Geologists have long recognized two major phases of the infamous 79 C.E. Vesuvius eruption: an initial rain of debris, followed by lethal pyroclastic currents—scalding, fast-moving flows of gas and debris that devastated the surrounding area.

That timeline was pieced together by looking at volcanic deposits and cross-referencing them with Pliny the Younger’s vivid eyewitness accounts, who witnessed the eruption from across the Bay of Naples.

Now, in two studies published this month, volcanologists from the University of Naples Federico II have mapped the deposits in unprecedented detail and uncovered previously undetected eruption pulses.

Study author Claudio Scarpati says the findings enable a minute-by-minute reconstruction, extending the timeline of the eruption from 19 to 32 hours and revealing a complex event with 17 destructive pyroclastic currents.

In his eyewitness account, Pliny the Younger observed an umbrellalike cloud looming over Mount Vesuvius around 1 p.m.

The researchers believe the eruption began an hour before that. In the 17 hours that followed, the volcano spewed a fluctuating column of volcanic fragments and gas, raining pumice up to 270 centimeters thick, crushing Pompeiians as roofs collapsed.

At 7:06 p.m., the researchers estimate, the eruption changed character, initiating the first scalding pyroclastic currents, often considered the most hazardous of an eruption. These currents continued overnight, occurring approximately 80 minutes apart.

The disaster peaked at daybreak the following day, when the eruptive column collapsed. During a brief lull, residents tried to flee the doomed city.

Then, suddenly, at 7:07 a.m., the deadliest pyroclastic current struck—a particularly thick and fast-moving concoction of hot gas and rock fragments.

This current roared for 9 hours, spreading scalding debris 25 kilometers across the plain and slamming into the distant Lattari Mountains.

Approximately half of Pompeii’s victims were found in the streets entombed in this volcanic layer. “You cannot survive this kind of phenomenon,” Scarpati says.