The Hawai'i That Was: There was a Monster in the Water at Laupahoehoe

There is a small bay a few miles northwest of Hilo on the Big Island of Hawai'i called Laupahoehoe. It's a raw section of the coastline, with waves that crash violently against the ragged exposures of basalt. I stand at the point and imagine the movies I've seen where monsters rise out of the waves. Godzilla would be at home here, and King Kong might wander down from the highlands to look out to sea. There is a monster here, though, and it is very real. It is a killer of the unwary.

Despite the ruggedness of the coastline, residents built a breakwater and boat launch many years ago, and fishing boats plied the waters offshore. A small town was built on the coastal flat, including a  schoolhouse. Accounts describe a pleasant community.

On April 1, 1946, a magnitude 8.6 earthquake struck in the Aleutian Islands of Alaska. The tremor suddenly moved the sea floor, displacing an immeasurable volume of seawater and setting in motion a powerful tsunami. The wave was as high as one hundred feet along the Alaska shoreline, but few people lived there. It was the energy directed into the Pacific Ocean that became the monster that consumed Laupahoehoe. The waves traveled across the ocean at the speed of a jetliner, reaching the Hawaiian Islands just 5 hours later. The waves would have not been noticed in the open ocean because the wave crests were far apart. It wasn't until they reached the shallow sea floor that the full fury of the wave energy would be demonstrated.

The 1946 tsunami hits Hilo Bay

In most places, the first hint that something was amiss was the withdrawal of the water offshore, as stunned townspeople watched. Fish and eels were left flopping on the exposed rocks. Few people knew what it meant and wandered onto the coastal flat, but a several did understand their peril. They started running or driving up the hill, trying to warn others. The first wave to arrive was not catastrophic, being only a few feet high, but the next wave reached a depth of 35 feet (I say "depth" because the wave arrived more as a surge of water rather than a vertical wall). The wave that hit Hilo down the coast killed more than a hundred people, but what happened at Laupahoehoe felt more tragic, if that is possible.

The 1946 tsunami destroys the downtown area of Hilo

The children of the town were at school on the coastal flat. The wave swept away the school house, killing 20 students and four teachers. Only a few children and one teacher survived. Some survivors floated at sea for more than a day before being rescued. How horrible it is to lose most of the kids in a community...I truly cannot imagine.

In the sad aftermath, the town was moved from the coastal flat to the hills above, and the site was made into a beautiful coastal park that almost belies the horrible tragedy that took place here. But the people of the town won't let their lost ones be forgotten. On the small hill above the bay there is a monument to those who were lost and after 70 years there are still flowers and leis being placed in their memory.

There was one positive change that occurred as a result of this horrible tragedy. It was the lack of warning that led to the deaths of so many, and after 1946 the Pacific Tsunami Warning Center was established, providing hours of warning to towns, states, and countries in the path of Pacific Ocean tsunamis. Tens of thousands of lives have no doubt been saved in the decades since. In the Japan earthquake of 2011 the waves that reached Hawai'i could have led to fatalities, but didn't because Hawaiians know what to do when the warnings come.

One can only wish that we had had the foresight to set up a similar system in the Indian Ocean prior to 2004. The magnitude 9.2 Indian Ocean earthquake produced a tsunami that killed 230,000 people.

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.