PADANG, Indonesia (AP) — Heavy rains and torrents of cold lava and mud flowing down a volcano’s slopes on Indonesia’s Sumatra island triggered flash floods that killed at least 15 people and injured several others, officials said Sunday.

Monsoon rains and a major mudslide from a cold lava flow on Mount Marapi caused a river to breach its banks and tear through mountainside villages in Agam and Tanah Datar districts in West Sumatra province just before midnight on Saturday. The floods swept away people and submerged more than 100 houses and buildings, National Disaster Management Agency spokesperson Abdul Muhari said.

Cold lava, also known as lahar, is a mixture of volcanic material and pebbles that flow down a volcano’s slopes in the rain.

By Sunday, rescuers had pulled out 11 bodies in the worst-hit village of Canduang and recovered four other bodies in the neighboring village of Sungai Pua, Muhari said.