The Hawai'i That Was: What the Worst Disaster You Can Think of? The Terror of Na Pali...

Wait, what? Terror? Na Pali? That place isn't terrifying, unless you have a fear of heights. It's one of the most beautiful places on one of the most beautiful islands in the world. What could be scary about it?

Well...there's history, and geology. What's the worst disaster you can imagine happening in the place where you live? Are big earthquakes possible? Volcanic eruptions? What about hurricanes or tornadoes? On our adventure today, we visit the site of one of the greatest natural disasters possible.

Kaua'i is a modest island by Hawai'i standards, covering only 553 square miles, fourth in size after Oahu, Maui, and the Big Island. Unlike the other islands, it was principally a single basaltic shield instead of four or five like the Big Island and Maui (it's a little more complicated than that, but I will deal with that story later in another post). It's also the oldest of the major islands, at about 5-6 million years. The coastal areas of the island are of mostly gentle topography, but on the northwestern side of the island, that gentleness ends. Dramatic cliffs 3,000 feet high drop precipitously into the Pacific Ocean. Welcome to the Na Pali. Why are these incredible cliffs here? And what does that have to do with disaster?

Try to imagine a much younger Kaua'i maybe 4-5 million years ago. The shield volcano rises to an elevation of perhaps 8,000 feet above sea level, and the slopes of the mountain are covered with dense rainforest. Myriad species of birds fly among the trees, along with thousands of species of insects and gastropods. All of them are unknown to humankind, because the kind of humans that would pay attention to such things would not be present in the world for a long time. All that was here was about to be lost.

The islands may feel permanent and unchanging in some ways. The lava flows that emerged from the shield were solid and hard and one might feel that they would not be easily eroded or altered by time. That's a delusion, of course. The volcanic rocks were originally deposited on the sediments of the seafloor, and many of the original lava flows were composed of relatively unconsolidated rock, small cinders and ash layers that are not nearly so solid as the lava flows above. The sheer weight of the overlying lava flows exerted such tremendous stress on the unconsolidated rocks that they destabilized and commenced slowly giving way in a lateral sense. The flanks of the island were weakening.

It's not at all entirely clear how the end came about. There may have been earth movements for centuries, maybe even violent earthquakes that produced scarps high on the flanks of the volcano. Such cliffs can be seen today on the southeastern margin of the Big Island near the Kilauea caldera. The quakes may even have produced small tsunamis that swept across the lower shores of the island. But these events would not have affected the animal of the rainforest all that much.

Maybe there weren't any warning signs. I find that to be less convincing, but maybe the end came suddenly, with no precursors. It didn't matter then, but we'd sure like to know today what transpired, because it would be nice to have some warning when an unimaginable tragedy is about to strike.

In any case, the final stroke must have come quickly. Who knows what kinds of sounds were heard as a significant percentage (a fifth? a quarter?) of the entire island suddenly broke away and sank into the sea? The collapse was so rapid that the debris flowed for sixty miles (100 km) along the sea floor. The rapidly sinking land broke up into large chunks and disappeared beneath the turbulent waves. Some of the fragments were miles across. The homes and habitats for hundreds of species disappeared in an instant, never to be seen again.

The loss of a significant part of the island beneath the waves was only part of the story. Displacements of ocean water on this scale produce tsunamis of unimaginable size. We aren't talking about the 30'-40' high waves of events like the tragedies of Indonesia in 2004 or Japan in 2011. We are trying to imagine a wave that exceeds a height of 1,000 feet. Or considerably more. There are chunks of coral on the island of Lanai that presently sit 1,300 feet above sea level. And Lanai is and always has been slowly sinking. Those blocks of coral were tossed there by mega-tsunamis that were produced by similar catastrophes on other nearby islands.

