1964 Alaska Earthquake: The Great Good Friday Quake and Tsunami

The 1964 Alaska earthquake, known as the Great Alaska or Good Friday earthquake, struck south-central Alaska at 5:36 pm local time on 27 March 1964. With a magnitude of 9.2, it is the most powerful earthquake recorded in North American history and the second strongest ever measured. Shaking, landslides and tsunamis devastated Anchorage, Valdez, Seward and many coastal villages, and the waves caused deaths as far away as California.

Background: where two plates meet

Southern Alaska lies above the Aleutian subduction zone, where the Pacific Plate moves north-westwards and slides beneath the North American Plate at around 5 centimetres a year. Strain builds up on the boundary between the plates until it is released in very large earthquakes.

In 1964 Alaska had been a US state for only five years. Its population was about 250,000, and Anchorage, the largest city, had grown rapidly since the Second World War. Much of the coast was dotted with small fishing towns, canneries and Alaska Native villages.

The earthquake

The rupture began beneath northern Prince William Sound, about 120 kilometres east of Anchorage, at a depth of around 25 kilometres. It spread south-westwards for roughly 800 kilometres along the plate boundary, towards Kodiak Island. In most places the ground shook for about four and a half minutes, much longer than in ordinary earthquakes.

Across an area of around 250,000 square kilometres, the land surface permanently changed level. Parts of the coast and seabed rose by up to about 11 metres, especially on Montague Island, while other areas sank by up to about 2.4 metres. Near Portage and Girdwood, subsidence let salt water flood coastal forests, killing the trees and leaving “ghost forests” that still stand today.

Destruction in Anchorage

In Anchorage, the shaking triggered large landslides in layers of weak clay beneath the city. In the Turnagain Heights neighbourhood, a strip of bluff more than 2 kilometres long slid towards the sea, breaking up some 75 houses. Downtown, part of Fourth Avenue dropped several metres in a landslide, and buildings including the new J. C. Penney department store were badly damaged. Government Hill Elementary School split apart as the ground beneath it failed.

Because it was Good Friday and early evening, schools were empty and many offices closed. This is widely thought to have prevented a much higher death toll.

Valdez, Seward and the tsunamis

The most deadly effects came from water. In several fjords the shaking caused underwater landslides that generated local waves within minutes, before any warning was possible. At Valdez, the waterfront and dock slid into the sea, killing about 30 people, many of them watching the unloading of the freighter SS Chena. At Seward, a submarine landslide destroyed the waterfront, oil storage tanks burst into flames, and waves spread burning oil across the harbour. At the Alaska Native village of Chenega, waves killed 23 people, about a third of the residents.

The earthquake also produced a larger tsunami that crossed the Pacific. Kodiak and other Alaskan towns were hit hard. Hours later, waves reached the west coast of North America. In Oregon, four children camping with their family at Beverly Beach were swept away. In Crescent City, California, a series of waves flooded the downtown area during the night and killed 11 people; others died elsewhere in California. Waves were also recorded in Hawaii, Japan and other parts of the Pacific.

Kodiak and the coastal villages

Many of the worst-hit communities were small towns and villages whose life depended on the sea. On Kodiak Island, a series of waves struck the city of Kodiak and the nearby naval station during the evening, destroying much of the fishing fleet, canneries and waterfront buildings. The Alaska Native villages of Afognak, Old Harbor and Kaguyak were badly damaged; Afognak was later abandoned and its people resettled at a new site named Port Lions.

Along the Kenai Peninsula and Prince William Sound, the changes in land level ruined harbours. Where the land rose, docks and boat landings were left high and dry; where it sank, high tides flooded streets, roads and the Alaska Railroad. Whittier, Cordova and Seldovia all suffered heavy losses to port facilities.

The economic effects lasted for years. Fishing grounds, clam beds and salmon streams were altered by uplift and subsidence, and some canneries never reopened. For many Alaska Native families, the loss of villages, boats and subsistence hunting and fishing sites meant lasting changes to their way of life.

The human and economic toll

Estimates of the death toll are usually between about 130 and 139. Only around 15 deaths are attributed directly to the shaking, while the great majority were caused by tsunamis, both local and Pacific-wide. Damage was estimated at around 311 million US dollars at 1964 prices.

Response and recovery

Governor William A. Egan led the state response, and President Lyndon B. Johnson declared a major disaster and created a federal commission to coordinate reconstruction. The US armed forces in Alaska provided rescue, shelter and supplies. Valdez was rebuilt at a new site on more stable ground about 6 kilometres from the old town, which was abandoned.

Federal and state agencies also invested heavily in rebuilding Anchorage. Engineers studied why certain neighbourhoods had collapsed, and the worst landslide areas, including part of Turnagain Heights, were not rebuilt with houses; a section later became a park. Downtown streets were stabilised, and new buildings were designed to stricter standards.

The disaster led to the creation in 1967 of what became the West Coast and Alaska Tsunami Warning Center in Palmer, Alaska, to issue rapid warnings for the region.

Scientific significance

The 1964 earthquake was studied in unprecedented detail by the US Geological Survey and other bodies. Mapping the patterns of uplift and subsidence, the geologist George Plafker concluded that the earthquake had occurred on a gently dipping fault where the Pacific Plate was being pushed beneath Alaska. This interpretation, published in 1965, provided strong evidence for the new theory of plate tectonics, which was transforming geology in the 1960s.

The Alaska and 1960 Valdivia earthquakes became the models for understanding megathrust earthquakes, a type later seen in the 2004 Indian Ocean tsunami and the 2011 earthquake off Japan. The lessons learned about ground failure in Anchorage also influenced building codes and land-use planning in earthquake zones.

Timeline

• 1959, 3 January: Alaska becomes the 49th US state.
• 1964, 27 March, 5:36 pm: The earthquake begins beneath Prince William Sound.
• 1964, 27 March, minutes later: Local waves destroy the waterfronts of Valdez and Seward and strike Chenega.
• 1964, 27–28 March, night: The tsunami reaches Oregon and California, killing people at Beverly Beach and Crescent City.
• 1964, April: President Johnson sets up a federal commission for reconstruction in Alaska.
• 1965: George Plafker publishes his interpretation of the earthquake as a megathrust event.
• 1967: A regional tsunami warning centre is established in Palmer, Alaska.

Why it matters

The Good Friday earthquake was one of the most powerful natural events of the twentieth century. It reshaped Alaska’s coastline and towns, showed the deadly reach of tsunamis, and gave scientists key evidence for how the largest earthquakes on Earth occur.