Vesuvius 1906: a case study of a paroxysmal eruption and its relation to eruption cycles

Abstract

The April 1906 effusive and explosive paroxysm of Vesuvius concluded a 34-year-long cycle, characterized by prevalent effusive activity. The eruption began on 4 April 1906 with limited summit explosions that preceded the lava effusion from vents between 1200 and 600 m a.s.l. on the southern flank of the cone. In the late evening of April 7 the explosive strombolian activity evolved to the paroxysmal phase with the formation of two-km-high lava fountains that continued with varying intensity for about 4 hours. This phase generated a moderately dispersed tephra-fall deposit consisting of strongly vesiculated black scoriae and rare lithic clasts. When the lava fountaining ended, the subterminal effusive activity increased On 8 April, at 12:37 a.m. a violent earthquake preceded a change in the eruptive style with the ejection of both strongly fragmented, incandescent, vesiculated juvenile material and lithic fragments generated from the violent cone demolition During this phase the eruptive columns progressively drifted toward the north-northeast causing severe damage to the town of Ottaviano. At 4 p.m. another drastic change in the eruptive style occurred, with the formation of a giant sustained gas jet with a low concentration of dense blocky hydrated glass (the intermediate gas phase reported by Perret). This phase was generated by a powerful interaction of phreatic water with a small amount of degassed magma. The paroxysmal eruption ended with a low column generated by the degassing of the hydrothermal system (dark ash phase of Perret). This last episode deposited only a thin ash layer constituted by non-vesiculated ash particles.