So first, a huge portion of the island sinks into the ocean, and then the water rises in response and sweeps across vast swaths of Kaua'i and the other Hawaiian islands. The level of destruction is incomprehensible. How many species went extinct that day? No one can ever say. Where a coastal plain once existed, there were only cliffs. Immense cliffs. In time, vegetation returned, and erosional processes sculpted the escarpment into the beautiful fluted cliffs we see today along the Na Pali coastline.

One immediately has to wonder whether it could happen again. The answer is, of course, sure. But these events thankfully don't happen often, maybe once every 300,000-400,000 years. And for now, knowing they have happened in the past, we'll perhaps recognize some of the warning signs that such a slide is again imminent. For the time being, we can instead appreciate the beauty that emerges from catastrophe.

The cliffs of the Na Pali are a bit difficult to see. You can drive to Kalalau or Pu'u o Kila lookouts above Koke'e Park and look down from the cliff tops to the sea (see the top picture in this post). These are two of the most astounding views I've ever seen in my life. You can walk the 11-mile long Kalalau Trail that winds along the base of the cliffs (an adventure I've longed to try). Or you float in the sea offshore for an astounding view. Some people take kayaks (another dream), and others take cruises. I had that opportunity in 2006, and that's when I took most of these pictures.

This post is part of a long-running blog series on the geology and history of the Hawaiian Islands, based in part on our summer field studies journey of last June.

The Hawai'i That Was: An Idyllic Paradise on the North Shore of Kaua'i. Sort of.

Photo by Mrs. Geotripper

If you have been there and think that Hanalei Bay is the most beautiful place on the planet, don't worry, I'm not going to diss it. It is indeed one of the most beautiful places I can imagine. It's been the setting for numerous films that needed an idyllic paradise for a backdrop, most notably South Pacific, the Wackiest Ship in the Army (with Jack Lemmon), Uncommon Valor (Gene Hackman, Patrick Swayze), and The Descendants (George Clooney). And who can forget She Gods of Shark Reef?

I've stood on the shoreline, looking towards Nāmolokama Mountain, and there were dozens of waterfalls in view, falling hundreds of feet. The slopes were choked with tropical vegetation, providing a contrast to the rich tan colored sand and the blue water. It's close to the ideal of paradise.

The secret is rainfall, of course. The average precipitation along the shoreline ranges from 80-120 inches a year, and the steep mountain cliffs above wring far more water out of the clouds. The mountaintop just to the south, Mt. Waialeale, has at least a claim to being the wettest place on planet Earth, with a yearly average of more than 400 inches per year!

There's a flip side to being paradise, though. One notices while driving through the small villages along the shoreline that many houses are built on stilts, sitting high off the ground. It's a hint that paradise comes with certain dangers.  The shoreline is exposed to tsunamis, and in some events, most notably in 1946, the surging waves reached a depth of 19 feet, causing severe damage. Even high winter surf (especially in the age of global warming and sea level rise) can endanger some structures as well as the coastal highway.

River flooding is another problem. The rains can come in torrents, and Hanalei River overflows its banks regularly. The pier at Hanalei Bay (above) is a favorite destination of mine (as well as many others!), and one might wonder why there's a roof over the end of the structure. There could be many reasons, but I suspect that since lots of people like to spend time there fishing and picnicking, it's nice to have a place to stay out of the rain, because the weather can change in an instant.

I was surprised by a fierce downpour a couple of years back when I was on the pier, and I took some snapshots of the storm. As I looked at the photos later on, I noticed something strange.

Those spots in the picture were not bits of spray on my lens. They were huge rain drops, caught in suspension by the fast shutter speed. I sort of knew it already, but the picture shows that raindrops are roughly spherical, and not the tear-drop shaped blob that illustrations usually make them out to be.

I am always telling my students that there is no place in the world where one is safe from geological hazards. It's not meant to scare anyone, but instead is meant to encourage people to seek an understanding of the potential threats that they might face if they want to put down roots somewhere. Paradise means different things to different people, but Hanalei Bay comes close in my opinion. Just pay attention to those tsunami sirens when they go off...

