The Indian Express (Delhi Edition)
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When does a volcano spout volcanic vortex rings, and what is it about Mount Etna and this activity?
SINCE LAST week, Mount Etna, the largest volcano in Europe, and among the world’s most active and iconic volcanoes, has been sending up almost perfect rings of smoke into the air that scientists refer to as volcanic vortex rings.
Mount Etna volcano
Mount Etna, or simply Etna, isa Unesco world heritage site on the east coast of Sicily, the largest island in the Mediterranean Sea, lying just off the toe of the Italian “boot”. Etna’s summit has five craters, which are responsible for most of its eruptions; there are also “flank” eruptions that occur out of 300-odd vents of varying sizes along the slopes.
Etna’s eruptive history can be traced back 500,000 years. Since 1600, at least 60 flank eruptions and many more summit eruptions have taken place. in recent years, summit eruptions have occurred in 2006, 2007-08, on two occasions in 2012, in 2018, and 2021; flank eruptions have taken place in 2001, 2002-03, 2004-05, and 2008-09.
Volcanic vortex rings
Vortex rings are generated when gas, predominantly water vapour, is released rapidly through a vent in the crater. The vent that has opened up in Etna’s crater is almost perfectly circular, so the rings that have been seen above the mountain since April 2 are also circular.
Boris Behncke, a volcanologist based in Catania, a port city at the foot of Etna, had said in a post on X in July 2023 that the rings “are produced by the explosion of gas bubbles within a narrow conduit, which shoots the gas at high speed toward the surface. Attrition along the conduit walls slows the movement of the gas jet, relative to the center of the conduit”.
A scientific paper published in february 2023 noted that the phenomenon was first observed at Etna and Vesuvius in Italy in 1724, and has been documented in an engraved plate from 1755. In more recent times, volcanic vortex rings have been observed at several other spots, including Re doubt in alaska, tung ur ahua in ecuador, etc. (‘Dynamics of Volcanic Vortex Rings’: Scollo et al., Scientific Reports)
Simona Scollo, a volcanologist at the INGV Etna Observatory in Catania, Sicily and a co-author of the 2023 study, told The New York Times that volcanic smoke rings were produced in the same way as dolphins blow bubble rings.
“They (dolphins) compress the water in their mouths... using their tongue they push it out of their mouths and create such a pressure that it forms a ring,” Scollo said.
According to the report, the rings can remain in the air for up to 10 minutes, but tend to quickly disintegrate if conditions are windy and turbulent.
Etna and the rings
Behncke said on Facebook this month that “no volcano on Earth produces as many vapour rings as Etna”. In July 2023, Behncke had reported seeing “dozens of gas rings every day” above Etna.
Behncke said: “…Now Etna is breaking all previous records. In the late afternoon of April 2, 2024, a small mouth opened on the northeastern edge of the Southeast Crater, producing gusts of incandescent gas. The next morning it was obvious that these blows were producing an impressive amount of steam rings, and the business has since been going on, having already issued hundreds if not thousands of these pretty rings.”
This activity does not, however, mean Etna is going to erupt in a particularly spectacular way. In fact, the activity from the new vent was slowing down.