A pyroclastic flow is a deadly, fast-moving mix of superhot gases and volcanic matter. Shimabara Mayor Ryuzaburo Furukawa noted in a speech that the volcano is still unstable. “A 100-million ...

YAMAGUCHI—An eruption of Mount Aso in Kumamoto Prefecture 90,000 years ago created a pyroclastic flow that traveled 170 kilometers north to the Sabagawa river here, the longest such distance ...