Contemporary accounts of the violent eruption of Vesuvius in 1631 are
reviewed, and recorded events are correlated with resulting volcanic d
eposits. Field study of the deposits in the proximal area revealed the
presence of tephra falls, pyroclastic flows and lava, with subordinat
e surge deposits. A total volume of 1.1 km(3) (0.55 km(3) DRE) of phon
o-tephritic to phonolitic magma was ejected during 24 hours. The diffe
rent magma compositions correspond with a transition from a lower, whi
te, aphyric, highly vesiculated pumice (layer 1) to an upper, gray, cr
ystal-rich, poorly vesiculated pumice (layer 3), showing reverse gradi
ng. Isopach and isopleth maps of the tephra-falls have been constructe
d to determine changes in the eruptive style and temporal evolution of
the eruption column which reached a maximum height of 16 to 28 km. Th
e recorded column height variations show a change in the mass discharg
e rate (8.9 X 10(6) kg/s to 8.2 X 10(7) kg/s) and the occurrence of py
roclastic flows during the deposition of the weakly vesiculated, dense
pumice of the upper part of layer 3. Pyroclastic flows are crystal-ri
ch and show St, Vincent-type features; The explosive phase demolished
the upper part of the pre-existing cone, and debris flows invaded the
southern side of the volcano. In the afternoon of December 17, 1631 an
outbreak of lava flow from a southern lateral fracture system occurre
d, and effusion of lava continued up to midnight of December 18. Inter
mittent steam blasts continued to the end of December, when the erupti
on ended and Mount Vesuvius entered a solfataric phase. The earthquake
s that had marked both the pre-eruptive and eruptive phases, continued
, however, well into March 1632.