.

Vesuvius today is rapidly getting known as the Garbage Dump of Italy. This is due to a large amount of both legal and illegal dumping of garbage and industrial waste in old flanking vents and cones. This has raised the toxicity around the volcano to a level where one should not eat anything growing on or around the volcano. Even the fabled wines of Vesuvius are now deemed not fit for human consumption. It is sad that Man’s folly is destroying one of the world’s most beautiful vistas.

Technically Vesuvius is a somma-volcano, a type of volcanoes named after its parent volcano. The term refers to a fully developed strato-volcano that has formed inside a caldera of an older destroyed strato-volcano.

Photograph by the US Air Force. Eruption of Vesuvius 1944 taken from a bomber plane.

Risks of Vesuvius

Vesuvius can theoretically have 3 types of eruptions if we look historically. These are in order of threat-level the regular eruptions, the plinian eruptions, and a possible recurring ultra-plinian Somman event. Let us look at them one at a time.

Before we go on I would like to say that the projected death tolls for the respective eruption sizes are from figures that have been calculated by INGV, The Italian Government, The regional government of Naples, independent catastrophe mitigation experts, EU and the UN Decade Volcano Program.

The lower end figure is the best possible figures. Basically it would require functioning scientific volcano predictions, and a high-powered highly ordered Government ruthlessly enforcing evacuations and other protective measures. Basically we are talking about northern European style Government with heavy military aid here. The high figure is based on INGV being disregarded for political reasons, week or no mitigative measures taken, lack of functioning roads being accounted for, and the general nonchalant attitude in the region. I would here say that INGV will do their work; they are highly capable and very diligent in performing their duties. I just hope that they will be allowed to do it by the highly corrupt Neapolitan local politicians.

The risk is of course heightened by the high population numbers, and that people live close to, or even on the flanks of Vesuvius.

Central crater of Vesuvius.

Normal Vesuvian eruption

Vesuvius is a highly prolific volcano, and it is known to have had several instances of magmatic intrusion since the 1944 eruption. The last major intrusive episode was taking place between 1996 and 1999. So far this is the largest of the intrusive events post 1944.

It is highly likely that Vesuvius will have an eruption during this century. When it happens it will almost certainly be in the range of VEI-2 to VEI-4. One should though note that there have been two out-layer small VEI-5 eruptions since the 79 AD eruption and also that there has been a few VEI-1 eruptions. Median eruption (most likely) would be a VEI-3 size. Ash, volcanic bombs and pyroclastic flows would be the largest risk for the population.

Death rate would be between 0 and 100 000 depending on size of the eruption, and the amount of protective measures taken.

Vesuvius in the background photographed from Herculaneum.

Plinian Vesuvian eruption

Vesuvius is from a short geological time-frame ranging in on a plinian eruption. Nothing points towards that the eruptive cycle that started 17 000 years ago has changed to the better. Judging by previous behavior the next plinian eruption will occur during the coming millennium.

The risk of a plinian eruption is driven by the rate of fractionalization of the magmas. Normally this type of explosive eruptive behavior requires the volcano to not erupt for a few centuries before the plinian eruption, thusly giving the magma time to evolve as intrusions bring in new material that mixes with older colder magmas to revigorate the explosivity until the volcano quite literally explodes. This seems to not be the case with Vesuvius. One suggestion might be that there are different magma chambers that are responsible for the larger eruptions and small shallow chamber responsible for the smaller eruptions. Be that as it may, do not expect a long period of repose between a normal eruption and a plinian. Risks for a plinian eruption would be large amounts of ash, large pyroclastic floods, and lava bombs ejected up towards 40 kilometers. There is also risk of tsunamis causing additional deaths in the low laying parts of the Bay of Naples. Larger pyroclastic flows can rush over the water’s surface and hit areas that are not close.

Death rate between 10 000 and 1 000 000 depending on prevailing wind and the amount of people evacuated.

Photograph from Whiteynet. Vesuvius encircled by Monte Somma caldera.

