The Great Cataclysm also known as the Great Earthquake occurred in the region around the town of River's Rest in 5018, M.E..
The earthquake irreversibly altered the fate of River's Rest as an end point of river trade on the Tempest River. It did this by shifting the ground up in some places as high as thirty feet and created the Tempest Falls. The quake was centered just east of the town and was powerful enough to be felt as far as Waterford and Fairport. Many of the stone buildings in River's Rest collapsed, and those structures built of wood later burned from escaped cooking fires.
A wizard, Kiergaunt Pandarre, who lived in a tower opposite of the town on Maelstrom Bay, was a victim of the earthquake. A purveyor of inter planar travel, the mage had ventured to a water world he had discovered. The cataclysm shattered the carefully prepared teleportation circle he had created, thus sealing him away in the world he had gone to visit.