Nevado del Ruiz volcano (Colombia): pre-eruption observations and the November 13, 1985 catastrophic event
An Italian volcanological mission visited the Nevado del Ruiz volcano a few weeks before the catastrophic eruption of November 13, 1985. Fumarolic gases of Arenas crater were sampled and analysed and proved to be basically a mixture of CO 2 and SO 2, indicative of a direct magmatic input to the surface environment. The existence of high lahar risk was stressed in the mission's report delivered on October 22, 1985 and some simple preparedness measures were recommended to local authorities. Some observations of the November 13 pyroclastic sequence on the summit glacier suggest that the climax of the ice melting occurred before the beginning of the sustained column (Plinian phase) and was related to the early emplacement of pyroclastic flows.