Mount Gamalama in the Molucca Islands sprang to life this month with a powerful, non-fatal eruption.
Government spokesman Yusuf Sunnya said Wednesday that days of heavy rains triggered flows of cold lava, rocks and other debris that slammed into villages near the volcano base Tuesday night.
He said four people were killed and more than a dozen others were hospitalized with injuries ranging from broken bones to head wounds.
Indonesia is a vast archipelago with millions of people living on mountains or near fertile flood plains. Seasonal downpours here often cause landslides.