The ocean waves triggered by a major volcanic eruption near Tonga traveled more than 5,000 miles to Bay Area coastlines Saturday, causing tsunami surges and violent surf from dawn until past dusk.
Tsunami advisories triggered in the early morning remained in effect throughout the day. They were canceled late Saturday in the Bay Area and early Sunday for the rest of California, according to the National Weather Service.
The explosion of the Hunga Tonga-Hunga Ha’apai volcano, largely submerged in the Pacific Ocean, appeared to be one of the most powerful eruptions in recent times, sending ash and smoke 12 miles up and 160 miles across the sky.
The event led to the most significant tsunami in California in a decade, with beaches closed up and down the coast and dock areas evacuated, including more than 100 live-aboard residents in the Berkeley Marina. Officials estimated tsunami wave heights to reach 1 to 2 feet.
The surges caused flooding at the Santa Cruz harbor, where cars and debris floated in the rising water, and resulted in at least one rescue of a surfer off Ocean Beach, whose surfboard broke in the pounding waves.
Some docks were also damaged at Richardson Bay in Marin County, according to the Sheriff’s Office.
The waves first hit the Monterey area around 7:30 a.m., and San Francisco around 8:10 a.m., just before high tide.
Authorities throughout the region urged residents to avoid the beach and in some cases called for those at the water’s edge to move to higher ground.
Advisories were also issued in Washington, Oregon, Alaska and countries around the Pacific Rim. The advisories expired throughout the day as the threat receded, with the U.S. Tsunami Warning System map showing none remained in effect around the Pacific Rim on Sunday morning.
The tsunami was the most significant in California since earthquake-fueled waves from Japan hit the West Coast in 2011, killing one person in California and damaging 29 ports and harbors.
Officials issued similar warnings Saturday about possible flooding and surges. “Do not go to the coast to watch the tsunami,” California authorities exhorted residents several times throughout the day.
Not everyone listened.
At San Gregorio State Beach in San Mateo County, two people who were fishing were swept into the ocean by the current Saturday afternoon and reached safety on their own, Cal Fire officials said. They were in stable condition after being taken to the hospital, one by helicopter.
In Pacifica, at Linda Mar Beach, surfers and families ducked under the “Beach Closed” signs, which alerted them to the tsunami warning. They laid out towels, set up picnics and settled in to build sandcastles as dozens of surfers caught large, churning waves.
Occasionally, the surf chased parents and children to higher ground before receding 50 yards or more back off the sand.
A group of beginning surfers in a lesson sat on the sand next to several surfboards, getting guidance from instructors before hitting the water.
Surfer Sean Knox, 41, drove to Linda Mar from Berkeley to ride waves for an hour or two, saying he was aware of the tsunami advisory, but had checked out the surf cameras and decided it was safe.
“You just keep an eye on the conditions,” he said as he pulled on his wet suit, adding that the waves didn’t look that unusual given the time of year. “This is the big season.”
He did note, however, the waves were big, “some of the biggest of the year,” and he — and apparently many others — didn’t want to miss it.
Nearby, Veronica and Ariel Ochoa sat on the sand up against the beach wall watching the waves and the surfers, a charcuterie picnic laid out between them. The Oakland couple had decided to spend the day driving down Highway 1, stopping at points along the way.
“I was under the impression it ended at 9 a.m.,” Veronica Ochoa said after learning the advisory remained in effect. “I guess I was misinformed.”
Still, the couple lounged, feeling safe given the large crowd around them. And if the tsunami siren sounded, she said, “we’ll run.”
In San Francisco, Ruben Canonizado, Kathy Loughlin, Julia Stroud and June Jobin, who all live in the city, ventured to Ocean Beach specifically to see the tsunami after hearing about it on the morning news. Watching the larger than normal waves crash onto the coast on a beautiful morning was exciting, they said as they took photos with their phones.
Canonizado said that he’d seen footage of the volcano erupting and that it was almost unbelievable. “Those poor Tongans,” he said.
The eruption was “significant,” said James Day, a professor and volcanologist at UC San Diego’s Scripps Institution of Oceanography.
The volcano has been erupting since Dec. 20, but this was the most explosive event, he said. While experts had not yet precisely identified the Volcanic Explosivity Index, a scale for measuring eruptions, Day said it appeared greater than 4.
By comparison, the blast from Mount St. Helens in 1980 was a 5 and that of Mount Pinatubo in 1991 was a 6, an eruption that “noticeably cooled the Earth’s atmosphere,” Day said.
The fact that the Tongan volcano is partially submerged means the seawater interacts with the hot magma as an accelerant, “much like spraying gasoline on a fire or barbecue might,” Day said. “The interaction of the underlying magma and hot-rock with the water has almost certainly enhanced the magnitude of this eruption. This is a different scenario to Mount St. Helens, but no less devastating for the community surrounding the volcano.”
It remained unclear how much damage occurred in the nearby Tongan islands. Early reports showed waves slamming into buildings along the coastline and ash falling on the capital, Nuku’alofa.
But as of Saturday evening, communication with the island nation remained limited.
Across the Bay Area, which has the largest concentration of expatriate Tongans and Tongan Americans in the state, with about 13,000 in San Mateo County, those with family near the volcanic blast were glued to Facebook and social media, watching satellite footage that captured the huge volcanic explosion from above, and amateur footage of its frightening boom scattering beachgoers before internet service evaporated.
“It’s really sad,” said Manu Manumua, who has numerous relatives in Tonga. “I cannot reach them and see the situation.”
Manumua was at home in San Francisco with her husband and three children Friday evening — Saturday in Tonga — when they learned on Facebook about the eruption. Her mother, 79, and father, in his 80s, live in the island nation and have two adopted children. Her brother and his wife, also there, have five children. Most are not on the main island of Tongatapu, where a 4-foot wave is believed to have washed through the capital.
“I cannot reach them and see the situation,” said Manumua, who has numerous relatives in Tonga. “It’s really sad.”
San Francisco Chronicle staff writer Nanette Asimov contributed to this report.
Jill Tucker and Danielle Echeverria are San Francisco Chronicle staff writers. Email: jtucker@sfchronicle.com, danielle.echeverria@sfchronicle.com Twitter: @DanielleEchev, @jilltucker
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