Friday, July 31, 2015

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).

Wednesday, July 29, 2015

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.

Sunday, July 26, 2015

Vagabonding on Dangerous Ground: The End is Coming (of the Cascadia Subduction Zone)!

Sugarloaf Rock at Cape Mendocino. Somewhere out to sea beyond the cape is where the Cascadia Subduction Zone is being destroyed, bit by bit.
The end is coming! I'm not referring to the possible destruction caused by the possible magnitude 9 quake that's been in the news of late. I'm talking about the actual destruction and disappearance of the Cascadia Subduction Zone itself. But if you are anxious to see this happen, you'll need to be patient. About 10 or 20 million years patient.

And you might want to be careful what you wish for anyway...

As mentioned in previous posts of this series, the Cascadia Subduction Zone is a spot where oceanic crust of the Pacific Ocean is being driven beneath the North American continent. The subducting plate, the Explorer-Gorda-Juan de Fuca is one of the smallest crustal plates on the planet. And it is being subducted faster than it is being created. It is indeed being destroyed...at the incredible (geologically, anyway) rate of a couple of inches per year. It will take tens of millions of years to consume the remaining plate material. When it is consumed, the subduction zone will cease to exist. The good people (or whatever species has evolved by then) of Portland and Seattle can stop worrying about subduction zone earthquakes.

As for being careful what you wish for? As the subduction zone is being progressively destroyed, it is replaced by the newly formed San Andreas fault/transform boundary. Although the San Andreas fault can't cause earthquakes as powerful as the subduction zone shakers (they top out at around magnitude 8.0, about 1/30th the energy of a magnitude 9.0), they are capable of serious mischief, as the quakes are often shallower, and that's a bad thing. The tragedy at Haiti a few years ago is a horrific example. The magnitude 7 quake killed nearly a quarter million people, despite having only 1/30th the energy of a magnitude 8 tremor. The focus was just a few miles deep.

The beach and sandbar at the mouth of the Mattole River, one of the very few undammed rivers in California
How can we know the subduction zone is actually ending? In the case of northern California, we can see that the plate has actually been disappearing for a long time, about 28 million years. It was once active in southern and central California. The rocks left behind by the collision ultimately became the Franciscan Complex, the rocks making up the core of the California Coast Ranges.  We explored those rocks in some detail in the last blog series, Driving the Most Dangerous Plate Boundary in the World.

Crowded Mattole Beach
The spot where one plate boundary ends and another begins is called the Mendocino Triple Junction (three plates are in contact, the Pacific, the Gorda, and the North American). It lies some distance offshore of Mattole Beach and Cape Mendocino, one of the most isolated spots in California. We drove winding Mattole Road for 70 miles or so between Humboldt Redwoods State Park and the small town of Ferndale. This isn't your average California coastline. There are just two very small villages, Petrolia and Honeydew, and only a handful of people ever wander the beaches. Mattole Beach is the trailhead for the Lost Coast trail and King Range, a 28 mile route along the only truly roadless coast in California.

This is one of the most geologically active corners of California, and California as a whole is a very geologically active place. Mattole Road is winding and steep because the land here has been uplifted very quickly, and the intense rainfall erodes the mountains at an astounding rate. Honeydew is one of the wettest places in the state with rainfall in some years exceeding 100 inches (2,550 mm). The dark rocks in the picture above are former sea stacks (small rocky islands) that were lifted up out of the water by the recurring earthquakes that raised the shoreline by a couple of inches or feet every couple of decades. A particularly damaging quake took place in 1992, the magnitude 7.2 Petrolia event.
So our journey along the Cascadia Subduction Zone began at the end, in a manner of speaking.  The road above Cape Mendocino was particularly steep, providing a marvelous view of the uplifted coastal terrace. The flat area used today as grazing lands was in the geologically recent past the wave zone. The heavy surf is eating away at the terrace, forming a new wave-cut bench, which will itself eventually be raised up out of the surf.

