Long Before the Tonga Volcano There Was the 1964 Alaska Earthquake

That volcano sits within what’s known as the Pacific “Ring of Rire”, an area that contains 75 percent of the world’s volcanoes, and where 90 percent of the world’s earthquakes occur.

The Ring of Fire

The Ring of Fire is over 25,000 miles (40,000 km) in length, running in a circular arc northward from New Zealand to Australia, then onward from Indonesia to the Philippines and Japan, then stretching eastward to the Aleutian Islands, and southward down the west coast of North America and along the west coast of South America.

The Ring of Fire is where several of Earth’s tectonic plates meet and create subduction zones. The theory of plate tectonics was formulated during the 1960s, and it describes the 60-mile-thick (100 km) outer layer of the Earth, known as the lithosphere. The heat from the mantle causes the rocks at the bottom of the lithosphere to become slightly elastic, which allows the plates to move.

The lithosphere is comprised of eight major plates and a number of smaller plates, including the North American, Caribbean, South American, Scotia, Antarctic, Eurasian, Arabian, African, Indian, Philippine, Australian, Pacific, Juan de Fuca, Cocos, and Nazca plates.

The plates move relative to one another, and at their boundaries, they can converge (called a destructive boundary), diverge (called a constructive boundary), or slip beneath each other (a transform boundary). This movement can lead to the formation of mountains, lakes, and seas, as well as earthquakes.

Subduction zones are areas where one tectonic plate slides beneath another, causing rocks to melt and creating magma. The magma then rises to the surface and can cause volcano formation. The Hunga Tonga-Hunga Ha’apai volcano was created by the Pacific Plate subducting beneath both the Indo-Australian Plate and the Tonga Plate.

Besides creating volcanoes, subduction zones are where Earth’s most violent earthquakes take place. It was in one such subduction zone, where the Pacific Plate was being overridden by the North American Plate, that Earth’s second most powerful earthquake ever recorded took place.

Almost the mother of all earthquakes

At 5:36 p.m. on March 17, 1964, Good Friday, most Alaskans were heading home from work and starting their dinners when the ground started to shake. The shaking lasted for a staggering four and a half minutes.

Fissures opened up in the ground, houses and buildings collapsed, and paved streets and sidewalks crumbled. Water and sewer mains broke, and electrical and gas lines were severed.

Underground landslides 15.5 miles (25 km) below the surface caused tsunamis that hit the coastal towns of Valdez, Whittier, Seward, and Kodiak. At Valdez, in Prince William Sound, the harbor and docks collapsed, enveloping a ship that was docked there and causing the deaths of 32 people. The tsunami also ruptured the Union Oil Company’s oil tanks, igniting a massive fire. 

Areas around Montague Island, Alaska rose between 13 and 30 feet (4 to 9 m), dragging millions of barnacles and starfish above the water to their deaths. By contrast, the area around Portage, Alaska dropped by 8 feet (2 m).

A 27-foot-high (8.2 m) tsunami hit the village of Chenega, Alaska, killing 23 people, while coastal areas of Canada’s British Columbia and the U.S.’s Washington State, Oregon, and California also experienced tsunamis. Twelve people near Crescent City, California were killed by the tsunami, while in Oregon, four children were killed while at the Beverly Beach State Park. The tsunami reached as far as Hawaii and Japan, but was much diminished by then and caused little damage to those areas.

At the Vancouver Island town of Port Alberni, the tsunami washed away 55 homes and damaged 375 others. Canada’s damage was CA$10, which in today’s U.S. dollars is $78 million. 

In all, 139 people are believed to have died as a result of the Alaska earthquake, and property damage was estimated at $116 million at the time, which in today’s dollars is well over three-quarters of a billion dollars.

Damage in Anchorage

In Anchorage, Alaska’s largest city, soil liquefaction destroyed the Turnagain neighborhood, moving parts of a bluff 2,000 feet into the bay and taking around 75 homes with it, while at Anchorage International Airport, the 60-foot-high (18 m) control tower collapsed, killing the air traffic controller on duty at the time.

About 20 miles (32 km) of the Seward Highway sank below the high water line and both it and its bridges later had to be raised and rebuilt. Following the earthquake, the U.S. military, which has a number of bases in Alaska, stepped in to re-establish communication with the lower 48 states, and troops were sent to the cities of Anchorage and Valdez. The city of Valdez was never rebuilt in its original location but was instead moved four miles (6.4 km) further inland.

U.S. Navy and Coast Guard ships were dispatched to aid coastal communities, while a military airlift delivered 2,570,000 pounds (1,170,000 kg) of food and other supplies in the days immediately following the quake.

The 1964 Alaska Earthquake was determined to have measured 9.2 on the Richter Scale, making it the second-largest earthquake ever recorded, with only the May 22, 1960 earthquake in Valdivia, Chile, which registered 9.6, being greater. 

The Richter scale, which is a measure of the strength of earthquakes, was developed by American seismologist and physicist Charles Richter in 1935. Today, scientists also use other scales, such as the moment magnitude scale, to measure earthquakes.