Lake Bolsena

Lake Bolsena ( it, Lago di Bolsena) is a lake of volcanic origin in the northern part of the province of Viterbo called ''Alto Lazio'' ("Upper Latium") or ''Tuscia'' in central Italy. It is the largest volcanic lake in Europe. Roman historic records indicate activity of the Vulsini volcano occurred as recently as 104 BC; it has been dormant since then. The two islands in the southern part of the lake were formed by underwater eruptions following the collapse that created the depression.

The lake is supplied entirely from the aquifer, rainfall and runoff, with one outlet at the southern end. A sewage treatment plant filters most of the raw sewage from the surrounding communities. Constructed in 1996, it features pipelines transporting the sewage from every major community around the lake to the treatment plant on the Marta River; that is, no effluents enter the lake.Mosello (2004) p. 2. Fertilizers are a second source of contamination. However, the chemical content of the lake is monitored at several stations around it.

The lake has a long historic tradition. The Romans called it ''Lacus Volsinii'', adapting the Etruscan name, Velzna, of the last Etruscan city to hold out against Rome, which was translocated after 264 BC, and its original location today has not been securely identified. The lake is bordered on one side by a modernized version of the Roman consular road ''Via Cassia''. In addition to the historic sites of all periods, Lake Bolsena is currently surrounded by numerous tourist establishments, largely for camping, agrotourism and bed and breakfasts.

One third of the lake was donated to the Catholic church by the noble family Alberici of Orvieto. In recognition of the donation the Alberici family was honored with a ceremony three times a year performed by the Bishop of Orvieto.

Geography

The lake has an oval shape typical of crater lakes. The long axis of the ellipse is aligned in a north-south direction. The bottom is roughly conical reaching a maximum depth at a point in the middle. The entire lake is surrounded by hills on the flanks and summits of which are the comuni. The watershed was home to 22,000 permanent residents in 2004, and 35,000 in the summer season.

Elevations on the north of the lake are the highest, with a maximum of . As the lake is at , no hill is more than higher than it. On the northern rim of the caldera is San Lorenzo Nuovo ("New Saint Lawrence"), which was moved from an older site (a hypothetical San Lorenzo Vecchio, "Old Saint Lawrence") further down the slope to avoid malaria. The northern shore of the lake once featured marshes, breeding grounds for the mosquitos that carry the disease. Currently it is agricultural. At the site of old San Lorenzo are Etruscan antiquities. To the north of San Lorenzo Nuovo and the caldera rim is Acquapendente.

The hills to the east are to . Bolsena extends upward on the northeast shore, with Orvieto further to the northeast, at the edge of the volcanic region. On the southeast of the lake is Montefiascone at an elevation of , up on the ridge of Montefiascone caldera. To the south of the lake is Marta, on the right bank of the Marta River, sole effluent of the lake. The shore there is straight and developed. Elevations are within of the lake. Next to Marta are Valentano and Capodimonte, the latter being built on and around nearly the only headland on the lake, which forms a protective harbor. About to the south are Tuscania and Viterbo, the latter being the regional capital.

From Valentano north is the Latera caldera, a shallow crater perhaps half the size of Lake Bolsena, with Lake Mezzano (usually too small for the map) at the western end. On its north rim is Latera. The floor of the caldera is mainly agricultural although the uncultivable rocky lava flows have been left forested. Although the hills on the west side of Lake Bolsena are only slightly higher than those on the south, the terrain is somewhat too rough for settlement. Fields extend as far as they can into v-shaped valleys and there is no flat shore.

The hills to the north loom over the lake. At their western edge are Grotte di Castro and Gradoli.Washington (1906) pp. 3-4.

Geology

Lake Bolsena is at the center of the Vulsinii (or Vulsino) Volcanic District of the Roman Comagmatic Region. The lake formed when a circular area collapsed after the depletion of the underlying magmatic chamber that fed the whole volcanic district. Although it is generally known as a volcanic lake, like its southern neighbor Lake Bracciano it is not a crater lake nor does it occupy a caldera. The major calderas of the area are found close to the lake's rim (Latera to the west and Montefiascone to the south east).

Islands of the lake

Bisentina

With an area of , Bisentina is the largest island, and is accessible via a ferry service from Capodimonte. On the island are groves of evergreen oaks, Italian gardens, and various monuments: the church of Saint James and Saint Christopher with its cupola built by the architect Jacopo Barozzi da Vignola; the Franciscan convent; the ''Rocchina'', a small temple dedicated to Saint Catherine. The latter was constructed in an octagonal floorplan by Antonio da Sangallo, over an Etruscan columbarium previously erected on a rocky outcrop on the lake. Another monument, the chapel of the Crucifix, contains frescos of the fifth century. The ''Malta dei Papi'', a former prison for ecclesiastic