We took a leisurely day exploring the beautiful coastline before grabbing some dinner in Fortuna and heading back to the campsite in Humboldt Redwoods. We would head north in the morning.

Thursday, July 23, 2015

Vagabonding on Dangerous Ground: In This Land of the Sasquatch There are Ancient Giants

Yep, the first part of our journey into Dangerous Ground took us to the land of the Sasquatch, the legendary ape-human of the Pacific Northwest forests. That's not him in the picture above, although I could understand the misinterpretation. That's actually me taking a rare selfie at the Golden Gate Bridge. We were only an hour into our journey, and we had 200+ miles to go, but we couldn't resist being tourists for a moment. It was a wonderfully clear day in the Bay Area.
Our real goal was to reach a part of ancestral California, the Redwood forests. The original range of the trees extended from the Big Sur Coast to the Oregon border, but the wood is durable and therefore valuable. The forests were removed and only a few intact forests remain, with only about 5% of the old growth groves left. Thankfully they are mostly protected, but there is still a sense of great loss as we drive past mile upon mile of either barren slopes, or slopes covered with brush and sometimes young redwood trees. But often not.
These trees are the tallest in the world. There are rumors from the past of 400 foot tall trees of other species, but the claims date from more than a century ago, and these supposedly huge trees were cut down. I don't know if loggers exaggerate any more than other workers, but who knows? I'm pretty skeptical of the claims, and they can't be tested. The tallest Redwood is 379 feet (115 meters), and it was discovered only in 2006. There may still be taller ones out there.
There is really nothing quite like wandering through a mature forest of Redwood trees. The sun may be shining, but the light at ground level is more of a diffuse emerald green. Once the sun gets low, the forest becomes gray, and then pitch-black. I have a hard time imagining orienteering in places like this. Landmarks can be hard to come by.
Because we were vagabonding, i.e. not really planning far ahead, we stayed at Humboldt Redwoods State Park only because I was able to score a late cancellation. We got two nights. We explored the old growth forest along Bull Creek, and had a close look at one of the truly giant trees, which is called (by some degree of coincidence) "Giant Tree". It's only 16 feet short of being the tallest tree in the world, at 363 feet (110.6 meters). It towered over us.
It was gigantic, but from the ground it was difficult to see how tall it really was. You can see it in the photo below, just a bit right of center. The picture was possible only because the tree was near the edge of the grove. If it were in the middle of the grove, we could have walked right past it without realizing how it towered above the other trees.

This new series is called "on dangerous ground", but in this instance the danger was more to the trees than to us. We were inland, far from the dangers of tsunamis, but not far enough inland to be threatened by volcanic eruptions in the Cascades. Giant earthquakes have no doubt knocked a few of these trees over, but some of these ancient giants have survived five or six of the magnitude 9 tremors that have shaken the region in the last 2,000 years. No, the real danger is us, and what we've done to this ancient forest.
About that Sasquatch thing. Of course I believe that a race of gigantic ape-people have managed to survive and stay hidden in these deep forests, leaving behind no traces, no tools, and only revealing themselves to charlatans and book authors. Of course I believe. I also believe that the range of Sasquatch sightings happens to correspond pretty close to the range of the Black Bear, but no one could possibly mistake a seven-foot tall bear covered in dark fur in a dark forest with a seven-foot tall ape-human covered in dark fur in a dark forest. Especially if one believes hard enough.

But belief, no matter how fervently felt, doesn't prove much...

