Photo by Italian Air Force from Green and Short (1971).
Vesuvius has erupted about three dozen times since 79 A.D., most recently from 1913-1944. The 1913-1944 eruption is thought to be the end of an eruptive cycle that began in 1631. It has not erupted since then, but Vesuvius is an active volcano, it will erupt again.
The oldest dated rock at Mt Vesuvius is about 300,000 years old. It was collected from a well drilled near the volcano.
Vesuvius erupted catastrophically in 79 A.D., burying the towns of Herculaneum and Pompeii. The Somma Rim, a caldera-like structure formed by the collapse of a stratovolcano about 17,000 year ago, flanks Vesuvius to the east.
The 79 A.D. eruption of Vesuvius was the first volcanic eruption ever to be described in detail. From 18 miles (30 km) west of the volcano, Pliny the Younger, witnessed the eruption and later recorded his observations in two letters.
Volcanologists now refer to sustained explosive eruptions which generate high-altitude eruption columns and blanket large areas with ash as plinian eruptions. It is estimated that at times during the eruption the column of ash was 20 miles (32 km) tall. About 1 cubic mi (4 cubic km) of ash was erupted in about 19 hours. Vesuvius has erupted about three dozen times since 79 A.D., including a large, explosive eruption in 1631 that killed 4,000 people. The most recent eruption was from 1913-1944.
An excellent source of information on Vesuvius is an article titled “The Eruption of Vesuvius in A.D. 79″ by Sigurdsson and others (Sigurdsson, H., Carey, S., Cornell, W., and Pescatore, T., 1985, The eruption of Vesuvius in A.D. 79: National Geographic Research, v. 1, no. 3, p. 332-387).
A superb online resource about the Vesuvius 79 A.D. eruption can be found at: http://www.gso.uri.edu/vesuvius/Home/index.html