THE Surf Report

 

Pretty sure that glowing warm orb in the sky is a UFO. 

SURF:

Been lots of talk lately about our government acknowledging there’s some things in our skies they can’t explain. I have something else to add to their list- a glowing warm orb I've seen the past couple days. I could be wrong, but it may be the sun. I saw it back in April- but May- not so much. Looks like the nice weather will continue for the time being AND a little bit of surf is headed our way AND it's a long holiday weekend! Hope you already found a parking spot at the beach 'cause it's gonna be PACKED. So what's in store for us? 

A little storm formed off New Zealand last week and sent us some fun chest high+ SW that starts filling in later tomorrow and lasting through Sunday. 

We also have waist high NW windswell filling in too. Look for shoulder high sets in far N County SD and head high sets in the OC. Memorial Day Monday will have leftover waist to chest high combo swell. And once the low clouds burn off in the mornings, days at the beaches will warm up to the high 60's with hazy afternoon sunshine. Sounds good to me. And here's the tides, sun, and water temps for the next few days:

• Sunrise and sunset:
• 5:42 AM sunrise (almost 5:30 AM!)
• 7:50 PM sunset (almost 8 PM!)

• The NW winds have subsided, the clouds have parted, and our water temps are 66-68! 

• And the tides this weekend are pretty drained in the AM:
• -1' at sunrise
• 3.5' after lunch
• 2.5' in the evening

FORECAST:

After a fun holiday weekend, Tuesday and Wednesday start off in the waist high range but we have a new good S filling in late on Wednesday for shoulder high+ sets into Thursday and overhead sets in the OC. The weather should be good too... so I'm turning on the Emergency Boardriding System. Not the biggest swell mind you- but plenty good and our water temps are finally warming up along with nice weather. Can't beat it. Next weekend the S will be a shell of its former self and we're back to waist high surf with chest high sets. Get it while you can!

WEATHER:

A few days ago, the weather models were hinting at another weak cold front setting up over the holiday weekend... but that's been tossed aside. Now it looks like mild weather this weekend; low clouds in the nights/mornings, hazy afternoon sunshine in the afternoons, and temps in the high 60's. One word: pleasant. Next week, high pressure may strengthen by Wednesday and temps in the deserts could approach 110. For us- just more nice weather and temps in the high 70's? We'll see. If anything changes between now and then, make sure to follow North County Surf on Twitter!

BEST BET:

Saturday/Sunday with fun combo swell and nice weather. Or the middle of next week with better SW and better weather?

NEWS OF THE WEEK:

I reported back in November that the Great White shark population seems to be increasing along the Southern California coast (like you didn't know that already). And it looks like our friends to the N also are seeing the same results- more 'men in gray suits' are swimming off of Central CA. Here's Newsweek with the 411:

The population of great white sharks off the coast of central California is increasing, according to a study, which means populations of other animals like seals and fish may also be healthy.

Between 2011 and 2018, and over the course of more than 2,500 hours, a team of researchers identified nearly 300 adult and sub-adult individual great white sharks at Farallon Island, Año Nuevo Island, and Tomales Point—three sites where the apex predators are known to gather.

A similar study conducted in 2011 found 219 great whites, which suggests that numbers are slowly increasing in the area. Paul Kanive, a marine ecologist at Montana State University and lead author of the study, which was published in the journal Biological Conservation, told The Mercury News: "A healthy population of white sharks means there are healthy populations of the sea lions and elephant seals they eat.

"And that means that the lower levels on the food chain, like fish, are healthy enough to support the marine mammals. "Great white sharks and other top marine predators have a varied diet, which means they don't tend to hunt any specific prey to exhaustion, thereby allowing the various species to recover.

The study is the latest piece of research to reflect the importance of healthy shark populations. For instance, a 2008 report by ocean protection organization Oceana found that a decline in large shark populations along the eastern coast of the U.S. coincided with a spike in ray, skate and smaller shark populations, with the number of some species increasing tenfold.

