The Icelandic Hotspot Hypervolcano™ – Why old traps won’t erupt again

Photograph by Jeff Shea. A range of north Greenland shield volcanoes eroded by glacier ice so that they more remind of a range of strato-volcanoes.

Earlier today commenter Lucas Wilson asked me about volcanism in Greenland. So, I thought I should write a short piece on what once used to drive the volcanism there.

But let us start with what we today call the Icelandic hotspot. In here we have a tendency to talk about large volcanoes now and then, and sometimes about what is called “super volcanoes” in the media. But, the fact is that Iceland is both the largest volcanic structure on the planet, and also by far the oldest active one.

Let us start with largest. Iceland stands for between one third and half of all the magma on the planet during the last 250 million years. The rate of lava produced is fairly prodigious. Also, few know how long this has been going on. The answer is that it all started far before Iceland was born. Time for a history lesson.

Iceland was born as the Icelandic Hotspot moved close to the Mid Atlantic Rift; Iceland was born from the mid parts to the west and the east. This is as a function of the hotspot giving extra magma to the normal volcanism of the MAR, and thusly building the volcanic edifice known as Iceland as the MAR rifts apart.

Photograph by Ansgar Walk. Trap formation eroded by Glaciers, Ice age glaciation, and coastal erotion. Baffin Island.

Okay, now to the age thing. The Icelandic Hotspot is one of the really few surface expressions on the planet that is stationary. I know, the hotspot per see is not visible, but its effects are. So, as the continents and plates have fun surfing around bumping in to each other they slide over the poor hotspot.

A few tens of millions of years ago it was a part of the North American plate that slid over the Hotspot, and as that broke apart magma pushed through and created Greenland. As the now archipelago of Greenland slid away it lost its capacity to have eruptions pretty permanently.

Before that it was Newfoundland that popped up as it slid over the hotspot. And before that we had the same hotspot creating the largest Large Igneous Province on the planet, the North Arctic Igneous Province (NAIP). Before that Labrador and Baffin Island slid over the NAIP, and that put us at about 95 million years ago. And 130 million years ago it created the Alpha Ridge. Any  super volcano will have an inferiority complex to that eruption.

Before that and even further down in time it was known as the Siberian Traps, the largest on land eruption. And now we are back 250 million years in time. Before that things get a bit harder to track.

Photograph by Jxandreani, wikimedia commons. This is a part of the Putorana-Norilsk Deposit.

Here comes an interesting thing. What is today known as the Icelandic Hotspot has been conveying about the same amount of magma since the Siberian Traps. Give or take the eruptive rate has constantly been around 0,5 to 1,5 cubic kilometer per year since day one. And as we all know the average erupted material is only 1 in 20 of the magma that comes up. The rest stays as intrusions or inside magma chambers. So, on an average year the Icelandic Hotspot will loft up 20 cubic kilometers of material.

Now some of you will say something like “Hey dude, it never erupted continuously, so it can not be the same. And dude, the Siberian Traps erupted more material than Iceland”.

The reason for it not having erupted constantly is that it need either pressure enough to crack a continental plate, or the magma had to wait for a spot that was weakened that it could crack. The Siberian Trap was a momentous episode, but the largest separate eruption was “only” 3000 cubic kilometers of lava erupted (Norilsk Deposit). In the end the Siberian Traps is only standing for a slight elevation in erupted material even though a lot of magma had accumulated under the Eurasian plate before onset of eruption. Average erupted material during the Siberian Traps was only twice what Iceland is popping out on average.

The Siberian traps carved by a river into a kilometer high cliff.

We should also remember that eruptions happen in cycles. The Norilsk Deposit is probably a hundred million year event, or in other word, it would take on average 100 000 000 years in between every eruption of that size. It is estimated that it took about a hundred years to erupt that amount. So, on average 30 cubic kilometers per eruption year and that is not a nice thing to be around, but far from what it takes to produce a mass extinction.

We know that there are about 2 to 4 eruptions on the scale of above 10 cubic kilometers in Iceland today per every thousand years. They tend to happen on a 270 year cycle. We also know that every few thousand years we get them in the 30 to 50 cubic kilometers. Most likely those come in about 1000 year cycles, but in various places over Iceland, and on average over time.

