Jose Miguel Viñas Meteored Spain 5 min
Calbuco eruption
Lightning formation in the gigantic plume generated by the Calbuco volcano, in Chile, during its eruption in April 2015. Source: wallhere.com

More than three weeks have passed since the start of the volcanic eruption of Cumbre Vieja, on the island of La Palma, on September 19, and its activity continues to be unrestrained, gaining strength even in recent days. This circumstance does not invite us to think to an end near the eruptive process, although it is impossible to know. To the lava flows, the formation of a first lava platform or fajana (in Canarian slang), the changing volcanic plume and the fall of ash, a new element has been added: the formation of some volcanic rays!

The generation of electric shocks in volcanic eruptions is well documented, although the eruption of La Palma, as it behaved so far, was not a candidate for generating lightning, because these require greater explosiveness and larger plume dimensions. Although we are facing a Strombolian-type eruption (relatively modest), the peaks of activity recorded at certain times made possible the formation of the aforementioned rays, captured in some of the videos and photographs.

The physical process that gives rise to these volcanic rays is similar to the one that takes place inside storm clouds, where the violent friction between the hail and the supercooled water droplets which form in the middle and upper part of the cumulonimbus, allow the phenomenon of electrical induction, generating what is commonly called static charge (or electricity). The separation of charges – positive and negative – which takes place within the cloud, gives rise to a large potential difference, which eventually causes the electric shock.

The particular case of Cumbre Vieja

In the particular case of volcanoes, such as Cumbre Vieja, it is the friction between the pyroclasts that allows the formation of these flashes (from tiny ash to larger solid elements like lapilli or volcanic bombs) and also the friction with the drops of water present in the plume, that which generates electricity and also results in the formation of rays, both between two internal zones of the eruptive column itself, and between a point of this one and another located outside (or in in the air or on land). At the time when the volcanic plume of the eruption of La Palma has increased in size and the density of the elements that compose it is also higher, favorable conditions have been created for the generation of electric shocks.

Volcanic lightning
Lightning bolt photographed during the eruption of the Sakurajima volcano in southern Japan in January 2016. © Martin Rietze.

It is estimated that between 27 and 35% of volcanic eruptions that occur in the world generate lightning. Many of them are not visible to the naked eye due to the high opacity of the plume, although with special observation techniques it is possible to detect them. Some were photographed during the eruption of La Palma. If the eruptive process continues with an explosiveness equal to or greater than the current one, these will not be the last rays that we will be able to see. If nothing is observed anymore, this will be the sign of a certain decrease or stagnation in the emission of pyroclasts, which does not necessarily lead to less emission of lava from the various mouths of the volcano, which is what worries the most today because of the damage caused by the lava.

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