The species whose numbers surged most markedly of all was the cownose ray, which proceeded to all but wipe out most of the scallops, oysters and clams in the area, resulting in the closure of a century-old scallop fishery.

Oceana said in the report: "As top predators, sharks help to manage healthy ocean ecosystems. And as the number of large sharks declines, the oceans will suffer unpredictable and devastating consequences."

In their study, Kanive and his team identified several factors that may have helped great white shark numbers to recover in the area. In 1994, California passed a great white shark fishing ban and introduced tighter restrictions on gill nets, which can trap sharks, dolphins, turtles and other species. 1972's Marine Mammal Protection Act also led to the recovery of populations of seals, elephant seals and other marine mammals, which form the main bulk of a great white's diet.

The authors of the study said that the increase in great white numbers is slight enough to be described as "equivocal," and could also be explained by regional fluxes in density. However, they said they were "cautiously optimistic." Kanive wrote in an update on a GoFundMe page set up to help fund the research: "The results reflect a small (<315) population of white sharks in this area.

"In addition, we investigated population trends for each demographic (sub-adult and adult males and females) and found evidence of a modest uptick in numbers of adult males and females over the study period. "We are cautiously optimistic of a small but healthy population off central California."

PIC OF THE WEEK:

Came across this image online and I immediately said ‘Yowza! Look at all those set ups! So many good surf spots!’ and then it hit me- it’s the Farallons…

The elephant seal population attracts a population of great white sharks to the islands. In 1970 Farallon biologists witnessed their first shark attack and during the next fifteen years, more than one hundred attacks on seals and sea lions were observed at close range. By the year 2000, biologists were logging almost eighty attacks in a single season. The seasonal shark population at the Farallons is unclear, with estimates from thirty to one hundred. The Farallons are unique in the size of the great whites that are attracted. The average length of a full-grown great white shark is 13 to 16 ft, with a weight of 1,500 to 2,430 lbs, females generally being larger than males. Farallon great whites range between the "smaller" males at 13 ft to the females, which generally range between 17 to 19 ft. And if that doesn’t scare you… a killer whale was recorded killing a great white near the Farallons in 1997. 

From 1946 to 1970, the sea around the Farallons was ALSO used as a dump site for radioactive waste. 47,500 containers (55-gallon steel drums) had been dumped in the vicinity. The materials dumped were mostly laboratory materials containing traces of contamination. By 1980, most of the radiation had decayed. Waste containers were shipped to Hunters Point Shipyard, then loaded onto barges for transportation to the Farallons. Containers were weighted with concrete but those that floated were sometimes shot with rifles to sink them. In January 1951, the highly radioactive hull of USS Independence, which was used in nuclear weapons testing and then loaded with barrels of radioactive waste, was scuttled in the area. 

And if the great white sharks AND radioactive waste don’t scare the living heck out of you, it’s also home to many shipwrecks; most notably the liberty ship SS Henry Bergh, a converted troop carrier hit West End in 1944 and the USS Conestoga, a US Navy tugboat that disappeared with its 56 crew members in 1921. Also, scientist Jim Gray was lost at sea after setting out on a solo sailing trip from San Francisco to the Farallons on January 28, 2007. Despite an unusually thorough search, neither his body nor his boat was ever found. Of course they weren’t. And on April 14, 2012, the sailing yacht Low Speed Chase capsized during a race at Maintop Island, killing 5 of the 8 crew aboard. 

But even with all of that… 3 people have successfully SWAM from the Farallons to the Golden Gate, with 2 more swimming to points north of the gate. The first, Ted Erikson, made the swim in September 1967, with the second, Joseph Locke, swimming to the Golden Gate on July 12, 2014, in 14 hours. The third person, and the first woman to complete the distance, Kimberley Chambers, made it in just over 17 hours on Friday August 7, 2015. Congratulations everyone?  