The Hawai'i That Was: Pu'uhonua o Honaunau, the Place of Sanctuary That Might Not Be So Safe (Geologically)

Kealakekua Bay

I mentioned earlier in this series that cliffs aren't that common on the Big Island, with the exception of the Pololu and Waipi'o coastline. There is another cliff, though, and its formation has had a profound influence on the island's history, even though it took place long before humans arrived.

Large cliffs develop on the Big Island of Hawai'i primarily as a result of gigantic debris avalanches that carry a large portion of the island into the deep ocean, leaving behind cliffs and a scalloped coastline. The Alika debris avalanche did this exact thing about 120,000 years ago, with a runout of about 60 miles across the ocean floor. The slide produced a huge tsunami that dumped chunks of coral more than 1,000 feet above sea level on Lana'i (most tsunamis generated by earthquakes rarely exceed 100 feet in height). If such an event were to happen today, the effects would be unthinkably horrific. Luckily, they are rare, tens of thousands of years apart. There would presumably be many signs of an impending collapse (one would hope, anyway).

Hikiau Heiau at Kealakekua Bay

In terms of human interest, the slide produced a deepwater bay, Kealakekua, that was of great value to the native Hawaiians who colonized this coast. For several miles south, the coast was unusually flat, as subsequent lava flows filled out and formed sort of a delta into the Pacific. The amount of level land led to a high population density. Important archaeological sites are extensive, most notably at Kealakekua Bay State Historical Park, and at Pu'uhonua o Honaunau National Historical Park.

The park at Kealakekua Bay preserves Hikiau Heiau (above), a huge structure dedicated to the war god Ku, and Lono, the god associated with fertility of the land. It has been damaged by a number of tsunamis, but has been repaired and is still sometimes utilized for ceremonies.

The cliff at Kealakekua Bay is of special importance to native Hawaiians. It's called Pali Kapu O Keoua ("the forbidden cliff of Keoua"), and the various holes and caves in the cliff contain the bones of royalty. Such bones are said to possess great power (mana), and so great effort was invested in keeping their location hidden (I seem to remember reading that a trusted servant would dangle from a rope on such cliffs, and when he had hidden the bones, the rope would be cut and the servant would plunge to his death; an honor, I guess, but not a great job benefit).

One more moment of history has to be mentioned when exploring Kealakekua Bay. The small white tower in the middle of the picture above marks a small bit of property owned by the British government. It's called the Cook Monument, and it commemorates the "discovery" of the Hawaiian Islands for the first time by someone other than Polynesians. Captain James Cook and his crew landed here in 1779, and through a set of odd circumstances were greeted as gods. They spent a month interacting with the islanders, and left on good terms. A broken mast necessitated their return a short time later and things didn't go so well. Captain Cook was killed in a fracas over a rowboat. The Hawaiians treated his body as a royal, and his remains were hidden on the pali (although some "bits" were returned to the crew).

The effect of European contact cannot be overstated. While the arrival of western technology allowed King Kamehameha I to gain control of the entire island chain, forming the nation of Hawai'i, disease decimated the Hawaiian people (from as many as 1,000,000 to maybe 30,000). Just over a century later the island was taken over by corporate interests, before becoming a territory of the United States. Although the Polynesians had caused the extinction of native species through the introduction of invasive animals and plants, the process was greatly accelerated with the arrival of the Europeans.

Pu'uhonua o Honaunau

Life on Hawai'i was difficult enough, with the danger of volcanic eruptions, earthquakes and tsunamis, but in the years before European contact, seemingly small slights could get you executed. The high population of the islands required a highly regimented society to maintain order, and the principle of kapu included a long list of transgressions that could result in an instant death penalty. These rules involved how commoners could interact with royalty (stepping on ali'i's shadow, or touching him or his possessions), how they interacted with each other (men could not eat with women), and relationships with the land (fishing and logging regulations). If you broke kapu, even by accident, the death penalty could be immediate. In essence, a person had one chance to survive. There were sanctuaries, the Pu'uhonua, where one could be cleansed of their sin and receive forgiveness. The kapu breakers simply need to get there before their pursuers caught them. Pu'uhonua o Honaunau National Historical Park in part preserves one of these sanctuaries.

