The Wandering Earth: when rocks flow

The wonder of water

The tell-tale sign of the suspension of the laws of physics is someone seen walking on water. The suspension is always temporary – as soon as a second person tries to follow, the laws of physics are re-instated and the person looking for the ‘me too’ experience instead encounters full immersion. But walking on water is in fact quite possible, even within the legal constraints of the natural world. It should be viewed as a seasonal activity. If you live in the right place (Sweden or Alaska comes to mind), in winter you can walk on water without requiring any special ability apart from some warm clothes and non-slip shoes. In Siberia, you can even drive on it. This is due to a strange oversight in those laws of physics. Water has found a loophole.

It so happens that the freezing point of water is within the range of natural weather variability. It also so happens that frozen water has lower density than liquid water. Most substances expand when they melt, so the liquid rises and the frozen phase sinks. It is what makes volcanoes so interesting: when you melt rock, the magma percolates upward. But if you melt ice, the water goes down while the ice stays up. If rock were like water, volcanoes would erupt their lava downward, into the crust, still of interest to a geologist but the viewing experience would be severely limited. Due to this double accident, in winter you may find a sheet of frozen water lying on top of the liquid phase below. It is a remarkable coincidence that the most common liquid on earth has such uncommon properties. If walking on water makes you doubt physics, you should realize that the miracle is not the walking. It is the water itself.

(Be aware that in England, or any other place with too much weather and not enough climate, walking on water is physically impossible because the ice remains too thin to carry your weight: it cracks, breaks, and leaves you just as submerged as in summer but in much colder water. Just a warning – we don’t want to lose any of our valuable readers and commenters to a fatal misunderstanding. Volcanoes are already dangerous enough without water.)

Water is also a brilliant example of the very different behaviour of solids and liquids: one is strong and stable, and the other weak and fickle. But in fact not all frozen water is equal. Try walking on snow and your experience will be very different. It may still be officially a solid, but you do sink – part-way at least. Snow is a solid disappointment.

But ice also does not always behave like a well-trained solid should. The video is an example of ice solidly misbehaving, where a flow of ice moves like a hostile, alien substance from Doctor Who. In the video, it takes a while before the person filming it realizes that this is more than a lecture in the wonders of physics, and that the army may be required. The moment the penny drops is indicated by a sudden R-rated, uncensored word.

(The videos are an important part of this post and I hope you have time to watch them.) Glaciers do much the same thing. Although made of solid ice, glaciers flow under the influence of gravity. The ice making up a glacier is constantly on the move. It does not move as a solid block, but like an exceedingly slow river. On occasion, this can go terribly wrong. If a glacier looses its footing, it can become run-away. A surge can reach speeds of many meters per day, but it can also form an ice debris flow with speeds reaching a hundred meter per second. We have called this a cryoclastic flow. It is very rare, but devastating. The video below gives a good introduction to the moving ice of a more sedate glacier.

And in fact the solid earth does much the same thing, just not on a time scale that we can comprehend. When Italy crashed into Europe and joined the EU, it created a crumple zone where the Alps were pushed up. Solid rock it might be, but mountains were on the move with layers being thrown up and over each other. One big block was pushed horizontally so far that it became a bit of Africa amidst solidly European rocks: the Matterhorn. We can illustrate the process in the lab, using sand rather than rock. Here is your lecture in sandpit geology. (The only thing missing is a volcano.) But if feels strange that solid rock can behave like loose sand.

Solids in motion

The essence of a solid is that it keeps its shape. There may be a bit of deformation: for instance when you sit on a sofa, the surface sinks a bit, thus providing a solid yet flexible anterior foundation. But when you stand up again, the sofa recovers. In its deformation, different parts of the sofa stretch. But the individual molecules are strongly attached to each other and don’t change places. After you stand up, all molecules go back to their original location. In physics, this behaviour is called elastic. A liquid behaves very differently: molecules in a liquid are only loosely attached and easily move past each other. It never retains its configuration: sit on it and stand up again, and even though the water surface will go back to the previous location, the individual molecules never will. The ability of the molecules to move around means that a liquid leaves no empty spaces. A moving molecule in a liquid will experience friction with the neighbouring molecules. A material where this happens is called viscous. In an ideal solid, this does not happen because the molecules all move together, locked in place. In an elastic process, no energy is lost. In a viscous process, energy is lost (or becomes heat). If you drop a ball on the road, it bounces back up, and keeps hold of its energy. If you drop it on mud, it gets stuck with a total loss of its energy. The first behaviour is elastic, the second is viscous. A viscous material gives you a soft landing.

