The tidal wave
The tidal wave originated from within the Sea of Time in the center of the Great Eastern Sea. It was generated when a mythical entity by the name of Poseidon violently reawakened from its slumber inside the sea's rocky perimeter, and Poseidon awoke in response to the activation of the Mercury Lighthouse and Venus Lighthouse.
Effects of the wave
Idejima, which recently tore itself off the continent of Gondowan when Venus Lighthouse was lit and became literally a buoyant island floating east out into the sea, was in the process of passing by the continent of Indra by the north end. The tidal wave drove it into the continent below, and the entire continent actually shifted positions southwest to physically collide between lower Gondowan and northwestern Osenia.
The Tidal Wave destroyed the boats in Daila on Indra's north end, and it destroyed much of the coastline town in Alhafra and damaged the Sailing ship the town recently completed. It also shipwrecked Briggs and his crew's ship, causing them to look for a replacement.