Volcanoes are nature at its most impressive – and most damaging. The fire and the lava are a deadly alluring combination. Once the flow gets going, it is unstoppable. It may be deflectable: people are currently trying hard to save their road by building a wall. We were wondering, will the wall work? It would be the first time that people have managed to change a lava flow by 180 degrees. We are doubtfully cheering them on.
Tornadoes too are nature at its most impressive – and most damaging. They come in many different forms and sizes, from small dust devils to the massively destructive ones in tornado alley. No wall will help there. And the damage can last: in the city of Utrecht, the cathedral is some distance away from its tower. In 1674, it was hit by a tornado which destroyed the church but left the tower standing. The church was rebuild, but an open square was left between church and tower, a lasting reminder of the power of nature. And not even Iceland is immune. In August 2018, a farm in South Iceland was damaged by a tornado. This was deemed so unusual that it made international news.
A combination of a volcano and a tornado must but the ultimate scare, one step above even sharknado. What are the chances of that happening?
It turns out, that depends on what you mean with tornado. A combination of a volcano and a true tornado is rare. But if you think ‘spout’ or ‘devil’ then the chance is rather high. Luckily they tend to hit where lava has gone before, with nothing left worth damaging apart from an occasional careless tourist.
On Thursday, the still camera covering the Geldingadalir eruption caught an amazing view – amazing, that is, for Iceland in spring. First there was the snow, proving to the world that Iceland never really left the ice age. It is waiting in the wings, and here ragnarok is always just around the corner. But this snow shower had more. It was only seen on one frame, a 1-second snap every 10 minutes. A beautiful spout showed, left of the cone that just at that moment wasn’t spouting anything. The image showed the funnel, the sharp thin edges and the horizontal striping that delineate the rotating winds. Towards the bottom it became fuzzy, clearly showing that it touched the ground and was picking debris – dust, presumably.
Once this was found, the twister was quickly located on other webcams. The still was taken at 11:50am, just as a heavy shower moved in. The Meradalir webcam was in snow, but this was only on its hill. The closer langihryggurNV webcam was in the clear, and showed no snow at the tornado itself. It had formed just after the storm passed through. If you like the full frames, click on these pictures.
The tornado was also seen in the life webcams. This is shown in the video extract below. The tornado forms on the left, over the lava field. Initially it is hard to see. It quickly rotated up the side of the hill, and now it became clear, forming a funnel of cloud. Once it reached halfway up the hill, it fragmented and disappeared. The still frame had, by pure accident, caught it at its best.
How did this form? Why was it in a snowstorm? And why did it end so suddenly?
Before addressing these questions, what are tornadoes anyway? Think hurricane – but with the action packed into one funnel. They are amazingly easy to make: all it needs is some upward movement of air, and something that gives it a bit of spin. And just let it go. We have a tornado chamber at work. It is about 2 meters tall, and creates a vortex of air inside. Add a bit of oil vapour, and you see a beautiful tornado. I lend it once to a science show for primary school children. The teacher was talking about different kinds of clouds while behind her the chamber was being powered up. After a minute or so the tornado-in-a-box suddenly appeared and all the children went wide-eyed.
A tornado forms within a thunderstorm. The storm can contain a rotating vortex, powered by the different winds around it. This is especially if the storm is fast moving. The downdraft around the thunderstorm can take this vortex below the cloud base. Now we have a funnel cloud. If the funnel cloud touches the ground (most don’t) it is called a tornado. Let mayhem begin.
A devil develops differently. They start on the ground, as a bit of excessively warm air begins to rise. The rising bubble can pick up rotation from variations of the wind, either with height or on the ground. A devil starts on the ground and moves up, while a tornado begins in the storm and comes down.
But there is a grey zone: a devil may connect to a cloud above, and it that case it is both a devil and a tornado. This only happens if it touches the cloud base and that is rare: if that happens it probably used both the updraft and the downdraft, a true mix. I’ll leave it up to you whether to call this tornado devil or a devil of a tornado. Strictly speaking, if the devil does not get its spin from the cloud but from the wind lower down it is not a tornado, but this is hard to tell from the ground! So in practice, if it connects ground and cloud it is called a tornado even when strictly speaking it isn’t.
