One of the leading killers during explosive volcanic eruptions is a family of superheated gas, ash, and debris known as pyroclastic density currents. These tumbling, turbulent paroxysms rush downslope at temperatures as high as 1,300°F and at speeds often exceeding 50 miles an hour.
Learning how these hard-to-predict and hard-to-escape currents work is paramount to protecting the communities that live in their potential paths. For instance, many pyroclastic density currents travel further than they should based on our present understanding of physics, with their long reach challenging scientists’ understanding of how they operate.
Now, researchers may have found out why: A new study published today in Nature Geoscience reports that a member of this family, the pyroclastic flow, is able to move so fast and so far because it can glide along on a cushion of air. These concentrated mixtures of fairly fine ash and gas take advantage of this air-lubricated base, which reduces friction during their race down slope, over horizontal surfaces and, if they have enough momentum, even uphill.