Vertical ground deformation on Mount Etna, 1975–1980
We present the results of repeated, precise leveling, between the years 1975 and 1980, of an 11-km traverse over the summit of Mount Etna, together with data from a network of dry tilt stations, measured between 1976 and 1980. Both methods demonstrate that little vertical movement occurs except on fresh lava flows, which show a consistent pattern of downward movement, interpreted as compaction and downhill sliding of lava after it has solidified. Other small vertical movements of a few centimetres, recorded on the leveling traverse, appear to be related to activity, particularly the eruptions from a new vent area on the southeast side of the summit in 1978 and 1979. Models of the recorded movement indicate that a small amount of magma was already stored in a dike below this eruption site as much as two years before it was erupted, although the bulk of the magma for these eruptions was not stored in the upper few kilometres of the volcano. The latter conclusion is supported by the dry tilt data, which are dominated by local movements of 10 to 20 microradians, with no consistent pattern of movement over the whole volcano.