A REVIEW ON PHREATIC ERUPTIONS AND THEIR PRECURSORS

An analysis of the reported information on 132 historical phreatic events indicates that most of these ( 1 15) were not followed by a magmatic or phreatomagmatic eruption. Only in 18 cases precursory phenomena are reportedly lacking, whereas they are recognized for the majority (72) of the considered cases. These precursors have been analyzed as a function of the kind of phreatic event and of its possible triggering mechanism. Unfortunately, the quality of the available information is poor. However, data suggest that anomalous seismicity, ground deformation, changes in the output, chemistry and temperature of fumaroles and thermal springs are potential mid-term precursors, whereas seismic tremor is a common short-term precursor.