Tal'Dorei During the Calamity

One of the first casualties of The Calamity was Lolth. Her suddenly leaderless drow followers fled from the surface world to rebuild their empire underground; in Gwessar they found themselves surrounded by aberrations, the eventual seat of their power would be Ruhn-Shak, and their leaders began hearing the whispers of Tharizdun.
During The Calamity  the cities of the Kuul'tevir were reduced to rubble, and those who perished in Vos'sykriss began to haunt the city as ghosts. The dwarven kingdom of Uthtor was likewise destroyed. A wandering colony of elves fleeing The Calamity formed the beginning of what would become the Orroyen tribes of the Rifenmist Peninsula.
In the northeastern reaches of the continent, Ioun baited Tharizdun to her central temple, resulting in her near-destruction. Pelor's subsequent vengeful battle with Tharizdun was so violent, it created the valley where the Parchwood Timberlands stand and raised the Alabaster Sierras. Badly defeated and wounded, Tharizdun retreated to Acek Orattim's realm, but Pelor chased and banished Tharizdun there, beneath Gatshadow.
Whether it was in that battle or another, the land bridge connecting Gwessar and Wildemount was shattered, creating the Shearing Channel.
In the far south of Gwessar, in one of the final battles of The Calamity, Bane and his Goblinkin armies waged the last of their many battles with Melora and her Free Children. After a tremendous battle that permanently reduced the area to sterile ash, Bane was defeated and banished, the gigantic suit of pitted iron armor he wore fell to the ground, and the surviving goblinkin were scattered. This area would become known as the Beynsfal Plateaus.
The final battle of The Calamity, in far-off Wildemount, sent shockwaves through Exandria and unintentionally collapsed much of the underground cavern network of Gwessar, bringing about the fall of the aboleth civilization there.