The "Roof of Europe" - Mount Etna has recently become popular again!

The "Roof of Europe" - Mount Etna has recently become popular again!

Mount Etna is located in Catania Province, Sicily, Italy, at an altitude of 3,357 meters. It is a large monogenic basaltic stratovolcano. It is also the highest active volcano in Europe and is known as the "Roof of Europe". Mount Etna is also a typical urban volcano, with a large number of towns and residential settlements around the volcano. Recently, Mount Etna began to spew out regular white rings one after another, resembling the "smoke rings" exhaled when smoking. This volcanic activity phenomenon attracted the attention of local tourists and was widely reported by various media.

In fact, in our lives, similar phenomena like "blow smoke rings" are common, for example, smoke rings blown out by people smoking, bubble rings blown out by diving and swimming, bubble rings blown out by whales playing, vortex rings formed when mortars are fired, vortex rings formed by aircraft turbine engines, etc. This is a phenomenon called "vortex ring". In aerodynamics, this kind of ring is called a "vortex ring", and the "vortex ring" in water is called a "foam ring". When the foam ring moves in the water, the air inside the ring and the nearby water will rotate angularly, similar to a bracelet rolling on the arm.

Smoke rings from smoking (this picture comes from the Internet)

Foam rings spit out when diving and swimming (this picture comes from the Internet)

Whales playing with foam rings (photo from the Internet)

The vortex ring formed when the Houthi armed forces fired mortar shells (this picture comes from the Internet)

The formation of these "vortex rings" is inseparable from an important principle: Bernoulli's principle. This principle was proposed by Swiss fluid physicist Daniel Bernoulli in 1726. Its essence is the conservation of mechanical energy of ideal fluids. That is: under ideal conditions, at any cross-section of the same flow tube, the sum of the kinetic energy, potential energy and pressure potential energy of a unit volume of fluid is a constant. The most famous inference is: when flowing at equal heights, the greater the flow rate, the smaller the pressure. The pressure often mentioned in fluid mechanics actually refers to the pressure per unit area, which is the pressure in ordinary physics. The following is the expression of the Bernoulli equation:

(Reference: Zhao Changyou. Bernoulli equation and its application. Journal of Chizhou University, 2014, 28(6):2)

The popular explanation of Bernoulli's principle is as follows: take two pieces of paper and blow air between them. You will find that the paper will not float outwards, but will be squeezed together by a force. Because the air between the two pieces of paper flows fast when we blow it, the pressure is small, while the air outside the two pieces of paper does not flow and the pressure is large, so the strong air outside "presses" the two pieces of paper together. This is a popular explanation of the "Bernoulli principle". Bernoulli's principle can be applied to liquid flow, the flight principle of aircraft, chimney ventilation, turbines, etc. This also provides an easy-to-understand scientific explanation for some of the "vortex ring" phenomena we encounter in life.

The vent of Mount Etna spewing "smoke rings" (original video)

Seeing the essence through the phenomenon: Mount Etna in Italy is a large active volcano that is active all year round. As of 2023, there are three main vents in the volcanic cone, and the volcanic activity is mainly manifested in volcanic degassing, volcanic earthquakes, volcanic thermal anomalies, volcanic deformation, etc. The active crater quickly spews out high-temperature volcanic gases, volcanic ash (0.01-2 mm, particle size) and volcanic dust (<0.01mm, particle size). These substances are mixed with the surrounding air and water vapor, and form a "vortex ring" through the airflow and convection movement of the volcanic eruption, resulting in the phenomenon of the volcano spitting "smoke rings". The essence of Bernoulli's principle and equation is "the conservation of mechanical energy of ideal fluids". Therefore, the "smoke ring" spit out by Mount Etna is also one of the common manifestations of the energy release of the volcano.

The "smoke rings" emitted by Mount Etna in the early morning (original picture)

Mount Etna spews "smoke rings" in the afternoon (original picture)

Mount Etna spews "smoke rings" in the evening (original picture)

This issue of science popularization ends! Friends, see you next time!

This issue's authors: Xu Zhitao, Sun Liying, Ye Xiqing, Ailin P

Planning: Ye Xiqing Luca F Salvatore G

Editor: Sun Liying, Wu Chengzhi, Li Mengmeng

Review: Pan Xiaodong, Kang Jianhong, Song Yujia

Publicity: Gu Guohui, Guan Sheng, Zhu Daqing

Produced by: Institute of Volcanology, China Earthquake Administration, Jilin Province Earthquake Administration, Catania Etna Observatory, Argentina National Space Activities Commission, Argentina National Scientific and Technological Research Council