Ultra-plinian eruption

This option is highly unlikely in the foreseeable future. Why? Compared to the size of the Monte Somma edifice we know what the maximum size the volcano can grow to before it suffers a catastrophic fail. Even if we count in the secondary caldera formation normally are smaller than the first one due to damages to the crust we still known that it will take quite some time to build the volcano up sufficiently both above ground and below ground.

If we calculate the growth rate of Vesuvius and compare it with the size of Monte Somma before the caldera event we see that it will take a minimum of another 75 000 to 100 000 years to grow to comparable size. Statistically we know that secondary caldera formations are 50 to 75 percent of the original event size. So, we are most likely looking at something in between 25 000 to 75 000 years of continuous growth before we need to worry about it.

The major risk of an ultra-plinian eruption would be ash covering a very large area, the explosions involved would instantly crush anyone within 25 kilometer. Think a hydrogen nuclear bomb shock-wave here. Between 25 and 50 kilometers there would be an initial 50 percent mortality rate due to high aerial ash content, lava bombs, and enormous pyroclastic flows covering large parts of the Bay of Naples. After the event pretty much no buildings within the 50km radius would be left standing up. Nationally deaths would occur due to ash and gas contamination. The coming year southern Europe would suffer crop failures. There will be an increased likelihood of hemispheric rapid cooling causing additional deaths and famine.

Death rate, 100 000 to 4 000 000. Supervolcano as a term is nuisance, but if one would erupt in a population the size of Naples it would have major impact. Regardless of the term, the effect on the population of southern Europe would be truly “super”. Remember, it is highly unlikely to happen.

This was the second installment in a series that will be five posts long. Remaining are the two other supervolcanoes encircling Naples, and of course the mentioned Pompeian eruption.

CARL

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

What’s going on at Katla?

Part 1, public awareness background

Fig. 1. Katla from the south, webcam capture.

The current hysteria over Katla started at the same time as the ash from the Eyjafjallajökull played havoc with European air travel. Some journalist noted that Iceland’s, at least publicly, most respected volcanologist Professor Páll Einarsson, the man who nailed down the February 2000 Hekla eruption to within 30 minutes, had made claims that Eyjafjallajökull and Katla were linked and that an eruption of the former would lead to the eruption of the latter within a few months. And Katla was a huge volcano whose unavoidably upcoming eruption would be tens of times greater… …at least in the minds of journalists trying to further their professional standing.

The basis for the supposed linkage is that the last two eruptions of Eyjafjallajökull, 1612 and 1821 to early 1823 were in both cases followed by eruptions of Katla a few months later, in October 1612 and June 1823. The previous eruption of Eyjafjallajökull in 920 AD, just after Iceland was settled, was not followed by an eruption near Katla until 934 AD even if Katla had erupted ahead of Eyjafjallajökull in 920. Also, while there have been only four eruptions of Eyjafjallajökull over the past 1000+ years, Katla has erupted at least 27 times during the same period.

It cannot be claimed that the hypothesis that an eruption of Eyjafjallajökull is always followed within months by an eruption of Katla is particularly strong or convincing. The historical evidence tells us that in at least 25 of 27 instances, Katla has erupted irrespective of what Eyjafjallajökull has done. Denison Professor Erik Klemetti succinctly says that “correlation does not equal causation” and Dr Boris Behncke of INGV Catania gave us an example of a volcano that simultaneously erupted magma of two distinctly different chemical compositions as an example of how difficult it is to correctly identify what goes on at depth below a volcano.

Fig. 2. Katla erupting in 1918. Origin of picture unknown.

Let us return to Professor Páll Einarsson. If he had been quoted out of context, as so often happens when journalists interview scientists, especially since the former have no concept of the differences between human and geologic time scales, Professor Einarsson has had plenty of opportunities to correct such misrepresentation. He has not done so. Instead he has repeated his assertion in front of other volcanologists at a conference in the United States. Early last autumn he reiterated his belief that Katla would erupt within 18 months of the end of the Eyjafjallajökull eruption, and this in spite of the minor subglacial eruption assumed last summer after a small jökulhlaup, which implies that he did not think this episode substantial enough to merit to be credited as the predicted eruption.