Warm air rises and cool air descends. This is a crucial part of the formation of tornadoes and devils. But the rising and falling is not automatic. To get a column of rising air, you need a fast change of temperature with height. Rising air cools – by about about 1C per 100 meters (less for humid air). The air only continues rising if the temperature of the surrounding air drops with height at least that fast. This works best if either the ground is very warm, or the upper air is very cold (or both). The temperature gradient can be very large near the ground when the ground is heated by the sun, but may be be much less a few meters up. So the devil may grow only to a few meters. At other times the temperature continues to drop fast with height and the air is called unstable: now the column continues to rise. The rising column can pick up rotation if the winds change with altitude, and becomes a funnel cloud reaching for the clouds above. The same can happen with the descending air coming from the cloud above and taking its rotation with it. The direction is different but the physics is the same.
The speed of rotation of tornadoes is enormous. Devils are a bit less vigorous. There is a lot of meteorology in here, but the principle is easy to understand. is something is rotating and it suddenly becomes smaller, the speed of rotation increases. The standard experiment is a victim siting on one those rotating office chairs, holding out their arms and given some spin. Now the victim pulls in the arms – and the chair spins up enough to make the person seasick. Dancers use this: in a pirouette, if you pull in your arms you go faster. It is called ‘conservation of angular momentum’ and it is a basic law of physics. As incoming wind is focussed on a small devil, the rotation it brings speeds up in the same way. In a devil, the wind may come in from 100 meters or so, and is focussed on something a meter across. The rotation increases by this factor of 100, so even an insignificant rotating movement of 10 centimeter per second can become a strong wind of 10 meters per second. In clouds, the circulation is faster. It also extends further: the circulation may measure kilometers across. So the amplification is higher and it gives much stronger winds. Tornadoes really are scary. Even Icelanders would not flock to watch a tornado. Tornado chasers are like rock climbers: admired, followed, but best not copied.
Water spouts form (the clue is in the name) over water. They can develop when the water is warm but the upper air cold, something that is most common in late summer. These are conditions that give rise to thunderstorms, and so water spouts may be true tornados: starting from the storm above and coming down to the water, connecting cloud and surface. Water spouts can also form from the water up, in which case they are water devils. True tornadoes are not that common over water: most water spouts come from rising convection and get their rotation from wind, not the storm above. Tornado may be strong enough to suck up water (and a few fish or frogs), but water spouts don’t normally do this. Forget about shark-infested tornadoes: this is one of the many things sharknado got wrong. However, a water spout can move over land and drop some of its animal load there. The song ‘raindrops keep falling on my head’ would not be the same if the rain included an occasional fish.
On land you may get dust devils forming above heated ground. They are land spouts, and they do not normally become tornadoes. The reason is that clouds stop the ground from heating, so dust devils do not easily form underneath thunderstorms. But they can grow large: on Mars they can become kilometers tall. And they can be dangerous. I know of one person who died when the driver of the car decided to drive through one.
But any ground heat will do. Forest fires are well known for forming ‘firenadoes’. The air over the fire rises, and the forest fire pulls in colder air from all around. This incoming air brings with it a bit of rotation, and the vortex, filled with burning fragments of the forest, rises up. It is not a tornado, though. They should be called fire devils.
Volcanoes also do it. Volcanic eruptions are much smaller than forest fires and their devils may not be as impressive. But air above a hot lava field will rise and if the wind over the lava field brings some rotation with it, it will form a rising vortex. It may even be strong enough to even pull up lava fragments from below. Again, they are not tornadoes as all their energy and rotation comes from below. These volcanadoes are really lava devils.
There have been several reports of such lava devils on the fields of Geldingadalir. They were most common on the hottest part of the lava. Here is nice video of one that tries to make its way to the centre of eruption. The air above the cone is rising, and this pulls in the air around it. The lava devil moves with this flow towards the cone, and probably picks up rotation from it as well.
