Indonesia’s Mount Semeru has unleashed a dangerous lahar, a fast-moving flow of rainwater mixed with volcanic debris, triggered by last week’s eruption. Authorities urge residents to avoid river corridors near Gladak Perak amid secondary explosions and evacuations. | Al Jazeera English

#Lahars are floods of water, rock, ash and debris that can happen during and after volcanic eruptions. Lahars can be immensely powerful, destroying bridges and buildings, and traveling great distances to bury vast areas in mud. If you live in a valley or on a flood plain near a volcano, you should be aware of the potential for lahars. If you hear a rumbling from upriver or notice the water levels rising, move to high ground immediately. This video is part of the #VolFilm volcano hazards series.