Vagabonding on Dangerous Ground: Northern California's Tsunami Central

Crescent City Harbor from the south

In the far northwestern corner of California beyond Eureka and Arcata, the coast is lonely and wild, but there is one outpost of civilization, the small village of Crescent City. There are around 7,000 people, a small harbor with a fishing fleet, and a beautiful lighthouse, constructed in 1856 for pretty good reasons. The region around the harbor is peppered with dozens of jagged rocks called sea stacks (see the photo below). The town is a crossroads of sorts, with highways connecting with Grants Pass and Brookings in Oregon, and Redding and Eureka in California.

It's also been described as a tsunami magnet.

Since 1933, tidal gauges in the harbor have detected at least 32 tsunami surges, five of which caused damage, and two that have caused deaths. The 1964 magnitude 9.2 Alaska earthquake caused catastrophic damage in the town, killing eleven people. And ominously, sediments in and near the town record evidence of damage from the 1700 Cascadia earthquake. It is the possible repeat of that event that has the Pacific Northwest in an uproar at the moment.

No other place in California has such a record.

Photo by Mrs. Geotripper

The most recent tsunami was caused by the 2011 Tōhoku quake in Japan, a magnitude 9 event. The wave surged into the harbor, reaching a height of 8 feet (2.4 meters). Five people (I assume they were tsunami tsight-tseeing) were swept out to sea, and one of them drowned. 35 boats were destroyed. Tens of millions of dollars have since been spent to better prepare the harbor for future events.

Photo by Mrs. Geotripper

It may seem strange that one particular spot should be the focal point of tsunami damage in the state. The intensity of a tsunami depends on many factors, including the distance and size of the earthquake, the depth and shape of the seafloor, and the arrangement of human developments in the coastal area. Tsunamis have been recorded in other parts of California, but offshore islands in southern California protect the shorelines to an extent. Monterey and Santa Cruz have configurations that seem to have provided some insulation from the worst of the waves. But Crescent City collects tsunami energy. The good news is that the city seems to take the threat seriously, a fact reported to me by a cherished relative who lived in the danger zone there for many years (she lives further from the coast these days, and I've noted there is a closet of emergency supplies in the hallway outside her room in the assisted-living facility). They've learned from the past, and seem to have prepared for the future.

Battery Point Lighthouse in Crescent City

What is it like to be in the midst of a huge tsunami? In 1964 quake, four waves struck Crescent City. The first three were not as damaging, so some people returned to the downtown area only to be overwhelmed by the larger fourth wave. It topped out at around 20 feet (6-7 meters). Eleven or twelve people were dead, 100 were injured, nearly 300 buildings destroyed or damaged, along with 1,000 cars. It's hard to imagine being in the middle of such an event, but the Battery Point Lighthouse keepers witnessed the event from an uncomfortable location. The waves surrounded their rocky point. Their story is recounted in the book The Raging Sea by Dennis Powers (2005):

The water withdrew as if someone had pulled the plug. It receded a distance of three-quarters of a mile from the shore. We were looking down, as though from a high mountain, into a black abyss. It was a mystical labyrinth of caves, canyons, basins, and pits, undreamed of in the wildest of fantasies.

The basin was sucked dry…In the distance, a black wall of water was rapidly building up, evidenced by a flash of white as the edge of the boiling and seething seawater reflected the moonlight.

Then the mammoth wall of water came barreling towards us. It was a terrifying mass, stretching up from the ocean floor and looking much higher than the island. Roxey shouted, “Let’s head for the tower!” - but it was too late. “Look out!” he yelled, and we both ducked as the water struck, split and swirled over both sides of the island. It struck with such force and speed that we felt we were being carried along with the ocean. It took several minutes before we realized that the island hadn’t moved.

When the tsunami assaulted the shore, it was like a violent explosion. A thunderous roar mingled with all the confusion. Everywhere we looked buildings, cars, lumber, and boats shifted around like crazy. The whole beachfront moved, changing before our very eyes. By this time, the fire had spread to the Texaco bulk tanks. They started exploding one after another, lighting up the sky. It was spectacular!

