Airplanes, sirens, radios and TVs will broadcast a tsunami warning test on Wednesday

FORT BRAGG, CA, 3/24/24 — Not many Mendocino Coast people heard last year’s tsunami test warnings. But a bigger and better test is scheduled for Wednesday. There are just four tsunami sirens along the entire 131-mile Mendocino Coast, with two of those in Noyo Harbor. And during the 2023 test, the siren at Pudding Creek malfunctioned.This year will be a full test, after problems and cancellations in recent years hampered other drills. The 2019 test was scarpered by a government shutdown, and the 2020 and 2021 tests were victims of the pandemic. 

The National Weather Service (NWS) and the counties of Mendocino, Humboldt, and Del Norte will test the entire tsunami warning system on Wednesday, March 27, between 11:00 a.m. and noon. The test will include tsunami sirens, the Emergency Alert System (TV, radio, and NOAA Weather Radio). The reverse 911 calling system also will be tested to ensure the tsunami warning systems are working properly. Even harder to miss will be a flyover by the Civil Air Patrol broadcasting that this is a test of the warning system. The air patrol is set to fly over the entire coast. Shorter flights and other problems have prevented the airplanes from flying over the coast twice in prior years.

The updated California tsunami warning system has a very simple process to find out what you should do in the event of a  tsunami. Step one is to enter your address into the mapping tool and find out if it is yellow or green. If yellow, you will know to head for a green area as soon as you hear a tsunami is coming.

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What to expect for Mendocino County residents:

• The NWS will send an Emergency Alert System message to Mendocino, Humboldt, and Del Norte counties.
• A crawler will appear at the bottom of TV screens indicating that a tsunami warning has been issued and a voice will indicate that it is only a test.
• Alert beeps followed by a voice announcing “test” will be broadcast on local radio stations. For those with a NOAA weather radio with the Public Alert feature, the radio will automatically turn on and you will hear the same message.
• Tsunami sirens will play their full wail, as opposed to “growls” that might be heard when the equipment is being tested by workers.
• The Mendocino County Office of Emergency Services (OES) will send a reverse 911 call to the coastal tsunami zone.
• A flyover by the Civil Air Patrol is scheduled 

For all questions, email [email protected] or call 707-234-6398.

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This reporter attempted to ascertain some facts, such as whether the Pudding Creek siren has been fixed, but the county office did not respond to questions or emails on Friday. 

See the new Mendocino County tsunami zone map here, and scroll down for details: https://www.conservation.ca.gov/cgs/tsunami/maps/mendocino

While authorities express worries each year that some people who hear the full siren might think an actual tsunami is underway, this is also an opportunity to learn about upgraded tsunami warning maps for the entire Mendocino Coast and how tsunami warnings have changed since the 2011 Japanese tsunami.

The California Geological Survey (CGS) spent a decade upgrading its tsunami hazard area​ maps, which now cover the entire state. This coming week is California Tsunami Preparedness Week, 

Tsunami evacuation mapping was greatly expanded for the Mendocino Coast in 2021, when maps were released using a new approach. The more detailed methodology revealed larger areas predicted to be inundated in a thousand-year tsunami event — that is, the rare tsunami expected only once every millennia. They are designed to show places that might need to be evacuated in the case of the worst tsunami.

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The new mapping also expanded some areas for lesser events. Those include properties farther up local rivers and streams than previous mapping indicated. A place recently added to the maps is the Ocean Lake Adult Mobile Home Park just north of Fort Bragg, said engineering geologist Jay Patton in a 2021 interview. He helped create the new maps as part of his job as engineering geologist at CGS. Although Highway 1 provides protection to the mobile home park to some extent, the walking tunnel under the road negates the highway from being a true seawall, Ryan Aylward of the National Weather Service said in a 2021 interview. Several oceanfront campgrounds are also in yellow evacuation areas.

The Albion and Noyo rivers both show that a tsunami could surge far inland. There is no siren in the Albion area, where a campground sits at sea level and people live along the river. Most of the coast’s other rivers have few homes along the bank.

People who live along coastal rivers and streams may find a surprise in the revised maps. Enter any Mendocino County address in the search bar and it will come up green or yellow, with the risk coding based on the thousand-year tsunami possibilities studied from different tsunami origin points, such as Japan, Chile, Alaska or the Pacific Northwest’s Cascadia Fault. The thousand-year tsunami would not have a consistent height or size, depending on factors ranging from the tides to the shape of the coast. One can then scroll around to see where the yellow danger areas are located. Evacuation from a tsunami should be on foot when possible, as roads may be impassable by car. 

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The 2021 maps now cover the entire coast of California, much of which has never been mapped for tsunami risk. In Mendocino County, the last set of maps, completed in 2009, mostly mapped tsunami risk around places like Fort Bragg and Point Arena — and even in such areas that were previously mapped, errors and omissions were found by the new high-tech mapping.

