Whirlwinds come in variations. The weaker category is known as dust devils, and the range extends to full-blown tornadoes – and even hurricanes can in some ways be seen as an outsized members. What they have in common is whirls, winds and heat. You can find them anywhere, from the deserts of Mars to the shores of Earth. They are almost always powered by the Sun, our major source of heat. But there are exceptions.

Whirlwinds have been a fairly frequent feature of recent eruptions in Iceland, in the original Fagradalsfjall events) and Hawai’i, both from Kilauea and Mauna Loa. In these volcanic whirls, the winds are provided by the atmosphere, the heat by the eruption and the whirl by both working together. HVO calls them tephra devils or lava devils, depending on where they occur. They also use the local name puahiohio which really sounds just right: even the whirl is there in the syllabic repetition. At VC, we know better: we have long called them volcanado. (The only problem with this word is that it may be attacked by autocorrect – manual proofreading and brain-software override may be required.)

Many of our readers have interest in both eruptions and weather (it is a natural combination) and these volcanic whirls nicely combine them. There is one regret: they cannot form in vacuum. No volcanadoes on Io. Sorry, Jesper.

Whirling

How do these whirls get themselves into a twist? Two things are needed: rising air and deflected inflow.

Let’s first look at the rising air. We can see this (perhaps) in the shower. If you use a shower curtain, during the event the curtain is pulled inward, but mainly at the bottom. Clearly the air is trying to get in, to join you in the shower and as side benefit cool down your toes. It does so to replace air already with you in the shower. The shower makes the air nicely warm (and moist). This makes the air less dense (as it expands) and therefore the warm air begins to rise. It is this rise that creates space at the bottom for the colder air to flow in. The rise comes from the temperature gradient between the shower-heated air and the colder air above the shower. As the air rises, it cools and cooler air can carry less water vapour. So moisture from the shower condenses and turns back into water. This releases latent heat: it take energy to evaporate water and this energy is returned when it condenses. The latent heat adds warmth back into the rising air and keeps it rising.

In reality, a shower cubicle is a bit small for all this. There is only a meter or two of height available and physics prefers to think a bit bigger. If we replace the shower cubicle with a tropical ocean, everything works much better. The warm, moisture-laden air above the ocean rises many kilometers, in the process condensing out massive amounts of water, and the latent heat of this condensed water keeps the air rising. The clouds can now reach up to the top of the troposphere. A thunderstorm is born.

We still need to spin up the air. If we take the ocean as example, the spin is naturally there from the rotation of the Earth. Air rises up, and this pulls in air from elsewhere to replace the loss. But now there is a problem. The air has to come from elsewhere on the world. And this comes with a different speed. Why? Because air that feels stationary to us is in reality moving with the rotating earth. At 30 degree latitude, this is at a staggering 1400km/hr! But further from the equator, the speed of rotation is less. At 60 degrees, it is ‘only’ 800 km/hr, and at the pole it is not moving at all – while still going around in circles. But if air moves to a different latitudes, it still has its speed from the old latitude- so now it is going too fast – or too slow.

The picture shows the effect. As viewed by us, nailed to surface of the planet, the air is moving towards us – and is then deflected because of its wrong speed. It is this deflection that causes the air around the budding storm to spin. Air flows in, but does not get to the centre. It is going sideways. A brilliant demonstration of the effect is in the first two minutes of this video.

The end result is a spin – with the storm sitting at its centre. Now we have the storm caught in a twist. A tropical storm is brewing.

This actually doesn’t work near the equator. The reason is that rotation speed of the Earth barely changes until you get some 10-20 degrees away from the equator. And without a change, there is no spin. This is why you don’t see tropical storms in the tropics close to the equator! You get isolated (but severe) thunderstorms but no cyclones. The region is called the ‘doldrums’, the region of the oceans where the normal winds don’t blow and sailing ships could spend weeks trying to catch the winds from the individual storms. The area was feared by the sailors.

Once the air is rising and spinning, the storm is in business. If the water temperature is above around 27C, the latent heat from the water vapour can provide the power the storm needs: the storm is now self-sustaining, and may be on the way towards hurricane status. But although hurricanes and volcanoes can interact (as in the case of Pinatubo), this is not what this post is about. We need to think small again. It is time to get back into the shower.

