Italy's Volcanoes: The Cradle of Volcanology

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Vulcano erupts, September 1889

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).

Geological evolution of Vulcano island

Piano Caldera
Looking down from Monte Saraceno over the vast Piano Caldera of Vulcano, 6 October 1996. The caldera floor is very flat and extremely scenic. The village of Vulcano Piano extends over most of the plain, bordered by a forest on its SW (far right) side. View is towards SSE.

Lentia lava dome
Spectacular section through a pre-Fossa Caldera lava dome or a thick lava flow sitting on the caldera rim next to the touristic village of Lentia. Height of the structure is 30-50 m. Photo taken on 6 October 1996.

Fossa Caldera and cone
Panoramic view of the Fossa caldera with the Fossa cone sitting in its center, from the S rim of Fossa Caldera (which corresponds with the N boundary of the Piano in the south part of the island); 6 October 1996.

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.
South Vulcano became active about 120 ka ago and built a large stratovolcano, made up mostly of trachybasaltic to trachyandesitic lava flows. Intercalations of pyroclastic fall and flow deposits constitute only a minor portion of that volcano. Activity of the South Vulcano eruptive center was interrupted about 97 ka ago by the collapse of the 2.5 km diameter Piano Caldera (Caldera del Piano).

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.

Geologic map
Map of the northern part of Vulcano island with the eruptive centers of Fossa and Vulcanello (from Frazzetta et al. 1984, slightly modified). Dotted areas are lava flows erupted during the past 15 ka from eruptive centers within the Fossa caldera (but not from Vulcanello). Irregular dots north of Fossa cone and on the Vulcanello peninsula are buildings of Vulcano Porto (as of 1983).
From Ventura (1994)

Eruptive history of Fossa cone during the past 6000 years

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.

Punte Nere cycle
The initial activity of this first recognized Fossa eruptive cycle was hydromagmatic and produced a >60 m thick sheet of dry surge deposits overlying the Punta Roia lava flows (14+/-6 ka). The basal strata of this sheet are composed of coarse and fine clasts and are overlain by sandwave and massive beds. Fragments of a trachytic lava flow that may have been ruptured by the eruptions and a thick block-fall deposit are present in the middle part of the sequence. A fall deposit composed of normally bedded and occasional reversely bedded layers with interbedded surge beds make up the uppermost pyroclastic unit of the cycle. It was followed by the emplacement of the trachytic Punte Nere lava flow that forms a delta-like feature on the N base of the Fossa cone. This flow was dated at 5400+/-1300 years.

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.

The Fossa cone
A view of the Fossa cone of Vulcano looming over the village of Vulcano Porto (at left). The photo shows the Pietre Cotte lava flow (erupted in the 18th century) on the near left flank of the cone, arriving at its base. This is the view from Lentia, a major tourist facility on the NW rim of the Fossa Caldera. Photo taken on 6 October 1996.

Palizzi cycle
Following a repose period of unknown duration, hydromagmatic activity led to the emplacement of wet surge deposits followed by dry surge beds. Accretionary lapilli in these initial deposits give testimony of a high water component during the opening stage of the cycle. Later activity produced a stratified, normally graded pumice horizon which shows evidence of a brief erosional interval at its top. When activity resumed, it was again hydromagmatic and deposited another set of basal wet and overlying dry surge horizons.

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.

Commenda cycle
This cycle began with powerful explosive activity of which a basal breccia gives testimony. The breccia is composed of yellow hydrothermally altered clasts and is overlain by a pyroclastic flow unit with numerous fumarolic degassing pipes. The activity then shifted to hydromagmatic and produced wet and then dry surge deposits with abundant Pele's hair (!) before it became again magmatic with the extrusion of the Comenda obsidian lava flow that is still partially visible on the SW flank of Fossa cone (see the map of lava flows). Its volume is 2.6 x 106 m3, slightly more than one tenth of the tephra volume (25 x 106 m3).

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.

Vulcano in 1888
The northern part of Vulcano seen from the southern tip of Lipari in August 1888, in a quiet moment between two explosive outbursts. The Vulcanello peninsula with its small cone complex and the extensive lava platform lies in the middle ground.

Vulcano in eruption, 1888
Vulcano in eruption in late 1888, seen from NW. A dense, vapor-charged plume mixed with some ash is rising from the Fossa crater. Note strong fumarolic activity on near crater rim, and the barren craters of "Forgia Vecchia" on the slope just below the eruption column.

Vulcano in eruption, 1889
Mild explosive activity and vigorous fumaroles photographed on 14 February 1889. The double crater of "Forgia Vecchia" is well discernible on the slope below the eruption plume. The two low hills in the foreground are the "Faraglioni", now surrounded by the village of Vulcano Porto.

Vulcano in eruption, 1889
Very strong explosion at the Fossa crater on 14 February 1889. Large bombs are rising ahead of a densely ash-laden plume, but there is also a lot of white vapor inthe plume. This type of activity was defined as "Vulcanian", a term still in use today. This photo shows slight evidence of editing, probably to highlight the size of the ejected bombs.
From Mercalli and Silvestri (1891)

Pietre Cotte cycle
Initial activity was hydromagmatic, producing wet surge and soon after, dry surge deposits. A pyroclastic fall sequence (described as "pumice" by Frazzetta and La Volpe 1991) rests on top of these early products. The exact timing of the eruption's beginning is not known but it is probable that one of its more peculiar events, the formation of the lateral Forgia Vecchia II crater (on the NW rim of Forgia Vecchia I crater), occurred in 1727. Twelve years later, lava seems to have filled the main Fossa crater and spilled over its low N rim, forming the obsidian lava tongue of Pietre Cotte ("Cooked Stones") that is still conspicuous on the steep northern slope of the Fossa cone (see the map of lava flows). Its volume is 2.4 x 106 m3.

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).

1888-1890 eruption
Vulcano last erupted in 1888-1890. Although it had erupted frequently in historic times, this eruption was the only one that was observed by scientists and was described in detail (Mercalli & Silvestri 1891). The activity observed by them was used for the introduction of a new scientific term, the so-called "Vulcanian" style of volcanic activity, now applied for powerful magmatic activity somewhere transitional between Strombolian and sub-Plinian (check the Glossary of Volcano World and "Types of volcanic eruptions" of the Volcano Information Center for more detailed information about these somewhat controversial terms).

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.
With the 1888-1890 eruption, the Pietre Cotte cycle seems to have come to a close. The volume of tephra produced during the entire cycle is given by Frazzetta & La Volpe as 25 x 106 m3 of which the 1888-1890 products do not make up more than one fourth.

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:

Vulcano, the 1985-1995 unrest.


Copyright © Boris Behncke, "Italy's Volcanoes: The Cradle of Volcanology"

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