To me the part of a volcano that is visibly erupting is the least exciting part. Perhaps a better way of stating it is, that it is only the effect of the cause. This is obviously not true to most people on the planet, so I think I owe everyone an explanation.
And that explanation is especially important since we need to look deep into the volcano, to understand its future.
Like most people I can obviously spend hours looking at lava bombs being hurled, and lava slowly filling valleys. But, getting to know the hidden innards of a volcano, and understanding their functions, is making the experience even better.
So, let us take a journey through the volcanic features of the Ballareldar from the bottom up. During this journey I will try to impart the wonders I see, and why this cute little tourist eruption is one of the most scientifically important eruptions ever witnessed.
To do this we must employ many tools of the trade, petrochemistry, geophysics, chemistry and garden average physics, to be able to look below the ground we walk on. As I go on, I will try to tell you what we know, what we can assume, and what are open questions to science.
In the beginning there was the mantle
The Geology department at the University of Iceland did wonders in the opening stages of the eruption taking samples and analysing them at breakneck speed. I wish we had later data at hand, but I think that is saved for some juicy future articles by the scientists in question. Which is fair enough, and they have let a few tidbits out that is highly intriguing.
What we do have is still enough to make me feel like a kid visiting his first candy store. Because things are sufficiently “out there” to make my eyebrows lift quite substantially.
Regular lava in Reykjanes is indicative of Mid Oceanic Rift Basalt (MORB) origin, coming up from the Mohorovic discontinuity between the crust and the mantle, it is normally partially evolved (fractionated), and has ample amounts of inclusions indicating that it has resided in the crust for a while.
Normally you will see a medium amount of sulphur in the lava, and it will be fairly cool compared to the plume derived lava coming out nearer to the Icelandic mantle plume, and the plume derived lava is among the most sulphur rich lavas on the planet.
If we look at the current magma being ejected as lava, we find that it is, first of all, unusually hot. The confirmed temperature is 1190 ºC from the first observations, but I have seen later unconfirmed figures up towards the 1220 ºC.
Higher temperatures than 1190 ºC is by far not impossible, remember that the official temperature was taken early on when the magma had been cooled and partially quenched as it passed between the cold sides of the 7km long and 15 km high dyke leading from the deep feeder conduit near Keilir, all the way to the surface.
As the surrounding rock is heated by the passing hot magma, over time the cooling effect will diminish and the temperature of the lava will go up a bit.
As far as I know the previous temperature record holder in Iceland was the Holuhraun III eruption at 1180 ºC. Here we had an origin that definitely was from a well-formed mantle plume, yes it had partially resided inside inside of Bárdarbunga and had travelled for a long stretch across a very long dyke.
But a big part of it was fresh material from inside the mantle that was newly arrived. On top of that the flow rate in the dyke was large enough to heat it very well indeed, decreasing the cooling effect considerably.
The temperature of the lavas erupted during the Ballareldar is high enough to be seemingly congruent with plume origin.
If we look at the regular lavas erupted at Reykjanes through the eyes of groundmass glass, we see that it usually contains about 250ppm of Sulphur, but the current lava is erupting an average of 1140ppm of sulphur.
And we do know that the Icelandic plume produces record breaking amounts of sulphur as the associated volcanoes erupts.
Here it is easy to think that what we are seeing is a tendril of magma that has squeezed itself merrily along the underside of Iceland until it arrived below Reykjanes during the last 800 years. Looking at the evidence so far, it is not a bad idea.
But we need additional data to prove or disprove our little plume origin hypothesis. This is the point where petrochemistry shines.
The first we see is that the lava is rich with olivine, a crystal that is called Peridot and Chrysolite when used as a gemstone. It forms in the upper mantle, so now we know that at least the magma is from the upper mantle.
Olivine comes in three distinct flavours, the magnesium flavour called foersterite (peridot) that can be green or transparent. It can only form above 400km depth, below that you get wadsleyite.
The other common one is the reddish-brown fayalite (chrysolite) that contains iron, this forms at lower pressures than forsterite, so as such it is not pointing towards deep mantle origin.
I will just briefly mention the third flavour, the whacky Manganese olivine named tephroite. From a volcanologic standpoint, it is the least understood of the 3. It can also have any colour visible to man, since it has a propensity to make love to pretty much any other metal. It is the penultimate slut in geology, making it into a darn good precursor when looking for mineralisations to mine.
The Ballareldar lavas are rich in magnesium olivine (forsterite), this means that the origin of the magma is somewhere between 15-400 kilometres down. We also know that many Icelandic lavas are forsteritic, so it seems like we have once more proved a plume provenance.
Now we need to compare the Ballareldar eruption (2021-) and the Holuhraun III eruption (2014-2015. The first thing that we see is that Holuhraun III has less olivine (forsterite) than Ballareldar has.
