How Volcanic Lightning Happened for Six Days

Volcanic lightning sounds pretty cool, right? How about  -80ºC cool?

A team of international researchers recently used Earth Networks Global Lightning Network (ENGLN) data to help study an extreme case of volcanic lightning.

The team, led by Andrew Prata and Arnau Folch from the Department of Computation Applications in Science and Engineering (CASE) at the Barcelona Supercomputing Center (BSC), has published a multidisciplinary study on the 2018 eruption of the Indonesian volcano Anak Krakatau.

You can skim through this post to learn the basics, but we highly recommend you read the full first detailed account of tropical deep convection triggered and sustained by magma-seawater interactions in Nature Scientific Reports.

Anak Krakatau 2018 Eruption

To understand the study, it’s important to understand what happened at Anak Krakatau in late December 2018.

Google map images of Anak Krakatau

After growing an average of 13 cm per week since the 1950s, Anak Krakatau erupted on December 22, 2018. The eruption sent the southwestern flank of the volcano into the Sunda Strait.

When this mass slid into the sea, it sent a 4m high wall of water around the Sunda Strait. This tsunami killed over 400 people throughout Sumatra and Java, becoming the deadliest eruption of the 21st century so far. It also injured 7,000 and displaced nearly 47,000.

The flank collapse didn’t just cause a tsunami. It also caused a thunderstorm that lasted six days.

Volcanic Thunderstorms at Anak Krakatau

Tropical thunderstorms can be triggered in several ways. While the more common methods include solar heating or convergence of surface winds, volcanic eruptions can also cause thunderstorms.

How do volcanic eruptions cause thunderstorms? An erupting volcano generates heat at the surface which initiates deep convection. Intense heating at the ground surface and entrainment of moist air generates positive buoyancy, which rapidly transports volcanic gases and ash particles up to the tropopause (boundary in the Earth’s atmosphere between the troposphere and stratosphere) and beyond.

Thunderstorm Timeline

Two thunderclouds with lightning and rain extending from one

Volcanically triggered deep convection lasted for six days over Anak Krakatau (Dec. 22 -28, 2018). Researchers identified four phases to the Anak Krakatau thunderstorm:

  • An initial explosive phase associated with the flank collapse
  • A waxing phase where convective development led to the formation of an anvil cloud (with cloud top temperatures reaching -80ºC)
  • A “volcanic thunderstorm” phase characterized by sustained deep convection and numerous lightning flashes
  • A waning phase where convection over the volcano finally subsided


How Volcanic Lightning Happened for Six Days

The continual source of heat (magma) and moisture (seawater) at the surface led to a sustained, positively buoyant plume and sustained ice production in the upper troposphere. This is why the thunderstorm lasted so long.

How Did We Help? 

From December 22-31, our global total lightning network (ENGLN) recorded an incredible 102,676 total lightning flashes (in-cloud + cloud-to-ground) near Anak Krakatau. With our data, researchers showed a strong correlation between lightning flash rates and satellite-derived plume heights for the first time.


If you want more detail, make sure you go read the full report!