Heiau in the sanctuary at Pu'uhonua o Honaunau

It's hard to understand how kapu was tolerated, but in the context of religion, breaking of kapu could result in the punishment of the entire community, which was meted out in the form of storms, floods, earthquakes, tsunamis, and volcanic eruptions. It's a powerful impetus to stay in line if one thought they could bring destruction on their entire society. The strict adherence to kapu ended with the death of King Kamehameha I in 1819. His son the new king abolished the system by dining with his mother.

Fishpond at Pu'uhonua o Honaunau

The park in general is one of the best places on the islands to learn about Hawaiian culture. There are examples of heiaus, hales (houses), temples, and the pu'uhonua itself. There are some brackish pools that served as fishponds for the royalty.

There are interesting critters about as well. Some species of gecko may have arrived with the Polynesians, but others arrived much later. Eight species are present on the islands now. They are usually considered good luck, since they have an appetite for cockroaches and other pests.

The creature above is actually a sea urchin, the Shingled Sea Urchin. The modified flattened spines give the animal extreme stability in wave zones.

Pu'uhonua o Honaunau and Kealakekua Bay exude a sense of peace today, but they mask a turbulent past, both geological, and anthropological. If you are ever on the Big Island, they are two very interesting stops.

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).

Is the Second Coming...Coming Because of an Earthquake in the Pacific Northwest?

No, it's not real, it's a photoshopped hoax after the Indonesia tsunami of 2004

Geotripper stands bravely on the coast of the Pacific Northwest, camera and binoculars in hand, ready to liveblog the end of the world during the apocalyptic earthquake that is going to happen SOON. Well, okay, I'm actually visiting with family, but if anything happens earthquake-wise, I will let you know.

I want to tread lightly here, because I'm not in the business of attacking anyone's religious beliefs. But I do want to provide some perspective to counter the kinds of headlines I've been seeing in the aftermath of an excellent piece in the New Yorker (please click here to read it; it's worth your time) concerning the potential for a large earthquake in the Pacific Northwest, one which will cause catastrophic damage to the infrastructure of the region and possibly kill 16,000 or 17,000 people.

I get a bit tired of the predictable hype that follows such viral stories. The idea that the Pacific Northwest will "be destroyed" by the earthquake feeds into the fears of people who have been reading too many headlines like this one:

"Jesus’s Prophecy Of Massive Earthquakes Is Now Confirmed As Fox News Reports Of A Mega-Quake To Soon Destroy U.S. Pacific Northwest Triggering Christ’s Soon Coming"

It's a real headline from the internet, but you'll have to Google it. I don't want to provide them with any more publicity than they've already gotten with their irresponsible hyperbole (and just how did FOX news end up in that title?).

The Great Wave at Kanagawa (from a Series of Thirty–Six Views of Mount Fuji), Edo period (1615–1868), ca. 1831–33  Katsushika Hokusai (Japanese, 1760–1849).

Here's the thing. This earthquake, should it happen in our lifetime, will be a horrible catastrophic event. But it will also be a natural event that is predictable with certain limits, follows the natural rules of physics and geology, and has happened numerous times in the past, most notably in the year 1700. Our understanding of the dynamics of this potential earthquake is one of the great detective stories in the science of geology, as the New Yorker article points out. 

USGS Simulation of tsunami pattern from 1700 Cascadia earthquake

It is not some kind of supernatural event that is planned to herald the second coming of Christ. I arrive at this conclusion because it is arrogant for Americans to think that a natural disaster that happens to us and results from well-known geological processes is somehow different from other natural disasters that have happened elsewhere and will continue to happen long into the future. Let look at some examples of earthquakes in the past (source is from the US Geological Survey via Live Science).

