Precursors to eruptions of Popocatépetl Volcano, Mexico

volcanic eruptions can be preceded by changes in seismic and volcanomagnetic activity, chemi-cal composition of the gases and spring water and sometimes deformation. recognizing these signals of impending eruption and their timing is essential for adequate volcanic forecasting. the popocatépetl eruptions that began on december 21, 1994, were preceded by increa-ses in volcano-tectonic seismic events vts, increasing temperature and sulfate and chloride concentrations in the crater lake, decreasing ph as well as rising pco2 in the spring water. long period seismic events also increased before many of the eruptions and harmonic tremor episodes as well as negative magnetic anomalies precede dome formation and are linked to magma ascent. the vt cumulative seismic energy rose sharply preceding the main eruptions. clear precursors were detected before the december-january 2001 eruptions. two months before the eruption, negative magnetic anomalies correlated with increased seismicity, as well as small changes in the spring water were observed. additionally, a few days before the eruption, episodes of high amplitude tremor and high so2 flux were detected and together with the analysis of the rsam data were the bases for the adequate evaluation and forecasting of the 2000 eruption.