twofacedgods:Vesuvius and the Eruption of AD79: Part II of the Vesuvius EditAfter noon on the 24th o

twofacedgods:

Vesuvius and the Eruption of AD79: Part II of the Vesuvius Edit

After noon on the 24th of August AD79 began an eighteen–hour eruption that would obliterate Pompeii, city of Ancient Rome, as well as Herculaneum, a port–side town some 13km away. Vesuvius had awoken: the precursory tremors that had shaken the land for days prior had gone unheeded, for such tremors were common in this region of Italy — and given the long period of inactivity that preceded this eruption, the people of these Roman settlements did not know Vesuvius to be a volcano, nor did they know that these tremors were quite literally portents of doom, signifying magma movement into shallow crustal reservoirs (as volcanic swarms are common precursors of eruptions).

The AD79 eruption of Vesuvius was bipartite, having first a Plinian phase, and then a Pelean phase. During the first phase, Vesuvius produced a column over 30km high that spread out into an umbrella cloud, raining pumice and ash down over the surrounding regions. Pompeii received the brunt of this airfall due to the prevailing wind direction, which dispersed volcanic material to the south–east of the volcano and buried the city. This stage lasted some seven hours, and many of Pompeii’s inhabitants were able to flee, carried to the safety of Misenum by boat. Still, an estimated 2000 of 20,000 people died; those who chose not to leave, were unable to leave, or were buried by collapsing buildings, which caved under the weight of the volcanic ejecta. The calcification of ash preserved the hollows in which their bodies once lay, and these hollows were infilled with plaster by archeologists to extract the impressions of these forms.

The second part of the AD79 eruption was Pelean in style, where instabilities in the convecting plume led to its collapse. In this stage, high density pyroclastic flows surged down the flanks of Vesuvius, covering Pompeii, though now the brunt of these pyroclastic density currents were partitioned towards Herculaneum. It was subsequently in this second phase that Herculaneum was destroyed, Herculaneum which had escaped burial via the pumice airfall of the first stage. For a long time, it was thought that the people of Herculaneum had escaped, given sufficient warning from the airfall phase, but a host of skeletons were discovered in the boathouses beneath the town: people who had tried to take shelter from the burning cloud, and who were instantly incinerated.