Bolsena Lake is the largest volcanic lake in Europe. Its large catchment basin (270 square kilometers) is not the relic of a huge volcano, but it was formed by many sinkings of the soil caused by volcanic activity of many eruptive vents. Two of them, the last active ones, became the Martana and Bisentina isles, where the lush vegetation and the rocks are wetted by the water. During the prehistoric period, the lake was less large than today; from the Bronze Age the levels of the waters began rising, submerging thousands of hectares of populated and cultivated plains, and stabilized its level to about 304 meters above sea level. This strong volcanic activity, lasted for millenniums, covered more than 2000 square kilometers of surface with large sediments which are 1300 meters wide at some points. This important water reservoir is almost unknown from a hydrogeological point of view. The town administration of Bolsena supported some scientific diving researches that led to the discovery of innumerable springs of purest water, flowing from the depths, coming from the rocks which formed the volcanic area. Since the catchment basin is very limited, due to its very steep slopes, the body of water maintains its oligotrophic conditions and it is balanced from an ecological perspective. In addition the lake is fed by many rich underwater springs and this is the reason why fishermen and all the people who go to the lake drink its water during the sailing or use it to cook the traditional “sbroscia” in their cabins on the shore.
HOW “THE LAKE YOU CAN DRINK” WAS BORN
The volcanic area, which includes Bolsena lake, extends for about 115 square kilometers and was born as the results of the eruptions which began about 850,000 years ago. After the cracks opened up in the Earth’s crust, violent explosions took place with a huge quantity of flying melted materials (ashes, pozzolana, lapilli): from the formed cones, very fluid lava flows came out, covering a distance of 10 – 20 kilometers until Orvieto, Canino and Tuscania. During periods of calm, small lakes formed in the lower areas. At the depths of these small lakes, silica skeletons of small organisms (diatoms) accumulated, giving rise to sediments of diatomaceous earth. Due to a strong increase of the subsoil pressures, 360,000 years ago, a long period of violent explosions began with leaks of ignimbritic lava flows, a very fluid mixture of gases, magma and high-temperature solid elements, which flowed for long distances with a velocity of 400 kilometers per hour. After the leak of a large quantity of materials, the subsoil emptied and consequentially the superficial crust fell into a 270 square kilometers area, creating in this way the caldera, which it will be filled up by Bolsena lake. The activity moved to the external areas with the formation of tuffs and lava flows. About 140,000 years ago, due to another emptying of the subsoil, more sinkings took place in the external areas which give rise to the calderas of Latera and Montefiascone. In the last periods of activity some explosions took place inside the lake – which it already took shape – giving birth to the isles of Martana and Bisentina. The large lava flows on western area (Selva del Lamone) ended the phase of the activity of the Volsino volcanic complex. On the cooled soil, vegetation developed, animals and then human beings appeared. 5,000 years ago frequent earthquakes and consequent variations of the level of the lake took place. An important volcanic activity like that, lasting for millenniums, involved more than 2,000 square kilometers of surface with sediments which, in some place, reach a width of over 1,300 meters.
THE CLEANEST LAKE IN EUROPE
Today, if you overlook from the high and green hills which surrounded Bolsena lake, you can see that it offers to the tourist the same scenario it used to offer to the “travelers” of the past: the poet Petrarch, the German writer Goethe, the English painter Turner, the French musician Berlioz – who described our lake as “a charming Eden” – came to Bolsena. “Via Francigena” crossed Bolsena, which from Middle Ages to Romantic era was the main arterial road, which witnessed centuries of wars, pilgrimages and jubilees from Europe to the legendary city of Rome. But reading the ancient chronicles we can notice that the admiration for the landscape didn’t correspond to the travelling and living conditions the “travelers” had to face: muddy roads on Winter and dusty roads on Summer, taverns and pubs were dirty hovels, sometimes without mattresses to sleep and dirty food that killed your appetite! Today the tourist can find another scenario, deeply mutated and improved. When you reach Bolsena you can find many hotels – included 4 star hotels – a wide choice of trattorias and restaurants with excellent feedbacks from famous foreign guide books, several religious and historical monuments, suggestive districts of the old town center, archeological excavations, the Territorial Museum (Museo Territoriale), Paleochristian catacombs, the Basilica of Saint Christina (Basilica di Santa Cristina), religious and popular festivals. The tourist port and the beach resorts guarantee to the water sports lovers many options: beach resorts; water skiing, sailing, swimming and scuba diving academies; rental canoes, paddle boats, windsurf boards, sail boats with or without a skipper; parking and technical assistance for pleasure craft, thanks to the port equipment where the ferry boats call and guarantee crossings to the isles and to the other towns on the shore of the lake. In addition, you will have the unusual pleasure to bathe in the lake “you can drink”: an environment with a high ecological value guaranteed by the consortium installations which collect the sewage and the polluted liquids and then drain them outside the basin of the lake.