From This Month In 79 AD: What Really Happened at Pompeii?

C.O.O.L.ᵀᴹ Time Capsule: This Month in History — October

Written by: Vickie Liou

The ground shook. Stones rained from the sky. People rushed through the streets as roofs cracked and daylight disappeared behind a thick cloud of ash.

The year was 79 AD. 

For hours, Mount Vesuvius hurled pumice and ash over Pompeii. Some people fled. Others stayed inside. Then the eruption changed: powerful earthquakes shook the city, followed by fast-moving clouds of ash, gas, and pieces of volcanic rock.

When it was over, Pompeii lay buried beneath layers of pumice and ash.

Figure 1: Artistic photo composition of Pompeii with Mount Vesuvius erupting (Source: Grafissimo, retrieved from iStock)

Why Was Pompeii There?

Now, rewind the story.

Before the ash. Before the falling stones. Before anyone was running through the streets, Mount Vesuvius looked very different.

Its green slopes were covered with fields. Grapes, olives, and grains grew in the rich soil around the mountain, and farms throughout the area produced wine and oil. Pompeii also sat near the Sarno River and its port, connecting the city to trade. The land around Vesuvius was not only beautiful—it was useful.

But the very thing that helped make the land so fertile came from the volcano itself. Over many eruptions, volcanic rock and ash can break down and add minerals to the soil, helping plants grow.

To the people living there, however, Vesuvius did not look like a volcano preparing to erupt. They had no modern tools that monitor volcanoes, no satellite images, and no warning systems telling them that magma—melted rock beneath Earth’s surface—was moving beneath the mountain.

For generations, Vesuvius had given the people around it fertile land, food, and ways to make a living.

But little did the people know, the gifts of the mountain had always come with a hidden price.

Figure 2. Map showing Mount Vesuvius, nearby Roman towns, and the spread of ash and volcanic material during the 79 AD eruption (Source: MapMaster, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons)

What Really Happened?

That hidden price came from deep below the mountain.

The warning signs had begun long before anyone realized what they meant. In 62 AD, seventeen years before the eruption, a powerful earthquake had badly damaged Pompeii. Smaller earthquakes continued in the region, but people repaired their homes, reopened their shops, and life went on.

Then, in 79 AD, the danger changed quickly.

Deep beneath Mount Vesuvius, magma was rising toward the surface. As it rose, the trapped gases expanded. Pressure built until the volcano erupted, blasting a towering column of gas, ash, pumice, and broken rock high into the sky.

Then gravity took over.

Pumice—light, bubbly pieces of volcanic rock—began falling back to Earth. Around Pompeii, it fell for hours, piling several feet deep in some places. Streets became harder to cross, and the growing weight of the rock caused roofs and walls to collapse. Some people fled. Others stayed inside, hoping the buildings around them would keep them safe.

But the eruption was not finished.

As the pumice began to fall more slowly, strong earthquakes shook the already damaged city. Buildings that had survived the falling rock were hit by yet another danger.

Then the eruption changed again.

The towering eruption cloud could no longer hold itself high in the sky. Parts of it collapsed, sending pyroclastic currents—fast-moving waves of hot ash, gas, and pieces of volcanic rock—racing down the volcano and across the land.

By the time the eruption ended, Pompeii was buried.

It wasn’t like the movies. The city had not been swallowed by a river of lava. Its destruction came from falling rock, shaking ground, collapsing buildings, and deadly clouds rushing across the land.

Figure 3. Diagram showing how a volcanic eruption happens. (Source: agung fatria, retrieved from iStock)

How Do We Know?

For nearly 2,000 years, Pompeii kept its secrets underground.

The same volcanic material that destroyed these cities also helped preserve them. At Pompeii, pumice and ash buried streets, buildings, and people. Nearby, Herculaneum was buried by hot volcanic material, preserving things such as wood and food that usually disappear over time.

Together, the two cities preserved different clues to the same disaster. Archaeologists study the past through clues such as buildings, objects, human remains, volcanic layers, and ancient writing. They also compare this evidence with the letters of Pliny the Younger, who saw the eruption from across the Bay of Naples.

But the clues do not always agree.

For centuries, copies of Pliny’s letter placed the eruption on August 24, 79 AD. Yet discoveries at Pompeii suggest it may have happened later in the fall, possibly in October. Archaeologists have found seasonal foods, along with a message written in charcoal on a wall and dated October 17.

Nearly 2,000 years later, Pompeii is still giving up new clues—and the exact date of its most famous day remains part of the mystery.

Figure 4. Plaster casts of victims at Pompeii, created by filling the empty space left in hardened volcanic material after the body decomposed (Source: sestovic, retrieved from iStock)

Vesuvius Is Still Here

Pompeii stayed buried, but people did not abandon the region around Mount Vesuvius forever. Today, the ancient ruins of Pompeii and Herculaneum are preserved as a UNESCO World Heritage Site, while millions of people live in the greater Naples area nearby.

Vesuvius, however, is not extinct—it could erupt again.

After the famous eruption of 79 AD, it erupted many more times. Between 1631 and 1944, it entered a period of especially frequent activity that scientists divide into 18 periods of repeated eruptions. Its most recent eruption came in 1944, when lava and ash damaged nearby communities. 

Since then, Vesuvius has been quiet—but its history shows that silence above ground can hide slow changes taking place deep below.

Today, scientists at the Vesuvius Observatory monitor earthquakes, ground movement, and gases escaping from below.

For now, the mountain is resting. 

But one question remains: what will happen when Vesuvius awakens again?

Figure 5. Mount Vesuvius overlooking the densely populated Naples area. (Source: Paolo Graziosi, retrieved from iStock)

---

References:

Sigurdsson, H., Carey, S., Cornell, W., & Pescatore, T. (1985). The Eruption of Vesuvius in A.D. 79. National Geographic Research, 1(3), 332-387.

Mastrolorenzo, G., Petrone, P., Pappalardo, L., & Guarino, F. M. (2010). Lethal thermal impact at periphery of pyroclastic surges: evidences at Pompeii. PloS one, 5(6), e11127.

Doronzo, D. M., Di Vito, M. A., Arienzo, I., et al. (2022). The 79 CE eruption of Vesuvius: A lesson from the past and the need of a multidisciplinary approach for developments in volcanology. Earth-Science Reviews, 231, 104072.

Scandone, R., Giacomelli, L., & Gasparini, P. (1993). Mount Vesuvius: 2000 years of volcanological observations. Journal of Volcanology and Geothermal Research, 58(1-4), 5–25.