Keep Surfing, 
Michael W. Glenn
Nobleman
May Have Shed A Tear At The Friends Reunion
Starred In '4 Summer Stories' Which Wasn't A Big Hit For Some Reason

THE Surf Report

 

May Gray? More like Mayday! Mayday!

SURF:

Last week I lamented about the May drizzle (For shizzle)! This week? It's getting serious. Lots of good surf has met its match in May Gray and the dreaded SW winds. So I'm sending out a distress call: Mayday! Mayday! Anyone hear me? Who can help with this unrelenting wind, overcast conditions, cool air temps, and drizzle? We may have to wait until Sunday for that. So until then, we've got strong SW winds for Friday as yet ANOTHER low pressure system moves by to the N. As it does, winds will be an issue, we'll have partly cloudy conditions again, and the surf will be blown to bits. 

If the wind wasn't blowing and it was sunny, you'd see we had a fun NW windswell in the water and building chest high S swell. Saturday is a transition day as the weather will start to clean up but won't be perfect. The NW will also be on it's way down as the S will be peaking for head high surf and overhead towards the OC. Sunday, things should clean up and we'll have leftover head high combo swell. I would have turned on the Emergency Boardriding System if it wasn't for all this wind! But I'll take what I can get. Plus- it's the weekend! And here's the tides, sun, and water temps for the next few days:

• Sunrise and sunset:
• 5:45 AM sunrise 
• 7:46 PM sunset
• Over 14 hours of sun! (If it wasn't so cloudy)

• The only bonus to all the SW wind? Water has been pooling up in the Southern California Bight and we're holding at 65 degrees. 

• And the tides this weekend are up and down:
• 4' at sunrise
• 0.5' at lunch
• 5' in the evening
• 4' at sunset

FORECAST:

Looks like we'll have nice weather by Monday and leftover S swell for shoulder high sets. 

Mid week looks slow with just waist to chest high combo swell- and the return of overcast conditions.

Charts though show a storm taking shape today off Antarctica and we could have more chest to shoulder high surf next weekend. And the return of the sun? Hope so. 

WEATHER:

I know it's May and we're supposed to have overcast conditions, but sheesh! I don't know if I'll be able to handle June Gloom too. As advertised above, look for partly cloudy, breezy conditions on Friday and some sprinkles. Saturday lightens up slightly but we'll still be in the mid-60's and only partial clearing along the coast. Sunday through Wednesday should see a little more sun at the beaches then... more May Gray the 2nd half of next week. If anything changes between now and then, make sure to check out Twitter/North County Surf!

BEST BET:

Sunday with leftover but good S swell or late next week with new smaller SW swell and overcast conditions again. 

NEWS OF THE WEEK:

As I reported last week, we're still technically in a La Nina phase (which is cooler than average water temperatures) and doesn't bode well for hurricane formation. We should though be in a neutral phase by summer (neither La Nina nor El Nino) so there's a chance of an average hurricane season. Well, that optimism took a slight hit this week: The National Hurricane Center's (NHC) Eastern Pacific hurricane outlook for 2021 came out a couple days ago, and even though it wasn't the kiss of death, don't bet on an ABOVE average hurricane season this summer. Here's the scoop:

• A 20% chance of an above average hurricane season
• A 35% chance of a normal hurricane season
• And a whopping 45% chance of a below normal season

How does that translate to actual storms? Not that bad, but my money is on the under:

• 15 named storms in a normal season. NHC says we could see anywhere from 12-18 this season.
• 8 actual hurricanes in a normal season. NHC says we could get anywhere from 5-10. 
• 4 major hurricanes in a normal season (major being a category or above with 111 mph+ winds. That's the real swell maker for us). We could see anywhere between 2-5 says the NHC this season. 

So as you can see, we'll most likely be stuck somewhere in the middle when it comes to our chances of hurricane surf this summer but let's prepare for the worst and hope for the best. 

