The new movie "Pompeii" reconstructs one of the most famous volcanic eruptions in history with unprecedented "3D" special effects - but even the best visuals can't help if the science is wrong - so how geological accurate is the movie?
Fig.1. Mount Vesuvius as reconstructed in the new film "Pompeii" (from the movie trailer – copyright for it is most likely owned by either the publisher or studio, it is believed that the use of low-resolution images for discussion and education purpose qualifies as fair use under United States copyright law).
The profile of Vesuvius dominating the Bay of Naples is today one of the most recognizable skylines in the world - however how did Vesuvius Mons, name given by the ancients Romans to the mountain, look at the day of the eruption, almost 2.000 years ago?
The appearance of Mount Vesuvius and the surrounding area before the catastrophic eruption has been - and still is - a topic debated by geologists and archeologists alike. In case of Vesuvius we not only have some geological clues, but also written descriptions and maybe some contemporary drawings.
Roman authors who cite Vesuvius in their works include Strabo (60 BC-23 AD), Vitruvius (80 BC-15AD) and Diodorus Siculus (90 -27 BC). Strabo describes in his "Geographia" the "burned" rocks of the mountain and compares Vesuvius with the more active Etna. Also Diodorus and Vitruvius seem to have grasped the volcanic origin of the mountain:
"It is said, that once a fire burned below Vesuvius and spilled out a boiling flood, inundating the nearby countryside: so that the rock now called Pompeian Pumice, once was another sort of rock, reduced by fire to its actual quality."
Naturalists of the time therefore acknowledged and described the ancient and true nature of Vesuvius - however the quiet mountain was not considered a real danger anymore at the time - Pliny the Elder (23 BC - 79 AD), who owned a villa near the Gulf of Naples and who shall die in the eruption, doesn't even mention the volcano in his works.
Also in the paintings found in the ruins of Pompeii mountains are not very prominent - with the exception of one fresco, discovered between 1879 and 1881 in the so called "House of the Centenary". The fresco of "Bacchus and Vesuvius" shows a mountain with steep slopes and a single summit.
Fig.2. Bacchus, god of pleasure and vine, shown with a mountain covered by vineyards. Soils of volcanic origin are very fertile and the sunny slopes of Vesuvius ideal for vineyards - however the interpretation as Mount Vesuvius is somehow dubious a s it doesn't match written descriptions (image in public domain)
Indeed Strabo describes the slopes of Vesuvius covered by vineyards and forests, but he mentions also a flat top or a volcanic dome (?) without vegetation, a detail not shown in the fresco.
"Vesuvius Mons overlooks these cities, covered entirely, with the exception of the summit, by cultivated fields. The top is mostly flat, without vegetation and of grayish color, it shows deep fissures, whose reddish rocks seems have been eroded by time. "
Another, less know drawing from Pompeii seems to support Strabo's description. In the background of a fresco from the House of the Citharist, discovered between 1853 and 1868, a couple (identified as Aeneas and Dido or Mars and Venus) is relaxing in the shade of a flat-topped mountain.
One of the most detailed descriptions of Vesuvius is provided by the historian Dio Cassius (155-235 AD), however his description could fit the volcano also after the historic eruption:
"... Mount Vesuvius overlooks the sea ... and contains copious sources of fire, the summit is of regular shape, so that the fire is found in the center.. the fire consumes the rocks in the middle, however the peaks around retain their ancient height, but the inner part, consumed by fire and time, has become hollow and was refilled by sediments, so that the entire mountain looks like an amphitheater. The higher ground of that mountain is covered by many trees and vines..."
Available geological data isn't good enough to settle the debate, but it also suggests that Vesuvius was probably more a flat-topped, quite unimpressive, mountain at the time of the 79 AD eruption. The distribution over a large area of the "Avellino pumice" suggests that Vesuvius lost much mass and height during a prehistoric eruption dated to 1.880 - 1.680 BC.
The crater formed during the 79 AD eruption was later destroyed by an eruption in 472 AD. Since 1631 pictures of Vesuvius show the today familiar outline, with the two peaks formed by the caldera rim of Monte Somma, surrounding the inner Gran Cono.
Fig.3. "View of Vesuvius and surrounding area after the destruction by the eruption of the year 1631" by Giovanni Morghen from G.M. Mecattis "Racconto storico-filosofico del Vesuvio" (1752) - showing the town of Resina (labeled with "I", and build on the ruins of Herculaneum) destroyed by a lava flow. The shape of Mount Vesuvius in 1631 already resembled its modern topography (image in public domain).
The Verdict : the movie-volcano looks probably much more dramatic than the real Vesuvius ever did...
DE CAROLIS, E. & PATRICELLI, G. (2003): Vesuvio 79 d.C. la distruzione di Pompei ed Ercolano. L´ERMA di BRETSCHNEIDER: 129
PARASCANDOLA, A. (1938): L' attività e la forma del Vesuvio nell' antichità e l' origine del suo nome. Gli Abissi, Vol.1.