Posted on behalf of Roberta Kwok

The columns of ash and gas spouting from volcanoes may have something in common with storms that produce tornadoes: an internal vortex called a mesocyclone. Mesocyclones could explain why volcanic plumes sometimes spin, form sheaths of lightning, and give off waterspouts and dust devils, according to a new study in Nature.

The researchers based their study on both historical and new satellite data. An 1811 report from a sea captain in the Azores archipelago described a volcanic column that rotated “like an horizontal wheel” and issued lightning flashes and waterspouts. Such features, which have since been seen separately but never for one volcanic plume, are similar to those of tornado-producing storms containing mesocyclones, the team says.

Satellite images of Mount Pinatubo’s 1991 eruption in the Philippines showed that the top of the ash column, called an ‘umbrella’, became wavy around the edges. This suggests that a mesocyclone formed in the plume, causing it to rotate and distort the umbrella’s shape, the researchers say. An outer ring of lightning spotted around the 2008 eruption of the Mount Chaiten volcano in Chile could also be due to mesocyclones, which are thought to create similar lightning sheaths around thunderstorms called supercells.

Mount Redoubt (pictured), which erupted this week in Alaska, “might be powerful enough” to create mesocyclones, says co-author Pinaki Chakraborty of the University of Illinois at Urbana-Champaign (National Geographic). But Michelle Coombs, a geologist at the Alaska Volcano Observatory, says they have not seen any lightning or cyclones yet.

Scott Bryan, a vulcanologist at the University of Queensland, Australia, says the rotation phenomenon is “not surprising” because similar effects are seen in water and ocean currents. Mount Pinatubo is near the equator, he notes, and even stronger plume rotation might be seen at higher-latitude volcanoes (Cosmos).

Image: USGS