In the first two videos, ice showed a very strange phenomenon. Even though ice is solid, and strong enough to carry your weight, it also flows like a liquid. In mountain building, rock does the same thing. What really happens? How can something act like a solid at one moment, but move like a liquid over much longer time? Politicians understand this very well. For how do you make people accept change? It turns out, people are resistant to change. A culture behaves like a solid: apply a force (i.e. enforce some unpopular law) and you may get a temporary shift in behaviour, but when you remove the force everyone goes back to their previous behaviour. But apply a little force over many years, and people become far more accommodating. They get used to the new situation, and when you remove the force, people’s behaviour and/or opinions have changed permanently. Politicians move in small steps, continuously assuring people that nothing will change and this is just a minor law which will never be used. People are malleable given enough time. Apply a sudden jolt and human culture applies a counter force, just like a solid body, ensuring nothing changes. But apply pressure over a long time, and reactions begin to shift. The glacier of culture is now on the move.

Physics has defined two parameters which are related to this phenomenon. With the risk of turning our readership away in despair, I’ll try to explain! Please bear with me – complaints can be discussed in the VC bar.

The first parameter is the elasticity, and it describes the essence of ‘solid behaviour’. If you stretch a solid material, a counterforce tries to pull the material back to its original shape. This counterforce comes from the strong attachment of molecules to their neighbours. Good examples are seen in springs and in elastic bands. Some quick experiments will show you that (1) not all springs/bands are equal: some solids are much stiffer than others; (2) the force increases with the stretch – stretch it four times as much and the force that pulls back is four times larger; (3) the material returns to its original state if you remove the force; (4) there is a limit, beyond which the material simply breaks. The force that pulls the material back is the elastic force; the fact that the material returns to its original state shows that no energy is lost in the process.

The second parameter is also already mentioned, and is also one you know from experience: it is viscosity, or ‘stickiness’ and it applies to liquids. The word comes from the Latin word for mistletoe. You may now have visions of stealing sticky kisses under the mistletoe, but this would be the wrong connotation: apparently the berries can be used to make a rather sticky substance. Viscosity is related to friction. Friction is a force that acts on things that are moving, and causes them to slow down by dissipating the energy of the motion. The next video shows an example of viscosity: dropping marbles into different kinds of liquids.

Now you know the meaning of the English (actually German) expression ‘blood is thicker than water’. It means that blood is more viscous than water – which it is. (In reality it means that family bonds are strong – so it is about the viscosity of blood relations.)


Now take a river. The water at the surface flows at some speed. The water right at the bottom is stationary, held in place by the rough rock below. But because of the low viscosity of water, this stationary level does not slow down the water above it, and the flow at depth is about as fast as the surface flow. The stationary level is rather thin. Now take a lava river. The flow at the top can be fast, as we saw at the infamous fissure 8. The very bottom again is stationary. The viscosity of lava is much higher than that of water, and so the bottom layer really slows down the lava above it. So only the top layer flows fast – the lava just below the surface goes much slower because of the friction with the layers below.

This behaviour is illustrated in the video below. It shows a fast flowing lava river from Hawai’i’s fissure 8, with bits of solidified crust on the surface, flowing at the same speed as the lava. But at some point in the video a large lava boat appears which moves much slower. It sits much deeper, and its speed shows how fast the lava goes deeper below the surface. And that is not nearly as fast as the top layer. The lava boat is not scraping along the bottom: you can see that because the motion is smooth. It gets its slowness from the river itself.

