Volcanic mountains

Red-Hot ‘Lava Bomb’ rolling down volcanic slope seems to come straight from hell

The 3-foot-wide lava bomb rolls down the slope of the Cumbre Vieja volcano in La Palma, Spain.
GIF: Harri Geiger / Gizmodo

Rocks rolling down mountains at high speed are a frightening sight, and even more frightening when they are still glowing with volcanic heat.

Geochemist Harri Geiger from Albert-Ludwigs University in Germany is currently studying the eruptions in progress at the Cumbre Vieja volcano on the island of La Palma in Spain. The volcano started erupting on September 19 and it doesn’t look like it’s going to stop anytime soon. Geiger is part of an international research team coordinated by the University of Las Palmas de Gran Canaria. He and his colleagues were sampling recent ash in the volcano’s exclusion zone when the boulder made its dramatic appearance.

On October 27, as Geiger stood about 1 kilometer from the volcanic vent, he captured an extraordinary video of a spallation lava bomb rolling down the slope. In an email, Geiger said he estimated the lava bomb to be around 1 meter wide and weigh around half a ton.

Scientists approached the boulder after it stopped rolling, and they could feel the heat escaping from it. Geiger said it was “still glowing” with scorching temperatures above 1,650 degrees Fahrenheit (900 degrees Celsius). Definitely a no-contact situation.

It's a hot rock.

It’s a hot rock.
Photo: Harri geiger

As you may have guessed, spallation lava bombs are ejected rocks produced by erupting volcanoes, and they are quite dangerous. In 2018, a lava bomb the size of a basketball smashed in a tour boat off the coast of Hawaii, injuring nearly two dozen people and sending four to hospital.

Fortunately, no one was hurt by this lava bomb in La Palma, but I asked Geiger if he was worried about his safety. “No, we were at a safe distance, and we’ve seen other lava bombs before – we’re on the lookout at all times,” he replied. Naturally, Geiger saw this as a learning experience. “Seeing a ‘live’ bomb is a rare opportunity, we can learn more about the ejection speed, trajectories, distance traveled and general formation of spallation lava bombs,” he added.

Parts of the thrown rock were still hot, even after rolling down the slope.

Parts of the thrown rock were still hot, even after rolling down the slope.
Photo: Harri geiger

Writing in the Landslide Blog, geologist Dave Petley of the University of Sheffield noted the incident demonstrates the surprising mobility of rolling rocks. “As the video shows, it was a roughly spherical boulder, and it was moving on a surface that was essentially free of obstacles and which had, until the end of the sequence, a constant slope”, Petley wrote. “The resulting video is a remarkable record of extreme mobility in these situations.”

Of course, if someone had been unlucky enough to come across this lava bomb while it was still rolling, it would have been curtains. Fortunately, Geiger and his colleagues avoided such a fate.

Related: Nearly two dozen injured after lava bomb hits tour boat in Hawaii.