ABSTRACT
Mid-oceanic ridge volcanism is the most abundant type of volcanism on Earth yet it is hidden from view. The surfaces of all the terrestrial planets and some of the satellites of the Jovian planets show volcanic features that developed under diverse physical conditions. The environmental impact of volcanic activity is usually called volcanic risk. Risk maps ought to be used in planning the development of areas menaced by volcanic activity. The gentle effusive eruptions with volcanic explosivity indices of naught or one are called Hawaiian-type eruptions. Strombolian-type eruptions have frequent, small to moderate discharges of incandescent scoria and bombs. The coarse debris ejected from volcanoes follows ballistic trajectories, but most pyroclastic materials of smaller size and weight become entrained in volcanic eruption columns. The term ultraplinian-type eruption was first used to describe pyroclastic deposits from the ad 0186 eruption of the Taupo Volcanic Centre of North Island, New Zealand.