Tsunami damage in Crescent City from the 1964 Alaska Earthquake

If there is a repeat of the magnitude 9 Cascadia earthquake of 1700, Crescent City will certainly be affected. How do we know? Hidden in some of the coastal flats are sand deposits from the 1700 event. In places the water rushed a mile inland. There is potential for greater damage because of the closer proximity of the epicenter, but that is mitigated by the expectation that the coastline could rise several feet during the quake, unlike areas farther north. They are are expected to sink before the arrival of the wave.

We visited our relative in Crescent City before continuing our Vagabonding on Dangerous Ground journey north on Highway 101. We were about to enter Oregon, and a beautiful stretch of coastline (as if it hadn't already been beautiful).

Vagabonding on Dangerous Ground: A Geologist Walks Onto a Bar in Cascadia...

A very strange-looking sandbar at Big Lagoon in Humboldt Lagoons State Park on California's north coast.

A geologist walks INTO a bar. She may get hammered, vulcanized, laminated, stoned, cemented, bombed, or petrified. And all her drinks will be on the rocks...

But when that geologist walks ONTO a bar, she just gets sand on her feet.

Yeah, yeah, I know, shut up and stick with the science...

We're traveling north on a journey through the Cascadia Subduction Zone, exploring this unique region with an eye to the geology, and the beauty, of the region. We've explored the Redwood forests of the Eel River, and the Lost Coast where the Cascadia zone begins. Today we are looking at a unique state park along the coast north of Eureka, California, and south of Crescent City. It's called the Humboldt Lagoons State Park, and the three lagoons found there are bounded by stunning examples of baymouth bars.

Big Lagoon at Humboldt Lagoons State Park (source: Google Earth)

One of the reasons that the already infamous Cascadia Subduction Zone earthquake might not be as bad as it could be is that so few people actually live on the coast of Washington, Oregon, or Northern California. Why is this? If one looks at a map, one notes the paucity of flat lands along the coast. There are sometimes some coastal terraces and a number of small natural harbors, but for most of the distance between Vancouver Island and Cape Mendocino, the mountains rise from the sea. There's no place to build. That's not to minimize the tragedy. There will be horrible results, but the largest cities like Seattle and Portland are inland, behind the coastal ranges, and they will be spared the worst of the tsunami damage, if not the shaking. There are certainly a number of towns along the coast, but there are also long stretches with few people. One of the lightly populated stretches of coast is between Eureka and Crescent City.

Big Lagoon at Humboldt Lagoons State Park

Along Cascadia's mountainous coast, wave action is violent and constant, and cliffs are quickly worn back, forming a relatively straight coastline. But there are also a number of drowned river valleys and coves, many caused by the rise of sea level after the last ice age. There are four small examples of these valleys at Humboldt Lagoons (one of which was filled in to allow some farming). But the coastline is very straight. Why?

Intense rainfall sends sediments down the many rivers and streams, and vast amounts are added to the coastal waters. When waves encounter the coast at an angle, the swash and backwash of the water causes sediment to be transported along the coast, a process called longshore drift. There is a tremendous amount of sediment in this coastal system.

Humboldt Lagoon also include a county park at the south end of Big Lagoon. It's a nice place to see coastal erosion!

When waves hit rocky coasts, they expend their energy wearing away at the rocks. When those same waves reach a cove of open water, the wave energy is dissipated as the waves spread out. When sand is being transported around the headland and into a cove, the declining energy causes the sand to settle into a curving sandbar, called a hooked spit. The spit may grow large enough to close off the mouth of the bay, becoming a baymouth bar.

In most bays along the Cascadia coast, rivers are large enough to keep the bays open, but at Humboldt Lagoons only small streams are present. Water can simply seep through the sandbar rather than flowing out. The bays are breached only during the wettest, most intense storms. The baymouth bars are miles long, and incredibly straight (see the Google Earth image above). They don't look natural, and yet they are.

