The Alban Hills volcano, the volcano under Monte Porzio Catone

Anyone who climbs up to Monte Porzio Catone is walking, without knowing it, on the side of a volcano. It has no obvious cone and it does not smoke, but the Alban Hills are what remains of a great dormant volcano, the Vulcano Laziale, and much of what you see around the town, from the lakes to the vineyards, comes from it.

What is the Vulcano Laziale?

It is the volcano of the Alban Hills, the Colli Albani, south east of Rome. According to the reference entry its base is more than 60 kilometres wide and over its history it produced about 297 cubic kilometres of material, almost all in the first phase. The ridge that marks its old rim takes its name from Tusculum and from the Artemisio.

The three phases

Scientists divide its activity into three main phases:

1. Tuscolano-Artemisio. The largest: the reference entry has it ending about 360,000 years ago, after four eruptive cycles. For its start, estimates range from about 600,000 to about 560,000 years ago.
2. Faete, or Campi d’Annibale. It began about 280,000 years ago, after a long pause, with a caldera about 15 kilometres wide; the central vent cooled about 260,000 years ago.
3. Hydromagmatic phase. Eruptions in which the magma met water, between about 200,000 and 19,000 years ago according to the reference entry. Another source places the start of the last phase around 45,000 years ago, after a pause of more than 200,000 years.

The dates do not match because they have been measured again several times with different methods: so when you read a single number, be wary of it.

The two lakes

From the last phases two lakes remain in ancient craters: Lake Albano, about 170 metres deep, the deepest volcanic lake in central Italy, and Lake Nemi, much shallower. Other similar basins, such as Pantano Secco and Prata Porci, were drained by the Romans or later, or disappeared on their own. The reference entry places them around Monte Porzio Catone. Prata Porci is the name of the plain where, in 1167, the battle of Monte Porzio was fought.

The rocks, the wine and the town

The volcano’s materials are everywhere. Pozzolana is widespread on the side facing Rome, peperino stone is found mostly between Marino and Albano, and the lava flows supply the stone for Rome’s sanpietrini cobbles. These soils drain well, and on them grow the grapes of Frascati: the vines grow mostly on tuff and pozzolana.

Frascati also lies along a fault line running towards Velletri, along which, in the third phase, the south western part of the volcano sank.

Is it still active?

It has not erupted for thousands of years, and there are no reliably documented eruptions in historical times. One source reports an event in 114 BC, which scholars consider unreliable. Estimates for the date of its last activity range from tens of thousands of years ago (for the youngest crater of Lake Albano one source does not rule out about 7,500) to about 5,000 years ago, and a more recent study, cited by one entry, puts it at about 36,000 years ago.

The volcano, however, is not completely “dead”. The sources describe frequent earthquakes, with swarms since the 1980s, and carbon dioxide emissions in some areas. The historical earthquakes that caused damage are those of 1438, 1806, 1829, 1899 and 1927. The data on ground uplift and gas date from the 1990s and 2000s: for its current state, refer to INGV, Italy’s National Institute of Geophysics and Volcanology.

In short

• What: the Vulcano Laziale, or Alban Hills volcano, south east of Rome; Tusculum is part of its old rim.
• Phases: Tuscolano-Artemisio (from about 600,000 to 360,000 years ago), Faete (from about 280,000), a hydromagmatic phase up to tens of thousands of years ago.
• Lakes: Albano and Nemi, in ancient craters.
• Rocks: tuff, pozzolana, peperino, the lava of the sanpietrini; the soils of Frascati.
• Today: no eruptions, but earthquakes and gas; for its current state, see INGV.