Violent strombolian and subplinian eruptions at Vesuvius during post-1631 activity

On the basis of historical chronicles and field investigations the tephrost ratigraphic sequence of post-1631 activity of Vesuvius is reconstructed. It has been established that. during this period. in addition to numerous tot ally effusive eruptions and/or normal strombolian activity, 16 explosive ev ents produced well-traceable tephra deposits in the area outside the Mount Somma caldera. Ages of tephra beds were established on the basis of stratig raphic relationships with historical lava flows and comparison with chronic lers information. The dispersal and lithological characteristics of tephra deposits combined with description of explosive activity lead to the identi fication of three styles: (a) periods of violent strombolian activity; (b) violent strombolian eruptions; and (c) subplinian eruptions. Violent stromb olian eruptions and periods of discrete activity are characterized by the f ormation of lapilli falls from eruptive columns only some kilometers high. Subplinian eruptions are defined on the basis of their lapilli fall volumes which is of the order of 10(7) m(3). on eruptive column heights of approxi mately 10 km, bt higher than 1.5. and mass discharged rate values not lower than 10(6) kg/s. During the first century of activity after the 1631 erupt ion. two periods of violent strombolian activity occurred at Vesuvius (1682 -1707 and 1707-1719) preceded, and followed, by a series of violent strombo lian eruptions (1660, 1682, 1707, 1723, 1730, 1790, 1872). Between 1730 and 1779 a relevant change in the eruptive style of Vesuvius occurred by an in crease in the explosivity of the eruptions. During the past two centuries o f activity, only a few eruptions reached subplinian magnitude and only five eruptions had a phreatomagmatic phase (1779, 1794, 1822, 1906, 1944). Ther efore, the previously accepted model of cyclic activity, in which each cycl e is closed by an important explosive eruption with phreatomagmatic charact eristics, is unfounded. The tephrostratigraphy of the 1906 eruption propose d in this work differs substantially from some previous reconstructions, on which the basis for the modeling of Vesuvius' behavior in this time span w as formed.