Tsunamis are probably the most dangerous natural disaster that could affect Seaside and Gearhart. A new map is now available from the Oregon Department of Geology and Mineral Industries (DOGAMI) to help these communities prepare for tsunamis.

"This map shows how three different tsunamis might affect the area," explains Dr. George Priest, a coastal hazards geologist with DOGAMI, who prepared the map in cooperation with the City of Seaside. "Tsunamis are a series of waves generated by undersea earthquakes, so we’ve used computers to simulate three different local earthquakes and the tsunamis they might cause." These simulations were used in conjunction with field–based mapping and analysis of core samples to produce the map.

Scientific research in the past ten years has established that great (magnitude 8 to 9) undersea earthquakes off the Oregon coast cause devastating tsunamis to strike every 300–600 years. "The last event was 298 years ago, on January 26, 1700, so another could happen at any time," Priest says. "The earthquake itself might last up to four minutes, damaging roads, bridges, and other facilities. Within 5 to 30 minutes after the start of the earthquake, the first of several large high velocity tsunami waves will hit the coast. It’s important that people know the safest way to go to high ground, or at least go as far inland as possible."

The map also outlines the areas flooded by the 1964 tsunami, which struck the Oregon coast. Earthquakes under much of the Pacific Ocean can create tsunamis that affect the Oregon coast. The 1964 event was triggered by a great earthquake in Alaska. Tsunami waves up to 170 feet high struck Alaska, killing 106 people. By the time the waves hit the Seaside-Gearhart area, they were small enough to cause only moderate damage to areas right next to the waterfront. However, the same tsunami killed people near Newport and in Crescent City, California, so even these smaller waves from distant earthquakes are cause for concern.

Officials from DOGAMI and Oregon Emergency Management are working with coastal cities to identify evacuation routes. The new map and similar maps will help them find routes that will be least affected by tsunamis. Signs to mark the routes so that residents and tourists can easily find them are available from DOGAMI.

DOGAMI is also coordinating tsunami education as part of a comprehensive strategy to reduce risk. Educational efforts include materials, such as videotapes and curriculum for schools to teach children how to react, information signs on beaches, and cards to be placed in motel rooms.

The map has an aerial photo as its base, so that streets and buildings can be identified. Each potential tsunami flooding area is outlined, as is the actual flooding level of the 1964 tsunami. A community advisory committee worked with Priest on the format and content of the map.

Because of the potential loss of life and property from these events, many government agencies have contributed to this map and will continue to work with the communities. The Oregon Graduate Institute of Science and Technology, Portland State University, and the National Oceanic and Atmospheric Administration provided scientific research to produce the map. The State of Oregon and the City of Seaside helped fund the project.

The publication, Tsunami Hazard Map of the Seaside-Gearhart Area, Clatsop County, Oregon, DOGAMI map IMS–3, is available for $6 from the Nature of the Northwest Information Center, 800 NE Oregon Street #5, Portland, 97232, (503) 872-2750; and the DOGAMI field offices: 1831 First Street, Baker City, 97814, (541) 523-3133; and 5375 Monument Drive, Grants Pass, 97526, (541) 476-2496.