A rocky avalanche that then triggered a massive mudslide struck the town of Bondo, Switzerland, near the Italian border on Wednesday.
The disaster unfolded quickly and with force. An estimated 140 million cubic feet of debris came crashing down the mountain. A senior Swiss police official told the Associated Press that the impact registered 3.0 on the Richter scale. Buildings were ripped apart by the fall, and nearly 100 people had to be evacuated. (See how a landslide triggered a deadly tsunami in Greenland.)
Several videos emerged from the disaster. The first showed the initially rocky avalanche as it broke from the mountainside. Rocks and mud can be seen cascading down, sending blooms of debris into the air.
Dave Petley is the pro-vice-chancellor at the University of Sheffield in the U.K. He wrote about the rock avalanche near Bondo for his site, The Landslide Blog. He hypothesized that the force created a shockwave seen at the bottom of the slope where the debris made impact.
What caused this avalanche is still to be determined. They can form through a number of factors, both human-influenced and natural. Heavy snowfall as well as melting snow have both been known to trigger them. In the days leading up to the slide, the weather in the region was reportedly normal.
According to Switzerland's National Platform for Natural Hazards, the country's temperatures and rainfall have both increased over the past century. Many glaciers are retreating as a result. But because a number of factors contribute to avalanches, the exact cause of the one that occurred in Bondo cannot yet be stated. Many landslides occur after years of pressure building on a slope that cascades down after reaching its limit.
While the rocky avalanche presented a daunting image, much of the resulting destruction came from the mudslide that followed, lower down the mountain. The lava-like flow of mud, which stretched more than three miles, can be seen overwhelming the small Swiss town's infrastructure. Mudslides can resemble flash floods in their speed and flow. (Read about what caused a mudslide in Sierra Leone that left hundreds dead.)
At least eight people are still reported missing. As of Friday morning, Swiss paper Le Temps reported that hope of finding the missing eight alive is diminishing.