To the northwest of Rome in Italy are a chain of several recent volcanic calderas. One of these
calderas, referred to as Vulsini, was the site of a RECENT volcanic eruption during the age of the
Roman Republic. As indicated by this documented eruption, this volcano will erupt again.
This video will discuss this active volcano, and mention what its future hazards are.
The Vulsini volcano is a large volcanic complex which is located adjacent to the
city of Montefiascone in west central Italy. This complex is spread out over an area of 2200 square
kilometers, contains four large overlapping calderas, and an assortment of smaller volcanic
features. Within the largest caldera is Lake Bolsena, which is technically a crater lake.
The Vulsini volcano began forming 590,000 years ago, due to subduction related magmas reaching
the surface along this section of Italy. The early eruptions from this volcano were highly explosive,
and created an assortment of volcanic cones and lava domes. More specifically, the lavas which
erupted from this volcano were highly silicous, and even contained more silica than typical lavas
at Mount Vesuvius. So, when this volcano erupted, its eruptions were typically larger than those
witnessed in modern times at Vesuvius. Over the next 90,000 years, the Vulsini stratovolcano was
built into a profile similar to that of a shield volcano. Unlike most stratovolcanoes, its eruptive
vents were spread out over a large area, which created numerous slightly overlapping features.
This indicated that a massive magma chamber was feeding Vulsini at depth.
Then, 498,000 years ago, this volcano experienced a massive eruption. As pyroclastic flows travelled
dozens of kilometers across the surrounding area, the magma chamber underneath was slowly drained.
Eventually, a 16 kilometer wide section of the volcano collapsed,
forming a massive caldera. The eruption which had just taken place likely produced more than
100 cubic kilometers of tephra, putting it on the same scale as the 1815 eruption of Mount Tambora.
However, there is a problem with this analysis. There isn't the expected quantity of volcanic
deposits in the vicinity of the caldera which you would expect from such a massive eruption.
Several thousand years after this large eruption, a series of fissures formed along
the northeast caldera wall. From these fissures, lava erupted onto the surface,
which built about a dozen lava domes. These eruptions continued in the area until 330,000
years ago, after which the caldera became dormant. 290,000 years ago, eruptive activity resumed to
the west of the modern day town of Montefiascone. Over the next 60,000 years, explosive eruptions
built a small 3 kilometer wide stratovolcano. Around the same time period, volcanic activity
occurred 12 kilometers to the west of the now filled Lake Bolsena. These eruptions
also constructed a stratovolcano, which had a much wider base of 10 kilometers.
Both of these stratovolcanoes subsequently collapsed into calderas. The 9 kilometers
Latera caldera formed 220,000 years ago, while the 2.5 kilometer wide Montefiascone
caldera forming 230,000 years ago. The last caldera collapse from this
volcanic complex occurred 166,000 years ago, and formed another caldera within the
larger Latera caldera. Since then, eruptions from this volcano have only occurred within
the confines of Lake Bolsena. Two of these eruptions formed Bisentia and Martana islands,
which represent a consolidated debris ring from a large mostly underwater explosion.
Although little activity has since been recorded, there was a reliable historical report of an
eruption in 104 BC. This report started that "a tall flame shot up near Vulsini". This report has
since been deemed credible, and indicates that the Vulsini volcano is still active.
When the next eruption from Vulsini occurs, it will almost certainly occur somewhere between the
two existing islands in Lake Bolsena. These islands align with numerous features in the
region, and likely represent a zone of weakness in the crust. Such an eruption would be explosive,
although an underwater eruption of lava is ALSO possible. Overall, Vulsini does have the potential
to form a new caldera, but it is far more likely for its next several eruptions to be relatively
small. This volcano is unlikely to produce an eruption in the near future, but historical
accounts show that it is still active. I hope that you enjoyed this video.
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