Volcanoes can be exciting and fascinating, but also very dangerous. Any kind of volcano is capable of creating harmful or deadly phenomena, whether during an eruption or a period of quiescence. Understanding what a volcano can do is the first step in mitigating volcanic hazards, but it is important to remember that even if scientists have studied a volcano for decades, they do not necessarily know everything it is capable of. Volcanoes are natural systems, and always have some element of unpredictability.