August 25, 79 A. D., Pompeii
Herculaneum had ceased to exist, entombed in 75 feet of igneous rock. Pliny’s lifeless body lay on the beach at Stabia where it would rest for another three days. Strong earthquakes shook the entire Vesuvian area, from Miseno to Stabia.
At Pompeii, many people who did not escape between the afternoon and night of the 24th took shelter in the ground-floor spaces of buildings and were trapped by the accumulation of pumice that blocked doors and windows. Eventually, they died from progressive asphyxiation, or from an attempt to flee. Others died when they were crushed by collapsing roofs and masonry structures. Those who had taken refuge indoors with access to a higher level of egress were able to climb out and escape.
Amidst this chaos, something strange happened at Pompeii on the morning of the 25th. The rain of pumice which had battered the city for 18 hours became much less intense. There was still the roar of the volcanic cloud, but the deafening clatter that the pumice made when it hit a structure was much diminished. It seemed as if the worst was over and the people who had taken refuge inside took to the streets to start their journey to safety. Many carried sacks with precious objects; others led children and the infirm. There was a sense of cautious relief that they had escaped the volcano’s fury and would ultimately survive. They headed toward the southern sector of the city, to reach the roads leading out.
What they didn’t realize was that this reprieve from the pounding of the pumice was not a good sign. It was a signal that the type of eruption was about to change from the Plinian, with its fierce eruptive column, to a Peleean with deadly pyroclastic flows. Pompeii was further from Vesuvius and the first two pyroclastic flows that buried Herculaneum, Boscoreale, Oplontis and Terzigno did not reach it.
At about 6:30 am, a third surge was the first to reach Pompeii. It stopped along the north side of the city wall near the Herculaneum Gate, but may have not penetrated into the town itself. It asphyxiated those who had taken refuge in the underground areas of the Villa of the Mysteries and the Villa of Diomedes, both outside the Herculaneum Gate.
At between 7:30-8 am, the earth shook violently, producing the new surges which would reach Pompeii. The first two surges, a few minutes apart, poured over the city walls and reached the center of the city. It caught the Pompeiians completely by surprise and killed everyone instantly. The surge was like a killer wave that descended on the city with temperatures of 212-750° F (100-400° C) and a toxic mixture of ash, dust and gas which wiped out every living thing in its path. Most of the victims of these two pyroclastic surges, both indoors and out, were discovered between layers of ash about 6-8 inches (15-20 cm.) thick, deposited by the two surges. It was the velocity of this surge combined with the instantaneous covering of a layer of ash that entombed the bodies intact and allowed casts to be made of the remains in the early 1900′s. This technique of casting was developed by Italian archeologist Giuseppe Fiorelli.
The fifth surge, then swept over the town, burying it up to a depth of 60 cm. (2 ft.) to the south and 1.8 meters (6 ft.) to the north. Continuing its deadly and destructive course, the surge took only a few minutes to strike the entire region south of Pompeii, arriving at the seaport near the coastal lagoon and the river port on the Sarno River. It killed all those who were still hoping to escape the eruption’s fury. It changed the course of the river and extended the coastline so that today Pompeii is landlocked, much different than its configuration as a port city in 79 A.D.
Around 8 am an enormous pyroclastic cloud, the sixth surge, was emitted, bringing the most destructive of the events that violently struck the city of Pompeii, which was by now buried beneath a blanket of pyroclastic deposits about 1.20 meters (4 feet) deep. The cloud was preceded by lightning and fire and by a strong smell of sulfur in the air. The same surge continued its violent and destructive course over the rest of the region, reaching Stabia.
This final surge was so powerful that it swept across the Bay of Naples to the island of Capri in the south and Miseno in the west, both 30 km (18 miles) from the volcano. Fortunately the surge had lost its heat and power and caused only dense deposits of ash. This is the surge which Pliny the Younger wrote about in his letter as having frightened everyone into abandoning their homes in Miseno and fleeing.
The activity of Vesuvius continued for days with lesser violence. In the end, the tops of the highest walls were the only things left unburied the sole testimony that remained of the city of Pompeii. Herculaneum had completely disappeared, and the entire region had taken on the appearance of a desert.
The morphology of the volcano was changed radically. The violent eruption had destroyed its summit and the mountain took on the desolate appearance described by Statius, a Roman poet born and bred in Naples and Martial about ten years after the catastrophe. They wrote of ash that, like a mournful blanket covered the landscape that had until then been green and lush.
“Such songs I intoned for you, Marcellus, from the Cumaean shores wherever Vesuvius vented its convulsive wrath, pouring out fires that rivaled the flames of Aetna. Surprising Faith! When the crops are reborn and these deserts flower anew, will a fortune-seeking generation of men believe that beneath their feet lie cities and people and that their ancestral companions were swallowed up below? And yet this summit does not cease its mortal threat.” (Silvae, IV,4, 78-86)
“Here is Vesuvius, so recently verdant with shaded vines, here prized grapes overflowed the vats; Bacchus loved these slopes more than the hills of Nysa, in the past satyrs performed their dance on this mountain; this was Venus’s abode, more agreeable to her than Sparta, this was the place named for Hercules. Now all lies submerged in flames and in sad stone; now the gods must regret that it was they who allowed such power to be exercised here.” (Epigram IV,44)
And so the mountain that had suddenly become a volcano, and the cities which had teemed with life just hours before, were obliterated. They became the stuff of myth. The landscape would be lush and fertile once more, but the cities slowly faded from memory until one day, some 1,500 years later they would be rediscovered.
Next up - The Vulcanalia
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.