Why Massive California Tsunami Alert Was Issued – Then Canceled

On December 6, 2024By Littum

Residents across the Northern California coast were asked to evacuate quickly Thursday morning and were encouraged to seek higher ground after a magnitude 7 earthquake off the coast of Humboldt County asked for one tsunami warning.

The warning just before 11 a.m. warned that “a tsunami with damaging waves and strong current is possible.”

But about an hour later, the alarm was cancelled.

It felt to some like emergency whiplash. Others were left confused.

But officials say they followed the correct protocol for responding to a potentially dangerous tsunami and that it was necessary to give residents enough time to get to safety.

“Time has to be respected to get people to safety,” said Dave Snider, tsunami warning coordinator at the National Tsunami Warning Center in Alaska.

“The No. 1 challenge with tsunamis is that we know a big event has happened,” Snider said of the earthquake. “We don’t know if a tsunami is actually going to happen.”

Given the size and location of the earthquake, his team immediately set their procedures in motion for a potential tsunami, the first step being to issue as targeted a warning as possible.

“There are only two ways we know a tsunami is occurring: We have the deep sea buoys and coastal observation stations at ports and harbors — that’s it,” Snider said. “We want to beat that wave and we want people gone too. … before we observe that wave.”

So initially, Snider said, there was no confirmation that a tsunami was headed for the West Coast, but all the ingredients for one were present. The earthquake’s proximity to the California coast made it especially urgent to begin evacuations because if a tsunami did form, it could hit much more quickly compared to a seismic event further out at sea, he said.

“We are completely reactionary to the earthquake,” Snider said.

After issuing a warning, his team spends the next 30 minutes to an hour understanding the earthquake’s “failure mechanism” to determine how it shook the ground, confirm its size and monitor these buoys and coastal lookouts for further signs of a growing tsunami. All these factors confirmed positive news: no major tsunami, no signs of danger. The warning was cancelled.

He knows the back and forth can feel frustrating, but he wants people to understand that it’s better to be overly prepared than the opposite.

“The feeling out there is, ‘Nothing happened, why did I evacuate?'” Snider said. “No, you did the right thing. … It could have moved a lot of water. We’re glad it didn’t.”

Not long after the tsunami warning was canceled, Snider said, his team noted that a small tsunami — measured at 2 inches — occurred in Arena Cove off Mendocino County.

“Something happened, something significant happened on our planet,” Snider said.

During the hour that the tsunami warning remained in effect, officials in Del Norte County, Humboldt County, Mendocino County, Berkeley and San Francisco urged people on the coast to evacuate inland.

In Fort Bragg, boat owners quickly tried to move their boats out of the harbor.

Sirens blared in Ferndale, signaling necessary evacuations.

In San Francisco, the fire department drove up and down the beaches, shouting to people to “clear the beach, tsunami warning.”

Dan Beniflah was walking his dog on the beach before the fire department arrived. He said the warning felt like a tsunami scare from decades ago, but he recalled that “nothing ever happened.”

Just like then, the water looked normal on Thursday, he said.

However, Snider urged people not to ignore such warnings – which are still quite rare – or go to the beach to watch the waves.

“Refresh what it means to live in tsunami country,” Snider said.

Staff writers Ruben Vives, Jessica Garrison and Hannah Wiley contributed to this report.

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This story originally appeared in Los Angeles Times.