Small explosion within the Fossa crater (Gran Cratere) of Vulcano, photographed from SW crater rim on 21 September 1889, during the most recent eruption of the volcano. Photo is from Mercalli and Silvestri (1891).
The island of Vulcano is geologically complex. Its evolution took place during the past >150 ka and is generally divided into four major stages:
South Vulcano center, Lentia
volcanic complex, Fossa cone and Vulcanello.
Post-caldera activity continued until about 50 ka ago. The earlier of these eruptions came from ring faults and later from eruptive centers aligned along N-S and NE-SW trending fractures. Then, no volcanic activity occurred on the island for more than 30 ka.
Renewed eruptions began about 15.5 ka ago from eruptive centers in the southern and western parts of the island (Quadrara and Spiaggia Lunga volcanics) as well as in the northwest where the large rhyolitic to trachytic lava dome and flow complex of Lentia was formed.
Violent ash-flow forming eruptions occurred from somewhere in the strait between Vulcano and Lipari and deposited brown tuffs over a large area of the Piano caldera. About 15-14 ka ago, another caldera collapse affected the island, this time in its northern part, forming the Fossa caldera.
Activity continued within the new caldera, producing pyroclastics and lava flows, the most significant being the Punta Roja lava flow that crops out at the E base of the Fossa cone. The most significant eruptive activity was the eruption of the so-called "Tufi di Grotte dei Rossi inferiori (TGR inf.)" pyroclastic deposits, recently described by De Astis et al. (1997) during near-continuous sequence of hydromagmatic activity from vents at shallow water depth in the caldera. Eruptions also occurred from N-S trending fissures in the NW part of the older Piano caldera where the Alighieri formation and the edifice of Monte Saraceno were formed.
About 6 ka ago, activity concentrated in the center of the Fossa caldera, leading to the formation of the still-active Fossa cone. Its activity, which comprises the most recent eruptions on the island, is described below.
Still more recently, a new eruptive center formed in the strait between Vulcano and Lipari. The first recorded eruption occurred 183 or 123 BC and formed a new island. Sporadic eruptions continued until the mid 16th century AD. By that time, the new island had significantly enlarged and eventually connected with the main island of Vulcano. The activity produced a cluster of three overlapping tephra and scoria cones with craters shifting from E to W, and a gently sloping lava platform mainly on the N, W and S sides of the cone cluster. The Vulcanello products are generally more mafic than most other Vulcano eruptives, being of leucite-tephritic composition, only the most recent lava flow (Punta del Roveto) is trachytic.
The evolution of the Fossa cone, the most recently active volcanic center on Vulcano island, has been described in detail by Frazzetta et al. (1983) and briefly reviewed by Frazzetta et al. (1984) and Frazzetta & La Volpe (1991). The following is a summary from those sources.
The Fossa eruptive center developed only during the past 6000 years, after the presumably tectonically triggered formation of the Fossa caldera, about 14-16 ka ago. Its birth followed post-caldera effusive activity of which the 14 ka Punta Roja lava flow gives testimony (see the geological map). Activity of the Fossa cone has been divided into several cycles by Frazzetta et al. (1983, 1984) and Frazzetta & La Volpe (1991) that have generally shown a characteristic succession of eruptive styles and each had an individual eruptive vent. Some cycles began with powerful vent-clearing explosions leading to deposition of "phreatic breccias" near the eruptive vents. The hydromagmatic initial stages of other cycles produced wet and/or dry surge deposits. Later products of each cycle show a decreasing influence of external water, the final products being fully magmatic (pumice-fall deposits or lava flows).
The complete lack of erosional surfaces and paleosoils between the products representing a cycle, it is assumed that activity during each cycle was more or less continuous. This contrasts with distinct erosional unconformities between the products of various cycles, evidence of longer repose periods separating different eruptive cycles.
Frazzetta & La Volpe (1991) estimate the volume of tephra produced during the Punta Nere cycle at 195 x 106 m3 and that of lava at about 3 x 106 m3. The activity left a cone about 250 m high, its NE crater rim is still well discernible in the eastern part of the Fossa cone.
At least three undefined eruptive cycles occurred after the Punta Nere cycle and left wet and dry surge deposits as well as the Campo Sportivo lava flow (see the map of lava flows), on the NW base of the Fossa cone. That flow has a radiometric age of 4600+/-1700 years and thus falls into the same time window as the Punta Nere flow; stratigraphically, though, it lies in a higher position. The volume of the Campo Sportivo lava flow is 2.6 x 106 m3 while that of the tephra presumably associated with it is 25 x 106 m3. The volume of tephra from the other undefined cycles is about 10 x 106 m3.
Like during the preceding cycle, the late stage activity was effusive, producing about 0.6 x 106 m3 of trachytic lava that forms a narrow tongue on the S flank of the Fossa cone (Palizzi lava flow, see the map of lava flows). The volume of all tephra emitted during the Palizzi cycle is given as 5 x 106 m3. The age of the Palizzi lava flow is 1600+/-1000 years. This is well within the historic period but no correlation of the deposits with recorded historic eruptions of Vulcano is possible. The historic eruptions (except the 1888-1890 one) are therefore handled separately on a different page.
Frazzetta et al. (1983) assumed that the upper and larger of the two Forgia Vecchia ("Old Forge") craters was formed during the Comenda eruptive cycle. These craters are well distinguishable on the two photos below of the 1888-1890 eruption but have been subjected to intense erosion since then and are densely vegetated.
The initial activity (breccia and pyroclastic flow) probably occurred before the mid 6th century AD since these deposits are overlain by the white ash from the most recent explosive eruption of Monte Pilato, Lipari that is thought to have occurred around AD 550. The Pilato ash is overlain by the wet and dry surge deposits. Historic documents indicate that the emplacement of the Comenda lava flow may correspond to an eruption recorded for the year AD 785.
Unlike other cycles, the Pietre Cotte cycle apparently did not end with the lava outflow. Following the effusive activity, eruptions resumed in 1771 and continued intermittently until 1890. All activity before the latest major eruptive episode, in 1888-1890, is not well documented whereas very detailed scientific descriptions of the most recent activity are available (see below).
The eruption was particular for the ejection of countless large breadcrust bombs. Meter-sized bombs fell in the area now occupied by the village of Vulcano Porto, on the crater rim they are much larger (see the previous photo).
The buildings of the sulfur mining company located at Porto Levante were heavily damaged by falling tephra already during the first days of the eruption (starting on 3 August 1888), their residents could escape without fatalities or injuries. Later eruptions caused occasional ash and rare lapilli falls at Lipari. No major damage was done there, but on the island of Vulcano, the area now occupied by the village of Vulcano Porto was subjected to heavy bomb and lapilli showers.
The eruption ended on 22 March
1890, after gradually declining for several days. There were repeated
unconfirmed reports about eruptive unrest at or near Vulcano, but no significant
eruptive activity took place after 22 March 1890.
Since the end of the 1888-1890 eruption, Vulcano has exhibited continuous fumarolic activity which has become a tourist attraction. Fluctuatiuons in the intensity and chemical compositions of the fumarolic emissions are common. The most dramatic increases of fumarolic activity occurred in the mid 1920's and between 1985 and 1995. Details about the latter event which was also accompanied by other geophysical phenomena are presented on another page:
Copyright © Boris Behncke, "Italy's Volcanoes: The Cradle of Volcanology"
Page set up on 6 January 1996, last modified on 20 January 2000