Tsunami

Tsunami
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Living on the Ring of Fire and its consequences: The 1964 Good Friday Alaskan Earthquake and Tsunami

The “Ring of Fire”

Scientists cannot accurately predict when or where an earthquake will occur. However, historically, the majority of earthquakes and volcanic eruptions have been observed along plate boundaries, such as the boundary between the Pacific Plate and the North American Plate. One of the most active plate boundaries where earthquakes and eruptions are frequently observed is the massive Pacific Plate, which is commonly referred to as the Pacific “Ring of Fire”. Some of the biggest earthquakes ever recorded occur at the intersection of these plate boundaries, where subduction zones are formed. These include the 1960 Chile earthquake (M9.5), 1964 Great Alaska Earthquake (M9.2), 2011 Great East Japan Earthquake (M9.0), and the 1700 Cascadia earthquake (estimated at M9.0).

The earthquakes themselves are relatively brief, but their effects can range far and wide. Aftershocks from these "megathrust" quakes may span days or even years. The impact of the quake may be felt hundreds of miles from its epicenter. A severe quake may trigger a chain of events, such as tsunamis, landslides, fires, floods, and pollution that extend the damage and complicate response and recovery. Even near the epicenter of a disastrous quake, much of the damage that occurs may be due to secondary events. Earthquakes on the ocean bottom may result in upward or downward shifting of large blocks of the earth’s crust. Such motion can generate a series of ocean waves called a tsunami. These waves may travel at speeds up to 500 miles per hour in the deep ocean, where they are too small to be seen. But when they reach land, they can mount to heights of tens of feet and can cause long surges that flood low coastal areas. Historically, the greatest loss of life during a subduction zone earthquake has been caused by the tsunami rather than the ground shaking.

1964 Alaska Earthquake

The 1964 Great Alaska earthquake, also known as the Good Friday Earthquake, was one the largest and best-reported distant historical tsunami to hit the Washington coast. Tsunami wave heights generally were greatest on the south coast and smaller on the north coast. Additionally, the tsunami was recorded inland in the Strait of Juan de Fuca (Friday Harbor), Puget Sound (Seattle), and the Columbia River (Vancouver).

Damages in Washington  from the 1964 Great Alaska Earthquake included debris deposits throughout the region, minor damage in Ilwaco, damage to two bridges on State Highway 109, a house and smaller buildings being lifted off foundations in Pacific Beach (the house was a total loss), and damage to the Highway 101 bridge over the Bone River near Bay Center.

What WE do TODAY will determine how rapidly our communities, our families and ourselves recover from an earthquake and/or a tsunami. Learn more about how to become better prepared for these emergencies www.shakeout.org/washington.


 

The Pacific Coast, Strait of Juan de Fuca, Puget Sound, and large lakes are at risk from tsunamis, trains of waves that threaten people and property along shorelines. Sudden raising or lowering of the earth’s crust during earthquakes generally causes a tsunami, although landslides and underwater volcanic eruptions also can generate them. Movements of the sea floor or lake bed, or rock fall into an enclosed body of water, displace the water column, setting off a series of waves that radiate outward like pond ripples.

Only as a tsunami approaches land does it become a hazard; in shallow water, it gains height as its waves slow and compress. Tsunamis do not resemble their usual icon, a towering wave with a breaking crest. Instead, they come onshore resembling a series of quickly rising tides, and they withdraw with currents much like those of a river. Swift currents commonly cause most of the damage from tsunamis. A Pacific Ocean tsunami can affect the entire Pacific basin, while a tsunami in inland waters can affect many miles of shoreline.

Tsunamis typically cause the most severe damage and casualties near their source. There, waves are highest because they have not yet lost much energy. The nearby coastal population often has little time to react before the tsunami arrives. Persons caught in the path of a tsunami often have little chance to survive; debris may crush them, or they may drown. Children and the elderly are particularly at risk, as they have less mobility, strength, and endurance.

Tips and Information about Tsunamis

Vertical Evacuation

Tsunami Warnings and Information

Understanding Tsunami Hazards in Washington - Fact Sheets by County (PDF)

Tsunami Preparedness Information

Tsunami Evacuation Maps by County (DNR)

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Vertical Evacuation

Project Safe Haven Reports

Final Report Cost Breakdown

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