An illustration of a volcanic eruption destroying a city

A CITY LOST: The ancient Roman city of Pompeii was destroyed by a volcanic eruption in about a day.

TRISTAR PICTURES/PHOTOFEST

STANDARDS

NGSS: Core Idea: ESS2.A, ESS3.B

CCSS: Writing: 1

TEKS: 6.10D, 7.3B, 8.9B, ESS.10C, ESS.11E

READING LEVEL

Fight Over Pompeii

Why two groups of scientists studying the ancient city of Pompeii and the volcano that destroyed it are at odds

February 17, 2020

By Andrew Klein

AS YOU READ, THINK ABOUT how scientists might study the site of a past natural disaster to better understand what occurred there.

Nearly 2,000 years ago, the ancient Roman city of Pompeii was suddenly wiped off the map. It was the year 79 A.D., and the city’s residents had been experiencing frequent mild earthquakes for months. Quakes are common on Italy’s western coast, so people didn’t pay them much attention. Little did they know that the seismic activity was a warning. Mount Vesuvius—a large volcano east of the city—was about to blow its top. It would be one of the most violent eruptions in human history, killing an estimated 30,000 people.

Today, historians have a detailed account of what happened that fateful day, thanks to a Roman teenager named Pliny the Younger. The 17-year-old documented the eruption from the nearby city of Misenum. He described seeing a massive, gray cloud rising from Vesuvius’s peak. It reached 32 kilometers (20 miles) into the sky. Hours later, a pyroclastic flow of ash, rocks, and superheated gases rushed down the slopes of the volcano, engulfing the city. “It traveled at hurricane-like speeds and killed instantly,” says Christopher Kilburn, a volcanologist from the University College London in England who studies the region.

Nearly 2,000 years ago, the ancient Roman city of Pompeii was suddenly wiped off the map. It was the year 79 A.D. For months, people in the city had been feeling many mild earthquakes. Quakes are common on Italy’s western coast, so people didn’t pay much attention. They didn’t know that the seismic activity was a warning. A large volcano, Mount Vesuvius, sat east of the city. It was about to blow its top. This would be one of the most violent eruptions in human history, killing about 30,000 people.

What happened on that deadly day? Historians have a detailed account, thanks to a Roman teenager named Pliny the Younger. The 17-year-old wrote about the eruption from the nearby city of Misenum. He described what he saw. A huge, gray cloud rose from Vesuvius’s peak. It reached 32 kilometers (20 miles) into the sky. Hours later, a pyroclastic flow of ash, rocks, and superheated gases rushed down the volcano’s slopes. The flow swallowed the city. “It traveled at hurricane-like speeds and killed instantly,” says Christopher Kilburn. He’s a volcanologist from the University College London in England who studies the region.

In a matter of hours, the city was buried under 3 meters (10 feet) of ash and rock. Pompeii was accidentally rediscovered by construction workers in 1748. Since then, scientists have flocked there to learn more about the city, which was preserved beneath the volcanic debris. Archaeologists, who study human history, continue to excavate the site to uncover the remains of Vesuvius’s victims, their homes, and their belongings. Volcanologists also analyze the grounds surrounding the archaeological site. It contains layers of volcanic material from Vesuvius’s past eruptions, shedding light on its violent history.

Recently, though, these two groups of scientists have been at odds over Pompeii. To do their job, archaeologists dig to find ancient artifacts. But that disturbs the deposits volcanologists use to learn about the behavior of the still-active Vesuvius. Without this valuable soil, volcanologists say, they can’t best study when this monster will unleash its wrath again.

Within hours, the city was buried under 3 meters (10 feet) of ash and rock. Construction workers accidentally found Pompeii again in 1748. The city was preserved under the volcanic material. Since then, scientists have flocked there to learn more about Pompeii. Archaeologists study human history. They excavate the site to uncover the remains of Vesuvius’s victims, their homes, and their belongings. Volcanologists also study the grounds around the archaeological site. It contains layers of volcanic material from Vesuvius’s past eruptions. This material reveals its violent history.

