Sakurajima is an active volcano! Based on the Wikipedia – The volcanic activity still continues, dropping volcanic ash on the surroundings. Earlier eruptions built the white sand highlands in the region. The most recent eruption started on May 2, 2017. On September 13, 2016 a team of experts from Bristol University and the Sakurajima Volcano Research Centre in Japan suggested that the volcano could have a major eruption within 30 years.
It might look very dangerous but to be honest its not! In fact – I even had the chance to get some foot onsen overlooking the volcano while I was walking around the island 🙂