Boulders rolling down mountains at high speed are a frightening sight—and even more frightening when they’re still glowing with volcanic heat.
Geochemist Harri Geiger from Albert-Ludwigs University in Germany is currently investigating the ongoing eruptions at Cumbre Vieja volcano on La Palma island in Spain. The volcano started to erupt on September 19, and it doesn’t seem to be interested in stopping any time soon. Geiger is part of an international research team coordinated by Universidad de 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 approximately 0.6 miles (1 kilometer) from the volcanic vent, he captured extraordinary video of a spallation lava bomb speeding down the slope. In an email, Geiger said he estimated that the lava bomb measured roughly 3 feet wide (1 meter) and weighed around half a ton.
The scientists approached the boulder once it stopped rolling, and they could feel the heat coming off it. Geiger said it was “still incandescent” and packing scorching temperatures in excess of 1,650 degrees Fahrenheit (900 degrees Celsius). Definitely a no-touch situation.
Spallation lava bombs, as you may have guessed, are ejected rocks produced by erupting volcanoes, and they’re quite dangerous. In 2018, a basketball-sized lava bomb smashed into a tour boat off the coast of Hawaii, injuring nearly two-dozen people and sending four to hospital.
Thankfully, no one was hurt by this particular 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 occasion, we can learn about ejection speed, trajectories, traveling distance, and general formation of spallation lava bombs,” he added.
Writing in the Landslide Blog, geologist Dave Petley from the University of Sheffield said the incident demonstrates the startling mobility of rolling boulders. “As the video shows, this was a boulder that was roughly spherical, and it was moving on a surface essentially devoid of obstructions and that had, until late in the sequence, a steady slope,” Petley wrote. “The resultant video is a remarkable record of the extreme mobility in these situations.”
For sure—had anyone been unfortunate enough to cross paths with this lava bomb while it was still rolling, it would’ve been curtains. Thankfully, Geiger and his colleagues avoided such a fate.