For the rotation of the Earth to create a vortex, we need the size of a weather system. A few hundred kilometers across will do – but a few meters will not. So how does a small vortex form?

The answer is that in the shower, just as with large weather systems, we begin with the updraft. This removes air, and in response air from outside the cubicle rushes in to replace it. Bur for some reason, there is a deflection. It may be the overlap in the shower curtains which causes the inflow to take a side step. Or it may be a minute disturbance in a bath tub or sink. This deflection gives rise to rotation. A small deflection to the left will give clockwise rotation and to the right give anti-clockwise rotation. (This is not applicable to digital clocks, by the way.)

Shower cubicles do updrafts and a bit of circular air motion, but they do not make twisters or tornadoes. Bathtub sinks are a bit more effective in showing the effect. But it is possible to make a mini-tornado, or at least something that looks like it. All that is need is creating an updraft, introduce rotating air, and make the result visible. An example is shown below. We have a machine that does the same thing but is much smaller and which we can take away for demonstrations.

Visibility

But the twist is not easy to see. Air is largely invisible! Something needs to be added that is not transparent. In the machine above, condensation is used. The air inside is very moist. Polluting droplets are now introduced in the air. These droplets get taken up by the vortex, and they act as condensation nuclei for the moisture. Suddenly a mini-cloud forms, tracing the vortex nicely. The mini-vortex in the machine is not dangerous: velocities are low and something as simple as a sheet of paper will stop it. But it looks just like the right thing.

Tornadoes have the same problem of invisibility. If it is ‘just’ rotating air, even at speeds of 200 km/hr, the tornado can’t be seen. But at this speed, air pressure drops dramatically and just like in the tornado-in-a-box, condensation forms. This happens first near the cloud level, and therefore it seems as if the tornado is growing downward. The condensation cloud is what we see in a tornado.

If the tornado reaches ground level (many don’t), it has another option. Dust can be sucked up from the ground, and this makes the lower level of the tornado visible. But whereas the cloud disappears again when it get too far from the centre, dust remains visible. So the dust cloud may shows a larger area around the tornado than the clouds.

(A large tornado can suck up things much worse than dust. Let’s not go there – this is not an ‘I-love-a-catastrophe’ post.)

Devils

In between the tornado-in-a-box and the real tornados are the dust devils. The name seems appropriate: a whirlwind of dust suddenly whipped up from the ground, disappearing as quickly as it comes. At least, this is how they can appear, especially around towns. The whirlwind is moving along the ground, but when it reaches a dusty place (such as a road), suddenly they become visible. As the whirl moves off into the field, the dust settles down again and the whirl returns to moving invisibly. I remember being caught in one once when sailing along a narrow stretch of water. There was a bit of rustling in the nearby field and suddenly the boat was pushed flat on the water; seconds later the devil had moved off to the field on the opposite side, with only bending of grass to show its path and the boat righted itself again.

These dust devils can start very easily when a surface is heated enough to trigger uprising of the air. (It requires a high enough temperature contrast with the air higher up.) Once in existence, they can travel some distance until a disruption of the airflow or a lack of heat stops the circulation. The Martian dust devils are famous: they can reach heights of up to 10 km in Mars’ rarified atmosphere.

Waterspouts (or water devils) start a bit different, as water does not show heated patches. Some develop from a normal dust devil or tornado which moved from land to water. To form in-situ, the spout develops above, in the air. This can be from a warm layer of air above the (warm) water, but is often from a thunderstorm. Once it touches the water, the vortex sucks up water (and sometimes fish) and a waterspout is born. The water should be warm, and therefore waterspouts are most common over shallow water which heats up faster, and in Europe are generally seen in late summer.

The centre

As an aside, waterspouts, dust devils and tornadoes have no central eye. Only hurricanes have eyes. In hurricanes, the eye is a column of descending air, located within the violent uprising around it. It is an oasis of calm, surrounded by the torrential winds; the clouds are gone, the sun is shining and people come outside the assess the damage – too early. Immediately around the eye are the strongest winds, and thus once the eye passes, the hurricane wind suddenly are back with a vengeance – from the opposite direction as before. But only large hurricanes have such eyes. Smaller ones, tornadoes and devils, do have a centre where the wind is still, but no descending column.

