This is both an informal start of our series about a promising central proto-volcano, and a story about the problems of sifting through the bewildering number of signals that the instruments yield for us to peruse.
Let me start out in the stars. A friend of mine work with SETI, the search for extra-terrestrial signals. In that field you must sift through enormous amounts of data to get very few promising signals. Now and then the computers cough up a signal that it can’t explain, and the scientists involved get to check it out.
So far, no signal has been from an extra-terrestrial intelligent source. And just a handful has been unexplainable.
One could say that they are walking in Sahara. In Icelandic volcanology you are instead walking in the Garden of Eve in regards of signals, you are drowned in delicious dangerous fruits every day.
In this article I will go through the most common instruments to try to explain their limitations, and how they can fool you if you do not know how to interpret them. As such this is not a guide to how they work, it is a guide to avoid the traps that they throw up in a setting as massively complex as in Iceland.
The ideal volcano conundrum
Let us start with stating something that should be obvious. All current theories are based on the concept of an ideal volcano. This hypothetical volcano is sitting in the middle of a uniform piece of crust and it will not be affected by anything else. All signals will be pristine and only belong to the volcano.
Even at this hypothetical clean and well-behaved volcano the theories start to diverge slightly if you start to compare let us say seismometers and GPS-trajectories. This divergence comes from the theories not really hooking up as they should.
For this volcano, this is such a minute issue that you can just look aside, after all you would be able to prognosticate it to a T given enough instruments to peruse. My point is that even here we have sources for misinterpretation unless you know the theories well.
The main point is that for this hypothetical volcano you can pick your favourite type of instrument and leave the others be, and you would still be able to understand the volcano fairly well.
The regular volcano mess
Problem is that regular volcanoes are quite messy, even a single volcano will be affected by the method it receives energy, local tectonic setting, the tectonic of the plate it is sitting on and so forth. And this is only for a solitary volcano.
Most volcanoes seem to be in relations, many of them even practice polygamy. This means that the volcanoes will start to scuffle about, squeezing and pushing each other, while they at the same time are affected differently by the local tectonic setting.
Here you are forced to employ an array of different methods to understand what volcano is doing what, and if they are about to erupt. A single method does not cut it. Problem is just that the human brain is lazy, in other words, most humans try to employ single-method solutions to a problem. The more simplistic and simpletonian the better in their world.
When trying to prognosticate one of these volcanoes you employ a linear approach. Let us say that you notice an earthquake swarm under volcano X, but you do not know in the beginning if it is caused by magma, the faultline under the volcano, or a combination of both.
So, you go and look at the GPS-trajectories and see that it looks like the mountain is indeed inflating (or not) from magma entering the system. Since the other volcanoes around are not rambunctious at the moment, you can fairly safely assume that all of the signals are coming from volcano X.
You then look at something specific like volcanic gas readings inside the crater, and when the volcano starts to emit higher values of these gases you will feel confident alerting various government agencies that something might happen.
Various volcanoes will obviously give off different signals before going boom, but the general process applies.
The Icelandic Signal Festivity
In Iceland on the other hand you have herds of volcanoes galumphing about, in a tectono-palooza setting. And that is just where the problem starts.
You also have to contend with global tectonic forces, two major continental plates, bonus platelets (micro-continents), a plume shoving Iceland upwards and outwards, Isostatic rebound from the last ice-age, glacial isostatic variations, glacial noise, Jökulhlaups, weird hydrothermal signals and effects, and so on and so forth ad nauseam.
All of these causes effect every single point of Iceland in an ever-changing pattern. What was true yesterday will not be true tomorrow.
Either it will be knocking things about, or it will make weird and confusing noise to content with. Many find this to hard, and they go for a simpler volcanic setting. Or, they find it to be a grand mental exercise trying to put it all into their brains at the same time.
Now we have the backdrop to stand upon as we talk about the various instruments and what they measure and their problems.
As matter heats up the energy level increases, in turn pushing the atoms further apart, creating lower density.
This means that magma normally has a lower density than the surrounding host rock, and that you have a good indication that you have found a volcano, and that it contains something fairly hot. If you are lucky it will even yield a rough estimate of how large the volume of the hotness is.