These two parameters distinguish solid and liquid behaviour. But the distinction between solids and liquids is far less clear than water makes it appear. Solids can behave as if they are very sticky liquids. Playdoh is an example of such a solid. It is in-between, solid but malleable. Its molecules can flow. In fact, this is true for all solids. They have very high viscosity, but it is not infinite. Solids can flow – if you give them long enough. It may take longer than the Universe is old, but anything can move. This is called creep. If you have a synthetic rope which carries a load over a long period of time, the rope slowly lengthens and eventually has to be discarded. Inside the rope, the chains of molecules move past each other and it is is this movement that makes the rope loose strength. The rope never returns to its old state: in the process, energy is lost. It behaves as friction, converting motion to heat.

The molecule chains inside a synthetic rope. Under a long-lasting load, the chains will begin to creep past each other. Source: https://youtu.be/opPWceW-YKc

Viscous physics

Still with me? Let’s now take something solid (such as a piece of rock, a sheet of glass, or a handful of sand) and apply a force – for instance, by standing on it so your weight pushes it down. It deforms a bit: by how much is determined by the elasticity. But this movement leads to internal friction, and therefore the material also has viscosity.

This was first studied by James Maxwell (1831-1879). He was probably the greatest physicist of the 19th century, best known for the equations of electromagnetism, which explained the speed of light and formed the foundations of Einstein’s work. But he did many more things. He deduced that Saturn’s rings had to be made up of small particles, worked on polarimetry, developed colour photography, initiated the field of control engineering, explained heat, and won prizes (as a child) for poetry. Maxwell died before his 50th – 20th-century physics may have been delayed by decades because of his early death. The theory of visco-elasticity must have been child’s play for him: it was something he published when he was 18(!), having already been at university for two years. Can anything good come from Scotland? I think we can answer that question with a resounding ‘yes’.

The way Maxwell envisioned an elastic but viscous material was with a spring and a damper. The schematics is shown in the diagram. If you pull on the spring, it expands. This puts a force on the damper (or perhaps a damper on the force), and the damper in turn slowly expands, like the synthetic rope discussed above. As the damper moves, it suffers internal friction, and the energy stored in the stretch of the spring is eventually lost to heat – the spring now relaxes over time. If the force continues, the result of the lengthening damper is that the spring slowly moves as a whole, without becoming any more stretched, at a rate that is determined by how quickly the damper can damp. The spring is the elastic bit, and the damper represents the viscosity.

The amount of expansion of the spring is set by the constant of elasticity, which is called E in the diagram. If the force is F, the spring extends by an amount x = F/E. Now the damper kicks in. This equation is slightly different, because friction relates a force to a velocity (friction doesn’t dissipate any energy if you are not moving). The extended spring puts a force on the damper, and it begins to move, with a velocity v = F/η, where η is the viscosity constant. As you can see, the larger this constant is, the slower things move. Think treacle (or re-watch the marble video above). The force from the extension is fully dissipated once the damper has moved the full distance x. Remembering the high school equation x = vt, you can now see how long this will take. The system has adjusted after a time t = x/v, when the elastic force has been dissipated. Fill in x and v using the equations above: x = F/E and v = F/η. The force F appears twice and cancels and you are left with the simple equation t = η /E. The values for the two constants can be looked up, and t calculated, for a particular material.

This t is called the Maxwell time. If you apply a force to a solid for a time shorter than t (for instance you hit it with a hammer) it behaves ‘elastically’ which is how a solid should behave. But apply the force over a time longer than t, such as the rope under a long-lasting load, and the solid absorbs the elastic energy – it ‘flows’. In geology, an earthquake counts as a sudden, fast force. Rocks quickly deform and go back to their original shape: this motion gives rise to the seismic wave traveling through the Earth. But apply a force over a very long time, and the rocks flow and a mountain can rise up.

What are typical values for the two constants? For η, this ranges from 0.05 Pa s for fruit juice and motor oil, to 1.4 Pa s for baby food, 70 Pa s for tooth paste and 30,000 Pa s for tar. (The units are Pascal-second.). For solids the values go very much higher: for glass it can be as high as 1021 Pa s. A famous experiment measured the viscosity of pitch (bitumen) at room temperature by counting drops dripping from a container of the material. There was a drop about once a decade. After 80 years the scientists found a value of 2.3×108 Pa s. Science gets there in the end. This experiment received the 2005 Ignobel prize.

