The 1960 Valdivia Earthquake: The Strongest Quake Ever Recorded

On the afternoon of Sunday, May 22, 1960, the ground under southern Chile began to move and, by the accounts of the people who lived through it, did not stop for about ten minutes. Church towers swayed and fell. Wooden houses slid off their foundations. Whole stretches of coastline dropped toward the sea. When seismologists later worked out the size of what had happened, they arrived at a number no instrument has matched since: magnitude 9.5. The 1960 Valdivia earthquake, often called the Great Chilean Earthquake, is still the most powerful earthquake ever recorded.

The shaking was only the start. Within minutes the Pacific came ashore along hundreds of miles of Chilean coast. Within fifteen hours the same waves were pouring into Hilo, Hawaii. Within a day they reached Japan, on the far side of the ocean. Two days after the main shock a volcano in the Andes began to erupt, and a mountain lake trapped behind landslides threatened to drown the city of Valdivia a second time. Here is the story of the 1960 Valdivia earthquake, the tsunami it sent across the Pacific, and the two months of work that kept it from getting worse.

A country braced, and then surprised

Chile sits on one of the most active plate boundaries on Earth. Off its coast the oceanic Nazca Plate dives beneath South America, and the strain built up along that boundary is released every few decades in large earthquakes. Spanish chroniclers recorded a great earthquake and tsunami at Valdivia as far back as 1575. People in the south knew their ground could shake.

What they could not know was how the weekend of May 21, 1960, would unfold. Early on Saturday morning a quake of about magnitude 8 struck near Concepción, roughly 100 miles north of the region that would suffer most the next day. It killed people and damaged buildings, and it was followed by a run of strong aftershocks. In the small fishing town of Queule on Sunday morning, the priest at Mass spoke to his congregation about earthquakes.

At 3:11 p.m. local time on Sunday, the main shock began. The rupture started near the Arauco Peninsula and tore southward along the plate boundary for roughly 600 miles (about 1,000 km), through an area more than 100 miles wide. The seafloor and the land above it lurched. In some places the coast rose, but across much of the region around Valdivia it fell, by as much as 2 meters (more than 6 feet). Farmland, pasture and riverside neighborhoods sank below the reach of the tides overnight.

Shaking was felt across more than 400,000 square kilometers of Chile, from Talca to Chiloé Island. Valdivia, a river port founded in 1552 and rebuilt many times, took a terrible beating. About 40 percent of its houses were destroyed, and some 20,000 people were left homeless. Puerto Montt, Ancud and dozens of smaller towns were badly damaged as well.

Waves on the Chilean coast

Along the coast, survivors noticed something strange as soon as the ground stopped moving. Rivers and estuaries drained. The sea pulled back from beaches and harbors, exposing streambeds and mudflats people had never seen dry. Then the water returned, not as one wave but as a series of them, some of the largest arriving long after the first.

In Corral, Valdivia’s port at the mouth of the river, the water first rose about 4 meters before it began to fall. The lower part of town, Corral Bajo, was swept away. Ships in the bay were torn from their anchorages. The freighter Canelo, loading timber when the quake struck, drifted for hours around Corral Bay and the Valdivia River before its crew abandoned it as a wreck that evening. Other vessels were lost in the same confusion of currents.

Decades later, the geologist Brian Atwater and the Chilean researcher Marco Cisternas interviewed survivors along this coast for a U.S. Geological Survey booklet, Surviving a Tsunami: Lessons from Chile, Hawaii, and Japan. Their accounts show how narrow the line between life and death was. In Queule, many residents walked to the nearby hills soon after the shaking ended, and that choice probably saved hundreds of lives. Jovita Riquelme’s family stayed in their house on low ground near the river. In the chaos of the waves she lost her five-year-old daughter, and her husband died of his injuries. The water reached as much as 13 feet deep in a town that sat a mile from the sea.

Outside the village of Mehuín, Vitalia Llanquimán heard from a man on horseback that the sea had drawn back from the shore. She was not worried, but her husband took it as a sign that the water would return. They carried their two youngest children up a hill and stayed there while the waves came in below them.

