Geologists from Ruhr Univ . . . visited Stromboli 15-18 September. On 15 September between 1900 and 2100, 10 eruptions occurred from at least 3 vents, ejecting glowing spatter to 50-100 m above the crater terrace. No ash plumes were observed, and only two of the eruptions were audible from . . . Punta Labronzo, at 125 m elevation, ~2 km NNE of the craters near the N tip of the island.

Activity seemed comparatively weak and irregular during observations of the crater terrace from about 1730 on 16 September until 1000 the next day (from Pizzo sopra la Fossa, 918 m elevation). Small Strombolian explosions from at least four vents ejected bombs and spatter to <125 m above the crater rims; no ejecta reached the observation site, roughly 200 m from the vents. Individual bursts were separated by quiet intervals of 2-45 minutes. The SE walls of the active vents seemed to have grown unusually high. The southernmost vent ([1-1] or [1-2] on figure 2) was most active with about 3 explosions/hour, but bombs were rarely ejected significantly higher than the crater rim and were mostly directed obliquely S or SW, preventing close access to the crater terrace. Next to the most active vent was a second ([1-3] on figure 2) which apparently contained a lava lake. Although not visible, the lava lake's presence was suggested by a continuous glow and dull surf-like sounds. Geologists suggested that the two vents probably coalesced sometime after midnight on 17 September, as explosive activity from the first vent was much reduced and glow was also visible above it. Between 0900 and 1000, two brown ash plumes rose from the center of Crater 1 to perhaps 200 m above the vents, dropping some ash on the observation platform. A small ash plume was visible during the evening when the volcano was frequently observed from the E coast.

Craters 3 and 4 were less active, but one or two explosions/hour from Crater 4 produced the highest lava fountains (up to 100 m) and the longest eruptive episodes. Crater 3 erupted only three times during the observation period, but often made loud crashing noises without visible ejections. Two vents erupted simultaneously only once during the observation period ([1-1/1-2] and 4). No earthquakes were felt.

Geological Summary. Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the "Lighthouse of the Mediterranean" in the NE Aeolian Islands. This volcano has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent scarp that formed about 5,000 years ago due to a series of slope failures which extends to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: B. Behncke, Ruhr Univ, Germany.