Typical values for the elasticity constant E are around 5 GPa (giga-pascal) for (cold) asphalt, 10 GPa for wood, 50 GPa for glass and 100 GPa for metals. (This is also called Young’s modulus.) They can change a lot with temperature. That is true for the viscosity as well, so it is important to measure both at the same temperature! The elasticity constant is only available for solids.

Compare the two constants, and you see that η varies all over the place, but E has fairly similar values for different materials. If you have a material with E = 10 GPa and η = 1018 Pa s, its Maxwell time becomes 108 s, which is about 3 years. If you keep it under a constant force for 3 years or more, this material will begin to flow. Keep the force on for less time, and it behaves elastically, in a manner worthy of a real solid. The most important force that stays on for this long is gravity. In fact, gravity does not have an ‘off’ switch. Under the force of gravity, any solid can begin to flow – eventually.

Creepy glass, un-runny honey, and salt of the earth

The problem is often discussed in connection to window glass. In old (medieval) buildings you often find that a glass pane is thicker at the bottom than it is at the top. Can it be that the glass has slowly crept downwards under the influence of gravity? This is often claimed. But let’s look at the numbers. Using the values listed above, the Maxwell time for glass becomes 5 1010 s. That is rather a lot – in seconds. A year lasts 3.15 107 seconds, so this becomes 1600 yr. That still seems a bit long, although not that much more than the age of European medieval buildings. On a hot day the glass may become a bit softer, so perhaps the creep happens during the occasional hot day. However, that doesn’t work because it would require that the hot day is as long as the Maxwell time: a couple of hours won’t do. I did use a high value for the viscosity: for some types of glass it can be one or two order of magnitudes less. So for some types of glass, the Maxwell time could be 10 to a 100 times less, which seems more reasonable to support the case of creeping medieval glass.

However, the argument still fails. For even if you wait this 1600 years, the creep will be by about the elastic extension. And this extension is very small. For a glass pane of 1 square meter, I get about an elastic extension under the force of gravity of about 0.4 micrometer. Even if you take the softest type of glass, you would still have to wait a VERY long time before it can creep even a centimeter: about half a million years, in fact. Not even our university buildings are that ancient.

I once had an office in a colonial building which dated from the 1820’s – and it had this kind of glass. The window frame (which was original) fitted the shape of the glass, including the thicker bit at the bottom. So it had already had that shape when the glass was put in. In those days, glass panes were made on a rotating disk. The glass on the disk would become thicker near the centre. The panes were cut from this disks, and would have one side thicker then the other. The installers would always put the thicker, heavier part at the bottom. Physics still works; however the effect came during manufacturing and installation, not during the long years of academic research.

Glass is crystallized sand, and crystals are hard. Adding some crystals can harden any material. (I won’t mention diamond.) The effect can be viewed by using your diamond ring to scratch the window glass. The harder material will scratch the softer one – diamond is even harder than glass. Try the same thing with graphite (also carbon but a non-crystal form) and the glass will laugh at you. However, an easier way to make the case may be hiding in your fridge: it may contain a jar of honey which someone (no names mentioned) has accidentally put there. Bring it out and all attempts to pour the honey are fruitless. But it is not a solid: the freezing temperature of honey is something like -40C. What happened? The cooling honey formed crystals and these turned the watery honey into a far more viscous fluid – one that won’t let itself be poured. And the crystals are not easy to get rid off: putting it back in the cupboard, at its original temperature, does not work: the honey retains its solid refusal to flow. It does still flow, though: put it upside and after some days you find that it has miraculously moved to the new bottom. But to make it fluid enough to pour, you have to heat the honey to well above room temperature. The crystals dissolve, and the honey can now be put back where it belongs, in the cupboard. But even at room temperature, over time the crystals will still grow and during the coming weeks the honey becomes less runny. The viscosity of runny honey is a few Pa s. That of crystallized honey at fridge temperature is around 1000-3000 Pa s.

t
The structure of crystallized honey samples: (a) rape honey and (b) buckwheat honey . Source: Sławomir Bakier (March 15th 2017). Rheological Properties of Honey in a Liquid and Crystallized State, Honey Analysis, Vagner de Alencar Arnaut de Toledo, IntechOpen, DOI: 10.5772/67035. Available from: https://www.intechopen.com/books/honey-analysis/rheological-properties-of-honey-in-a-liquid-and-crystallized-state

