Search - The Dolphins' Bell (Dragon Riders of Pern)

Okay short novelette. To bad she's given up writing.

Nine years after human beings first came to the planet Pern, the colony at Landing, far to the south, faced a catastrophe that threatened to undo much of what they had all worked so hard to accomplish.
Two long-dormant volcanoes were on the verge of erupting, and the settlers' only hope of survival was to rejoin those who had long since gone north, seeking a haven from Threadfall.
It was a time when the telepathic 'dragons' were yet in their infancy, a time when the humans' most dependable allies in the taming of a world were the dolphins they'd brought with them from Earth. So they rang the big bell at Monaco Bay to summon their seagoing dolphin friends to help in moving the Landing colonists to safety in the north, in wild weather, across treacherous seas, in the face of the inimical Thread.