But recently, these two groups of scientists have been at odds over Pompeii. To do their job, archaeologists dig for ancient artifacts. But that disturbs the volcanic deposits. Volcanologists use these deposits to learn how Vesuvius behaves. The volcano is still active. Volcanologists say that without this soil, they can’t best study when this monster will erupt again.

TRAPPED IN TIME

So many scientists are interested in studying Pompeii because its ruins are unlike those of any other known ancient city, explains Steven Ellis. He’s an archaeologist at the University of Cincinnati and a member of the scientific committee for the Great Pompeii Project. This organization aims to conserve Pompeii’s remains and manage visitors to the site.

Most lost ancient cities suffered “a rise and a fall,” says Ellis. That means the cities grew until an event, such as a natural disaster, conflict, plague, or economic decline forced their populations to abandon their homes. Buildings and items left behind slowly decayed, often becoming overgrown with vegetation, sometimes never to be found. Pompeii, though, was preserved during a period of prosperity. “It was a bustling, thriving city that was demolished overnight—quickly destroyed by an unimagined catastrophe,” says Ellis.

Pompeii’s ruins are unlike those of any other known ancient city. That’s why so many scientists want to study it, explains Steven Ellis. He’s an archaeologist at the University of Cincinnati and a member of the scientific committee for the Great Pompeii Project. This organization aims to protect Pompeii’s remains and manage visitors to the site.

Most lost ancient cities suffered “a rise and a fall,” says Ellis. That means the cities grew until an event forced the people to leave their homes. It could have been a natural disaster, war, disease, or economic trouble. Buildings and items got left behind. They slowly decayed, and often vegetation covered them. Sometimes they were never found. But Pompeii was preserved when it was booming. “It was a bustling, thriving city that was demolished overnight—quickly destroyed by an unimagined catastrophe,” says Ellis.

MUSEO ARCHEOLOGICO NAZIONALE, NAPLES, ITALY/SCALA/ART RESOURCE, NY

HIDDEN TREASURES: Archaeologists excavated this gold armband at Pompeii.

Since Pompeii’s rediscovery, archaeologists like Ellis have been unearthing artifacts that tell stories about the city. They’ve learned that the city had roads paved with stone, restaurants, and indoor plumbing. Walls were adorned with beautifully detailed paintings. There was even graffiti promoting elections and gladiator fights.

“The real excitement comes from identifying an object that can tell us a story,” says Ellis. For instance, “we’ll find a kitchen and uncover a drain that leads out to the street. As we dig, we’ll find bones from pigs and fish that tell us about what people ate—their last meals.”

Since Pompeii was found again, archaeologists like Ellis have been uncovering artifacts. These items tell stories about the city. It had roads paved with stone, restaurants, and indoor plumbing. Paintings with beautiful details decorated the walls. Archaeologists even found graffiti. It promoted elections and gladiator fights.

“The real excitement comes from identifying an object that can tell us a story,” says Ellis. For example, “we’ll find a kitchen and uncover a drain that leads out to the street. As we dig, we’ll find bones from pigs and fish that tell us about what people ate—their last meals.”

DEADLY CLUES

One of the most remarkable things archaeologists have found are body-shaped cavities in the ash that buried Pompeii. They formed as victims of the disaster slowly decomposed. Excavators preserve these body-shaped voids by pouring plaster into the holes. Once it dries and hardens, they chip away at the ash to reveal statue-like casts of the victims.

To archaeologists, Pompeii’s true treasures are buried in the soil. But to volcanologists, the soil itself is worth more than gold. It holds the secrets of Vesuvius’s eruptions. Without these deposits, volcanologists can’t make discoveries that could help them understand when the next big blast will occur—and how to protect those living in the volcano’s shadow.

