Pliny the Younger, a Roman historian who witnessed the 79 AD eruption, wrote the oldest surviving description of the tall, tree-shaped cloud that rose above the volcano. The 79 AD eruption of Vesuvius is why volcanologists use "Plinian" to describe large volcanic eruption clouds. Vesuvius is currently quiet, with only minor seismic (earthquake) activity and outgassing from fumaroles in its summit crater, but more violent activity could resume in the future.
Plinian eruptions (huge explosions that create columns of gas, ash and rock which can rise dozens of kilometers into the atmosphere) have a much greater reach, and have destroyed entire ancient cities near Vesuvius with huge ashfalls and pyroclastic flows. Strombolian eruptions (explosions of magma from a pool in the volcano’s conduit) and lava flows from the summit and flank fissures are relatively small. Andesite lava creates explosive eruptions on a variety of scales, which makes Vesuvius an especially dangerous and unpredictable volcano. Most rocks erupted from Vesuvius are andesite, an intermediate volcanic rock (about 53-63% silica). The cone known as Mount Vesuvius began growing in the caldera of the Mount Somma volcano, which last erupted about 17,000 years ago. This photo was taken by Lancevortex and is distributed under a GNU Free Documentation License. Plaster casts of people who died in the city of Pompeii during the 79 AD eruption of Mount Vesuvius.
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