Why are noises generated during lightning?


Volcanic lightning and volcanic thunderstorms

Volcanic thunderstorms occur particularly in the eruption clouds of volcanic and Plinian volcanic eruptions. Occasionally volcanic lightning flashes also occur during smaller eruptions: on Sakura-jima, Anak Krakatau and Mount Etna I have occasionally been able to observe individual lightning bolts in the ash clouds of strombolian eruptions. The lightning bolts mostly formed between 5 and 10 seconds after the explosion. At the Sinabung lightning manifested itself in the rapidly rising ash clouds of pyroclastic currents.

Images of volcanic lightning

Volcanic lightning at Colima.

Volcanic thunderstorm on Sakurajima.

Volcanic thunderstorm on Sinabung.

The initial speed of the rising tephra seems to be decisive for the occurrence of volcanic lightning, because at least with the Strombolian eruptions the lightning occurred mainly when the eruption cloud rose unusually fast, so the gas pressure of the explosion was particularly high. The friction between the ash grains creates an electrical voltage field that is discharged in the lightning bolts. Another factor could be the grain size of the volcanic ash. The finer the ash, the greater the lightning potential. During the day, the electrical discharges in an eruption cloud can hardly be seen, but they can be heard! I can only faintly remember the rumbling of thunderstorms, what stuck in my memory is the crackling sound of static electricity that makes the hair on the back of your neck stand up.

However, scientific studies of this natural phenomenon are very rare, because even with large eruptions, lightning does not necessarily occur. So it seems to depend on the atmospheric conditions, whether volcanic thunderstorms occur or not. Ronald Thomas from the NMT in Socorro investigated this question in January 2006 on Mount St. Augustine in Alaska and installed two measuring devices 100 km from the volcano. These recorded the direction of the radio wave emissions caused by electrical discharges. On January 28, the Augustine erupted and produced 4 major eruptions, of which clouds of ash rose several kilometers high. The detectors registered two phases of electrical discharges in the first eruption cloud. First of all, at the beginning of the eruption, countless micro-discharges were registered directly above the crater, culminating in a few very high-energy flashes. From this, the researchers concluded that the hot tephra already had a strong positive charge in the extraction slot.

During a second lightning phase, which began about 3 minutes after the first explosion, Thomas registered over 300 lightning bolts emanating from the eruption cloud. The longest lightning bolt was 15 km long. This volcanic thunderstorm was similar to a conventional one. In addition to the residual electrical charge of the tephra from the initial stage of the eruption, electrical charges built up in the ash cloud as a result of the collision of the ash particles. Something similar happens in normal thunderstorms in clouds when ice crystals collide.

In addition, the measuring devices registered an approx. 4 km long lightning bolt that shot straight up into the sky from the summit of the volcano and then bent horizontally into the drifting ash cloud. This leads to the conclusion that negative charges built up at the summit, which discharged into a positively charged ash cloud.

Volcanic lightning also plays a role in a theory of the origins of life on earth. The processes in which organic molecules are created from inorganic matter have meanwhile been partly modeled in laboratory tests. As early as 1953, the chemists Miller and Urey demonstrated in their "primordial soup experiment" that amino acids and fatty acids are formed from ammonia, hydrogen and methane when they are supplied with energy in the form of lightning bolts. However, this only works under the influence of a reducing environment, i.e. an atmosphere without free oxygen. However, the sensitive building blocks of life quickly fall apart under such conditions. One thing is necessary for them to remain stable: water!

Conditions such as are necessary for the creation of life existed only in the vicinity of primeval volcanoes. Not only were the required inorganic compounds concentrated there, but the necessary reducing environment also prevailed. In addition, the volcanoes spewed out water in the form of water vapor, which quickly condensed on fine particles. When energy is supplied in the form of lightning bolts, which are often associated with volcanic eruptions, stable organic molecules are actually formed under these conditions.

As of 2016

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