Mount Vesuvius

Deep under Vesuvius there is very hot, melted rock.

When the volcano erupts, ash and lava come out. They pile up in layers. Layer by layer, the mountain grew taller. A new cone grew inside an older, broken volcano.

Vesuvius is a composite volcano, also called a stratovolcano. The US Geological Survey explains that these volcanoes are built from many layers of lava, ash and rocks, piled up eruption after eruption, as melted rock rises from deep underground through a pipe called a conduit.

The older volcano, Mount Somma, came first. Its top later fell in, leaving a big bowl-shaped hollow called a caldera. The younger cone of Vesuvius has grown inside that hollow, which is why the mountain looks like a cone wrapped by a curved ridge. Britannica says Vesuvius probably began somewhat less than 200,000 years ago, which makes it a young volcano.

The USGS describes composite volcanoes, or stratovolcanoes, as steep cones built of alternating layers of lava flows, ash, cinders, blocks and bombs, fed by a conduit from a magma reservoir in the crust; a caldera forms when a volcano's summit collapses after large eruptions drain the magma beneath. The Global Volcanism Program applies this to Somma-Vesuvius: an older Monte Somma stratovolcano with a summit caldera partly filled by the Vesuvius cone.

Britannica dates the volcano's origin to probably somewhat less than 200,000 years ago. Its behavior has changed through time. It had been dormant for centuries before AD 79; after the sub-Plinian eruption of 1631 its activity became more continuous, in cycles with an open vent and long eruptive stages separated by quiet stages, ending in violent eruptions such as those of 1906, 1929 and 1944. The Civil Protection Department summarizes the pattern as rest periods interrupted by high-energy explosive eruptions, followed by frequent eruptions of medium and low energy.

Scientists watch Vesuvius every day.

They use machines that feel tiny shakes in the ground. They measure the gases too. If the volcano starts to wake up, people will be told to move away safely.

Vesuvius has been watched for a very long time. Britannica says a volcano observatory opened on its slopes in 1845. Today scientists at the Vesuvius Observatory measure earthquakes, how the ground moves, and the gases and temperatures coming from the volcano, because changes can be warning signs of an eruption.

Italy has a national plan for Vesuvius. The area closest to the volcano, called the red zone, includes 25 towns and parts of Naples. If the volcano ever shows signs of erupting, the plan is for everyone in the red zone to leave before an eruption begins. Alert levels go from green, which means normal, through yellow and orange to red.

Britannica dates serious scientific study to the late 18th century and the observatory's opening to 1845, at 608 m; later came stations at many heights, a laboratory and a tunnel for seismo-gravimetric measurements. Today, the Civil Protection Department explains, a monitoring system tracks seismicity, ground deformation, gas composition and temperature, whose changes may forerun an eruption; INGV's Vesuvius Observatory reports the data, and the department declares alert levels from green (ordinary activity) through yellow and orange to red.

The national plan's reference scenario is a medium-energy explosive eruption with an eruptive column, falling volcanic material and pyroclastic flows, which it identifies as the most dangerous phenomenon for people. The red zone of 25 municipalities in the provinces of Naples and Salerno, plus parts of Naples, Nola and Pomigliano d'Arco, would be evacuated before an eruption, the only safeguard measure for that area; in the yellow zone of 63 municipalities and three Naples districts, evacuation would depend on the wind and the size of the eruption. Each red-zone municipality is twinned with a host region.

You can walk up to the crater with a grown-up.

The path is steep and rocky, so wear good shoes. The path closes in bad weather. Stay on the path and follow the rules.

Visitors can climb to the rim of the crater on a path called Trail 5, 'Il Gran Cono', inside Vesuvius National Park. It starts from a parking area at about 1,000 meters above sea level near Ercolano. Tickets are sold only online, and children under six go free with an adult.

The park closes the crater path when the weather is dangerous: in October 2026, for example, it shut the Gran Cono during orange weather alerts. Check the park's news before you go, stay on the marked path and follow the guides' instructions. If you live in or visit the area, it also helps to know the Civil Protection Department's advice about what to do if the alert level ever changes.

Access to the Gran Cono is by nature trail no. 5, which begins at a park-managed square at about 1,000 m in the municipality of Ercolano, at the end of the Ercolano-Vesuvius provincial road. Tickets are sold only online, in timed slots (50 every 10 minutes, released 30 days ahead), through the park's single authorized vendor; children under six accompanied by an adult enter free, and visits must end within an hour of the last permitted entry to the crater. The park closes the trail for orange weather alerts and events, and announces closures on its website.

The Civil Protection Department's 'Io non rischio' pages explain what residents and visitors should know about Vesuvius: the alert levels, the red and yellow zones, and the fact that in the pre-alarm and alarm phases people follow the evacuation routes and schedules set in the municipal plans. Visitors to the park should also follow the instructions of park staff and guides.