Mount St. Helens

Mount Saint Helens is a mountain and a volcano in Washington state, America.

History
As the Olympians move westward following Western Civilization, Mount Saint Helens replaces Mount Etna as the resting place of the Titan Monster Typhon. Though he remained dormant for millennia all through the Percy Jackson and the Olympians series until The Battle of the Labyrinth when Percy fights the telekhines who are using Hephaestus's forge to remake the Titan Lord Kronos's scythe, the seal binding him began to weaken during Kronos rise to power.

The Battle of the Labyrinth
When Percy Jackson and Annabeth Chase investigated the mountain of Hephaestus, they located a group of Telekhine forging the blade of Kronos's scythe. Percy then called on the power of the sea and caused the mountain to erupt. This weakened the seal on Typhon's prison and lead to a reaction within the mountain that awakened him, allowing him to become active in The Last Olympian.

The Last Olympian
The mountain kept erupting and is obliterated, torn apart in half when Typhon escapes.

Trivia

 * In the real world, Mount Saint Helens was almost completely destroyed during an eruption in 1980.