Archaeologists have found something amazing in Pompeii. The ash that buried the city contains body-shaped spaces. They formed as victims of the disaster slowly decayed. To preserve these body-shaped holes, the scientists pour plaster into them. They wait for the plaster to dry and harden. Then they chip away at the ash to reveal statue-like casts of the victims.

To archaeologists, Pompeii’s true treasures are buried in the soil. But to volcanologists, the soil itself is worth more than gold. It holds the secrets of Vesuvius’s eruptions. Volcanologists need these deposits to make new findings. This could help them understand when the next big blast will happen. It could also show how to protect those living near the volcano.

For example, scientists weren’t sure exactly what killed Pompeii’s citizens until recently. They theorized that most of the victims were either suffocated by volcanic gases and falling ash or pummeled by chunks of pumice. These small volcanic rocks formed when lava was ejected by Vesuvius.

Then in 2010, volcanologists created a computer simulation based on soil samples they’d analyzed. It identified six different pyroclastic waves released by Vesuvius during its 79 A.D. eruption. The researchers combined this information with a chemical analysis of victims’ remains and artifacts. That helped them determine that the pyroclastic surges reached temperatures of 300°C (572°F)—hot enough to kill a person in a fraction of a second.

These waves left little evidence behind. Their deposits were only about 3 centimeters (1 inch) thick, hidden within other layers of volcanic soil. Without this evidence, we wouldn’t know the dangers that modern-day populations could face during the next eruption.

For example, what killed Pompeii’s citizens? Scientists weren’t sure until recently. They thought that most of the victims died in one of two ways. Either volcanic gases and falling ash smothered them, or they got pounded with chunks of pumice. These are small volcanic rocks. They formed when lava shot out of Vesuvius.

Then volcanologists created a computer model in 2010. It was based on soil samples they’d studied. It showed that Vesuvius released six different pyroclastic waves during its 79 A.D. eruption. The researchers also did a chemical study of victims’ remains and artifacts. They combined all the data. It revealed that the pyroclastic surges were as hot as 300°C (572°F). That’s hot enough to kill a person in a fraction of a second.

These waves left little evidence behind. Their deposits were only about 3 centimeters (1 inch) thick. They were hidden between other layers of volcanic soil. This evidence shows what could happen to modern-day people during the next eruption. Without it, we wouldn’t know the dangers.

SLEEPING GIANT

Vesuvius has erupted dozens of times since the destruction of the ancient city of Pompeii. It most recently spewed an enormous mushroom cloud from its crater in 1944. “The eruption that destroyed Pompeii was about 100 times larger than the 1944 eruption,” says Kilburn, the volcanologist. But the latter still caused damage and the deaths of 26 people.

“The fascinating thing about Vesuvius is that the type of eruption it produces varies from time to time,” says Kilburn. By examining layers of volcanic material deposited in the area around Vesuvius, scientists discovered a pattern: After a period of lava flows, the volcano slumbers. This allows a rock plug to form, trapping gases inside. The gases build up, and so does the pressure inside the volcano. Eventually, like opening a shaken bottle of soda, the volcano goes KABOOM! This type of volcano, which alternately erupts flowing lava then clouds of ash is classified as a stratovolcano (see How Vesuvius Formed).

It’s only a matter of time until Vesuvius erupts again. And if it turns out to be one of the volcano’s more explosive eruptions, it could mean big trouble for the nearby city of Naples. It lies just 12 km (7.5 mi) away from the foot of the volcano.

Since Vesuvius destroyed the ancient city of Pompeii, it has erupted dozens of times. The most recent eruption was in 1944. The volcano shot a giant mushroom cloud from its crater. “The eruption that destroyed Pompeii was about 100 times larger than the 1944 eruption,” says Kilburn, the volcanologist. But the latter still caused damage and killed 26 people.

