1631 Eruption of Mt. VesuviusWhen it became active in 1631, Vesuvius had not experienced any significant eruptions since 1139, and had been quiet until the eve of the eruption. On 16 December 1631 between 0600 and 0700, following 24 hours of earthquake activity, a series of vents became active. The eruption rapidly gained in vigor as more vents opened on the flanks of the cone. A large eruption column rose 20 to 28 km in altitude, making the commencement of the eruption Plinian, and ash began to fall. During the forenoon hours, a continuous tremor began to be felt in Napoli, which did not cease until 8-10 hours later. Darkness fell over the entire area around the volcano, reaching Napoli at 1600.
After the initial Plinian phase, between 1900 and 2200 on 16 December, the eruption assumed a pulsating character with occasinal surges of sub-Plinian to Plinian activity. This was accompanied by strong earthquake activity. During the night of 16-17 December, earthquakes occurred at intervals of 1-15 minutes.
At about 0200 on 17 December, a heavy rainfall began which mobilized fallen ash to form lahars that caused damage and disruption to the N and NE.
At about 1100 on the 17th, after a strong and continuous series of earthquakes, a large mass of ash, gas and stones shot out of the crater and spilled down on all sides of the erupting cone, covering it almost completely. Reports at the time speak of the apparent disintegration, or liquefaction, of the mountain. The swift movement of the material resembled the flow of water, thus many reports actually speak of water that came from the volcano at that stage. In fact, the phenomenon was pyroclastic flow. Some 10 minutes after, a tsunami with runup heights of 2-5 yards hit the shores. The pyroclastic flow sped downward along the main ravines and valleys, destroying all vegetation and buildings in it's path and killing all living beings it's way. Where the pyroclastic flows entered the sea, small headlands were formed, extending up to 570 m from the former coast. This culminating phase of the eruption lasted for several hours.
After 1800 on17 December, there was a marked decrease in the strength of the activity. Further activity continued, but with declining intensity for the next several days.
When the main phase of the eruption was over, at least 3000 and maybe up to 6000 people were dead. In a daring manoeuvre, rescue teams saved thousands of survivors on 19 December who had been lucky to stay in areas spared by the pyroclastic flows. Besides the towns destroyed or damaged by the pyroclastic flows, other towns were severely stricken by heavy tephra falls, mostly on the NE and E sides of the volcano.