About once every 10 000 years we get one upwards to a 100 cubic kilometers. I do not know of any eruption in Iceland significantly larger than that, and would be surprised if anyone finding one. The reason of course is that the MAR creates a fairly open passageway for the magma. Norilsk was happening due to the dense rock of the Eurasian plate storing up magma under it until it cracked, so the necessary magmatic pressure can most likely not build like that in Iceland.

So, now we know that old huge volcanoes cannot erupt again due to the magma-hose being disconnected as the plates slide away from the “gas-station”, and we also know how persistant the hotspot is.

Super volcanoes, well all is relative…

Bonus Riddle from Alan

Many of you might have missed that we tend to have volcanic and geologic riddles every friday in here. Lately we did not have that due to El Hierro taking center stage. But we do know that there are many that love them, so here is bonus riddle. Remember, it should end up in something rocky.

Huh! Last week, I went into a nice bakers – they only had this rock-cake!

CARL

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

Tungnafellsjökull – Tectonic Earthquakes

Photograph by our own Jamie. Tungnafellsjökull seen from Sprengisandur area. Notice that the Jökull is almost gone from Tungnafellsjökull, soon to become known as Tungnafjöll only.

There has been an earthquake swarm at the northern end of the Tungnafellsjökull during the evening and throughout the night. The swarm is still ongoing. There has been a lot of speculation out there in the blogosphere about it being volcanic in nature. It is not, it is purely tectonic.

As some of you know Iceland is divided by the Mid Atlantic Rift (MAR). The MAR in turn is divided in Iceland into two separate active seismic zones, the Eastern and the Western Icelandic Seismic Zone. Lately it has been the EISZ that has been most active of the two. But the WISZ is not in any way dead or dormant. Both of them are driven by the spreading of the MAR. From the WISZ the North American Plate is spread, and from the EISZ the Eurasian Plate is spread. In between them are two micro-plates that have formed by volcanism caused by the rifting.

The map is showing the Icelandic Volcanic Zones, where the MAR runs up into Iceland, where the MAR leaves Iceland and the more important volcanic features. The Icelandic Seismic Zones are corresponding to the volcanic zone.

Along both the WISZ and EISZ are lines of volcanoes spread, it is where the spreading causes magma to pour up and fill the spaces created by the spreading.

If you look at the map you see that WISZ runs from Hengill, up to Langjökull (2 known volcanoes), via Hofsjökull (at least one volcano), onwards through Tungnafellsjökull, and then ending up at the triple-junction at Bárdarbunga.

During the last few years the area of Tungnafellsjökull has been inactive, but there is ample evidence of it having been tectonically active, something that can be found in the Sprungur (tectonic faults) found in the area. The dormancy is likely due to the area having been locked at depth, probably by old magma that has solidified the area.

Various versions of tectonic faulting. Tungnafellsjökull is suffering from strike-slip faulting.

Lately the area has been subject to an uplift not seen in Iceland since de-glaciation after the last Ice age. This is due to the melting and diminishing of the glaciers of Tungnafellsjökull (almost gone) and Vatnajökull. This uplift process has accelerated during the last decade. It is now up to 3 cm year in the area according to Sigrún Hreinsdottir (source, private email). Yes, the famed inflation of Hamarinn is not happening, it is a combination of Grimsvötn motion and isostatic rebound.

This motion might have started to release the seismic lock at Tungnafellsjökull. If that is so, there is a risk that the swarm of earthquakes is just precursor quakes for a large earthquake.

This map shows the features discussed in this text in relation to the Bárdarbunga triple-junction and the hotspots location.

What makes this interpretation the more likely one is that there is no discernible evidence of any harmonic tremoring during the earthquakes. This makes it into tectonic seismicity, not magmatic seismicity.

If there would be a large earthquake that tears the rift-lock, then magmatic movements could start in the area, but not before that. Worst case scenario here is not a volcanic eruption; it is a 6M earthquake as the slip-lock disintegrates over a large area.

Another thing that I want to point out, the earthquakes are all of low probability and some of them are as I write this due to change after revision, and some of them will be removed due to being false representations of earthquakes, so called Ghosts. And as I wrote this IMO has started to revision the earthquakes, right now there is at least one at 3M.

CARL