“The fascinating thing about Vesuvius is that the type of eruption it produces varies from time to time,” says Kilburn. Scientists studied layers of material in the area around the volcano. They found a pattern. After a period of lava flows, the volcano sleeps. This allows a rock plug to form and trap gases inside. The gases build up, and so does the pressure inside the volcano. Finally, it’s like opening a shaken bottle of soda. The volcano goes KABOOM! This type of volcano changes between erupting flowing lava and clouds of ash. It’s called a stratovolcano (see How Vesuvius Formed).

Sooner or later, Vesuvius will erupt again. What if it’s one of the volcano’s larger eruptions? That could mean big trouble for the nearby city of Naples. It lies just 12 km (7.5 mi) away from the foot of the volcano.

HOW VESUVIUS FORMED

Italy is located near the edges of two tectonic plates—giant slabs of rock that make up Earth’s crust, or outer layer. Mount Vesuvius formed over a subduction zone, where one plate dives below another.

The African plate has a tear in it, called a slab window. As this area descends, it melts when heated deep inside Earth.

This produces magma and volcanic gases that rise up beneath the volcano.

Once enough pressure builds, gases and lava erupt from the volcano.

HOW VESUVIUS FORMED

The African plate has a tear in it, called a slab window. As this area descends, it melts when heated deep inside Earth.

This produces magma and volcanic gases that rise up beneath the volcano.

Once enough pressure builds, gases and lava erupt from the volcano.

WARNING FROM THE PAST

Today, about 700,000 people live in Vesuvius’s “red zone.” This area is considered to be at greatest risk and would be the first to be evacuated when the volcano next shows signs of an eruption (see Blast Area). A million more people live in the “yellow zone,” with lesser risk.

Why would anyone decide to live so close to this ticking time bomb? Past eruptions have made the soil in the area extremely fertile, so it’s ideal for farming. Tourists from around the world are also drawn to the beautiful region.

Today, about 700,000 people live in Vesuvius’s “red zone.” This area is thought to be at greatest risk. When the volcano shows signs of an eruption, this zone would be evacuated first (see Blast Area). A million more people live in the “yellow zone,” with lesser risk.

Vesuvius is a ticking time bomb. Why would anyone decide to live so close? Past eruptions have made the nearby soil extremely fertile, so it’s perfect for farming. Tourists from around the world also visit the beautiful area.

To help protect people visiting or living near Vesuvius, volcanologists analyze samples left behind by the eruption that destroyed Pompeii. By doing so, they can learn about the chemistry of rock spewed by the volcano. “That tells you what the magma [melted rock below Earth’s surface] must have been like before the eruption began,” explains Kilburn. If scientists detect a similar makeup in Vesuvius’s magma today, it might be a warning sign that the volcano is reawakening.

Studying the physical patterns and shapes of the deposits left behind by the deadly pyroclastic waves could reveal more about how they behaved as they rolled through the city. “To have this understanding, we need to be able to gather samples all the way through the volcanic deposits,” says Kilburn. But, he adds, if the soil making up these deposits is removed by archaeologists to excavate artifacts, there will be nothing left for volcanologists to study.

Volcanologists want to protect people visiting or living near Vesuvius. So they study samples from the eruption that destroyed Pompeii. This reveals the chemistry of rock shot from the volcano. “That tells you what the magma [melted rock below Earth’s surface] must have been like before the eruption began,” explains Kilburn. Scientists also study the chemistry of Vesuvius’s magma today. If they find a similar makeup, it might be a warning sign that the volcano is becoming active.

The deadly pyroclastic waves left behind deposits with physical patterns and shapes. These could reveal more about how the waves behaved as they rolled through the city. “To have this understanding, we need to be able to gather samples all the way through the volcanic deposits,” says Kilburn. But he has a concern. What if archaeologists remove the soil of these deposits to uncover artifacts? Then volcanologists will have nothing left to study, he says.

BLAST AREA

This map shows the yellow and red zones, at great and greater risk, respectively, when Vesuvius erupts. The green line depicts the 79 A.D. pyroclastic blasts that wiped out Pompeii and Herculaneum.