“Most of Mendocino County is not as susceptible to a tsunami as are places like Crescent City and Half Moon Bay,” said Patton. This is due mostly to the tall cliffs and bluffs that protect much of the Mendocino Coast, although underwater topography and other factors such as the angle of the coast also play a role, studies show.

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Patton said there are two tsunami warning systems for those living in the yellow areas of the map, which indicate tsunami evacuation zones. The first is common sense, he said. “If you feel an earthquake for a long time, it’s time to get to higher ground,” said Patton. The second kind is the official warning system that will be tested on Tuesday.

A tsunami is a wave series created by an undersea disturbance, most commonly an earthquake. Although tsunamis usually come from the simple up and down motion of the sea floor in an earthquake, there is much about how they work that might seem counterintuitive. Different kinds of earthquakes have different effects. A strike and slip fault, like the San Andreas fault, which goes to sea at Point Arena, creates a lesser tsunami risk than a quake in a subduction zone. The most likely destructive tsunami for Northern California areas south of Cape Mendocino would likely come from a major earthquake in Alaska, Patton said. The Mendocino Coast would have just three to four hours to prepare for such a tsunami. Another possibility is that any earthquake could cause an undersea landslide, which would then create its own tsunami.

Rick Wilson, head of the CGS tsunami program, said in a press release that the yellow and green areas have a margin of error.

“There is some uncertainty when we draw the inundation lines,” Wilson said. “The maps are based on the best data we have, but there’s a margin of error when you’re trying to consider a thousand-year event, so we err on the side of caution. The [one meter] buffer zones included in the [yellow areas of the] new maps account for that uncertainty, “ Wilson wrote.

The Redwood Coast Tsunami Workgroup has developed evacuation brochures for Humboldt and Del Norte counties using the maps, Aylward said.

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More than 150 tsunamis have hit California’s coast since 1800. Many are barely noticeable but nearly a dozen tsunamis have caused fatalities or significant damage, most recently during the March 11, 2011 tsunami generated by a magnitude 9.1 earthquake off Japan. After traveling 10 hours across the Pacific Ocean, the Tōhoku-oki tsunami caused damages ranging from $28 million in Del Norte County, more than $4 million in Mendocino County to Noyo Harbor, and $100 million statewide.

Noyo Harbor has one of the highest tsunami risks, and that did not change in the new maps. The 2011 tsunami featured after-midnight heroics by local boat owners and the Noyo Harbor Commission. The commission staff contacted all the boat owners in the marina and most got their boats out of the harbor before the tsunami arrived from Japan the next morning. When boats are at sea, a tsunami will pass harmlessly beneath them, which was what happened here in 2011. If the 2011 tsunami were to happen today, a much more accurate prediction of the height of the wave could be given, Aylward said. This is because tidal information is now better incorporated into the prediction. The height of a tsunami depends entirely on the state of the tide when it arrives at the shore. If the Japanese tsunami had arrived in Noyo Harbor at high tide, the destruction would have been much greater.

The most devastating tsunami to hit California in modern times occurred March 28, 1964. Several surges reaching 21 feet high swept into Crescent City four hours after a magnitude 9.2 earthquake in Alaska. Ten people were killed, and half of the waterfront business district was destroyed. Crescent City has the state’s highest tsunami risk. An offshore ridge funnels tsunamis into the area.

Patton said each possible tsunami involves a variety of factors, which is why people are not encouraged to debate evacuating based on factors like the predicted size of the surge.

“Every earthquake and every tsunami is different. We really don’t want people to decide on their own whether to leave based on the size of the tsunami,” Patton said.

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South of Cape Mendocino, the biggest tsunami threat to most of California would result from another massive earthquake in the Alaska and Aleutian Islands regions. The biggest threat to areas north of Cape Mendocino is a major earthquake on the Cascadia subduction zone — the 700-mile undersea boundary where tectonic plates are colliding. Scientists have evidence that the subduction zone generated a magnitude 9 earthquake and tsunami in 1700.

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A similar event could send surges onshore up to 50 feet high toward Crescent City and 30 feet high along the outer coast of Humboldt Bay and the Eureka area. A big quake on the Cascadia megathrust subduction fault might cause five to six minutes of shaking and give people along the Del Norte and Humboldt coasts a maximum of 10 minutes to get inland or to high ground.

Many maps and apps have out-of-date information about coastal elevations. 

“The elevation of the tsunami hazard area varies across the landscape, so it is not a good idea to have the public bring into their minds an elevation criterion for being out of the Tsunami Hazard Area,” Patton said. Mendo Ready has information on all the disaster warning systems in the county.

(A reporting error gave the correct date and incorrect day of the week in a previous version of this story)

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