Update of the Eruptive Activity at Mt. Etna: Multidisciplinary Evidence of Magma Refilling

Following the July-August 2001 flank eruption, Mt Etna volcano did not show any significant eruptive activity for several months. The new supply of fresh magma within the volcano was detected since December 2001 by gravimetry and especially by ground deformation, which showed a general trend of inflation of the whole volcano. The mass of gas-rich magma entering the system has been localised at 3-4 km b.s.l. The refilling of new magma caused growing stress within the volcanic pile. In turn, stress accumulation triggered sudden release and a diffuse seismicity in the upper crust (0 to 5 km depth) of the eastern and south-western flanks of the volcano. This behaviour has been observed on Etna a number of times, and most recently before the last flank eruption. It is commonly recorded several months before flank eruptions. Refilling of the shallow feeding system became evident in March 2002, when lithic ash was emitted from Bocca Nuova, one of the four summit craters of the volcano. Ash emission interested also NE-Crater in April, with ash becoming increasingly richer in the juvenile component. Between June and August, Strombolian activity resumed at NE-Crater, with bombs falling well outside the crater rim. Several pulses of gas-rich magma entering the system have been detected by COSPEC measurements of SO2 gas flux and FTIR measurements of the SO2/HCl ratio. Thermal surface measurements and structural surveys have shown the gradual but limited expansion of a field of fractures along a N-S direction between NE-Crater and SE-Crater for a total length of 4 km.