PIC OF THE WEEK:

Never seen a swell bend like this before. Even Black's Beach on a good day doesn't get this twisted. And of course, I have to ask again... where the heck is everyone?!

Keep Surfing, 
Michael W. Glenn
Groovy
I Can Explain All Those UFO Videos
Mathematically Not Eliminated From The World Title Chase. Yet. 

THE Surf Report

 

May drizzle? For shizzle!

SURF:

Spring is in full swing! This past week had overcast conditions, more wind then you'd like, and almost fun surf- if it wasn't for the overcast conditions and the wind of course. For the weekend- more of the same!

We've got new SSW filling in tomorrow for chest high surf, overcast conditions, and more early W winds. Saturday picks up to the shoulder high range (bigger towards the OC) and that peaks on Sunday. And right on track for spring- drizzle or light showers are expected late Saturday into Sunday morning from the 6,000' deep marine layer. Beach weather? Not exactly. But it will generate a little NW windswell so it may peak up the new SSW swell. So we've got surf this weekend- but ugly conditions. And here's the tides, sun, and water temps for the next few days:

• Sunrise and sunset:
• 5:50 AM sunrise 
• 7:41 PM sunset

• Water temps earlier in the week warmed up to 65 with all the sunshine then dropped slightly to 62 today with the W wind and overcast conditions. Expect it to hold in the low 60's over the weekend. 

• And the tides this weekend are a little odd. Again:
• 0' at sunrise
• and pretty much 3' at lunch through sunset

FORECAST:

The SW/NW starts to back off Monday/Tuesday for chest high surf then we fire up the Emergency Boardriding System as we get a reinforcement from the SW/NW on Wednesday for head high surf- and better weather. 

Charts this weekend show a large storm taking shape off Antarctica which would give us head high+ S swell next weekend (and bigger in the OC). After that storms in the southern hemisphere take a slight breather but we still should have chest high SW swell later in the month. 

WEATHER:

I guess it's good things are predictable around here, right? Spring is acting like spring with overcast cool conditions. We've got another low pressure system moving by to the N this weekend and as it does, the marine layer will deepen and squeeze out some drizzle or light showers during the nights. Temps at night will be in the high 50's and during the day, low 60's; only a 3 or 4 degree difference. Yawn. (And if you want some beach weather this weekend, head 2 hours E to Palm Springs where it will be 90 and sunny. Anyone have an idea when those wave pools will be done)?! The low pressure moves to the E early next week and we're back to low clouds in the nights/mornings and sunny afternoons. Temps should be in the low 70's by then. If anything changes between now and then, make sure to check out North County Surf on Twitter here!

BEST BET:

Tough call as this weekend will have waves but winds could be an issue (which was the call LAST weekend). Or wait until mid week for the EBS to kick in with good SW/NW. OR... wait until next weekend with solid S swell!

NEWS OF THE WEEK:

As you may have heard earlier this week, Tropical Storm Andres formed in the Eastern Pacific off Mainland Mexico on May 9, becoming the earliest named storm on record to develop in that area (important for us because that's where Southern California sees their hurricane summer swells). Andres' formation at 8 a.m. PDT on Sunday marked the earliest in the satellite era, or since the mid-1960s, that a named storm has developed in the Eastern Pacific Ocean. The previous record was set by Tropical Storm Adrian, which formed 12 hours later May 9th, 2017 (yeah, I know, technicalities). 

On that note, the Eastern Pacific hurricane season officially begins this weekend on May 15th. Besides being a swell generator during our summers, does it matter for the rest of the U.S.? Yep. Sometimes quite impressively. I'll let the Weather Channel take it from here:

The Eastern Pacific hurricane season is often overshadowed by the Atlantic, but it can have impacts in the United States. At two weeks earlier than the official beginning of the Atlantic season, this is due to warmer waters and the fact that wind shear is typically weaker earlier in the season compared to the Atlantic.

