The first eyewitness account of a volcanic eruption comes to us from the letters of Gaius Plinius Caecilius Secundus, better known as Pliny the Younger (63 - ca. 113 AD). Although he was a capable lawyer and administrator, Pliny the Younger is best known for his writings, the Epistulae. This collection of letters to friends and colleagues was published later in his life, probably between 99 and 109 AD. Among the most famous of these letters is correspondence describing the eruption of Vesuvius and the heroic actions of his uncle, the famous natural historian Pliny the Elder (23 – 79 AD), as witnessed by the then-teenaged Pliny the Younger from his home in Misenum, directly across the Bay of Naples from Vesuvius.

In letters written to his friend Tacitus, also an historian, the younger Pliny describes the sequence of events leading up to the cataclysmic eruption.  Pliny the Younger wrote that on the 24th of August, his uncle “climbed up to a place which would give him the best view of the phenomenon. It was not clear at that distance from which mountain the cloud was rising (it was afterwards known to be Vesuvius); its general appearance can best be expressed as being like an umbrella pine, for it rose to a great height on a sort of trunk and then split off into branches, I imagine because it was thrust upwards by the first blast and then left unsupported as the pressure subsided, or else it was borne down by its own weight so that it spread out and gradually dispersed. In places it looked white, elsewhere blotched and dirty, according to the amount of soil and ashes it carried with it.”

The Elder Pliny sails into the eruption
Pliny the Younger in Misenum

Source: "The Destruction of Pompeii, 79 AD," EyeWitness to History, (1999).