Boarhead Island

Boarhead Island is an island that was mentioned in "Appetite for Destruction", but was completely sunken by the Screaming Death.

Dragons: Defenders of Berk
During the events of "Appetite for Destruction", Hiccup and the rest of the riders, in a dragon migration census, tag the dragons found on Boarhead Island with Periwinkle Blue paint. The Screaming Death soon tears through the island, sinking it, while the wild dragons flee across to surrounding islands like Crescent Island.