MEDIUM-TERM ANOMALIES IN GROUNDWATER TEMPERATURE BEFORE 1991-1993 MT ETNA ERUPTION

In 1991, a hydrogeochemical surveillance program was set up on Mount E tna, involving periodic measurement of several chemico-physical parame ters in springs and wells along the eastern and southwestern flanks of the volcano. Significant increases in the temperature of these waters were observed some months before the 1991-1993 eruption. The energy r esponsable for this heat anomaly represents less than 0.3% of the tota l thermal energy released by the following eruption. The contribution from thermal conductivity of the rocks is negligible. The ascent of th e gases released from the magma determined the transfer of energy from the magma to the aquifers of Etna. The energy that produced the therm al anomaly in the groundwaters is one order of magnitude lesser than t he minimum estimated energy transported by the gases released from the erupted magma. Continuous monitoring of groundwater temperatures and other parameters may not only predict eruptions in the future, but als o permit an estimate of the volume of magma involved.