So Sphene clearly calls it the "Calamity of lightening" and in FF14 lore that references the 2nd calamity. Right off the wiki
The Second Umbral Calamity or Calamity of Lightning came on the heels of the First Astral Era, an age where mankind learned to forge stone tools and established settlements and towns, which grew into kingdoms that soon went to war, each seeking to expand their domain. To forge their tools and weapons, mountains were gutted and skies blackened.
This calamity occurred before the 5th Calamity of Ice.
The Fifth Umbral Calamity or Calamity of Ice is shrouded in mystery, much like the preceding Fourth Astral Era. It began the Age of Endless Frost, a seemingly never-ending winter that brought raging snowstorms and giant rivers of ice.
According to the endgame zone the South Sea Lalas evacuated to the shard Sphene is from and invented Electrope on that shard. The world went to war and Emet or someone caused a rejoining by tricking probably Cid into using the Lightening weapon.
How does the 5th Calamity occur leading the Lalas to leave for a place that ends up having the 2nd Calamity?!?!?
It has to be time travel right?!?!?