CATASTROPHIC VOLCANIC COLLAPSE - RELATION TO HYDROTHERMAL PROCESSES

Catastrophic volcanic collapse, without precursory magmatic activity, is characteristic of many volcanic disasters. The extent and locations of hydrothermal discharges at Nevado del Ruiz volcano, Colombia, sugg est that at many volcanoes collapse may result from the interactions b etween hydrothermal fluids and the volcanic edifice. Rock dissolution and hydrothermal mineral alteration, combined with physical triggers s uch as earthquakes, can produce volcanic collapse. Hot spring water co mpositions, residence times, and flow paths through faults were used t o model potential collapse at Ruiz. Caldera dimensions, deposits, and alteration mineral volumes are consistent with parameters observed at other volcanoes.