(You may be interested how honey compares to magma. The viscosity of basaltic magma is between 10 and 100 Pa s, in between runny and non-runny honey. Andesitic and rhyolitic magmas are far more viscous, around 103 – 105 Pa s. (Rhyolitic is the most viscous.) It is quite dependent on temperature. But it is clear that such magmas do not flow easily. Even the very best rhyolitic magma is only about as runny as the honey in your fridge. )

Another example of a crystallized material is salt. Wherever large bodies of water have dried up, large deposits of salt were left behind. Many places have these deep salt layers underground. But they are not entirely stable. The salt is not very dense compared to the rock, and therefore is buoyant: it tries to rise and flow. In some places, salt domes have formed from this rising. Elsewhere, whole mountains were made by rising salt. A well known example is near Hormuz in Iran. They are not actually mountains: once above ground, salt erodes rather quickly, and the salt sticks out perhaps 20 meters. The salt is rising at velocities up to 7 mm/yr. From the size and velocity, a viscosity has been derived of around 1019 Pa s.

Making mountains

So salt can flow to make mountains. How about real mountains? How are they made? Rock is strong but it does have limits, and these limits are reached faster if the rock is heated. This happens deep under ground: the rock here is hotter, and under long-lasting pressure of an approaching plate (think India or Italy), it buckles. Later, erosion removes the layers above and the buckled layers become visible at the surface. It is worth searching in mountain regions for places where this is visible, hidden places where the root of the mountain is revealed. The image below is for the Swartberg in South Africa, near Oudtshoorn. If you have time and a fairly decent car (a four-wheel drive is not needed), the drive over the Swartberg pass is spectacular. The road is in good shape but unpaved. Driving towards it from the north, the mountain range rises steep from the plain and it is impossible to see a path the road could take. It just clings to the side. The rock contortions are on the far side where you descend into a deeply eroded valley.

So flowing rock can be used to build mountains. They can also be used to get rid of one, a bit like the lake above. Mountains require strong crust to carry them. Volcanoes, on the other hand, form where the crust is heated, partly liquid (magmatic) and not as strong as it should be. This is not quite the right combination for strong and stable. Take Hekla. It is a young mountain, datinf from the holocene, and is rapidly growing. But the growth is being hampered by a small detail: the area around it is sinking. The crust responds to the weight of the new mountain. In itself, this is not abnormal. Mountains don’t do magic and something needs to carry their weight. The rocks below Hekla are not quite up to the task. This is because they are hot and ductile (and partly melted). It is as if Hekla is sitting on very old brie (or camembert if you can stand the smell). It sinks over time. (Actually, it is growing faster than it is sinking, so Hekla is getting higher while going down. But that is beside the point.)

The time it takes Hekla to sink is given by the equation t = η/ρ gλ where η is the viscosity of the ductile rocks, λ is the depth of those rocks, and g is gravity. The sinking should not be overstated – it is a small effect. Measurements have indicated that the relaxation time is 100 yr and the thickness of the upper elastic (i.e. stiff) layer is 3.5 km – the ductile layer is below this. Put those numbers into the equation, and the viscosity of the hot deep rocks can be calculated. Underneath Hekla, a rough estimate gives a value of order 3 × 1017 Pa s for the ductile layer below 3.5 km. It is a local effect: over most of southeast Iceland, the elastic layer is around 10 km thick, underlain by a 30 km more viscous layer (1 × 1020 Pa s) on top of quite a ductile layer (1 × 1019 Pa s). The last layer may represent magma accumulation at the Moho.

Fast-sinking mountains are not the only indication of a ductile crust. A more common sign is a lack of earthquakes. Earthquakes happen in brittle rocks, and their absence (as in the Lurking Dead Zone in Iceland) can indicate low viscosity. Of course it may also just be due to a stress-free region where there is nothing to cause shakes!

We have looked at why solids flow, why mountains grow and how volcanoes sink. The next part will look at a bigger scale. Why do continents move, and what makes the mantle convect and plume? Find out in the next instalment of The Wandering Earth.

