The paradox of Anak Krakatau, the Indonesian volcano that froze the atmosphere

27 February 2020

For six days, cloud-top temperatures hovered around -80ºC at heights of 18 km and triggered an impressive number of lightning flashes (100,000) .

Volcanic activity that occurs in tropical moist atmospheres can promote deep convection (heat transfer) and trigger volcanic thunderstorms. However, these phenomena are rarely observed to last continuously for more than a day.

An international team of researchers, led by Andrew Prata and Arnau Folch, from the Department of Computational Applications in Science and Engineering (CASE) at the Barcelona Supercomputing Center (BSC), has published a multidisciplinary study on an extreme case in Nature Scientific Reports.

On December 22 2018, the Indonesian volcano Anak Krakatau partially collapsed in the sea, and caused a deadly tsunami that killed more than 400 people. For six days, the convection process, sustained by heat generated from phreatomagmatic activity at Anak Krakatau volcano, caused the plume to reach heights of between 16 and 18 kilometers above sea level, which caused cloud-top temperatures to reach -80ºC. The steam and water vapour froze at high altitudes and generated up to ten million tons of ice.

"The amazing aspect of this eruption was the tremendous amount of ice that was produced and maintained in the upper troposphere. This process led to significant amounts of lighting. At one point the volcanic storm was generating 72 lightning flashes per minute, which is extremely rare compared to flash rates observed in meteorological thunderstorms. We were also able to relate the flash rate to the height of the plume and we are now planning a follow-up study to see how well this relationship holds for other cases such as the recent eruption of Taal volcano in the Philippines”, says Andrew Prata, lead author of this study.

Researchers' analysis indicate that rising steam currents and huge ice production explain the unprecedented stormy activity that was recorded during those six days: more than 100.00 lightning flashes.

For the study, data were collected from satellite and lightning observations, as well as those obtained thanks to the plume column modeling.

Caption: Photographs used with permission of the copyright owner Dicky Adam Sidiq/kumparan