Many Eastern Pacific tropical storms and hurricanes move away from land and are only a concern to shipping interests. But sometimes, the weather pattern can allow these systems to affect Mexico, Central America and the southwestern U.S. Hawaii is also occasionally threatened by tropical storms and hurricanes that make the long trek from the Eastern Pacific into the Central Pacific.

Here's a breakdown of how Eastern Pacific storms can be a threat to the Southwest and Hawaii, including recent examples.

Southwest Tropical Flood Threat:

Arizona is the Southwest state with the history of the most tropical storm encounters. According to the National Weather Service in Tucson, eight tropical storms or depressions have remained intact and impacted Arizona directly since 1965. Five of these were tropical storms with sustained winds of 39 mph or higher.

Flooding rainfall is typically the biggest concern from any tropical systems that survive the journey into the southwestern U.S. Sometimes, this rainfall can be triggered by the remnant moisture of former Eastern Pacific tropical storms and hurricanes. While such a storm might no longer be intact, the remnant tropical moisture can fuel drenching rains as it moves into the region.
In August 2020, moisture from short-lived Tropical Storm Fausto played a role in a rare flare-up of lightning in Northern California, including around the Bay area. The lightning started several devastating wildfires in the region since the storms had little rainfall. Moisture from both Tropical Storm Ivo and Hurricane Lorena reached the Southwest in 2019. Moisture from Ivo's remnants triggered flash flooding in Las Vegas in late August.

The interaction between moisture from the remnants of Hurricane Dolores in July 2015 and a disturbance moving into California resulted in historic July rains in Southern California. Both Los Angeles and San Diego broke all-time July rainfall records at a time of year when rainfall is almost always scant in Southern California. San Diego in fact received over 1" of rain from Dolores. To put that into perspective, an inch of rain during a storm in our WINTER months is significant. And for July? We typically do not receive ANY precipitation. Also in 2015, moisture partially associated with Hurricane Linda led to flooding that killed 20 people in Utah on Sept. 4, according to the National Hurricane Center.

From the Eastern Pacific to Hawaii:

Hurricane Douglas was an extremely close call for the Hawaiian Islands late last July. Unlike a number of other hurricanes that originated in the Eastern Pacific, Douglas didn't lose its intensity that quickly as it tracked into the Central Pacific toward Hawaii. Hurricane warnings had to be issued for Maui, Oahu and Kauai since Douglas' forecast track was a potential threat to those islands. Luckily, the southern eyewall of Douglas passed just north of Maui, Oahu and Kauai, sparing those islands from seeing the worst of the hurricane's strong winds and heavy rainfall.
In the case of Oahu, the hurricane's center passed just 30 miles north of the northern tip of Oahu on July 26.

Hurricane Lane's Hawaii approach in 2018 was another close shave for the nation's 50th state. Lane developed over the Eastern Pacific in August 2018 and crossed into the Central Pacific Ocean. After intensifying to a Category 5 hurricane southeast of Hawaii, Lane weakened significantly as it passed more than 100 miles south of the island chain. Parts of the islands were swamped by flooding rainfall.

Also in 2018, Olivia was the first tropical storm to make landfall over Lanai and Maui. Olivia triggered flooding on Maui and downed trees on Maui and Oahu a few weeks after Lane.

In 2014, Iselle made landfall on the Big Island of Hawaii as a tropical storm on Aug. 8. There were reports of structural damage, trees downed, power outages and some flooding on the Big Island.

Hurricane Iniki in 1992 might be the most serious example of the impacts Eastern Pacific tropical systems can generate in Hawaii. Iniki is the costliest hurricane in Hawaii's history; It originated in the Eastern Pacific on Sept. 5 and moved into the Central Pacific, where it became a powerful hurricane. The island of Kauai was hit especially hard by damaging winds when Iniki made landfall there as a Category 4 storm. Many structures were wiped out by storm surge flooding and large, battering waves along the southern coast.

