Pyroclastic block flow from the September, 1976, eruption of La Soufrière volcano, Guadeloupe

A phreatic eruption occurred at 19:22 H from a new set of fissures on the southeast side of the summit dome. The steam jet from the narrow fissure incorporated accessory fragments of the existing dome that ranged in size from 3 m blocks down to particles of a few microns in diameter. No juvenile material was erupted. The branching 550 m pyroclastic block flow is surrounded by a zone of total destruction extending out to 900 m from the vent. An outer zone of directed blast projects to at least 1500 m. Profiles of the destructive cloud and the pyroclastic flow allow energy decay curves to be constructed for this eruption. From these curves the potential surface for flows associated with this type of phreatic eruption can be constructed as an initial step in developing a volcanic hazard map.