Records show that, long ago during the Sixth Pass, a great Plague ravaged Pern. It devestated much of the population and even laid low the great Dragons that protected them from Thread. Slowly, it seemed, a cure was found and the people recovered. Over the next few decades, Pern seemed to recover from the devastating plague. People and animals flourished.
Then, centuries later, towards the end of the Seventh Pass, Pern suffered another massive blow, even as Thread continued to fall. Sigran Weyr, Pern's only Weyr, suffered a virulent plague that wiped out most of its population. During the last few months of the plague, a large offshore volcano, too near Sigran and its protected lands for much comfort, started exhibiting signs of activity. All too soon, it exploded in a massive eruption that swamped Sigran and destroyed the Hold, killing more than half of the remaining population.
Now, in the first few turns of the Eighth Interval, there are only a handful of riders and holdfolk left. With so few people left, they struggled to find a new home. Soon, they found it in a large extinct volcanic crater at the edge of a fertile grassland that overlooked the sea. An underground spring had erupted in the middle of the caldera to form a large lake. This lake had expanded, then broke through one wall to drain out to the distant sea. Distant forests and mountain ranges would give them much-needed supplies as soon as the mines reopened and those interested in gathering could be sent out.