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Vulsini volcanic complex, Italy

volcano number: 0101-... (according to Volcanoes of the World, 1994 edition)

summit elevation: XXX m

location: XXXXX°N, XXXXX°E

The following is summarized from De Rita (1993).

Panoramic view of the Vulsini volcanotectonic depression, filled with marvellous Lago di Bolsena. View is from Montefiascone to the NW, on 5 March 1994. Two small islands, Martana (left) and Bisentina (right) lie in the southern central area of the lake, formed by post-caldera lacustrine eruptions. Historic records indicate that eruptive activity of Vulsini volcano occurred as recently as 104 BC, but geologic evidence exists only for eruptions until about 150 ka ago.

Simplified geologic map of the Vulsini volcanic complex, showing Lago di Bolsena and other volcanic features next to it, among which the Latera caldera and the Montefiascone caldera (on the NW AND SE sides of Lago di Bolsena, respectively) are the most important ones. Taken from De Rita (1993).

The Vulsini Volcanic Complex is the northernmost of the volcanic districts in Lazio. Its activity has been of areal character and been principally explosive. The main structural element is the vast basin of Lago di Bolsena which is interpreted as a volcanotectonic depression that has formed during successive phases of subsidence. This subsidence has been controlled by regional fault systems.

The activity of the complex has occurred from four main eruptive centers that lie on the margins of the main depression, probably along the main tectonic lines of weakness. Activity probably initiated about 0.8 Ma ago from regional fissural eruptive centers ("areal volcanism") in the E part of the complex, and led to the construction of scoria cones and effusion of lava flows.

About 0.6 Ma ago, the activity concentrated at a center now denominated "Paleovulsini" of which nor morphologic traces remain but that may have been present in the area now occupied by the depression of Lago di Bolsena. The oldest volcanic products that crop out in the E and S parts of the lake basin are referred to this period.

Another important eruptive center then grew immediately near the suggested Paleovulsini center and is called "Bolsena-Orvieto". Voluminous air-fall deposits with considerable thicknesses and an ignimbrite called "Bagnoregio Tuff" or "Orvieto Ignimbrite" stem from this eruptive center. The responsable eruption probably occurred 370 ka ago and likely triggered the collapse of the Bolsena Caldera which is located in the NE part of the present volcanotectonic depression.

Contemporaneously with the Bolsena-Orvieto center, another center named "Montefiascone" was active on the SE margin of the lake basin, at the site now occupied by the town of Montefiascone. The Montefiascone center had a complex eruptive history including the production of several ash flow units, airfall deposits and violent hydromagmatic eruptions during a period spanning 300 to 150 ka.

Still another major eruptive center was active during that same period, on the W side of the Bolsena depression, named "Latera". The volcanic history of this center has been divided into two main periods of activity by Nappi (1969) and a third, earlier period was revealed by Barberi et al. (1994). Thus, the activity began at about 0.9 Ma in the course of which a first caldera collapse occurred. The Torrente Arrone ignimbrites, a late product of this eruptive cycle, was dated at about 0.8 Ma.
The following cycle (the "first eruptive period" of Nappi, 1969) produced lavas and pyroclastics dated at 0.4-0.6 Ma. Activity during the next cycle (the "second eruptive period of Nappi, 1969) was much more explosive with intervening minor effusive activity, resulting in the emplacement of large pyroclastic flows, the most important being the "Onano Complex" and the "Pitigliano Complex"(about 160 ka). During this period of large-scale explosive volcanism, several episodes of caldera collapse occurred, leaving a depression about 8 km wide.
Minor postcaldera activity was predominantly effusive and led to the construction of small edifices within the caldera and on its rims.

Close up view of Isola Martana (center), a youthful post-caldera cone in the SW part of Lago di Bolsena. Isola Bisentina lies in the background immediately to the left; apparently part of its volcanic cone has been destroyed by erosion. View is from the SW shore of Lago di Bolsena, 5 March 1994.

The area of Viterbo, a beautiful city lying between Vulsini, Cimino and Vico volcanoes, has several areas of continuing "post-volcanic" activity, i.e. fumaroles, hot springs and mudpots. This is a pond with a central area of boiling water. Unfortunately, many persons used to drop thir garbage in these beautiful natural attractions, causing the construction of the ugly fence around. Garbage is still being dropped in the channel of the outlet (in the foreground), beyound the fence. This is one really annoying aspect of Italian society. - Photo taken on 5 March 1994.

Drainage system constructed during the Roman time, to divert water from the host springs at the nothern margin of Viterbo to bath ponds. Carbonate has precipitated from overflowing water on the walls of the aquaeduct, forming beautiful miniature sinter basins. Taken 5 March 1994.

Mudponds at the Bulicame hot springs, a few km north of Viterbo (visible in the background, before the skyline of the Cimino-Vico complex). They are a popular resort, very similar to the mudpond at Vulcano island, and people are taking baths at any time of the year (photo was taken on 5 March 1994).

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