Awesome explanation of the Calalmities. Thanks for this!First Calamity was Wind and I'm pretty sure nothing is known at all. That would have been the Ascians' second attempt at a Rejoining, after the failed first attempt with the Thirteenth.
Second Calamity was Lightning. Generations of nature being despoiled as man expanded and became civilized threw nature out of balance until it hit back with volcanic eruptions that spat out ash that turned the sky dark, which in turn created lightningstorms that lasted a year.
Third Calamity was Fire. The Second Calamity had led to a religious age of people fearing the power of the gods, but that in turn led to holy wars being waged as different religions fought each other for control. "Towns were burned, children sold into slavery, all while men and women died in the thousands. With no one to tend the fields at home, crops withered, leaving those few who had not marched to war to starvation." The Calamity itself was the sun expanding so much that the heat sapped away the life of the land. The only cause we are given for it is the gods grew tired of mankind's fighting, so clearly that's not accurate.
Fourth Calamity was Earth. Dalamud's power backlashing against the Crystal Tower caused a massive earthquake that decimated Allag.
Fifth Calamity was Ice. We don't know the cause but we know the accompanying Umbral Era was an ice age that froze the oceans.
Sixth Calamity was Water. The War of the Magi upset the balance of aether until there was a massive flood.
Seventh Calamity was all of the elements aspected toward Astral (Darkness). That's Bahamut.
The Eight Calamity in the bad future we stopped with Shadowbringers was all of the elements aspected toward Umbral (Light). The Black Rose, its power amplified by the light aether flowing in from the First, killed thousands of people including the WoL and Scions, and stripped life from the land, leading to the collapse of civilization and centuries of people fighting each other for what little resources remained.