This volume is obviously not the same as the magma volume, but it gives an upper limitation.
Iceland obviously did not read this rule-book, so upon occasion it produces a positive gravimetric anomaly in well-known volcanoes.
Either these volcanoes are colder than the host rock, or something else is going on. Since this happens only in old frequently erupting volcanoes with a large magma influx, we can surmise a more probable theory.
Magma is a mixture of various atoms and molecules with different weight. We know that as magma resides inside the volcano it will start to fractionate with lighter materials going upwards, and heavier materials going towards the bottom.
For a volcano frequently ejecting the lighter components the mass-balance will start to shift as the heavier substances increases its percentage. In other words, sticking a tube at the bottom of the chamber and sucking out the content would most likely be a viable form of mining, albeit technically almost impossible to perform.
The problem is that parts of a magma reservoir could be anomaly positive while others are anomaly negative, and in some magma reservoir topologies you could even get anomaly equilibria totally throwing things out of whack as you spelunk for volcanoes.
So, we need a way to verify any result of a gravitometer in Iceland. Thankfully there is an instrument suitable for that.
Some materials and/or Chemical elements are magnetic. In the mining industry it is quite popular to run around measuring for positive magnetic anomalies, since this often indicates that you have a mineralisation in the ground. Iron is especially easy to find this way.
There is though a quirky effect to this, as you heat things up, they at various temperatures lose their magnetic charge. The specific temperature at which a chemical element becomes amagnetic is different between the elements. This point has a name, the Curie-temperature.
Pretty much all volcanoes contain ferrous materials, and we know the Curie-temperature for iron to be 1043K. That would be 769.85C for those of us who are sensible, and something weird in Fahrenheit.
The interesting thing is that at that temperature more than 15 percent would be melt in any reasonably pressurized magma reservoir, or that is very close to magma.
The problem is that it works well with large volumes, or smaller volumes close to the surface. Also, magnetometers do not really like large volumes of ice and water.
The problem is that large areas of Iceland are hot, really hot. This tends to produce results that are just to large (at least we think so), so at the same time as the Magnetometer is proving the Gravitometer, the same goes in reverse.
Well, at least a bit. Both are after all affected by heat. So, to further refine things we must go for a Volcanocafé tried classic, plotting earthquakes to chase for magma reservoirs.
The seismometer is the closest we have to being King of the instruments in practical volcanology. After all, all causes that we must contend with will emit noise (at least in theory but remember that this is Iceland).
Different causes will create an array of different acoustic signals, and the good news is that we can with a fair degree of certainty recognize a few of them. We also have a few solid theories about at what points those noises are generated, at least we have fair reasons to assume that our theories are relatively solid. Good news indeed!
For instance, we have fairly good grounds for a theoretical standpoint that most magma in Iceland is originating from the bottom of the crust, and that the magma has to travel upwards to erupt. At least at some point, and in some cases. Let us not get bogged down into intra-crustal decompression melt and other things that Iceland is quite capable of throwing our way.
After all, the hot area conducible for the intra-crustal melt is hot due to magma that probably came up from the bottom of the crust to start with.
So, a starting point for using our seismometers would be to look for deep origin magma rising upwards, indicating a fresh batch of magma arriving into our volcanoes.
If that magma enters a magma reservoir it will increase the pressure, if fluid dynamics is a solid scientific theory, and thankfully it seems to be just that.
And as the pressure rises it will cause creaking and groaning in the host rock. These earthquakes are defined as short brittle earthquakes caused by fracturing rock. If the pressure is high enough the crack created will be large enough for magma to enter and there will be a discernible coda to the signal as magma rushes into the crack.
As magma enters a reservoir it can also create a monochromatic tone, exactly like an organ pipe, this is called charging tremor or tornillo.
So, according to our theories we should be able to “hear” magma moving. And the creaking and groaning should also give us the shape of the magma reservoir since magma is to hot and “fluid” to be able to cause earthquakes. In other words, if there is a void covered by earthquakes, we can assume that this is the 3-dimensional outline of the magma reservoir, especially if the gravitometer and the magnetometer has told us that there should be one there.
