The water rises and melts rock in its path. A by-product of the metamorphism is the release of hot fluids, especially water. The rocks on top of the plate are metamorphosed due to the great temperatures and pressures at those depths.

Farther east the Juan de Fuca Plate descends deeper and deeper. Near the western edge of the continent, the Juan de Fuca Plate plunges downward and some of the layers of hard crust and ocean sediments are scraped off the top and squeezed upward as the Olympic Mountains and other coastal ranges. Two parallel mountain ranges have been forming as a result of the Juan de Fuca Plate subducting beneath the edge of North America. The Cascadia Subduction Zone, extending from northern California through western Oregon and Washington to southern British Columbia, is a type of convergent plate boundary. And as time ticks on, the region awaits sudden release of energy locked between the converging plates as a devastating earthquake. They contain explosive volcanoes formed as fluids rise from the top of the subducting plate and generate magma as they melt their way to the surface.

But parks in the Cascade Mountains – within the same subduction zone – are dramatically different. National Park Service sites in the Coastal Ranges of Washington, Oregon and northern California contain rugged mountains of rocks that were manufactured in the ocean, then scraped off the plate and lifted out of the sea. The Pacific Northwest is an exciting place to observe geologic processes in action.

Subduction boundary