What catastrophic event destroys Númenor in J.R.R. Tolkien’s legendarium?

The catastrophic event that destroys Númenor in J.R.R. Tolkien’s legendarium is the Downfall of Númenor.

The Downfall of Númenor is told most fully in “Akallabêth,” one of the major sections of The Silmarillion. Númenor is an island kingdom granted to Men who remained faithful to the Valar after the First Age. Over time, fear of death and resentment toward the immortal Elves grow among its rulers.

King Ar-Pharazôn eventually challenges the divine order by sailing west with a great armada. Sauron, who has been taken to Númenor as a captive, manipulates the king and encourages the worship of darkness. The attempt to invade the Undying Lands leads to divine intervention: Númenor is overwhelmed and sinks beneath the sea.

The event also changes the shape of the world from flat to round. Elendil and his sons survive by sailing away and later establish kingdoms in Middle-earth. The catastrophe is therefore both a mythic punishment and a turning point in the history before The Lord of the Rings.