Eruption of 1631
Pre- eruption. Before the eruption Mount Vesuvius was covered by dense vegetation also inside the crater. The Gran Cone was high about 1187m, 55m more than the Monte Somma, crater with a diameter of 480m and a depth of about 250m. There geysers along the edge and bottom of the Great Cone, whereas in the Hall of Somma were small ponds of thermal and mineral waters.
In June 1631 the residents around the volcano began to experience tremors and earthquakes, in August, we began to see, on the north side of the cone, increased fumarolic activity. In December the pre-eruptive phase began, with some earthquakes felt in the Vesuvian area and a gradual lifting of the crater bottom; a few days before the eruption it reached the hem. The temperature rose and lakes thermal inside the caldera disappeared.
On 15 December 1631, at 19, the earthquakes began to be felt in Naples and in the night they intensified in number and energy, in conjunction with the formation of eruptive fractures in the Atrium and on the walls of the Great Cone.
Eruptive column. At dawn on December 16, 1631 eruption began, a tremendous explosion caused a giant cloud, the convective eruption column, which pushed by high pressure inside the volcano reached about 13 km altitude ("... someone said that after measuring it, that it rose to more than 30 miles high ... "[Braccini, 1632]). The cloud was at first of a light color and then, when fully raised, darker due to the high concentration of particles [Rosi et al., 1993] ("... not much that stood changing thus form became a huge cloud, which is not already white as before, but rather black, rising to wonder and passing far with infinite veementa the first region of the air ... "[Giuliani, 1632]).
Ash fallout. The roar of the eruption were felt also, according to the reports, in Marche, Umbria, Abruzzo, Calabria and Puglia regions ("In the valley of Spoleto to Perugia and from all the mountains of Norcia for an hour continued to be felt, barrel and rumble like artillery, anyone thinking it was somewhere near the place and no one could understand where it was occurring. "[Frat'Angelo de Eugeni, 1631]). Many heavy ash and cinder blocks began to fall around the volcano, up to several kilometers away, mainly in the areas north and northeast of Somma ("... Not only ashes, but also stones falling down from the sky like fiery waste manufacturers who quarried from the forges, as big as a hand and even more ... "[De Contreras, 1633]).
Collapse of the eruption column and pyroclastic flows. Around 10 am on December 17, 1631 a violent earthquake was felt, in conjunction with the collapse of the central crater that ended the phase or sustained Plinian column ("... there came a final, but more than all other fatal earthquake, which made vacillar like reeds each building and quite a lot collapsed to the ground... "[Sant'Agata in Palomba, 1881]).
There was a passage from an eruption column to a collapsing column, descending quickly down the volcano's slopes, generated pyroclastic flows that destroyed vegetation and objects, causing many casualties among the population ("... the fire was huge and growing at double time taking two directions; a part went up and into the sky so fast that soon passed away all high clouds, and dilated in the foot down the mountain in the shape of a river ... "[" Letter "of Manzo reported in: Riccio , 1883]. Pyroclastic flow deposits are found mainly in Boscoreale and, to a lesser extent in Torre del Greco and San Sebastiano al Vesuvio.
The collapse and the intense fracturing, with the emptying of the magma conduit, caused further decompression of the volcanic system, taking water from aquifers or from the sea in the ducts. The magma-water interaction brought about strong phreatomagmatic explosions throughout the day on 17 December and the 18th of December.
Mudflows (lahars). The large amount of water vapor released into the atmosphere and the nucleus of condensation formed by the ash particles unleashed torrential rains. In a short time, large portions of the pyroclastic blanket that covered Mount Somma and the cone of Vesuvius were activated again, generating ruinous mudslides (Lahar) along the slopes, due to floods up to 10km away from the volcano, particularly in the areas in north and northeast.