After attacks by the Screaming Death, Thor Rock Island has been reduced to to cluster of five large, pointy sea stacks with jagged rocks piercing out of them. The holes from the burrowing Screaming Death can still be seen on its bare surface.
During the events of "Appetite for Destruction", the Dragon Riders survey dragon populations on several islands. As the Riders each mark dragons with different colored paint, they realize that dragons from one island are ending up on the others. They discover that these islands are being systematically destroyed and the dragon populations are migrating. Astrid and Hiccup travel to Boarhead Island which has vanished, then to Thor Rock Island and find it crumbling into the sea. A Screaming Death is responsible, destroying islands as it makes its way to Berk.