What Happened When Vesuvius Erupted in 79 CE?

The eruption of Mount Vesuvius in 79 CE stands as one of the most significant and well-documented natural disasters in human history. This catastrophic event had far-reaching consequences, not only for the ancient Roman cities of Pompeii and Herculaneum, but also for our understanding of ancient life, culture, and geology. Traveling back in time, we explore the phases of the eruption and its impact on the cities and their inhabitants in the years following that fateful day.

Mount Vesuvius, located in the Bay of Naples in Italy, had been dormant for centuries before its eruption in 79 CE. Situated in the Campania region, southeast of the city of Naples, the volcano is part of the Campanian volcanic arc, which includes several other volcanic structures known collectively as the Campi Flegrei. Vesuvius is perhaps the most famous of these volcanoes, owing to its historically significant eruptions, particularly the one that led to the destruction of Pompeii and Herculaneum.

The fertile soil around the volcano attracted settlers, leading to the establishment of prosperous cities at its base. Prior to the Roman period, local settlers included the Oscans, Etruscans, and Greeks who arrived by sea and looked to benefit from the area’s excellent ocean links.

The many layers of volcanic ash and pumice in the area meant that the Bay was perfect for growing vines and trees for food and wine. Many of these reached right up to the summit of the volcano. This phenomenon was even captured by an artist from the city of Pompeii in a fresco that once decorated the walls of a domestic shrine. The fresco shows the God Bacchus wearing a cloak of grapes standing by the volcano, where vineyards can be seen on the sides of the mountain.

Although local residents were unaware of the deadly true identity of the volcano, some had their suspicions about the mountain. Strabo, an ancient Roman writer, mentioned the volcanic activity in the region, noting that it was prone to earthquakes and that the soil was fertile due to volcanic ash.

Similarly in his work Natural Questions, Seneca the Younger, a Roman philosopher, discussed the phenomenon of subterranean fires and their potential to burst forth, creating mountains. While he did not specifically refer to Mount Vesuvius, his observations about the earth’s internal processes and the presence of subterranean fires could be considered a general acknowledgment of the volcanic activity in the region. Elsewhere he mentions the mass unexplained death of 600 sheep near Pompeii during the earthquake of 62/3 CE, which was likely due to toxic gases.

Before the catastrophic eruption, there were signs of volcanic activity. Minor earthquakes and tremors likely unsettled the residents of the region. However, the Romans, unfamiliar with the signs of an impending volcanic eruption, did not recognize these as warnings.

In the run-up to an eruption, earthquakes tend to become more frequent and destructive. One of these earthquakes, which hit the region in 62/3 CE, was especially damaging to the town of Pompeii, destroying much of its infrastructure. This event is even recorded on the reliefs that surround the household shrine (lararium) of L. Caecilius Iucundus in his Pompeiian home. The relief illustrates the earthquake’s impact on structures like the Temple of Jupiter, the Aquarium of Caesar, and the Vesuvius Gate.

Other less obvious signs included ground uplift and the emission of gases in the local area. There were also some reports of contaminated well water in the region, rendering the population’s main water source undrinkable. This contamination might have been caused by the infiltration of volcanic gases and minerals into the groundwater, another sign of the volcanic activity brewing beneath the surface.

The earthquake inspired Seneca the Younger to dedicate the sixth book of his Naturales Quaestiones to the subject of earthquakes. Within this work, he described the events of February 5th and attributed the cause of earthquakes to the movement of air. By the time of the 79 CE eruption, some of the damage caused by the main earthquake and subsequent tremors had been partially repaired. But much was still to come.

During the late morning of October 24, 79 CE, a family living on the north side of the Bay of Naples overlooking the mountain of Vesuvius were going about their daily business. The mother, seeing a large, dark cloud appear over the mountain, alerted Pliny the Elder, her brother. Pliny happened to be Commander of the Roman fleet at nearby Misenum and the noted author of the now invaluable historical text, The Natural History. Tremors had led up to the cloud’s appearance, but this was not out of character for the area.

The winds were blowing south that day, so much of the cloud was drifting out toward Surrentum (modern-day Sorrento). This phase, described by Pliny the Elder’s nephew (of the same name) in letters to the writer Tacitus, would later be known as the “Plinian phase.” As the cloud turned into a column of ash, rising high into the sky, the area was plunged into darkness and panic began.

As the winds carried the volcanic ash southeast, blanketing the towns of Pompeii and Herculaneum, the falling ash and pumice created a layer that gradually built up. The phenomenon resembled a relentless, ashy rain that transformed the landscape into an eerie, monochromatic scene.

As the eruption intensified, Vesuvius unleashed pyroclastic surges, deadly clouds of gas, ash, and debris that rushed down the slopes at incredible speeds. These surges, reaching temperatures as high as 500 degrees Celsius (932 degrees Fahrenheit), rapidly engulfed Pompeii and Herculaneum. The intense heat and toxic gases caused instantaneous death for those caught in their path.

The cities faced different fates during the eruption. Pumice fell on Pompeii at a rate of 10-15cm (4-6 inches) per hour, leading to an eventual thickness of three yards deep. After around 5 hours of pumice and ash fall, roofs began to collapse in the town from the sheer weight of the volcanic matter. Those attempting to run from the city amid the dark, ash, and pumice had to be careful to dodge falling debris and large rocks of pumice now being shot from the volcano.

The first pyroclastic surges rolled down the side of the volcano at around 11 pm that night and hit Herculaneum, Boscoreale, and Oplontis at temperatures of up to 400° Celsius (752° Fahrenheit). Everyone still remaining in the town was killed instantly. Because of the proximity of Herculaneum to the volcano, the town was hit with incredibly strong heat, causing the individuals there to be burned alive and any organic matter, such as wood, to be carbonized. When excavators uncovered the town centuries later, they were able to uncover and preserve much of this matter, including a baby’s crib, wine racks, and doors.

Pompeii, while also hit by pyroclastic flows, was further away from the volcano and therefore was not hit with such high-intensity heat (though it still reached temperatures of up to 300° Celsius (570° Fahrenheit). This caused the bodies of individuals still remaining in the town to undergo a different process during and after death.

When they were hit by the flows, peoples’ bodies contorted into “boxer poses.” This is when the muscles contract due to heat. At the same time, their bodies were cooked, leaving behind their physical remains, in some cases still with clothes and items on their body.

Around them, pumice and ash continued to fall and solidify. Eventually, their bodies decayed leaving a cavity behind with a skeleton inside. When excavators discovered these cavities some 1,800 years later, they filled them with Plaster of Paris. The casts depict the final moments and poses of the victims, offering a chilling and emotional connection to the individuals who perished during the eruption. These casts serve as powerful symbols of the human tragedy that unfolded on that fateful day.

Even after centuries of exploration, ongoing excavations continue to uncover new aspects of Pompeii and Herculaneum. Advances in technology, such as ground-penetrating radar and 3D scanning, have enhanced our ability to explore these ancient sites without compromising their integrity. Each layer of ash unearthed reveals more about the people who lived in these cities and the broader Roman world.

The eruption of Mount Vesuvius in 79 CE was a cataclysmic event that left an indelible mark on history. The preservation of Pompeii and Herculaneum has provided a unique and invaluable glimpse into the past, allowing us to connect with the people of ancient Rome and comprehend the impact of natural disasters on human civilization. As ongoing excavations and technological advancements continue, the story of Pompeii and Herculaneum will undoubtedly unfold further, revealing more secrets from the depths of time.