The oldest dated rock was collected from a well drilled near the volcano and was probably part of the Somma volcano. After Somma collapsed about 17,000 years ago, Vesuvius began to form. Vesuvius is a stratovolcano. The volcano originally only had one peak, but now is structured with a semicircle ridge surrounding the main cone, known as Mount Somma. There is a large slope on the distance between the cone and the ridge that begins at the ridge at an altitude of 600 meters and climbs to 1132 meters at the height of the cone.
The area between the ridge and the cone is called the Valle del Gigante in Italian, meaning Giant's Valley. At the top of the cone is a large crater that measures 600 meters across in diameter and 300 meters deep. Everyday the temperature of the volcano is measured to help predict forthcoming eruption, because a rise in temperature can mean an upcoming eruption. Common temperatures for the volcano are around and above 1000 degrees Fahrenheit.