Date Location Deaths Magnitude Comments January 23, 1556 China, Shansi 830,000 ~8 Damage up to 270 miles away July 27, 1976 China, Tangshan 255,000 (official) 655,000 (estimated) 7.5 Estimated death toll as high as 655,000. Dec. 26, 2004 Sumatra, Indonesia 227,898 9.1 Deaths from earthquake and tsunami August 9, 1138 Syria, Aleppo 230,000 n/a   Jan. 12, 2010 Haiti 222,570 7.0 1.3 million displaced. May 22, 1927 China, near Xining 200,000 7.9 Large fractures. December 22, 856+ Iran, Damghan 200,000 n/a   December 16, 1920 China, Gansu 200,000 8.6 Major fractures, landslides. March 23, 893 Iran, Ardabil 150,000     September 1, 1923 Japan, Kanto (Kwanto) 143,000 7.9 Great Tokyo fire. October 5, 1948 USSR (Turkmenistan, Ashgabat) 110,000 7.3   December 28, 1908 Italy, Messina 70,000 to 100,000 (estimated) 7.2 Deaths from earthquake and tsunami. September, 1290 China, Chihli 100,000 n/a   May 12, 2008 Sichuan, China 87,586 7.9 More than 45.5 million affected Oct. 8, 2005 Pakistan 85,000 7.6 More than 69,000 injured November, 1667 Caucasia, Shemakha 80,000     November 18, 1727 Iran, Tabriz 77,000 n/a   November 1, 1755 Portugal, Lisbon 70,000 8.7 Great tsunami. December 25, 1932 China, Gansu 70,000 7.6   May 31, 1970 Peru 66,000 7.9 $530,000,000 damage, great rock slide, floods. 1268 Asia Minor, Silicia 60,000 n/a   January 11, 1693 Italy, Sicily 60,000     May 30, 1935 Pakistan, Quetta 30,000 to 60,000 7.5 Quetta almost completely destroyed. February 4, 1783 Italy, Calabria 50,000     June 20, 1990 Iran 50,000 7.7 Landslides. SOURCE: USGS

The question I have for the hucksters and frauds on the internet and elsewhere: what gives you the right to decide that a particular earthquake is somehow a harbinger of the religious end of the world? People throughout history have found it far too convenient to blame natural disasters on the perceived moral failings of those who were most affected. It's not an old tribal thing either. Pat Robertson tried to blame the Haiti quake on the Haitians themselves. It's truly disgusting.

I suspect I'm mostly preaching to the choir here, to use a religious metaphor, but if you happen to have stumbled onto this site while tracking down biblical prophecies, please consider something as you do your research: If an event has happened many times before, is predicted by science to happen many times again, then it doesn't really fall into the realm of supernatural judgement. It's the Earth doing what it has been doing for a very long time. If the death tolls from natural disasters seem to be rising, it is because more and more people are being forced to live in ever more dangerous and marginal environments.

Just because bad things happen to human beings doesn't mean they are being punished by a capricious god. Earthquakes, tornadoes, hurricanes, tsunamis and other disasters are part of living on the Earth, and they happen to the good, the bad, and the ugly alike.

A Pair of Large Earthquakes in the Indian Ocean

It's the stuff of nightmares at first glance, but there is some positive news about two huge earthquakes that struck several hundred miles offshore of Banda Aceh in Sumatra this morning. At 8:38 UTC (1:38 AM in the Pacific time zone) there was a magnitude 8.6 event with an estimated depth of about 14 miles. It was followed by a magnitude 8.2 event in the same region a little over two hours later. Given the horrific tragedy of 2004 when a tsunami generated in the region killed a quarter million people, this surely caused a sense of concern and panic. But there is a huge difference in the quakes that happened this morning.

