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Earthquakes and Volcanoes

Related OREGON EXPLORER Info

At the beach, winter storms strip away sand covering a buried forest. A road-cut reveals massive submarine landslides triggered by earthquakes. Surf crashes on lava at a headland.

Powerful forces have shaped the Oregon coastline. Many of these are familiar: waves, water and wind. But less familiar forces have also been at work here. The Oregon coast has been wrenched by earthquakes and seared by volcanoes, and much of its beauty was born in incredible violence.

Until about 60 million years ago, Oregon was, in geologic terms, a quiet place. Then, as the North American tectonic plate slid over the ancient Farallon plate, the subduction zone began to affect Oregon. Today, a remnant of the Farallon plate, the Juan de Fuca plate, is slipping under North America. Approximately every 300-500 years, a major subduction zone earthquake occurs.

The subduction zone formed by the collision of plates also fueled volcanic activity, including the upwellings of basalt that became the heart of the Coast Range. The largest known lava flow on the face of the earth, the Columbia River Basalt Group, which began near the Oregon-Idaho border, terminates in the cold waters of the Pacific off the north Oregon coast. Today, some of the most vigorous volcanic activity in the region takes place offshore. Axial Seamount, an undersea volcano about 300 miles west of Cannon Beach, erupted as recently as 1998.

For data about coastal hazards use the Hazards Reporter. From the "Maps" tab either enter an address or place name, or use the map to select the appropriate map layer.

Sources

Bishop, Ellen Morris. In Search of Ancient Oregon: A Geological and Natural History. Portland, OR: Timber Press. 2003.

Ludwin, Ruth. Cascadia Megathrust Earthquakes in PNW Indian Legend (Link Gone) . Seattle, WA: University of Washington Earth and Space Sciences. [Accessed April 13, 2007].

Niewendorp, Clark A. and Mark E. Neuhaus. Map of Selected Earthquakes, for Oregon, 1841 through 2002. Portland, OR: Department of Oregon Geology and Mineral Industries. Open File Report 03-02. 2002.

Oregon Department of Geology and Mineral Industries. Earthquake Hazards in the Pacific Northwest. Portland, OR: The Department. [Accessed April 12, 2007].

Oregon Department of Geology and Mineral Industries. Volcanic Hazards. Portland, OR: The Department. [Accessed April 13, 2007].

Orr, Elizabeth L. and William N. Orr. Geology of Oregon. 5th ed. Dubuque, IA: Kendall/Hunt Pub. Co. 1999.

Orr, Elizabeth L. and William N. Orr. The Other Face of Oregon: Geologic Processes that Shape Our State. Oregon Geology, vol 61 (6): 131-139, 143-150.

Compiled by Susan Gilmont, Staff, OSU Libraries

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