Strange Skies over the Great Valley Today

Tell me this isn't one of the stranger looking skies you've ever seen. I would have been rather freaked seeing this without having known the origin. It's not clouds.
We were driving home after our latest journey, and could see a wildfire burning on the west side of the Great Valley north of Sacramento. We couldn't get details until we got home, but it turns out to be burning in the Lake Berryessa area, and it's engulfed 4,000 acres so far, and is threatening 150 structures (an update can be found here).
Our usual experience, which we feared would be happening as we approached the smoke plume, is to have the smoke at ground level, leading to impaired visibility and smoke inhalation problems. Instead, something about the weather today kept most of the smoke just above the ground. I suspect the "Delta Breeze", the landward flow of colder denser air from the Sacramento Delta, may have kept the warmer smokier air aloft. That was a relief to us.
I'm not looking forward to the continuing wildfire season. We don't need anymore of this. Word is circulating that we may have a record El Nino condition developing in the western Pacific Ocean, and if it does, the record California drought may break. It's a two-edged sword though. The last strong El Nino in 1997 caused record flooding in the central part of the state.
We crossed the Sacramento River at the Yolo Causeway and emerged from underneath the smoky plume. The skies were again clear and blue (and windy). I found myself wondering if this is what it is like to be living in the path of a volcanic ash eruption. 
Mrs. Geotripper snapped all these pictures. She insisted, since I was driving the car.

Tuesday, July 21, 2015

Vagabonding on Dangerous Ground: Following the Cascadia Subduction Zone on Highway 101

Lake Crescent in Olympic National Park at the north end of Highway 101.
I'm sure that NO ONE in the various forms of mass media WOULD EVER stoop to using HYPERBOLE to increase their readership/viewership. You know, saying things like "THE BIG ONE IS COMING", that the GIGANTIC TSUNAMI is going to DESTROY EVERYTHING WEST OF I-5, that EVERYONE WILL DIE in the BIG EARTHQUAKE (or at some point decades afterward of old age). I would, for instance NEVER use capital letters in my opening paragraphs to try and catch the reader's eye. That being said, I really did have half of my trip completed before the media storm began concerning the chances for a magnitude 9 earthquake in the Pacific Northwest. I would have been describing my trip anyway, but the brouhaha over the possible earthquake and tsunami provides an opportunity to inject some level-headed geology into the discussion.
Route of Highway 101 through California, Oregon and Washington (red line). Interstate 5 runs parallel to Highway 101 just inland.
The fact is that the Pacific Northwest IS dangerous ground. But so is California. So is Oklahoma. And Minnesota. And Florida. And every bit of land across the world. There is nowhere that humans can live on this planet that is free of natural hazards. It doesn't work to go moving somewhere else, because no place is truly safe. The best we can do is to is to understand the nature of the threat, and to be prepared for the disasters when they happen.

The latest tempest involves a New Yorker article on the coming magnitude 9 earthquake along the Cascadia Subduction Zone. The basics of this potential earthquake have been known for nearly half a century, ever since the theory of plate tectonics came to be accepted by geologists. The details of a massive earthquake that took place in 1700 came to be known more than a decade ago. But it seems there is sometimes a tipping point when the public becomes aware of such hazards, and the New Yorker article seems to have done the trick. People in the northwest are talking earthquakes and tsunamis. The Cascades volcanoes must be feeling very neglected right now; they were once the main topic of any discussion of geologic hazards in the region.
The Juan de Fuca and Gorda crustal plates, among the world's smallest. The Cascadia Subduction Zone is the black line with the converging arrows. Many of the most important Cascade volcanoes are shown as red triangles.Source: NASA
So our journey quite literally was an exploration of nearly the entire subduction zone, as seen from U.S. Highway 101 and Highways 1 and 99 in British Columbia. As can be seen in the diagram above, the zone begins near Cape Mendocino in Northern California and extends to Vancouver Island in British Columbia, Canada. The highway parallels the coastline, and follows the coastal terraces and beaches in many places, especially in Oregon. We spent ten days making our way north from San Francisco to Canada and northern Washington, and three days heading home again along Interstate 5. We camped when spots were available, and stayed in hotels (if we had to).

