Monte Nuovo seen from Pozzuoli harbor, May 1996

Campi Flegrei caldera, Italy

The 1538 Monte Nuovo eruption

On 29 Sep 1538, an eruption began which built the cone Mte. Nuovo (123 m) during one week. A modern summary of the eruption has been given by Di Vito et al. (1987), also containing citations from contemporary reports.

The eruption was preceded by a period of uplift in the area that ended a long (at least 1400 years) period of subsidence. Although the beginning of this uplift is not precisely known, the emergence of new land from places formerly occupied by the sea was first noted by residents of Pozzuoli in 1502. This uplift was, from the early 1530's, accompanied by unusual seismicity that reached a first climax in the spring of 1534. Still more earthquakes were felt in the area during the following 4 years, dramatically increasing during Sep 1538. On the 28th, about 20 tremors were felt between daybreak and nightfall.

Meanwhile, other dramatic changes were taking place. In the area between M. Barbaro, Lake Averno and the coast there was a remarkable uplift of the ground, displacing the coast by several hundred m. Some sources tell of an uplift amounting to about 7 m (a value that is not exaggerated: uplift by up to 6 m occurred during the night preceding the 1994 eruption of Rabaul, Papua New Guinea; volcano 0502-14).

At about 2000 on 29 Sep, a crack opened in the area of maximum uplift, next to the ancient (Roman) settlement of Tripergole. According to contemporary sources, the newly opened vent emitted vast amounts of pumice, fire, and black and white "smoke". Much of the ejecta fell as muddy ash, indicating that water played a significant role in the initial stages of the eruption.

Studies of the deposits revealed a sequence of rapidly alternating eruptive styles reflecting varying degrees of magma-water interactions (Di Vito et al. 1987). The basal Mte. Nuovo deposits are flow (surge) deposits. That the flows were relatively cool is indicated by the lack of welding, degassing pipes and signs of plastic deformation. The flows (or surges) did not flow beyond a few hundred m from the vent. When entering an inlet several hundered m to the W (that was then filled by volcaniclastics with Lake Averno remaining at its N end), the surges obviously did not cause large waves; an ancient temple standing on the shore was not affected by any wave damage.

Vigorous activity of this kind occurred during the first 24 h of the eruption, followed by 2 days of lesser activity. Ash from the initial activity fell over a wide area, as far as Apulia and Calabria, and larger fragments fell even in the Vesuvian region.

The bulk of the new cone was probably built during the first 24 h or little more, and when first climbed on 2 Oct, some kind of "boiling" was observed within the crater. This activity was interpreted by Di Vito et al. (1987) as Strombolian (maybe fountaining from a lava lake).

Activity increased somewhat on 3 Oct (possibly Strombolian followed by hydromagmatic), but was very weak again on 4-5 Oct, and during most of the 6th. The low level activity caused many curious to visit the new volcano on that Sunday. At 2200 on the 6th, however, a sudden explosion occurred, killing 24 visitors. This explosion apparently broke through the SSE flank of the cone or occurred as a powerful blast of scoria directed southwards. The deposit left by this explosion consists of coarse (50-60 cm diameter) scoria with very limited extent (occurring only in a small depression on the SSE flank) that show no welding or plastic deformation.

Alternating deposits of magmatic and phreatomagmatic activity during the late stages of the Monte Nuovo eruption, photographed near the S crater rim in September 1989. The dark scoria deposits below the light-colred phreatomagmatic tephra may be of the lava lake and Strombolian activity of 2-3 October 1538, the upper scoria are probably of the fatal 6 October explosion. Boris Behncke gives scale.

Following the fatal 6 Oct explosion, all activity of the volcano was limited to fumarolic activity.

Di Vito et al. (1987) give the volume of pyroclastics ejected in the 1538 eruption as about 2.5 x 10^7 m^3 DRE, with much of this material being pre-eruption country rock.

Photo mosaic of the crater of Monte Nuovo, taken in September 1989, from the SW rim. The mountain in the background is the volcano of Gauro.

Fumarolic activity continued into the mid 19th century. Nowadays, there is no visible activity from the well-vegetated cone.