SO 2 flux measurements at Mount Etna (Sicily)

Since 1987, over 220 measurements of the SO 2 flux at Mount Etna have been carried out using a correlation spectrometer (COSPEC) with different measuring techniques (mainly with COSPEC mounted on a ground‐based vehicle). This paper reports and analyzes the data obtained between October 1987 and December 1991. During this period, three distinct time intervals characterized by particular SO 2 emission patterns were identified. The first interval (A) showed a mean SO 2 flux of 5500 t/d associated with relatively quiet summit crater eruptive activity. The second interval (B) included two eruptive periods, September–October 1989 and January–February 1990, associated with high fluxes reaching 10,000–25,000 t/d. The third interval (C) started in concert with a regional earthquake (December 13, 1990) and showed first a decrease and then an increase of SO 2 emissions before the onset of the major 1991–1993 flank eruption. Analysis of the data reveals a cyclic pattern to the SO 2 emissions over prolonged periods; a nearly constant supply of SO 2 from the volcano's main feeder system, especially evident in the long term; a two‐ to fivefold increase above mean flux values (from 10,000 to 25,000 t/d) when occurring with paroxysmal eruptive activity; and minimal flux values (∼1000 t/d) about 1 month prior to important eruptive events.