To me, this looks like a clear-cut case of a scientist, confident in his own ability after previous successes, going out on a limb and then not have the courage of his convictions to stand up and admit that his pet theory has been proven wrong. As long as he refuses to do so, the 2012, Grub Street or otherwise inspired Katla-mongering has an extremely reputable figurehead and spokesperson, albeit an unwitting one.

The most prolific source for information about Katla is the “Iceland volcano and earthquake blog” hosted by Jón Frímann Jónsson. If you google Katla, alone or accompanied by key words or phrases, you will find that his blog comes up frequently. As an example, I googled “Katla tremor” and the top three results refer you to entries in his blog. He is even credited on the Wikipedia entry for Katla as the source for volcanic unrest in 2010 and the minor eruption of 2011 that led to a minor jökulhlaup in 2011.

Now Jón to his very great credit has made no secret of the fact that he tries to make money from his blog, primarily to support the purchase of more instruments for his hobby but also himself. One of the forms this takes is renumeration for advertisments carried based on the number of visits to his site. As he is a clever young man, he cashes in on the current interest in Katla – he would be a fool not to – and posts topics about her on an almost weekly basis. It is in his interest not to antagonise his visitors with either claims that every minor twitch was a sure sign of impending doom or that nothing was going on. Thus he couches his statements in ambiguous terms such as “time will tell” and it comes as no surprise that he is sometimes quoted as the source for the latest “unrest” at Katla by less reputable sites.

Fig. 3. Katla-mongering “at its finest”.

When it comes to the question of reliability, Jón is not a professionally trained volcanologist. He is self-taught. He always supports his topics by screen captures of IMO maps and charts or with print-outs from his own set of seismometers, or “geophones” as he calls them. However, he does make claims that there have been harmonic tremor pulses in named volcanoes or that a certain pattern of earthquakes portents something volcanic, without any professional corroboration of his interpretations whatsoever. Much as I respect Jón, I am not always satisfied with the scientific accuracy of his interpretations. This situation is unfortunate as Jón reaches a very wide audience, one that in many cases is not as critical as it should be, one that accepts as fact what it chooses to believe Jón’s latest word to be.

Unfortunately, there is one aspect of the human psyche that professional volcanologists sometimes seem to blissfully oblivious to. If we are interested in something and feel a need to understand what is going on but cannot obtain reliable facts, we look to the opinions of others whom we often absurdly assume must be better informed than ourselves. If not even that is available or if there are still gaps left, we fill those in with our own, invented, “facts” and/or interpretations. Unfortunately, scientific institutions tend to care more about what other scientific institutions think of their work than about supplying accurate and up-to-date information to, and education of, the general public.

If we apply this to Katla, it is easy to see why so many people are convinced that Katla not only will, but “must” erupt within the very near future: We have Iceland’s most respected volcanologist repeatedly saying that Katla will, is bound to, erupt very soon and really should have done so by now. We have little, verging on none, official information about her true state. We have Jón Frímann Jónsson almost continuously feeding us updates of dubious scientific accuracy with the intent of guaranteeing a steady traffic to his blog, updates couched in suitably ambiguous language that can be interpreted as support for Professor Einarsson’s hypothesis as well as Doomsday prophecies. And Mila have just repaired their Katla webcam at the same time that a very minor flow from the glacier has been reported, an occurrence gratefully seized upon by Jón Fríman Jónsson to proclaim “Katla volcano warming up for an eruption. Small glacier flood continues”

Fig 4. “Katlatubo” (montage), the Katla-mongerers’ favourite scenario…

But as I have pointed out, we have had no official statement, which in itself ought to be a good indication that nothing alarming is going on. Or are there really people out there, intelligent people at that, who believe that Allmannavarnír with their excellent track record would say nothing or even cover up such vital information if available?

HENRIK

Editors comment:

Páll Einarsson have been notified via email that he was mentioned in here and also been informed that he is more than welcome to comment the issue in here. Jón Frimann has also been notified.