#Plate boundary series#

The Coast Range (including the Olympic Mountains) consists of sedimentary rock layers and hard crust scraped off the ocean floor where the Juan de Fuca Plate begins to dive downward. Visits to coastal NPS sites in the Pacific Northwest can help us appreciate the landscapes that develop over time because of these large quakes, and learn how we are preparing our homes, communities, and infrastructure for the next “Big One.” Coast Range These mega-earthquakes occur every 200 to 600 years or so, and the last one was in the year 1700.

#Plate boundary series#

When the plates suddenly let go, a massive earthquake will shake the entire Pacific Northwest, a series of tsunami waves will pound the Coast, and landslides will make it difficult to reach some of those in need. The largest (locked zone earthquakes) occur where the Juan de Fuca and North American plates are stuck together, as they have been for the past three centuries. But thousands of eruptions over less than a million years have built Mount Rainier and other Cascade peaks to elevations of more than 10,000 feet (3,000 meters)!Ī variety of earthquakes shake the Pacific Northwest due to plate-tectonic activity. Likewise, individual volcanic eruptions may add only a thin layer to the surface. That may not seem like much, but when tens of thousands of earthquakes occur over a few million years, coastal ranges form. Individual earthquakes can offset or lift the land a fraction of an inch or a few inches (centimeters) at a time. This beauty is part of the reason that residents and visitors have learned to tolerate, and develop ways to mitigate, the effects of earthquakes, tsunamis and volcanic eruptions-beasts that are consequences of the same tectonic forces that create the region’s beauty. Lillie, Wells Creek Publishers, 75 pp., 2017, Subduction in the Pacific Northwest creates incredible beauty in the form of coastlines, mountains, and valleys-iconic features of the many National Park Service sites in the region. Modified from “Oregon's Island in the Sky: Geology Road Guide to Marys Peak, by Robert J. Rainier national parks showcase the contrasting landscapes of the two parallel mountain ranges. Subduction of the Juan de Fuca Plate results in the formation of the Coastal Ranges and Cascade Volcanoes, as well as a variety of earthquakes, in the Pacific Northwest. Garibaldi to Lassen Peak, coincides with the north-to-south extent of the subducting plate boundary.

The Cascades form above the line where the subducting plate extends to depths where it heats up, dehydrates and causes magma to form.

Puget Sound and the Willamette Valley are areas near sea level between the coastal and volcanic mountain ranges.

The Coast Ranges, including the Olympic Mountains, are made of oceanic sediments and hard rocks that were caught in the vise between the converging plates, uplifted, and added to the edge of the continent.

The Cascadia Subduction Zone is the Region where the Juan De Fuca and North American Plates Converge The low region between the two mountain ranges is the Puget Sound area of Washington and the Willamette Valley in Oregon. Some of the resulting magma makes it all the way to the surface and forms Mount Rainier, Mount Hood, Mount Shasta and other spectacular volcanoes of the Cascade Range. 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.