The problem here is that some regions and volcanoes in Iceland are to varying degrees aseismic in Iceland. The reason for this is that the host rock is to hot and ductile to crack in any way we know how to recognize. Say goodbye to the earthquakes that we are chasing.
So, all the tools so far in the toolbox is affected by temperature variations, variations that can render them more or less useless at some volcanoes. How about we leave the ground and go for something that is not affected by heat?
The Global Positioning System is a technological marvel based on the most fundamental scientific theory that humanity has come up with. The theoretical precision of a good GPS-network is astounding, and the practical side of it is not that far behind.
The problem is that the level of sensitivity when employed on Iceland is akin to poking a 3-dimensional anthill with a stick. Things will continuously be running around at high speed trying to bite you in the ass.
First you must choose your reference station to which you are measuring. If your volcano is in American Iceland you have to use Reykjavik as a reference, and if you are in the Eurasian part of Iceland you have to use a station named HOFN. This way at least the worst continental movements will be removed.
Problem is just that REYK and HOFN are moving about on their own. Upon occasion this will throw an entire half of the network out of whack since it would seem like half of Iceland is rapidly inflating. The way to catch this is to cross reference everything against this possibility.
Next you must cross reference away local tectonic effects by using a number of GPS-stations. The same goes for local tectonic effects from earthquakes and movements in fissure swarms.
After that we will have to contend with large spatiotemporal isostatic rebound from the last ice age, and the seasonal variations caused by the glaciers in Iceland.
And, let us not forget that ice and dust on the antennas will have quite drastic effects. At this point in your search your hair will file for divorce and emigrate on its own to Australia due to the frustration.
Now, time to make things even worse, this is after all Iceland. As you are looking at the GPS-network for your favourite volcano you must always reconcile yourself with the not so unimportant fact that your GPS-stations are impacted by what is going on at the same time in quite a number of volcanoes.
At this point you are reduced to becoming a medieval scholar divinating truths out of a concoction mostly resembling a good bowl of chili while drinking heavy amounts of agave spritus. Life as you used to know it is after all gone down the mental drain.
And to top it off, GPS-es do not do well if placed upon glacial ice, and most likely your volcano of interest is hidden below a large honking glacier, so you are reduced to relying on distal GPS-stations.
After eating the content of your divination bowl and fortified by fortified fluids life once more will start to feel worth living and you throw yourself against the problem with renewed gusto.
You start to work your way down the list of instruments at your disposal removing every erroneous signal, starting at the gravimeter and working yourself towards the GPS-trajectories.
If you are methodical you will end up with a surprising amount of information that you feel that you are fairly certain about.
You enter this into the best computer for this particular kind of work that you have at hand, your brain, and out comes a 3-dimensional static image of what is happening, then you start to spool this image backwards and forwards along the fourth dimension (time), and after a while you should have a pretty good inkling at what is happening not only at your volcano, but in the volcanic vicinity (or more).
This should not take more time than it will take a pair of Turdus Merula to burrow a nest and hatch in your newly grown beard. Time is after all both relative and geological in our case, so why care?
A final comment or two
Obviously, there are other instruments, but they are not good when dealing with an intra-glacial volcano. So, I omitted those.
The direct reason for writing this prequel is to put the level of mental strain, problem solving, raw learning, theory building, and time that lies behind the upcoming series of articles. This has after all been in the making since 2013.
Even though I wrote this prequel this is a group effort. At the dawn of time there was obviously Lurking, who plotted the beginnings before spawning an entire lineage of plotters. Without Lurking we would never have been even remotely as adept at reading and using plots for everything.
Albert is happily waiting in the background to kick us in our scientific nuts if we can’t produce a convincing case, misinterpret data, or take a theoretical downturn. It is a boon to have someone of that implacable scientific moral around forcing us to do the job correctly.
The heavy writing work will be done by me and Gaz, while Andrej Flis is doing the heavy plotting. There will also be an unusually high number of sources for this article, normally we write more in the popular science style, but here we will at least try to reference things.