What is the name of the catastrophe that destroyed Númenor in J.R.R. Tolkien’s legendarium?

The catastrophe that destroyed Númenor in J.R.R. Tolkien’s legendarium is called the Downfall of Númenor.

Númenor was an island kingdom founded for the Edain after the wars of the First Age. Its people were granted long life and great knowledge, but they became increasingly fearful of death. Under King Ar-Pharazôn, Númenor challenged the power of the Valar and eventually sailed against Valinor.

The Downfall followed when Eru Ilúvatar changed the shape of the world. Númenor was overwhelmed and sank beneath the sea, while the surviving Faithful escaped to Middle-earth. Their leaders, Elendil and his sons Isildur and Anárion, later founded the realms of Arnor and Gondor.

The event is recounted in the section called Akallabêth, a Quenya word meaning “The Downfallen.” It is often compared with the Atlantis tradition, but Tolkien gave the story its own theology, chronology, languages, and political history.