Hawaii is usually protected from tropical storms and hurricanes approaching directly from the east due to cooler waters and strong winds aloft, which contribute to weakening. Many other tropical storms and hurricanes have passed safely to the south of Hawaii because of high pressure north of the islands. It's the rare cases illustrated by Iniki and Lane – when a hurricane first moves south of the island, then arcs northward – that pose a greater threat to the state.

A California Rarity:

Southern California is the only portion of the Pacific coastline in the Lower 48 that could see a tropical storm or hurricane landfall from the Eastern Pacific. Although such an event is extremely rare, history shows it can happen. On Oct. 2, 1858, the only known hurricane to hit Southern California slammed into San Diego. Sustained hurricane-force winds resulted in extensive property damage.

Only one tropical storm has made landfall in Southern California since then. In September 1939, a tropical storm with winds of 50 mph hit Long Beach. Flooding caused moderate crop and structural damage, according to the NWS in Oxnard. High winds surprised the shipping industry in the area, killing 45 people.

While technically not a tropical storm at the time, what had been Hurricane Kathleen raced northward into the desert of southeastern California in September 1976. Wind gusts to 76 mph were measured in Yuma, Arizona, and a 4- to 6-foot wall of water destroyed 70 percent of homes in Ocotillo, California.
Cool ocean temperatures in the path of the tropical systems trying to reach the Pacific coast are the primary reason landfalls are so rare in Southern California. Coastal waters get dramatically cooler as you move north along the coast from Mexico.

As in 1858, any hurricane would have to be moving fast enough, over waters just warm enough, to maintain its intensity on the way northward in order to have a California landfall. How warm does the water have to be? Let's just say above 80 degrees is a rough estimate. And since the water temps along our shores in Southern California usually hover in the mid-70's during the summer... we're safe. 

So does the early formation of Andres this week a harbinger of things to come this summer? Like an active hurricane season? Most likely not since we're still technically in a La Nina phase which is cooler than average water temperatures which does not bode well for hurricane formation. We should though be in a neutral phase by summer (neither La Nina nor El Nino) so there's a chance of an average hurricane season- which is better than last summer I guess. The National Hurricane Center's Eastern Pacific hurricane outlook for 2021 comes out in a couple weeks and I'll make to report on it here. Keep your fingers crossed for good surf this summer. 

PIC OF THE WEEK:

I L-O-V-E set ups like this. Feeling brave? Surf the outside point at 6-8'. Want something a little more mellow? Try the inside sandbar at 2-4'. On a side note, where the heck is everyone?!

Keep Surfing, 
Michael W. Glenn
Swell
Pretty Sure I Just Saw A Bengal Tiger On My Front Lawn
Surfed 38,480 Waves And Counting

THE Surf Report

 

Windswell with a smidgen of wind. 

SURF:

SD county finally go their due earlier this week after the winds subsided and the swell slowly emerged from the bump. Lots of fun surf made up for the phantom 'La Bomba' swell a couple weeks ago. Hope you got some surf though as this weekend is looking a little... funky. 

We have another trough of low pressure hanging around the next few days and as it does, the SW winds will blow and the NW windswell builds. 

We also have a small S filling in too which will help keep things rideable. In summary: Friday starts off small, Saturday/Sunday have chest high sets from the combo swells, and finding a clean window will be tricky. And here's the tides, sun, and water temps for the next few days:

• Sunrise and sunset:
• 5:55 AM sunrise (if it wasn't overcast, you could probably paddle out at 5:30...)
• 7:36 PM sunset (if it wasn't overcast, you could probably paddle in at 8:00...)

• Water temps have finally rebounded and are in the mid-60's. Hope I never have to wear a 4/3 again!

• And the tides this weekend are easy to remember:
• 4.5' at breakfast
• 0.5' at lunch
• 4.5' at dinner

FORECAST:

Monday has some leftover waist high+ NW/S and Tuesday isn't much better but we do start to see some small sets from the SW late in the day. That builds on Wednesday for chest high surf around here and bigger in the OC. That swell continues to build on Thursday and we should see shoulder high surf through the 16th. 