Farther south, around Maullín, the tsunami killed about 122 people. Ramón Atala, the town’s most prosperous merchant, went into his waterfront warehouse between the first and second waves. The second wave carried the building away, and his body was never found. On a low peninsula nearby, José Navarro’s family watched the first wave destroy the bridge they had hoped to cross to high ground. They ran instead for a barn three quarters of a mile away, which happened to belong to Atala. They reached it just as the second wave did and spent the night in its loft with 14 other people. Estimates of the wave heights along this coast run as high as 25 meters (about 80 feet) in the hardest-hit spots.

Nobody knows exactly how many people died in Chile. Official tallies and later estimates range from about 1,000 to 6,000. The USGS puts the toll from the earthquake and tsunami at more than 2,000, with property damage of around $550 million in 1960 dollars.

A volcano wakes up

On May 24, about 38 hours after the main shock, the Cordón Caulle, a long volcanic fissure beside the Puyehue volcano in the Andes, began to erupt. A plume of ash and steam rose above the mountains. Because the region was remote and the country was overwhelmed, the eruption was first reported from the air. It kept going for weeks and finally ended on July 22. Volcanologists still debate exactly how the earthquake triggered it, but few doubt the two events were linked. It was nowhere near the scale of the Laki eruption of 1783, which fouled the air over Europe, but it added ash and fear to a region already in crisis. The Cordón Caulle erupted again in 2011, spreading ash as far as Argentina, Australia and New Zealand.

Across the Pacific to Hilo

A tsunami does not lose much energy as it crosses deep ocean. The waves from Chile spread across the Pacific at the speed of a jet airliner, low and almost invisible at sea, and rose up again wherever they met shallow water.

In Hawaii there was time to get ready. At 6:47 p.m. Hawaiian time on May 22, the U.S. Coast and Geodetic Survey issued an official warning that waves were expected to reach Hilo at about midnight. Around 8:30 p.m., the coastal sirens in Hilo sounded and continued on and off for 20 minutes. But people interpreted the sirens in different ways. Earlier alerts had been followed by tsunamis that did little damage. Some residents thought the sirens meant they should leave at once; others thought they were only a first notice.

Just after 10 p.m., seismologist Jerry Eaton and four colleagues from the Hawaiian Volcano Observatory set out with cameras, notebooks, flashlights and steel measuring tapes to record the waves. They drove to the Wailuku River Bridge on Hilo Bay. The first wave, only a few feet high, arrived just after midnight. Many people who had been watching from high ground decided the danger had passed and went back down to the waterfront.

At about 1 a.m. the men on the bridge heard a roar and saw a pale wall of tumbling water moving across the bay. By 1:04 a.m. they understood that they had to run. They turned in time to watch a nearly vertical front about 20 feet high strike the bridge. The wave tore through Hilo’s low-lying waterfront and the Waiakea district, crushing frame buildings and floating others off their foundations. Only structures of reinforced concrete or structural steel stayed standing, and even those were gutted. Parking meters were bent flat by the debris.

In Hilo, 61 people died and 282 were badly hurt. Damage in Hawaii came to about $24 million. The town clock in Waiakea stopped when the largest wave hit, and it still shows 1:04. It stands today as a memorial to the 1960 tsunami.

A day later, in Japan

The waves reached Japan about 22 hours after the earthquake, early on the morning of May 24 local time, with no shaking to warn anyone. In Onagawa, a fishing town in northeastern Honshu, a fireman named Kimura Kunio was on early watch by the harbor when he noticed the water moving in an unusual way. He raised the alarm, and many townspeople climbed to high ground. Waves up to 14 feet high, carrying floating timber like battering rams, kept coming into Onagawa for hours. No one in the town died. Elsewhere in Japan, the tsunami killed 138 people, by the count in the USGS booklet. Waves also caused deaths and damage in the Philippines, and they were measured on coasts all around the Pacific, from New Zealand to Alaska.

The lake that threatened Valdivia

For the people of Valdivia, the most dangerous part of the disaster came after the earthquake and the tsunami were over. About 40 miles (65 km) east of the city, in the foothills of the Andes, lies Riñihue Lake, the lowest in a chain of lakes that drain through the San Pedro River toward Valdivia and the sea. During the earthquake, several landslides near Tralcán Mountain collapsed into the river just below the lake’s outlet and blocked it. The largest dam of earth and debris stood about 24 meters high.