The vortex can also form around the edges of the lava field, fed by the heat. The air flow can take it off the lava field and up the slopes of the hill (warm air, after all, rises). Now it becomes a real dust devil. There was one visible on Thursday, shortly after the tornado. In true Icelandic fashion it decided to take a good look at the local camera and show off for the world while obliterating the view of the lava fountain behind it.
As an aside, what makes a tornado or devil visible? In the videos you can see that they can sometimes move invisibly. There are two main possibilities. The low air pressure inside the vortex, combined with humid air, leads to condensation. The funnel cloud really is a funnel cloud: it forms a cloud. The other way to become visible is by what it picks up from the ground. This can be dust, or it can be larger debris. Sometimes dust devils have no dust, and become invisible. I once was sailing in a narrow canal, when a dust-less dust devil came of the fields, unnoticed and invisible. The boat suddenly was flat on the water. In a forest fire, the fire is what makes the fire devil visible. And above lava, tephra does the trick. In the video above, the lava devil becomes visible when it hits open lava but is difficult to see otherwise.
But let’s go back to our original tornado. Can we understand what happened?
It started just like the lava dust devil of the previous video. It formed on the lava field, moved to the side and up the hill. But the conditions were unusual. The upper air was very cold and a snow shower was rolling in. There was even a bit of rotation in the cloud: this is visible in one of Virtual’s beautiful time lapses. If you look at https://youtu.be/NrWWCT5Lu9k, towards the end around 11:40 you can see rotation in the cloud. The snow brought the cold with it, setting up a very large temperature gradient. The rising lava devil, aided by the very cold air above, met the downdraft from the cloud and took off. The rising bubble of low pressure in the cold air caused condensation and formed a cloud, which made it visible at heights where the dust could not reach. It went high enough (150 meters, perhaps) to touch the base of the cloud. And so it became a tornado. This is actually pretty rare for volcanic vortices. On the images you can distinguish both the funnel cloud above and the dust devil below.
But it did not last. The wind took the vortex up the slope of the hill, away from the lava. It lost its source of hot air on the ground. The updraft lost power as the temperature gradient was now much less steep than before. It quickly lost the connection with the downdraft from the cloud above, it survived for a few seconds more after its downgrade to a dust devil, but then disintegrated. But by then it had already become immortalized by the webcam.
The tornado (let’s call it that, even though this name is disputable) happened on the tail end of a snow storm. Snow tornadoes (really, snow devils) are known, but they are very rare. They have been seen mainly during snow storms over warm(ish) water. Wikipedia claims that only 6 snow devils have been photographed, all in Canada. I am not aware of any having been seen during a volcanic eruption. However, do correct me on this!
So this was a very unusual development in what was otherwise a fairly common event. Lava devils do not normally become tornadoes. They don’t normally form during a snow storm. This was, as seems typical for this eruption, exceptional.
The current eruption may be exceptional, it is also a small one. You would expect that anything this adorable toddler volcano can do, grown-up volcanoes can do better. And indeed, larger eruptions can have larger lava devils. There were some very impressive examples seen during the 2014 Holuhraun eruption. Here is one which was caught on infrared camera. It reached a kilometer high. There was a bit of cloud on the infrared camera, but not the kind that would have given any downdraft. And so this was a superb lava devil, but not a tornado. And though it had fire, it lacked snow. But it was a very good try.
And Hawai’i can do it too. How do you feel about a volcanic water spout? Sounds scary? One was seen in Hawai’i in 2008, formed in the cloud of steam where lava entered the ocean. It does connect to a cloud but this is the steam cloud of the lava ocean entry itself, so it does not qualify as a tornado. Our Gedlingadalir tornado remains unique.
Eruptions are both scary and beautiful. And it is not just the lava. It is also the atmosphere.
What are your stories of volcanic weather phenomena? Please us the comment box to share your knowledge and experience!
Albert, May 2021
And for a bit of volcanic atmosphere, I can strongly recommend the Meradalir camera.