Since 1987, over 220 measurements of the SO2 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 SO2 emission patterns were identified. The first interval (A) showed a mean SO2 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 SO2 emissions before the onset of the major 1991–1993 flank eruption. Analysis of the data reveals a cyclic pattern to the SO2 emissions over prolonged periods; a nearly constant supply of SO2 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.
The event chronology of the 1983 Etna eruption is summarized, and the development of a compound lava field at different time intervals during the eruption is described as observed from aerial photographs.The morphological evolution of the lava fronts has been compared with effusion rate and principal modifications occurring in the main channel, and it has been inferred that the development of the lava flow units is related to the formation of lava tunnels and particularly of lava channels. The total volume of lava emitted has been estimated to be 100+20×106 m 3 according to two different methods. Finally, the comparison with previous historical eruptive activity shows a good correlation to other quiet eruptions.
Summary
Mean directions of magnetization from Mounts Arso (Ischia Island, Gulf of Naples), Etna and Vesuvius lava flows have been determined based on very stringent linearity criteria. These indicate that, regardless of the source volcano, the lava flow mean directions of magnetization form a common path, the SISVC (Southern Italy Secular Variation Curve). This curve enables a reassessment of the age of eruption of several lavas. A date of AD 1169 is demonstrated to be the only possible time of emplacement for one Etna lava flow previously assigned an age of AD 812/1169. It is also demonstrated that two Etna lava flows, which, according to the literature, were emplaced in AD 1536 and 1595 respectively, were actually both emplaced around AD 1037. Three other Etna lava flows, one ascribed to AD 1566 and two to AD 1595, were actually emplaced between AD 1169 and 1284/85. The same time window also holds for a Vesuvius lava flow for which only an upper time threshold was previously available. Only one of the studied flows needs further sampling and analysis to verify whether this flow has been affected by a complete remagnetization or has an erroneous historical dating. The applied procedure seems to be the most appropriate one in carrying out palaeomagnetic surveys of lava flows, as also suggested by the broad agreement with some 17th and 19th century measurements of the geomagnetic field in Rome, relocated to Etna, and is likely to improve knowledge of past history of a volcano significantly.
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