The lake began to rise. Each meter of extra depth held around 20 million cubic meters of water. If the lake topped the natural dam and the dam failed all at once, billions of cubic meters would race down a river built to carry only a few hundred cubic meters per second. Engineers estimated that the flood would wipe out the riverside towns between the lake and the sea in a matter of hours. About 100,000 people lived in the danger zone. The chronicler Pedro Mariño de Lobera described a similar dam forming after the 1575 earthquake, followed by a catastrophic flood that hit Valdivia months later.

Chile’s national electricity company, ENDESA, put engineer Raúl Sáez in charge. The effort became known as the Riñihuazo. Hundreds of workers from ENDESA and other state agencies joined soldiers, including a battalion of young conscripts that grateful locals nicknamed the Iron Battalion. Twenty-seven bulldozers were brought in, but they bogged down in the deep mud around the slides, so much of the digging had to be done with shovels. A proposal to blow the dam apart with explosives was rejected as too risky.

The plan had two parts. First, slow the lake’s rise by temporarily damming the outlets of the lakes upstream, including Calafquén, Panguipulli and Pirihueico, so that less water flowed into Riñihue. Second, cut a channel through the main landslide dam and lower it step by step, so the lake could drain through a controlled spillway instead of through a sudden breach. The crews worked through the southern winter in rain and cold while the water crept higher.

By late July the lake had risen about 26 meters above its normal level. Between July 24 and 26, the water began pouring through the cut channel, eroding it wider and deeper, with peak flows estimated at around 7,450 cubic meters per second. It was still a flood. Los Lagos, Antilhue and low-lying parts of Valdivia went under water, in some places by about 2 meters. But the rise was gradual, the city had been evacuated where needed, and it was not the sudden wall of water people had feared. No deaths were attributed to the release. Most of the upstream dams were later removed, though Calafquén’s still controls that lake’s outflow today.

What the earthquake left behind

Some changes from 1960 are visible from the air. Along the rivers around Valdivia, the land that sank during the earthquake never fully came back. Pastures and farms became tidal marsh. Today part of that drowned land is protected as the Carlos Anwandter Nature Sanctuary, created in 1981 and known for its black-necked swans. In Corral Bay, sandbars built up by sediment from old gold mines sank and compacted, which actually improved navigation.

The earthquake also changed science. It was so large that it set the whole planet ringing. Seismographs around the world recorded the Earth vibrating in its free oscillations, slow motions of the entire globe that had been predicted in theory but never clearly measured before. Those records helped scientists probe the planet’s interior. Studies of the 1960 rupture, along with the 1964 Alaska earthquake four years later, helped confirm that the largest earthquakes happen where one plate slides beneath another. That idea became a pillar of plate tectonics.

The Pacific-wide damage pushed governments to improve tsunami warnings, much as Galveston raised its city and built a seawall after the 1900 hurricane. The Hilo experience showed that a siren is not enough if people do not understand what it means. Hawaii revised its warning system, and in 1965 an international coordination group was set up to share data and warnings across the Pacific. In Chile, the response to 1960 and later disasters led to the creation of a national emergency office, ONEMI, in 1974.

The lessons recorded by Atwater and Cisternas are simple ones. Treat strong shaking as a tsunami warning. Go to high ground and stay there, because the next wave may be bigger. Do not go back for belongings. When the magnitude 8.8 Maule earthquake struck central Chile in February 2010, many coastal residents did exactly that, and memories of 1960 were part of the reason.

Treat strong shaking as a tsunami warning. Go to high ground and stay there, because the next wave may be bigger.

More than six decades on, the Great Chilean Earthquake remains the yardstick for every large quake that follows. It is remembered in Valdivia’s rebuilt waterfront, in the marshes that were once farms, in a stopped clock in Hilo and in a town in Japan where one fireman’s watchfulness saved everyone. The forces behind it have not gone anywhere. Somewhere along the edge of the Pacific, the next great subduction earthquake is building, and how many people walk uphill in the minutes after it ends will matter as much as its magnitude.

Further reading