Neither Pliny nor his uncle knew that deadly surges had already overwhelmed the town of Herculaneum. Pliny, sitting with his mother at Misenum, and his uncle, lying on a beach at Stabiae, were comparatively distant from the volcano. Stabiae lay sixteen kilometres to its south-east; Herculaneum, just seven kilometres to its south-west. Although Herculaneum had experienced little pumice-fall owing to the direction of the wind, the earthquakes had been catastrophic. In a bid to take cover, hundreds of its residents had made their way to the shore where a series of arched vaults, probably boat stores, was set back from the coast. Each vault was barely three metres wide by four metres deep. Those who could not fit inside one or reach their shelter in time—many men ceded their places to women and children—remained exposed on the coast.
The people of Herculaneum saw the avalanche coming. Huddled beneath the arches and spread out over the beach, they clung to each other. They were entirely helpless. As floods of volcanic matter hurtled towards them, they died upon impact with its heat. In its second stage, a nuée ardente produces pyroclastic flow, a current of magma and gas of around 400 degrees Celsius. Struck by a series of volcanic surges and flows, Herculaneum was buried deep beneath the layers of debris. The arches under which its inhabitants lay became their funeral vaults, shrouding their remains for the next two thousand years.
The panicking crowds at Stabiae were now witnessing what was probably the last of six pyroclastic surges. Two had already struck Herculaneum, a third hit Pompeii, a fourth overwhelmed any Pompeians who remained, and the fifth buried their city. Roused from his blanket on the beach, Pliny the Elder got up, leaning on two slaves for support. He managed to stand, but then he fell, defeated.
Pliny later reasoned that his uncle died because the thick fumes and air had obstructed his fragile airways. He was probably right. The surge cloud from a nuée ardente is low in oxygen and would have filled his lungs with ash, asphyxiating him. When his body was discovered a few days later, it was said by whoever found and reported it to be intact and unharmed, with the look more of sleep than of death. The body of a victim of thermal shock does not look peaceful. It is rigid, the hands typically clenched like a boxer's, the result of tendons contracting in the heat. Many of the bodies later uncovered at Pompeii would show signs of thermal shock.
Pliny and his mother were further away from the volcano and better placed to escape. By daybreak, the earthquakes at Misenum had become so severe that they threatened to bring the villa down on top of them, and they quickly decided to leave the town. As mother and son made their way through the streets they found themselves followed by a crowd, 'favouring someone else's plan to their own, which in moments of fear is akin to prudence'. Crowd mentality steered the refugees clear of the falling buildings and into the possibility of safety.
Pliny and his mother proceeded by carriage. They were joined by one of Pliny the Elder's friends who had recently come to visit from Spain. As the earth tremored, they darted one way then another, their vehicles twisting and turning. Over the course of their journey, they witnessed scenes which defied explanation. The sea seemed to 'be absorbed back into itself and sort of be pushed back by the earthquake', leaving a trail of marine life stranded in its wake. This was either the beginning of a tsunami or simply a further effect of the force of the earthquakes. Inland, meanwhile, 'a terrifying black cloud, burst by twisting, quaking flickers of flame, began to gape to show long fiery tongues, like lightning, only bigger'. The cloud descended upon the earth and covered the sea until neither the island of Capri, nor even the promontory of Misenum itself, was visible on the horizon. Ash began to fall, only lightly, and hardly noticeable at all against the thick gloom that pressed them from behind, spreading over the earth like a torrent. Pliny did not know it, but the cloud was very probably the edge of the nuée ardente that had already killed his uncle at Stabiae. Pliny the Elder's friend urged Pliny and his mother on before fleeing the danger himself: 'If your brother, if your uncle, is alive, he would want you to be safe; if he has died, he would have wanted you to survive him. So why do you hesitate in your escape?'
There was now little time. Pliny's mother begged—ordered—her son to leave her behind, knowing she would slow him. She told him that she was 'heavy in years and body and could die happy, if only she was not the cause of [his] death'. Reflecting on this moment, Pliny thought of Virgil and his description of the fall of Troy. In the poem, Aeneas' wife, Creusa, follows behind him as they make their escape. By the time Aeneas reaches safety, she has gone.