Written by | Ziv
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At the beginning of last month, Etna in Italy was seen spitting out "smoke rings" floating over Sicily.
These "smoke rings" take the form of white rings that dangle in the sky like small jellyfish.
Volcano: I'm not smoking! (Image source: Youtube-AP)
This "smoke ring" is called a volcanic vortex ring by volcanologists. Their main component is water vapour, mixed with other gases such as sulphur dioxide and carbon dioxide.
When a stream of hot air gushing out of a crater meets the cold air above, it causes water vapor to condense. They are colorless on their own, but when they condense to a certain extent, they turn white and we can see them.
According to a volcanologist, the rings come from a new opening in the southeast crater of Mount Etna. It first emitted wisps of glowing gas, and the next day began to produce a large number of rings.
(Image source: Youtube-AP)
It is not easy to form such a round and white volcanic vortex ring.
First of all, for a volcano to form such a perfect ring, the crater must be very round.
Weather conditions are also very important, as strong winds may not allow the formation of volcanic vortex rings, which can hang in the air for several minutes when the weather is very calm.
Smoke rings from Mount Etna have previously been observed (Image source: Reference [4])
What really puzzles people is where does the "hot gas" inside the volcano come from? And, why do some volcanoes breathe smoke rings and others cannot? Why is it that sometimes a volcano can spit out a lot of smoke rings and sometimes it doesn't? None of these questions are easy to answer.
It wasn't until last year (2023) that scientists finally simulated the process inside the volcano through computer models.
One of the scientists involved was Simona Scollo, a volcanologist from Italy, who said the formation mechanism of the volcanic vortex ring was a bit like that of a dolphin spitting bubbles.
（图片来源：YouTube-Raymond Holmes JR）
Dolphins go to the surface of the water to take a deep breath and then push the air out of their mouths or blowholes to form a ring under pressure.
Scientists have observed through thermal imaging cameras that in the first few minutes of the volcanic vortex ring, a stream of hot water vapor erupts from the crater at a very fast speed, and then the water vapor rolls outward along the rim of the crater, forming a tubular vortex ring.
The central part of the vortex ring is pushed out of the crater at a higher speed, dragging the vortex ring upwards. The vortex ring also becomes clearer and clearer as the water vapor condenses.
Computer simulation of the formation of vortex rings in a volcanic crater (Image source: Reference [4])
Through simulations, scientists believe that these air masses come from small bubbles in the magma deep in the volcanic passages. Small bubbles clump together to form larger, pressurized air masses that rise with the surrounding magma.
When the magma comes to the exit with bubbles, there are two situations, the first is that the top of the magma channel is open, and the other is that the top of the magma channel is blocked by the magma that has cooled and solidified before.
In the open passage, there is a pressure difference between the pressurized air mass inside the magma and the outer atmosphere, which will break through the thin layer of magma above and explode in small bursts. You can imagine the small bubbles that "poof" on the surface when cooking porridge.
Two different situations encountered by magma rising. The orange part of the image is magma, and the blue part is the air mass in the magma (Image source: Reference [4])
In the blocked passage, gas will accumulate under the solidified magma "plug", and if there are bubbles rising below, the air pressure will increase further. In this case, there may be a sudden explosion where the gas can push the plug up, or shatter it.
Both of these conditions at the top of the channel produce a very fast upward airflow that meets the conditions for the formation of the volcanic vortex ring. The first case is easier to understand, and in the second case, if the plug ruptures, it can make way for the escaping gas.
As dangerous as it sounds, scientists say there is no risk of eruption from volcanoes that spit smoke rings.
Mount Etna has erupted dozens of times, the most violent of which occurred in 1669. The lava flow destroyed more than a dozen villages under the hillside, and people dug a ditch above the village in an effort to divert the lava flow away, which may be the first time in history that humans have successfully diverted the lava flow.
Scene from the eruption of Mount Etna in 2013 (Image source: wiki)
However, the probability of an eruption of Mount Etna is not very high, and volcanologists say that the volcanic exhaust reduces the likelihood of an eruption, and if it does eventually erupt, it will only spew out a few puffs of ash, maybe a little magma, but it will not be destructive.
Therefore, people can safely admire the volcano's smoke rings from afar, after all, this phenomenon is not common.
Resources:
[1]https://www.straitstimes.com/world/europe/italy-s-mount-etna-recorded-blowing-smoke-rings-into-the-sky-in-rare-occurrence?close=true
[2]https://www.smithsonianmag.com/smart-news/mount-etna-puffs-smoke-rings-into-the-sky-180984120/
[3]https://www.nytimes.com/2024/04/09/world/europe/smoke-rings-italy-volcano.html?auth=login-google1tap&login=google1tap
[4]https://www.nature.com/articles/s41598-022-26435-0
[5]https://www.britannica.com/place/Mount-Etna
Source: Bringing Science Home
编辑:ArtistET