HUNTING FOR THUNDEREGGS

Uncovering A “Ghost” Volcano’s Treasures

- JIM LANDON

Washington State bears a complex geologic history. Millions of years of plate tectonic interactions have led to a diverse assemblage of exotic terrains, massive deposits of flood basalts, and multiple stratovolcano volcano formation cycles. Mt Saint Helens, Mt Rainier, and Mt Adams or Pahto — as members of the Yakama Nation call it, are three of the largest and still active representatives of these stratovolcanoes.

Perpetually snow-covered peaks command the Cascade mountain range that divides the state into a lush rainforest on the west and sagebrush-dominated desert on the east. To the average person, these imposing volcanoes look like they have been a permanent part of the landscape, but in reality, in geologic time, their presence is somewhat fleeting, having formed and eroded into obscurity in the course of two million years or so. The nature of how they develop from repeated ash, pyroclastic mudflows, and lava eruptions make them vulnerable to rapid erosion, especially in a climate with high rainfall and glacial action. There have been multiple cycles of cone formation and subsequent erosion in the past 24 million years. A remnant of one such ancient ghost volcano is Edgar Rock.