Heavy rain in Indonesia over the weekend triggered flash flooding and sent torrents of cold lava coursing down a volcano and into towns, killing at least 37 people, officials said.

Hours of rain on Saturday night carried volcanic rock and ash down Mount Marapi, an active volcano on the island of Sumatra. Those mudslides are known as lahars in Indonesian, which translates to cold lava.

The rain also caused a nearby river to overflow.

Four areas on the western part of Sumatra were badly impacted, according to Indonesia’s disaster management agency. Nearly 200 houses were inundated and 159 people were evacuated, the agency said. Some of the flooding left mud deposits high enough to reach an adult’s calves, it said.

By Sunday night, 37 residents had been killed and another 17 were missing, the agency said.