Interstate 5 is a freeway from Mexico to Canada. It's a fast and efficient way to get from one place to another (except for the traffic jams in Seattle and Portland). But it's also not very interesting over much of its length. Highway 101 is more a patchwork of freeways, highways, and two-lane roads, and because of the challenges of the geology it is a route to be followed in a more leisurely manner. It is far more scenic, and for that manner, more dangerous in the geologic sense. It's never a surprise to see signs referring to falling rocks and tsunami evacuation routes.
Side view of the Cascadia Subduction Zone (source: U.S. Geological Survey)

The source of all the geological mayhem is one of the smallest crustal plates in the world. The Juan de Fuca plate forms a few hundred miles out in the Pacific Ocean where new basaltic lavas emerge from an oceanic divergent boundary. The plate moves east at a rate of few inches per year. It then dives beneath the North American Continent, where the buildup of frictional stress results in earthquakes, both big and small. Eventually the plate begins to melt, releasing plutons of molten rock that sometimes leak out at the surface, forming the Cascades volcanoes like Rainier, St. Helens, Crater Lake and Shasta.
Source: http://crew.org/sites/default/files/cascadia_subduction_scenario_2013.pdf
I imagine you could be thinking "what's the difference between this blog series (Dangerous Ground), and my just completed series (Driving Across the Most Dangerous Plate Boundary)? The facetious answer is, of course, that in this series, we will be driving along the plate boundary instead of across it. But the more serious answer is that the ancient Cascadia Subduction Zone in Central California is extinct. It stopped activity tens of millions of years ago. The subduction zone of the Pacific Northwest is presently active, and capable of causing catastrophic damage. And the landscape is different in many ways. In the series I plan to talk about the geology, of course, but I also find it to be a land of majestic beauty. That's the thing about geological hazards; they may be dangerous and cause human catastrophes, but they also result in some of the most spectacular landscapes on the planet.

Sunday, July 19, 2015

Vagabonding on Dangerous Ground: On the Road in the Pacific Northwest (a new blog series)

The Lost Coast of Northern California
If you've been following my blogs for the last few weeks, then you know I've been on the road in the Pacific Northwest. I'm not quite home yet, but I'm headed that way soon, and I've realized that there has been a convergence of events that are leading to my next blog series. I've decided to call it "Vagabonding on Dangerous Ground".
The Devil's Churn on the Oregon Coastline
If this were a BBC or NPR production, it would have started out with a statement like this: "Because this story has been in the news of late, we decided to go there to investigate". But with me, it happened backwards. Mrs. Geotripper and I had decided to conduct our second ever vagabonding trip, and we chose to go to the northwest, with a couple of vague goals in mind, but no schedule or itinerary. We rarely made a reservation more than a day in advance, and quite a few days had us at a crossroads late in the afternoon with no clear place to spend the night. It's been a marvelous trip!
Cape Disappointment State Park at the mouth of the Columbia River in southern Washington.
And then the New Yorker article on the potential for a devastating earthquake on the Cascadia Subduction Zone went viral, for both good reasons and bad. I was suddenly receiving facebook shares and emails asking if the article was accurate, and asking for my take on the subject.
Maple tree (really!) in the Hoh Rainforest, Olympic National Park, Washington
One of the "money quotes" in the article was a statement from a FEMA director saying that “Our operating assumption is that everything west of Interstate 5 will be toast.” It sounded like an apocalypse (and yes, some people took it that way): gigantic earthquakes, horrific tsunamis, landslides, power outages, communication lines cut, loss of internet access, and spilled lattes. As I read the article, I realized that I had just spent the last week and a half exploring that very region, from its southern limit along the Northern California coast to the northern boundary in British Columbia. And so the exploration of "toast' country will be the topic of my new blog series. What is the landscape like? In what ways has the Cascadia Subduction Zone left its mark on the land? Did we get rained on in the rainforest? How many Starbucks are there outside of Seattle and Portland?
North Cascades National Park and Ross Lake National Recreational Area, Washington
For all our travels across western North America, we actually covered a lot of brand new territory on this trip. I love seeing new places, and there was a bounty of them on this trip. I'm looking forward to sharing this beautiful (and hazardous) country with you.
Mt. Baker and Boulder Creek near North Cascades National Park