At least 41 people have died in Sumatra due to flash floods and 'cold lava' from Mount Marapi, the island's most active volcano. Heavy rains on Saturday caused torrents of ash and rocks to flow down the volcano, inundating two districts and damaging over 100 homes and public facilities. Seventeen people remain missing. Survivors described fleeing from the 'cold lava' – a mix of volcanic material and pebbles. Rina Devina used her cellphone as a torch to escape, recounting how her neighbour's house was flattened, and four neighbours died. 'Cold lava' or 'lahar' typically has temperatures below 50°C and moves like a slurry, incorporating debris in its path. Rescuers found 19 bodies in Canduang village and nine in Tanah Datar district. Experts blame recurring natural disasters on excessive exploitation of natural resources and poor development practices. Recent events around Mount Marapi include a deadly eruption last December, flash floods in February, and eruptions in April which disrupted flights, closed roads, and forced over 11,000 evacuations.