Fatal Eruption Triggered a 'Volcanic Freeze'

Anak Krakatau before an eruption in December 2018 collapsed both its summit and southwest section into the sea, triggering a deadly tsunami. (Photo: feygraphy/Shutterstock)

On Dec. 22, 2018, the Anak Krakatoa volcano in Indonesia erupted in a violent display of ash and lava. The event was so powerful that it caused an underwater collapse of the southwest portion of the volcano, reducing its height by more than 700 feet and triggering a tsunami that killed more than 400 people along the coastlines of Sumatra and Java.

Over the next six days, as sea water came in contact with magma, an enormous cloud of ash and steam towering 16 to 18 kilometers high rose over the volcano. Researchers studying this massive plume using satellite imagery were astounded to learn that it contained a massive amount of atmospheric ice.

"The amazing aspect of this eruption was the tremendous amount of ice that was produced and maintained in the upper troposphere," lead author Andrew Prata said in a statement. "This process led to significant amounts of lightning. 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."

So how much ice are we talking? According to the research team, which published their work in the journal Nature Scientific Reports, it's estimated that the Anak Krakatoa eruption resulted in the formation of up to 10 million tons of ice.

A volcanic freezer

A volcanic plume, like this one over the Taal Volcano in the Philippines on Jan. 12, 2020, is capable of pushing a massive quantity of water vapor into the freezing cold of the upper atmosphere.
A volcanic plume, like this one over the Taal Volcano in the Philippines on January 2020, is capable of pushing a massive quantity of water vapor into the freezing cold of the upper atmosphere. (Photo: CherylRamalho/Shutterstock)

As the research team describes in their paper, the magma-seawater interactions resulted in a swift vertical release of water vapor that rose with the volcanic plume to a height of at least 18 kilometers. At this altitude, average temperatures hover around minus 80 degrees C (minus 112 F). The ice-rich cloud that formed created a lot of atmospheric instability that directly lead to the unusually high concentrations of lightning. Over the course of that week-long thunderstorm, more than 100,000 electrical discharges were observed coming from the plume.

The team says studies of volcanic lightning could prove beneficial to the aviation industry, where planes with ash-susceptible jet engines need to be wary of flying too close to plumes.

"So, essentially, the greater the flash rate, the higher the plume," Prata told the BBC. "This is something that could be important and useful for aviation."