Albert Zijlstra, June 2019

64 thoughts on “The Wandering Earth: when rocks flow

  1. Fantastic article, especially for someone like me who took college physics more than 30 years ago.

  2. Hubby wants to know how You measure the thickness of glass while still in the casing and i want to know if they forgave You putting the honey in the refrigerator. 🙂

    • Fastest way is to break the glass. Using ultrasound is more accurate (you can buy handheld ones) but breaking and replacing the glass is cheaper.

      • Its probably in lead and this is ductile and can carefully be prised apart until the glass can be wiggled out. Replace in a similar manner.

        Do not forget to mark which is the front and top of the glass before removal because it can be surprisingly hard to work this out after the glass is removed.

    • Current swarm at Torfajökull is at the tip of the previous swarms towards the dead zone. That is potentially not a good sign since it has the looks of a dike progressing towards the dead zone. It is still not very energetic and not all quakes have been manually checked, but if there is a progression towards the dead zone and it continues, however slowly, it could have the potential to turn into some real unzipping action. I’ll leave the rest to Carl and others to elaborate.

      Shallow quakes directly under Hekla is a good illustration of Albert’s article, since it is probably due to settling from the weight of the edifice.

      • So, they were checked as I wrote the comment. None of the quakes are deep and I think that speaks against this being a progressing dike, at least for now. The other swarms had much deeper quakes. There is also some activity to the south that lines up with the current swarm, so it could just as well be related to that. Torfajökull is quite seismically active in general, but this little swarm is in a new place and it does line up with the previous swarms. Hard call. Carl? Anyone?

        • Depth is not normal for a dyke, so I would go with it being strain related.
          And that would probably point towards that fissure swarm being a suspect for the next Fires-episode.

          • It would be something for me to get into volcanology a few years before a laki, eldja or god forbid, a veidvotn scale effusive eruption but that would fit with my bad luck.

          • I would say “no luck is bad” but that would be a lie. Everything is at its core, bad for sombody.

            “They guy got a name for the winners in the world,
            I want a name when I loose.
            They call Alabama the Crimson Tide,
            call me Deacon Blues…”

            –Steely Dan.

            BTW, the glass is never half full. The other half contains air.

    • Yes, I realize this post may take more effort to read than most, and may not suit people less confident in their math. But it seemed worth a try.

      • Very entertaining and clear to me and I am NOT very good in math! 😊

      • I enjoyed reading it and I am 130% a maths dunce (yes, that’s a joke). It put to rest the old glass sagging argument for me, and I learnt a lot from it.

        I’ve read a lot of science over the years. I can’t do the maths at all, yet I have a good grasp of physics due to an ability to grasp mechanical forces and physics (without the maths!). My school teachers were confounded by it. Sigh. Got me a job in Librarianship!

        I have a kind of dyslexia for numbers and number forms and I’ve never been able to surmount it even with extensive additional tuition as a kid. But that does not stop me learning and tackling head on challenging papers, even laden with maths.

        Thank you Albert! Keep the complexity coming!

  3. Thank you for this article and for the refresher on the physics of viscosity…and I do hope this will lead to a good discussion of tidal warming on other celestial bodies such as that happy li’l ball of volcanoes circling Jupiter.

    PS for those of you who find that watching the plots and waiting for Orae to erupt is just too fast-paced an activity, you can (sometimes) watch the U of Queensland pitch experiment webcam here > http://www.thetenthwatch.com/ or follow Pitchy RealPitchDrop on Twitter.

  4. Albert excellent article on Viscosity
    I haves a question for you
    Water seems to have an extremely low ( lowest viscosity of all everyday liquids )
    Is there any true liquid that have a lower viscosity than water? I know when I pour light car petrol.. it seems extremely thin and fluid. Lower viscosity than water?
    Also some metals becomes extremely low viscosity when molten .. but they are much denser than water too

    • Plenty do. Even water is less viscous than water: you can reduce its viscosity by a factor of 4 by heating it to near boiling. Acetone and Perfluorohexane are examples of liquids with lower viscosity than water at the same temperature. And superfluids have no viscosity. But I hope we are not getting into another discussion on ‘what is the lowest/highest/biggest’.

      Density and viscosity are different things. You can have lower viscosity and higher density.

    • In my science lab I’m frequently working with High Performance Liquid Chromatography (HPLC). There you can really see the different viscosity of liquids.