After that, models show a bigger storm taking shape off Antarctica that would give us head high+ sets from the SW starting around the 18th and lasting into the 21st. So 2 good SW swells about a week apart. I'll turn on the Emergency Boardriding System next week if all systems look like a go! As far as the conditions are concerned, May Gray is here to stay (or at least for 24 more days until June Gloom arrives) and we'll have off and on sunshine for the next few weeks. So some days may be clean... and other days cloudy with a SW breeze. Hope you like playing the lottery. 

WEATHER:

As you can see, May Gray is our unwanted house guest. And with a slight La Nina in control, don't expect the pesky low clouds to go away in the near future. We've got a trough of low pressure hanging around this weekend so expect cool, cloudy conditions with a slight SW breeze and temps in the mid-60's. That will most likely hang around through Wednesday. Hopefully the 2nd half of next will have less clouds, slightly warmer temps, and less of a SW wind. If anything changes between now and then, check for updates at Twitter/North County Surf!

BEST BET:

Looks like the 2nd half of next week with fun SW and maybe some sun? Or around the 18th with bigger SW (and who knows that the weather will be by then...)

NEWS OF THE WEEK:

If you'll remember, Japan's devastating earthquake in 2011 sent a tsunami across the Pacific and ultimately to our shores- albeit in a weakened form thankfully. But the threat is still there from various points across the Pacific. But what about closer to home? Scientists think we've got a problem of our own off our coastline that could cause serious damage. Here's the L.A. Times to explain:

Although California’s most dangerous tsunamis come from thousands of miles away, scientists say they’ve pinpointed a wave trigger that’s much closer to home. Earthquakes along strike-slip faults can cause potentially dangerous waves in certain contexts, a new model shows — and such faults do exist right off parts of the Golden State’s shores. If confirmed, the findings described in the Proceedings of the National Academy of Sciences could affect future local tsunami risk assessments for coastlines along California and beyond.

Tsunamis can be caused by a variety of events, including landslides, volcanic activity and most commonly, earthquakes.  But not every earthquake can trigger a rogue wave. Quakes along underwater thrust faults, in which one side gets pushed up higher than the other, are thought to be the main culprit, because the vertical motion can induce a wave in the water above.  Quakes along strike-slip faults like the San Andreas, in which two plates slide past one another, weren’t thought to cause tsunamis on their own because they cause largely horizontal motion That’s why the 2018 Sulawesi earthquake and tsunami in Indonesia raised geologists’ eyebrows. On Sept. 28 of that year, a wave estimated to be 13 to 23 feet in height struck the provincial capital of Palu following a magnitude 7.5 earthquake that occurred along a strike-slip fault. Together, the two events killed thousands.  Scientists surprised at the power of the wave suggested that perhaps it caused landslides with vertical motion that was able to trigger the wave. “We didn’t think so,” said Ares Rosakis, an engineer specializing in solid mechanics and the study’s senior author. The blame, he suspected, lay with the fault alone. “The unzipping of the bottom of the ocean in the Palu area ... would be enough to explain the creation of this tsunami.”

As Rosakis and his team — which included experts in every aspect of the process, including seismology and fluid dynamics — began probing this potential solution to the Palu mystery, they started seeing evidence that the earthquake rupture wasn’t your average unzipping of a fault. It fit the profile of a “supershear” event, in which the actual physical rupture moves faster than the seismic waves traveling through the material. That causes a triangle-shaped shock wave called a Mach Cone. (It’s very much akin to the sonic boom caused when an extremely fast plane moves faster than the speed of sound.) They fed this information into a powerful computer model that took into account the seismic waves, the earthquake rupture, the shape of the bottom of Palu Bay and the fluid dynamics of the wave itself. The result: An earthquake on a strike-slip fault like the one that devastated Palu could indeed trigger a tsunami. “This is a fascinating study in terms of the physics,” said Eric Geist, a research geophysicist with the U.S. Geological Survey based in California's Moffett Field. “It’s kind of a new way to look at tsunami generation.” Complex models like this, which combine the dynamics of both earthquake and tsunami, require powerful computers but are likely to become the norm, he added.