Smaller Stone Lagoon is just north of Big Lagoon.

The lagoons are a fascinating spot along the north coast, and they get a bit less attention than Redwoods National Park and the state parks. They are an important link in the ecosystem of the region, and are marvelous spots for birdwatching and looking for other animals. If you ever travel that way, the state park (and associated county park) is well worth a visit.

The next stop on our vagabonding tour of the Cascadia Subduction Zone is Crescent City at the far north end of California. We'll have some things to learn about tsunamis in California.

There's No Place Like Home...There's no place like California

Yeah, it was a flirtation...spending a few days along the Oregon coastline was wonderful. The sea stacks, the arches, the dunes, it was all beautiful. But in the end, I'm a Californian and proud of it. To get to Oregon, we...well...just had to see the northern California coast too, and caught this golden sunset at Crescent City.

To see the vast fir forests of western Oregon, we just had to pass through Humboldt Redwoods State Park in Northern California, even camped there. It is simply awe-inspiring to walk among the 300 foot tall giants in the dusk. I imagined a velociraptor peeking out from the trees...or maybe Sasquatch.

We saw Oregon's big stratovolcanoes Mt. Hood and Mt. McLoughlin in the mist, and while in Washington we saw Mt. Rainier and Mt. St. Helens. But to get home, we just had drive under the brooding presence of the largest of the Cascades stratovolcanoes: Mt. Shasta. It is a huge mountain, visible for a hundred miles. In one view, we took in the largest glaciers in California, the largest stratovolcano complex in the Cascades and possibly in the world, and a debris avalanche that defies imagination. It was 28 miles long, more than two times the length of St. Helen's giant 1980 slide. Of course, no one saw the Shasta avalanche happen since it took place more than 300,000 years ago. Those hillocks on the center right side of the picture above are the hummocks from that incredible event.

Yes, I'm a Californian, born and raised. I love my state, warts and all. Dang if summer isn't ending all too soon. School starts soon, and I'm gonna need to start helping my students find that they too live in a geological wonderland, worthy of awe and wonder.

600th Blogpost: Sunset in Crescent City, and the Spheres

I noted the day I posted my hundredth blog, and might have said something about 200, but the others just didn't seem worth mention. Neither is this one really, but I did just happen to notice that it was post #600. It's kind of like the way you really notice mile 1,000 on a new car, but hitting 60,000 just means you need a tune-up. We do like our even numbers.

Nothing really significant tonight, but it has been a fascinating day which included a milestone: I finally completed my personal journey along Highway 1 along the coast of California. Over the years I've filled in the map with selected journeys that ultimately covered the entire extent of the incredible highway from Southern California to northernmost California, all except for one forty-mile stretch: Fort Bragg to Leggett. It was a beautiful stretch, and no doubt will appear soon as an "Other California" entry.

The day also included one of those odd moments that sometimes happen in life. I was parked at an overlook on Highway 1 snapping pictures of the stunning seacliffs. There were four motorcyclists there, also snapping photographs, and one of them walked over to me and said "Are you a geology teacher? From Modesto?". It turned out to be one of my students from a decade ago. At the other end of the parking lot his mom (the family that bikes together, stays together?) was recognizing my wife as a fellow teacher from a decade ago. Go figure...

Tonight's picture is a sunset at Crescent City in the far north of California. It was a beautiful clear evening, and as I glanced at the photo, I was struck by the intersection of the spheres that I always teach about: the lithosphere as exemplified by the rocky shoreline, the hydrosphere (the restless Pacific, an oxymoron if you think about it), the atmosphere, all combining to support the biosphere, represented here by the two flying dinosaurs. The energy source that drives the whole system was disappearing behind the distant fogbank. It has been a satisfying day.

So, sorry for a bit of ramble; it's the essence of blogging as I see it. I am collecting my thoughts on this month's Accretionary Wedge Carnival, hopefully to be posted soon. As blogpost #601 or some other random number