The rotating winds can not reach the very centre. This is because of angular momentum. As a packet of rotating air moves close to the centre, it has to speed up. This can be considerable. Take a bit of air moving sideways at 1 m/s, 100 meters from the centre. As it reached 10 meters from the centre, it is now rotating at 10 m/s, and at 1 meter, 100 ms. (This ignores turbulence and friction – reality is sometimes not as exciting as it could be.) At the centre, it would need to go at infinite speed (in theory..). But the speed it can reach is limited by the available energy. The higher the energy (heat), the closer in the rotation can get and the faster it can go. It is all bout heat.

Firenado

So these are twisters. All that is needed, really, is air and heat. Obviously, more heat is better. Forest fires are a good example. They are hot, and they are large. The rising air above a forest fire can form cumulus clouds (pyrocumulonimbi). So naturally, they can also form twisters. Smaller ones are called fire devils, larger ones are known as fire twisters or firenadoes. A large one was seen during the bushfires in Canberra in 2003, the famous fires which destroyed the Mount Stromlo Observatory. It reached wind speeds over 200 km/hr and was caught on video.

(If you are wondering, the commentator does speak English. The tall spikes are on the goals on the nearby sports field.)

Volcanado

A volcanic eruption is also a major source of heat. Naturally, they too form twisters of varying sizes. As in forest fires, no thunderstorm is required: volcanoes can make those themselves quite nicely, but they are not essential. The lava is hot enough.

Here at VC, we saw a surprising dust devil during the early phase of the 2021 Geldingadalir eruption – a valley that no longer exists (we had to change the name fo the eruption several times) and an eruption that in various phases would continue until (at least) 2025. The surprise was to see a twister in Iceland (a country not known for its heat). There was one in 2018 which caused some damage – which was so unusual that it became world news. The second surprise was that it was seen during a snow storm.

This one had formed over the lava fields, and once formed, moved off the lava and there became visible by picking up dust, which in this case will have included some tephra.

Here is an even better one, from the same eruption but now forming at the heart of the action, above the freshly erupted lava. This is a true lavanado! The prosaic name lava twister is probably more appropriate, but lavanado has a nice ring to it.

Kilauea-nado

During the current Kilauea episodes, we have seen some nice phenomena, including fire jets and rainbows. We have also seen several twisters, which form in the wind rushing in towards the lava fountain. It is sidetracked by the cone, and ends up above the hot tephra. All ingredients for a tephra devil are now in place.

In the most recent episode, such a devil formed, and as usual, moved around a bit trying to find its feet. At first the rotation was fairly wide; I estimate the winds at some 15 m/s. But it lasted unusually long and became impressive. It contracted and rotated much faster, perhaps 40 m/s. (It is hard to estimate at this point.) Finally, it made a wrong move and disintegrated. Here is the view from the HVO V3 camera. (For V1, the twister was hiding all the time behind the lava fountain!) Get a coffee and take your time: the video lasts as long as the twister did.

It is interesting that this twister did not start above the fresh lava. The lava stream was perhaps too narrow. The rotation may have come from the shape of the surrounding caldera. If you are curious, I would recommend against going inside this one. The dust you see is burning hot tephra, the air is hot from the lava fountains and your survival time would be a battle between the heat and the sulphur. In fact, I would not recommend going inside a dust devil either, knowing of one person who did so out of curiosity, got his car overturned in one and his passenger killed. I just mention it.

Litla Rhút-nado

Have we seen better? Not often, I think. However, there was one in Iceland which was not as clear as this one, but in my opinion more spectacular.

It was during the July 2023 eruption at Litla Rhút, the last of the Fagradalsfjall events. The video shows a very large vortex which split up into several distinct vortices, all rotating around a common centre. It formed at the borderline of the lava flow. People who were watching the eruption rathe close to the lava flow, found themselves in the forming volcanado and as the twister strengthened, quickly dispersed to watch from a safer distance.

This is a volcanic version of the dance of the seven veils. What a world we live in.

And finally, the video from which the image at the top of this post is taken.

Albert, June 2026