Volcanic rays, the spectacular phenomenon that only occurs in a third of eruptions

• TERESA GUERRERO

  @teresaguerrerof

  Madrid

Updated on Friday, 22october2021-10: 55

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Both during the day and at night, a volcanic eruption is one of the most impressive phenomena in nature. Its roars, rhythmic explosions, the tongues of fire that run down the slopes of a volcano and the emission of ash make up an overwhelming spectacle in itself, but which also has other phenomena associated with it, as we have seen during the last month on La Palma.

In addition to the earthquakes that occur in the area before and during the eruption to readjust the system, volcanic rays are sometimes generated, such as those that arise during some storms. In La Palma we have also seen them, by dropper of course, because as José Miguel Viñas, meteorologist for the portal

,

explains

,

: "Lightning does not occur in all eruptions. In general, in order for them to form, they have to be more explosive and form a plume larger than that which occurred during the first days on La Palma, "he said in a telephone conversation.

"As we are seeing since it erupted, there are times when it emits more material from one of its mouths and the plume reaches higher and has a higher density, and other times its explosiveness decreases and less material accumulates. It becomes larger when conditions are more favorable for an electric shock to occur, which is why most days the conditions are not in place for it to be generated, "adds the Meteored scientist.

Last October 11 was one of the days in which those favorable conditions occurred in the Cumbre Vieja volcano and rays such as the one shown in the photo that illustrates this news were formed:

. If there are not more, it will be a sign of a certain stagnation in the emission of pyroclasts, which does not necessarily entail a lower emission of lava from the different mouths of the volcano ", he points out.

"These rays are produced by the collision between the particles that make up the pyroclastic plume or tephra of the volcano (any volcanic material, including ash, lapilli and bombs / blocks, according to the classification we make by their size). However,

. This collision produces static electricity, which is what ends up generating the rays. Consequently, the formation of the rays and the production of static electricity is mainly the product of a frictional charge between particles ", explains Felipe Aguilera, a volcanologist at the Universidad Católica del Norte, in Chile.

Because the volcano not only emanates sulfurous materials, it also expels gases such as water vapor, so inside the plume there are both pyroclasts and water, says Viñas. The physical process that is behind is the same that occurs inside the storm clouds when it is charged with electricity, the only thing that changes is the materials that collide: "

the separation of both positive and negative charges within the cloud causes a potential difference just causing electric shock ,

"he explains.

It is similar to what happens when we generate static electricity, for example, by touching a metal surface on which electrical particles have accumulated that generate a potential difference with the finger and a spark jumps.

Or when you rub your hair with an object: "Friction ionizes the air."

According to the meteorologist, it is a well-documented phenomenon and it is estimated that lightning is generated in about a third of the world's volcanic eruptions.

Some are visible to the naked eye.

"In Chile they have been relatively frequent, especially in large-scale explosive eruptions such

as those observed in the early stages of the eruptions of the Calbuco and Cordón Caulle volcanoes, in 2015 and 2011, respectively, where at the time when the eruptive columns reached their highest point, these rays were clearly observed ", recalls Aguilera.

The rays generated in Mexican volcanoes such as Colima or Popocatepetl, the most studied and dangerous in the country, or in Sakurajima, in Japan, were also very spectacular.

You may have seen a photograph showing several rays at the same time.

However, Viñas points out that although several simultaneous rays can occur, the normal thing is that they arise individually.

The majority of images in which several rays are seen are of high exposure, they have been taken with the camera open for two minutes and three or four minutes can appear ".

Changes in the weather

Can volcanic eruptions alter the weather?

José Miguel Viñas points out that "a volcano has to expel huge amounts of material and reach above 10 or 20 kilometers in altitude so that it can have an effect on temperatures."

Historically, the eruption of the Indonesian volcano Tambora in 1815 (of magnitude 7 according to the volcanic explosiveness index, which has a scale of 0 to 8) is among those that have been documented the one that had the most effects on meteorology. It emitted enormous amounts of sulfur dioxide into the atmosphere and caused a drop in the average temperature of Europe of between two and three degrees that had serious consequences on food production, causing great famines.

But eruptions like those of La Palma (with an index of explosiveness 2), he

adds, can only lead to

some changes meteorological small -

scale and local: "For example,

violent winds like a kind of gale ", he points out.

The sulfur dioxide that emanates from the Cumbre Vieja volcano remains in lower areas of the atmosphere and "although it can alter the quality of the air in the area and part of the Canary Islands, its impact does not go further", according to the meteorologist .

"It can also happen that the wind itself displaces volcanic materials and these are incorporated into existing clouds, and the so-called acid rain occurs, but they are very local phenomena," he clarifies.

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