The Last Eruption

Kyris unrolled the old scroll carefully. The vellum had been water damaged at one point, and the edges of the scroll were beginning to crumble. The ink on the scroll was well-preserved, however, and the old glyphs were crisp. The writing, however, was familiar.
"Another Halisse religious scroll. Ugh." Kyris pushed it across the desk. "You get it down."
"Could just copy over the last one." Alistair took a glance at it. "Looks pretty much exactly the same. I bet it was the same group of scribes forced to churn these out by the dozens."
Kyris sighed. "Those scribes probably started dreaming about it. 'The end day will come! The earth will be rent asunder, and great spires will emerge to guide the chosen!'" She made a phallic hand motion. "Probably a metaphor for something more mundane, yeah?"
"I think that says more about you than about the old Halisseans." Alistair was transcribing the glyphs into Etoilean. "No, wait, there's something new here. 'Only the virtuous can walk the path, those who pledge obesiance to the ancient gods and the new ones.' Haven't seen that before."
"What happens if the old and new gods disagree? I guess we'll all end up falling off the big spire." Kyris reached for another scroll. "Could you imagine having to read this doom-and-gloom stuff on the boards each morning walking to work?"
Alistair raised an eyebrow. "How is that different from what we read now? 'Prices in the Capital City rising again! Crime is up in the Eastern Docks! The Princeps caught in flagrante delicto!' Mud and dirt and blood is what people want to read, not happy stories about everyone getting cookies and chocolate at the end times."
"Sometimes I think you're spending too much time in the Capital, Alistair." Kyris began unrolling her scroll. "You were such a nice and cheerful kid when you first arrived, and now you've gone all salt-and-vinegar on us. What would your mom say?"

Summary

The prophecy at the center of the myth is quite simple. The Preordained, the prophet of the Halissean religion, states that the world will be destroyed, with huge earthen towers emerging from a sundered landscape, and only those with the purity of soul required will be able to ascend the towers to the stars to escape their fate. Others will simply fall through the holes in the earth, never to be seen again. 
As with all religious texts, the myth around the prophecy attempted to fill in the details that the Preordained left unsaid. Halissean religious writings eventually converged in their interpretation and evolution of the prophecy, with the less interesting elements being naked graft (only those who tithe Halisse will survive the coming apocalypse). More interesting are several teleological statements describing the purpose of the spires, with the general idea being that the spires will end up carrying people to some sort of ship in the sky, letting the 'pure of soul' survive the events on the surface. The earth itself isn't merely being torn apart, in this understanding, but 'remade' (the explicit word from the writings being resurrection), with those survivors returning to live our their immortal days in a paradise version of Creus once the prophecy is complete.
Left unsaid in any of the mythology is precisely what has to happen or trigger for the Last Eruption to take place.

Historical Basis

The story of the Last Eruption is a prophecy embedded in the culture of old Halisse, an old theocracy of West Saibh that collapsed well before the rise of the Principality of Etoile. As with many of the religions of the era, the scriptures tended towards the apocalyptic. In the case of Halisse, however, the scriptures are noted as being the explicit prophecies of a single person, the founder of the Halissean religion, entitled the 'Preordained'. The Preordained won great acclaim in their era for being a prophet of some skill (or luck), successfully predicting the outcome of several wars as well as significant events such as eclipses and natural disasters. In the modern era it is recognized that this was likely the result of an advanced scientific or analytic mind.
Whoever they were, the Preordained had virtually all of their public prophecies committed to paper and widely distributed in an era predating the printing press, indicating that the Halisseans invested significant resources attempting to spread their faith. Well after the passing of the Preordained, their writings had been expanded and annotated by the religious scholars of each successive era, with entire books being dedicated to specific statements and prophecies the Preordained made in their era.
While there's no sign the Last Eruption will ever come to pass, nor is there any historical justification for the prophecy itself, the Halissean religion is well known in contemporary history and its mythology is well documented in the historical record.

Spread

Surviving Halissean writings are, for ancient historical texts, very common, with dusty scrolls a regular find in old storerooms and archives. The existence of the Halissean religion is common knowledge, but the actual details of its theology and mythology are generally only of interest to academicians and researchers.

Cultural Reception

While the Halissean religion is long-dead, it is a matter of archaeological fact that the Halisseans themselves took their religion quite seriously, including the prophecy of the Last Eruption. Many digsites of Halissean residences uncover climbing picks and old ropes, an odd possession for a Halissean, as their nation was situated in the Flats in South Saibh.

In Art

Many recovered Halissean tapestries depict the Last Eruption - jagged brown and red shapes against a blue backdrop, with small dots presumably portraying sinners falling to their deaths. Some contemporary artists have produced works along the same themes after study, with one Radonn Tural of the Academy painting a monumental mural, incorporating an abstracted Last Eruption in the backdrop of his Ending.

Date of First Recording

Unknown