Mount Nyamulagira, 25km (16 miles) from the eastern city of Goma, erupted at dawn on Saturday, sending lava into the surrounding Virunga National Park.
About 40 endangered chimpanzees and other animals live in the area.
But the country’s famous critically endangered mountain gorillas are said to be safe as they live further east.
These are very special chimpanzees. I believe I’ve blogged about them elsewhere, but I’ll write new something about them soon.