A crater is the big bowl-shaped hole at the top of a volcano. Karthala's crater is so enormous that you could fit a small town inside it. Sometimes steam and gases drift up from inside the crater, reminding everyone that the volcano is still alive underground. The word 'active' means a volcano can still erupt — and Karthala has erupted many times in the past.
Even though it is a volcano, Karthala is covered in thick green forest. Rare birds and plants live on its slopes. When it rains — which is often — the jungle gets very misty and mysterious. Hikers who reach the summit say the view of the Indian Ocean in every direction is incredible.
The rich volcanic soil that Karthala created over millions of years is one reason Comoros can grow so many wonderful plants. Farmers on the island say their soil is a gift from the volcano. Children sometimes draw Karthala as the 'heart' of their island because it sits right in the middle and can be seen from almost anywhere on Grande Comore.