August 25, 79 A.D., Herculaneum
Pliny’s lifeless body lay on the beach at Stabia. His friends had fled in horror, desperate to save themselves. With the once beautiful countryside transformed into a hellish landscape, the inhabitants of the entire area wandered frantically in an attempt to escape the inferno that surrounded them. It was difficult to make a decision about where to flee as it seemed to be a case of “damned if you do, damned if you don’t.” Unfortunately, pockets of people remained trapped in the areas they thought would be the safest.
The residents of Herculaneum reacted differently than those of Pompeii. Herculaneum was not pummeled by vast amounts of pumice and debris, but earthquakes and deafening noise were intolerable; so they fled, mainly taking the road towards Naples. Those who did not leave stayed indoors or sought to escape by sea. The inhabitants of Pompeii found it much harder to leave, given that the streets and paths were covered with volcanic debris and the air was toxic. Their decision to stay inside and wait was totally understandable.
Herculaneum was an ancient fishing village. It was most likely founded by the Samnites in the 6th century B.C. but later came under the control of the Greeks as evidenced by its name Herakles, (Hercules in Latin). It was probably a quarter of the size of Pompeii. Although located in Roman territory, Herculaneum was never a formal Roman colony so its history is one rich with many different cultures and inhabitants from many parts of the world. The village was laid out in orthogonal blocks, revealing its Greek origins. Only 10 of its 20 blocks have been found and of those 10 only 6 are exposed. The other parts of Herculaneum are covered by buildings in the modern town of Ercolano.
After the initial violent Plinian eruption on August 24, the second phase, called Peléean, (after the famous eruption of Mount Pelée in Martinique in 1902) began on the following morning, August 25. The volcano’s column of hot gas and pumice was unable to maintain its buoyancy and between 4-6 a.m. began to collapse, causing a series of flows and surges called nuée ardente (pyroclastic flow) of steam, hot ash and gases which swept down to the south and west at 450 mph (725 kmph). These were the fires that Pliny had seen and attributed to “farmers burning their fields”.
Herculaneum, only 4 miles (7 km.) to the west of Vesuvius, was destroyed well before Pompeii. The people who remained in Herculaneum did not know what hit them when the first lethal surge hit the city just before dawn on August 25. Many of Herculaneum’s citizens fled toward the sea but were now trapped. The sea had pulled back. This pull back was a result of a phenomenon connected to the beginning of an intense phreatomagmatic (where water comes into contact with magma) phase. This was caused by the collapse of the roof of the magmatic chamber during the violent Plinian eruption of the day before, and the entry of groundwater into the magma chamber. When the groundwater came into contact with the molten magma, large internal explosions occurred, causing the volcano and the surrounding area to swell.
The first nuée ardente reached Herculaneum 2 to 5 minutes after the eruptive column started to collapse, near dawn on August 25. It bore down on the city with temperatures of 400 degrees C (752 F) and buried it in 10 feet (3 m) of hot ash. A few seconds later the surge reached the beach, penetrating the dockside boat houses where people had taken refuge, vaporizing their flesh with a blast of searing steam, killing them instantly.
The people from Herculaneum did not die from asphyxiation or from collapsing buildings but due to rapid exposure to the intense heat that developed from the cloud. Those who remained on the beach felt the full effect of the surge, being thrown to the ground they died instantaneously from the immediate boiling and vaporization of their bodies. Those who had found shelter within the dockside boat houses did not feel the direct action of the surge, but died from the shock of their burns due to the elevated temperature of the cloud. This is why in Herculaneum the bodies of victims were not found. They had been vaporized, leaving only charred skeletons.
The pyroclastic flow continued on, depositing ash and debris 10’s of meters into the sea. Since this turbulent, torrid cloud did not destroy structures, it allowed buildings to be covered in layers of ash and allowed the remains of victims to be found where they had died. This surge, extended along the south and west sides of Vesuvius, covering Boscoreale, Oplontis and Terzigno in addition to Herculaneum.
An hour later, between 5-7 a.m., a second surge, was even more violent and piled another 5 feet (2 m) of hot ash on Herculaneum. This surge also devastated the entire north side of Vesuvius. During this phase, the eruptive column reached the astounding height of 20 miles (32 km).
Four more pyroclastic flows buried the town to a maximum depth of 23 meters (75 feet) and extended the coastline by around 400 meters (1,300 feet).
Herculaneum was very rich as evidenced by the magnificent frescoes found in the private homes and the discovery of the largest, grandest, and best preserved villa in the ancient Mediterranean, Villa of the Papyri. While we are not sure who constructed it or for whom it was built, it was, in the 40’s B.C., the home of Lucius Calpurnius Piso, the father-in-law of Julius Caesar. The villa produced one of the most astonishing finds—a library, the only library ever preserved from antiquity. The villa’s name comes from the fact that the library contained over 1,800 scrolls of papyrus, mainly works on Epicurean philosophy by Philodemus of Gadara. Due to the fragility of the scrolls, only a few hundred have been opened (carefully and slowly) and read (the scrolls are stored at the National Library, Naples).
Since it took the pyroclastic surge of hot gas and ash less than a minute to rip through the city and instantaneously encase everything in a cover of ash that hardened in place, it allowed objects as delicate as the scrolls to be preserved.
What had just 36 hours before been an idyllic seaside settlement, Herculaneum was no more. As the dust settled, cooled and hardened, Herculaneum was entombed in a 75 foot deep layer of igneous rock.
Now that Herculaneum no longer existed, Pompeii was next.
Next up – Pompeii – The Last Days Part IV
Ann Pizzorusso is a geologist and Italian Renaissance scholar. After many years of doing virtually everything in the world of geology (drilling for oil, hunting for gems, cleaning up pollution in soil and groundwater) she turned her geologic skills toward Leonardo da Vinci. See her work on Leonardo’s Geology. You can find Ann on Facebook at Leonardo da Vinci Virgin of the Rocks and on Twitter @VirginoftheRock.