If we look at the weight percentage of TiO2 at Holuhraun III we find that it is at 1.75 to 1.9%, whereas at Ballareldar we see a figure of 0.9%. On the other hand, we see weight percentages of MgO at around 6.7% at Holuhraun III versus 8.8-9% in the Ballareldar samples.
Did we just find a spanner crashing into the spokes of the wheel of our hypothesis? Can we save our our pet theory?
Yes, sadly our pet theory dies here in the warm embrace of TiO2, this is due to us knowing that the distance from the Icelandic plume center does not indicate decreasing TiO2, or vice versa. Plume derived forsteritic basalt does not drop in TiO2 with half. Bummer!
At best we have a partial influence of the Icelandic plume, but sufficiently small to not explain the sulphur and the temperature as such.
Here one could come up with the crutch-theory that it is another unknown plume at work. That is amply gunned down by geophysics, since we know from tomography mapping of the mantle, using measured differences in the travel speed of sound indicating temperature variations in the mantle. In simpler terms, we have a fairly good map of where there are plumes, or not, in the mantle.
There is obviously no special plume under Reykjanes. At this point we will have to wait for new data from young strapping Ph.D. students.
This is written a couple of days later as an addendum. I had already edited in the article when I found new data from the geology department at the University of Iceland. Problem is that the new data made mince-meat of what I had written above.
My first instinct was to do a complete rewrite of the article, so that it would no look like I used the southern end of northbound donkey as a brain. Instead, I am leaving out the first part as it is, as an example of how new data is driving scientific discovery and creates the need for new models and hypothesis-formation.
I love the smell of fresh science in the morning, well that and coffee. So, without further ado we will boldly go where no person has gone before.
Let us begin with what is the same. The sulphur content is same at the high levels, and the release of SO2 is keeping steady at 2000 to 3000 tons per day. The variations closely follow eruption flow rates, so we can safely say that it will not increase nor decrease over time in any significant manner.
Several people have asked me lately about the noticeable increase in “smoke and gas” from the vents. And yes, there has been an increase in the visible gas volumes at the volcano. Problem is that there is no increase in release of CO2 or SO2 from the volcano, and this is to be expected since the lava flow rates are constant while the Sulphur content has been consistently high.
So, why then are we seeing more gas? There are two reasons for this. The first is that it is likely that water vapour has increased due to the magma moving through a number of aquifers, and that a few of those contain super-critical fluids.
I have however not seen any data on water content, so this is speculative. The second reason is simple: from an actively erupting vent you have sufficient thermal uplift to chuck the gas straight up and out of the way as a visual hindrance.
That is why we see more visible gas from dying colder vents; they do not have the energy for effective thermal convection.
In short, the gas increase is mainly more a question of altitude than attitude.
Now, let us talk about the differences. MgO has increased from the previously high number of 8.8-9 percent, now it is 9.7-10 percent. This means that there is more forsterite in the mixture. This in turn points towards greater depth.
Now, let us turn to the TiO2, it has increased from the low number of 0.9% to 1.5%. These two increases in TiO2 and MgO indicates a deeper origin.
This indicates that the original magma most likely was of Icelandic Plume origin and that the plume head is slightly wider than previously believed. It also points towards some process depleting the magma during its long and slow movement towards Reykjanes from the plume core under Kistufell.
One solution that is likely, is that TiO2 due to it’s higher melting point trends towards attaching itself to the bottom of the crust in a process called underplating, whereas the MgO does not.
Now, here we arrive at a monster of a question. Was the eruption caused by arriving deeper material that first pushed up the depleted magma under the eruption site? Or, has the eruption depleted the supply of depleted magma and new deeper material is going up to fill the gap?
If it is the latter, we are most likely seeing a smaller version of the process that created the Icelandic plume to begin with, eruptions causing a void creating lowered pressure increasing the melt process at depth.
At the Icelandic plume this process has been running for 14.4 million years now, so it has burrowed itself deep and become a true monster among plumes. Whereas Ballareldar is too small in the greater scheme of things, and it will putter out when the eruption dies out.
I should here point out that we do not know which one of the two options given above is true, I lean towards thel atter idea of burrowing. But, as per usual, until a strapping young Ph.D. Student has done the heavy lifting and done a garnet study we will not know for sure.
What I would like to see is a study of garnets in lava. Various garnets form at different depth in the mantle, so have a garnet study would be helpful to constrain further the depth of the formative melt. Want to get a doctorate in petrochemical volcanology..? Go garnets, go!
I had initially planned to write about the dyke, and the future for the Ballareldar. I had also planned to write about the name Ballareldar. That will though have to wait for part two of the article since I got rolling with the petrochemical part of life.
So, in part two we will leave the mantle behind and become crusty indeed.