      Basically, in HPLC you have a small stainless steel column (250 mm length and 4 mm in diameter) filled with modified silica particles. It is used to separate compounds such as drugs by pumping the mixture through the column with high pressure.

      Typically, we use a flow rate of 1 mL/min. With a mixture of 90% and 10% methanol, the pressure typically is around 220 bar. When you reverse it (i.e. 90% methanol and 10% water), the pressure drops to 100 bar. So more 100 bar difference in the rather simple setup, caused only by fluid dynamics and viscosity.

      Even more often Acetonitrile is used which is one of the organic liquids with an even lower viscosity than methanol. With the same setup, a mixture of 90% acetonitrile and 10% water you typically get 70-80 bar.

      I really like working with the instrument – the difference in viscosity of liquids is really astonishing (although the main purpose is something else).

      Best regards,
      Dirk

        • Let’s just say I certainly could throw an interesting party with the contents stored in the safety cabinets. 😉

          • Labs I worked in had the following amusements:
            – throwing different brands of Eppendorf tubes into the liquid nitrogen to see which brand’s lids stayed on best. Necessary for purchase decision, of course
            – dry ice in the sink with water to create “arena rock” atmosphere
            – caricatures of certain people, and also chickens, made from exam glove balloons and felt pens.
            – Hall of Shame photo wall featuring ugly gels and failed experiments.

  5. A thought just crossed my mind: What if Greip is a deep feeder for Grímsvötn? Carl always says that Bárdarbunga gets its magma from Kistufell. Now, Kistufell is at about the same distance and direction from Bárdarbunga as Greip is from Grímsvötn. In the latest swarm from Greip, one of the hypocenters is off to the side in the direction towards Grímsvötn. I don’t say that that is proof of anything, but it’s the detail that made the idea pop up in the back of my head. I can’t remember if that option has been discussed here before.

    • I think you are over-interpreting me a bit.
      Yes, it is possible, but we can’t find a single evidence for it in the data-records.
      I think it is more the other way around, sort of.
      Both Grimsvötn and Greip is on the elongated Grimsvötn Fissure Swarm, that is in itself a very large magma storage unit. From there both are fed with magma. So, brother-volcanoes are perhaps the best guesstimate so far (until Greip erupts and we get our definite answers).

      In regards of Kistufell and Bárdarbunga.
      Kistufell is not feeding all magma to Bárdarbunga. During the 1996 intra-caldera eruption of Bárdarbunga there was no magma going from Kistufell to Bárdarbunga. And, as Holuhraun II started Bárdarbunga was already filled to the brim with it’s own magma.
      Now over to what I said about it.
      During the rampup prior to H2 a lot of magma vent up into Kistufell, but could not go through the roof of the chamber, instead it followed the mutual fissure swarm from Kistufell and either rebounded on Bárdarbunga, or actually entered the reservoir (pushing Bárdarbunga over the limit).

      There is actually evidence in the seismic record for both versions…

      • It can be difficult to distinguish actual magma transport from the pressure effects of communicating vessels.

        • You just wait until it starts gushing to decide what was going on…

          Back at my college we had a fairly capricious set of communicating vessels in the form of the lavatories.
          It often rumbled, but it was not until a toilet seat gushed forth that you knew how the communications between the vessels ran that day.

          It is probably the only school building where every single student did their business with an unlocked door, one hand on the handle of the door, and the other hand holding the underwear.
          Better to suffer the indignity of jumping out of a lavatory with the arse bare, compared to saunter out covered in a flood of shit.

          Ah, the joys of education in physics…

          • Not unusual. On ship, flushing water comes from the ship’s fire-main and is salt water. On my first ship (an aging FFG) the engineering department would take care of clogged soil lines by isolating the toilets and blowing down the line with high pressure water fed towards the CHT tanks. Lord help you if you were doing your business when the CHT system got over pressurized.

          • Well someone had to introduce the fleet to the new high-pressure bidets … you were just unlucky enough to be on the trials ship for that system.

          • I tended to time my visits to non working hours when it was relatively safe from geyser activity.

      • Along with full contact baseball.

        (The batter gets to keep and use the bat as he makes the bases, but can only swing at who has the ball.)