The "beachball" symbols on the map above from the U.S. Geological Survey show the type of fault that produced the earthquake, and they indicate that this morning's quakes exhibited right-lateral strike-slip motion. This is good news because it means that the seafloor shifted sideways during the quake, instead of vertically. Accordingly, a large tsunami is unlikely, although a warning has been quite logically announced. Make no mistake, these are huge seismic events, and if they had occurred on land anywhere near a population center, they would have been horrible disasters. Preliminary news reports indicate that warning systems worked as people moved away from low ground along the coast. A sense of panic, no doubt, but at least there were warnings given, unlike in 2004.

For some details on the somewhat odd nature of these earthquakes, check out this analysis at Lithics.

When a Magnitude 6.9 Earthquake is an Aftershock....

There wasn't a whole lot of information when I wrote about the 8.8 earthquake in Chile in the earliest hours of the morning. Information is starting to flood in now from many sources, and my first impression is media coverage is a bit better than it was for the Haiti quake and other earlier events. When I say "better", I don't mean more cameras, I mean evidence of an effort by the reporters to educate themselves about the basic science of earthquakes.

My first thought is for the people who have been affected, both in Chile and across the Pacific basin. A quake this big is going to have huge impacts. The aftershocks are going to be an issue: my USGS notifications are set for any quakes bigger than 5.5 and there have been 11 of them so far, with the largest at 6.9. For perspective, 6.9 is the size of the Loma Prieta earthquake here in California from 1989. It killed 4 dozen people and did around $10 billion in damage. The quake in Haiti was a somewhat larger 7.0. Aftershocks are going to continue for a long time, over a region about 600 miles long (the size of the fault zone that shifted in this quake).

The tsunami is a huge threat. The size of a tsunami in any particular place is dependent on many factors, including the size of the earthquake (which was colossal), how the quake transferred energy to the ocean water (unknown to me at this point), and the shape and depth of the coastline where the tsunami strikes. All I can say to my Pacific Basin friends is that when the Civil Defense folks set off the sirens, take it seriously! Hawaii in particular has a tragic history with tsunamis, and there has been a vast amount of coastal development since the last major tsunami (in 1960, also caused by an earthquake in Chile). There will be a big problem of people wandering down to the beach to watch the tsunami, which can only be described as an act of idiocy. Get to higher ground or higher floors. If the warnings are inaccurate, you've only lost a bit of time, but if they are accurate, your life will be saved. Don't go to the coast until the "all clear" is given, because there will be more than one surge of water. You can't swim your way out of a tsunami; they are one of the most dangerous of geologic events, as the Indonesian tsunami of 2004 demonstrated.

Tso, can you Tsurf a Tsunami?

Hokusai's 1831 "Great Wave off Kanagawa" and a picture of the Hilo Pier in 1946. The man (who did not survive) was named Antone Aguiar. According to the story at the Tsunami Museum in Hilo, he cut the ship Brigham Victory free from the dock, allowing it to ride out the disaster. The picture is from the archives at NOAA.

There are two main kinds of waves, those that are produced by winds blowing over the ocean surface, the subject of the last two posts on the huge waves that struck Southern California last week, and those that are produced by massive disturbances of the ocean floor, either by earthquake, volcanic eruption, or landslides. These are tsunamis, often (incorrectly) called tidal waves (there are tidal waves of a sort, called tidal bores, but they cannot be mistaken for a tsunami).

After my adventures this summer, which included a grand tour of the Hawaiian Islands with two dozen of my students, and a mini-vacation in Southern California that coincided with the arrival of unusually large waves along the coast, I am writing a short blog series on the dynamics and geology of waves. Tsunamis have been on my mind, having seen perhaps hundreds of tsunami warning signs all over the coastal areas of Hawaii, and seeing, for the first time, tsunami warning signs in Southern California. I don't know when they started appearing (I suspect in 2004), but they certainly weren't there in the years when I was growing up in the southland.