Part of the reason for the Sulawesi tsunami was the very narrow shape of Palu Bay. Rosakis compared it to the violent sloshing you might see after jostling a tall, skinny glass, compared with the gentler motion that would be seen in a wider vessel. Rosakis and his colleagues pointed to areas along the Northern California coast that fit the profile, including the San Francisco Bay and Tomales Bay in Marin County. The San Andreas fault sits just offshore of both those areas, and both are narrow enough to potentially see some very violent sloshing. 

Other bays around the world also fit the profile, including Izmit Bay in Turkey and the bay formed by the Gulf of Aqaba in Egypt. “This is the first time that this has been recognized,” Rosakis said, “so really a lot more work has to be done in order to be put inside the hazard evaluation maps. At this point it’s completely absent — these areas are declared safe.” Diego Arcas, director of the NOAA Center for Tsunami Research, called the authors’ conclusion “interesting.”

The study helps explain how quakes along strike-slip faults might generate tsunamis, and why the risk they pose may have been underestimated, he said. But he added: “I don't think it is going to change how we do things in terms of tsunami forecasting or hazard assessment.” That’s because tsunami hazard maps are generally made by estimating the effects of the biggest and most potentially damaging tsunamis.

For California, those would be great waves caused, say, by a magnitude 9 earthquake from thousands of miles away across the Pacific Ocean, or a similarly large quake off the Cascadia subduction zone north of Cape Mendocino, said Rick Wilson, a senior engineering geologist with the California Geological Survey, which has been updating the state’s tsunami hazard maps. It’s unlikely that any additional tsunami risk, if confirmed, would make a dent in those worst-case scenarios. “We’ll continue to review papers like this to see if we really need to update anything, but based on our experience and all of the large sources that we’ve incorporated into the maps, we feel pretty comfortable that the existing maps are safe to use and good to use,” Wilson said.

The study results may have an effect on probabilistic hazard assessments, which consider not just the worst case but also the likelihood that earthquakes of various magnitudes will take place, Arcas said. Ultimately, it will take time for more scientists to independently test whether they can reproduce the results, said Lori Dengler, a geophysicist and professor emeritus at Humboldt State University. “My guess is that this paper will cause a number of tsunami modelers to look more closely" at the role of quakes along strike-slip faults, Dengler said. “There also needs to be a closer look at what conditions allow supershear to occur. If this idea holds up to more careful scrutiny, it will be included in the next generation of tsunami maps.”

While it's important to understand the potential tsunami risk from these local sources, it's unlikely to affect how tsunami forecasting is conducted because information about ground rupture is not available in real-time, Arcas said. Even if it was, he added, "many of the faults with this type of mechanism can be found in close proximity to the coast, and while they can be hazardous locally, there would be no time for a local warning due to the proximity of the source." Dengler said that in these situations, the earthquake itself is the warning. 

"As far as public safety is concerned — whenever you feel an earthquake near the coast, especially one where the shaking lasts a long time, assume that a tsunami could be generated and evacuate the coastal area," she said. "In Palu, a festival was occurring at the time of the earthquake that brought many people from inland areas to the bay. Many of these people might not have recognized that the shaking was their warning to get away from the coast."

PIC OF THE WEEK:

I used to know a guy who would hem and haw before deciding to surf or not. "Not big enough" he would say. "The wind looks like it's picking up" he would say. "Probably going to get crowded" he would say. Then he'd drive home. Ultimately, he quit surfing. Moral of the story? When in doubt, paddle out; the worst day of surfing is better than the best day at work! 

Keep Surfing, 
Michael W. Glenn
Exemplary
Still On Spring Break
I'm Not Really A Surfer, I Just Play One On TV