  6. Tuesday
    18.06.2019 22:30:52 64.631 -17.455 5.0 km 3.4 99.0 3.6 km ESE of Bárðarbunga

    • The interesting thing right now is if this will be followed by one of the larger ones in the next few days or not. The CSM graph currently needs a big one (close to M5) to stay on track with its previous trend, but the GPS trajectories suggest that inflation has stopped. Personally I think that the plug movement acts as a pressure relief so that accumulation of magma below the plug can still continue without a visible inflation signal.

      Does anyone know if there has been any radio-echo sounding of the caldera floor since the eruption stopped? It would be really interesting to see what, if anything, is going on.

  7. Greip Swarm from deep today but it looks off the center of what we have seen in the recent past

    27.3 km 1.1 15.4 km ESE of Bárðarbunga
    1.8 km 0.6 19.4 km ESE of Bárðarbunga
    17.9 km 1.4 17.3 km ESE of Bárðarbunga
    16.2 km 0.0 17.5 km ESE of Bárðarbunga
    30.4 km 0.1 15.2 km E of Bárðarbunga
    1.1 km 0.7 19.6 km ESE of Bárðarbunga
    17.5 km 0.1 16.8 km ESE of Bárðarbunga

        • I agree. Almost every day there are quite a few earthquakes on the list. I made a bet with another hobby volcanologist in Cologne. I say it will before March 2020, he says not before 2021.

          If I recall correctly:
          Albert‘s projection is 2020 (although 2021 cannot be ruled out), Carl predicted a period of December 2018 – December 2019 with an uncertainty caused by a 3.5 earthquake.

          But given the increasing number of earthquakes, I‘d say that an eruption within the next 6-12 months is more likely than an eruption in 12-24 months.

          • dirk schepmann
            Yea its slowly steady refilling

            How was Grimsvötn 2012?
            Almost no quakes at all right?
            How was it the first 2 years after 2011 ?

    • Albert
      I think that this is a ok to teach different thought processes to solve a problem. I see the reasoning in the simple problem “Find the number which is the sum of 20,000 and 30,000 divided by two” (a typical mathematical problem) and “Find the midpoint number between 20,000 and 30,000” (an example of a mathematical mindset problem).”

      What if the numbers are 14,234 and 37,433, still need the math for the correct answer.

      Mac

      • Some people have trouble with order of operations. Given the word problem, do you add 20,000 and 30,000 then divide by two (50,000/2, or 25,000), or do you divide 30,000 by 2 then add 20,000 (30,000/2 + 20,000, or 35,000)? (I hope I did my math right, or I’ll be really embarrassed!)

        • Well, in this example, it says “find the sum of” and then “divided” so the answer is 25,000.

          In general, when there are no clues like that, remember the operation order as BODMAS (brackets, orders, division etc.).

          A (strange) example:

          2^3 + (17 + 43) / 3 – 3.6 x 4
          = 2^3 + 60 / 3 – 3.6 x 4
          = 8 + 60 / 3 – 3.6 x 4
          = 8 + 20 – 3.6 x 4
          = 8 + 20 – 14.4
          = 28 – 14.4

          Therefore, 2^3 + (17 + 43) / 3 – 3.6 x 4 = 13.6.

          To simplify this completely, it can be re-written as
          ((2^3) + ((17 + 43) / 3)) – (3.6 x 4) = 13.6.

          Brackets are your friend in maths!

          • I agree wholeheartedly re. brackets. My kids learned it as PEDMAS (Parentheses, Exponents, Multiplication/Division, and Addition/Subtraction). if no P or E, you do M/D before A/S, no matter the written order (as you have in your example).

            I still think the example is a little ambiguous and could honestly be read by different people as:

            (20,000 + 30,000)/2 or, 20,000 + (30,000/2).

    • Hubby is a retired math teacher and was interested in how to communicate in different ways in order to teach different thought processes… i have my own theory of math which drives him crazy… as in there are real numbers in my world and fake numbers in his theorical world….. i deal in donuts not in the holes. 🙂 Best!motsfo

      • Go to Vieux Carré and get a sack of powdered doughnut holes and you’ll change your mind… 😀 😀 😀

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