I used to have a more difficult time teaching about tsunamis, but that changed in 2004 when the Indonesian Earthquake produced the tsunami in the Indian Ocean that killed around 230,000 people. Because it hit tourist beaches, thousands of videos and photographs documented the event, and international media coverage was intense. Prior to that event there were not a great many photographs that documented what a tsunami could do, and the really tragic events, like those in 1946 and 1960 in Hawaii, had receded into ancient history for most people.

Wind-driven waves and tsunamis are very different. Waves travel as swells across the seas, with turbulent water extending only a short distance beneath the surface (about half the wavelength). They travel slowly, a few tens of miles per hour, so they can take a week to cross an ocean, as the Tahitian waves did on their way to California this last week. The energy of the wave is expended only in shallow water at the coast, as the waves build up and fall over as rolling breakers. The amount of energy in a storm or typhoon is immense, but the energy is transferred to the water over time, and is dissipated over a period of days and weeks.

A tsunami is generated in a moment, as an earthquake shifts the ocean floor, or a volcanic caldera collapses. Large landslides off of islands sometimes generate tsunamis as well. The disturbance affects the entire column of ocean water, from surface to seafloor, and all of the energy begins traveling very fast outwards from the point of the disturbance. Very fast. As in the speed of an airliner, around 500 miles per hour. In open water, they may pass without notice, as the wavecrests may be a hundred miles apart, and only rise and fall a few feet. Ships at sea are rarely affected by tsunamis.

At shorelines, the story is vastly different. The oncoming waves hit the shallows at a high rate of speed, and friction slows the forward motion, but the energy is still there and it must be expended. The water surface rises and surges forward, quickly inundated the low coastal areas to depths ranging from a few feet to more than a hundred in some of the most disastrous events. The first indication that something is amiss often is a sudden emptying of shallow bays and a drop in sea level lasting several minutes. The surge follows shortly after. Other times, the sea just suddenly surges forward without warning.

Even when warnings are given, people can make bad choices based on misinformation. They may evacuate as ordered, but may enter the devastated area after the first wave recedes, only to be swept away by the second or third wave they didn't know was coming. Of course the millions of people living along the shoreline of the Indian Ocean didn't even get the chance to make those kinds of mistakes in 2004. Since 1946 there has been a Pacific Ocean-wide warning system that has given people many hours notice that a tsunami was approaching. The poorer countries bordering the Indian Ocean have never had such a system, even though it was well known that tsunamis were a distinct possibility. A horrific injustice...

So, does California have to worry about tsunamis? The good news (sort of): we have big earthquakes on the San Andreas and other faults offshore, but they usually involve lateral motion that does not disturb the sea floor in such a way as to cause tsunamis. The bad news is that the northernmost coast of the state is close to the Cascadia Subduction Zone that is very much capable of producing huge tsunamis, and did in the year 1700. And of course as noted above, tsunamis can cross entire oceans, so large quakes in Mexico, South America, Alaska, Kamchatka, Japan, and all the other major seismic zones in the Pacific Rim can cause tsunamis that could reach the California coast. In 1964, the magnitude 9 Alaska quake produced a tsunami that killed a dozen people in Crescent City on the far north coast.

Southern California is perhaps a bit more protected because of the presence of the Channel Islands, which would tend to break up some of the wave energy. But major tsunamis coming out of the south and west have some potential of reaching parts of the coast. And thus, the tsunami warning signs that have appeared.

I don't advise surfing a tsunami...it's hard to avoid breaking the third-story windows of the building you will be mashing into....

One last comment: when I lived in Santa Barbara many years ago, there was a tsunami warning based on the major quake that had devastated parts of Mexico City in 1985. Of course, people evacuated and headed for high ground, right? Of course not. They went down to the beach to watch. Thank goodness the tsunami was a dud in that case.