I watched the "Visual Record of the Day of Lavos" again.
On the
1999 AD world map, Lavos erupts from the middle of the eastern continent. In 1000 AD this correlates with Heckran Cave, WSW of Medina and of the Gate connecting Medina to Proto Dome.
Death Peak is also WSW of the Medina-Proto Dome Gate, and by roughly the same distance. I don't know if it is Lavos's shell, but it certainly seems to have been created by Lavos's awakening, as there is no mountain there in 1999 AD.