The recent volcanic eruption on the island of La Palma has put the phenomenon of volcanism in all its facets in the spotlight. Apart from getting acquainted with lava flows, and ash ejections, it was possible to observe impressive electrical discharges in the ash cloud above the volcano.
These volcanic Lightning is a very strange and relatively common phenomenon in eruptions. Moreover, the presence of volcanic Lightning can have a significant impact on the environment near the volcano where they occur.
Volcanic lightning and the origin of life
A very important aspect of this phenomenon is its possible involvement in the origin of life. Billions of years ago, volcanic activity on Earth was much greater than it is today. It is therefore certain that volcanic lightning was a very frequent and almost continuous phenomenon. Laboratory experiments and computer models have attempted to simulate these conditions.
And indeed, volcanic electrical discharges have been found to be the source of some of the molecules necessary to explain how life began. This makes the study of the production and consequences of volcanic lightning an area of great scientific interest.
How is volcanic lightning produced?
Lightning on volcanoes is produced by a variety of mechanisms, some of which are similar to those that occur in thunderclouds.
In the cloud, ice crystals and water droplets move at high speed and are at the mercy of strong winds. Friction and collisions between crystals and droplets result in electrical charges. When the accumulated charge reaches a certain value, lightning is generated.
Two basic mechanisms of electrical charge production have been proposed in volcanic eruptions. It is important to note that these mechanisms are not mutually exclusive and are probably acting simultaneously in eruptions.
Triboelectricity is the electricity generated by rubbing and scraping materials. It is the origin of the electricity that draws scraps of paper onto a comb after we rub them against our clothes. Or the clicking sounds we hear when we take off a garment in a dry environment. And it is also the mechanism that charges thunderclouds with electricity, as described above.
During the expulsion of gases and ash through the volcanic cone, strong currents are produced that cause a turbulence and a very intense friction of the expelled ash grains and lava.
This friction gives rise to the electric charge that, once it reaches a certain value, causes the electric discharge that we observe as lightning.
Scientists have been able to reproduce this phenomenon on a small scale. They expelled gases and ash at high pressure through a tube. As the gases exited the mouth of the tube, electric sparks – lightning – a few centimeters long were produced.
The second mechanism, Fractoelectric charging, results from the violent fracturing of the volcanic material as it emerges from the crater. These fractures and the pulverization also generate significant electrical charges. Again, when the amount of charge reaches a critical value, lightning strikes.
Both mechanisms, occur simultaneously. The contribution of each to the initiation of lightning depends on many factors, e.g., the:
- Composition of the lava
- The gases
- The ejection velocity
Clouds above the volcano
Sometimes the water vapor present, emitted from the volcano itself or present in the nearby atmosphere, creates large clouds above the volcanic cone. Processes can occur in these clouds that are almost identical to a thunder cloud. Therefore, lightning may also occur.
Volcanic lightning, like thunderstorm lightning, poses a potential hazard to people and animals in the vicinity of the eruption. Regardless of the mechanism that produces them, volcanic lightning is known to occur 20 and 30 km from the volcano. Therefore, precautions must be taken in the vicinity of an eruption.
Since the eruption itself is a major hazard, people usually leave the vicinity of the crater quickly, so lightning strikes are very rare.
Lightning disturbs the volcanic environment
In recent years, scientists have been able to identify some of the consequences of volcanic lightning. For example, ash floating on the volcano can be struck by lightning. Because of the very high temperatures that can be reached during these discharges (more than 20,000 ℃), the ashes melt. When it solidify again, it take the form of microscopic spheres.
These volcanic glass spheres can affect health if inhaled. They can also change the chemical properties of the particles themselves and the soil when they fall out of the air.
In addition, lightning is a major source of gases that are harmful to health. They produce nitrogen oxides (NOx) and ozone. NOx are the main pollutants in large cities. Ozone is a desirable gas for protection from ultraviolet light as long as it is at high altitudes, in the stratosphere. Its presence near the surface is not desirable and can also cause respiratory problems.
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