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‘Giant’ Tsunami Science

Old Wisdom and New Technologies for the Next Wave

Above the Pacific coastline in Iwate Prefecture in the northern Tohoku Region of Japan stands an ancient moss-covered stone, carved with a clear instruction to future generations. Like many others that dot the Japanese landscape in strategic, high places along the coastline, it cautions:

“A home built high above waters provides ease to our children and grandchildren. Remember the calamity of the great tsunamis. Do not build any homes below this point.”

Iwate Prefecture, Japan. This old inscription warns not to build below the stone.  ©Kishimoto/Wikimedia (CC BY-SA 4.0)
Iwate Prefecture, Japan. This old inscription warns not to build below the stone. ©Kishimoto/Wikimedia (CC BY-SA 4.0)

This stark warning from the ancients was either forgotten or disregarded, as modern settlements were built below the high-water line of an earlier tsunami south of Sendai, with buildings stretching all the way down to the shore.

Tragically, in 2011, when the Great Tōhoku Earthquake shook the land, the resulting tsunami devastated the area and killed more than 18,000 people.

Is building in tsunami zones simply an example of modern hubris ignoring the lived experience of the forebears? Or is economic necessity the driver, coupled with Japan’s increased population density along its coastal areas?

Iwate Prefecture, Japan (2011).  ©Mitsukuni Sato/Wikimedia (CC BY 2.0)
Iwate Prefecture, Japan (2011). ©Mitsukuni Sato/Wikimedia (CC BY 2.0)

Expertise Gained from Decades of Fieldwork

To tsunami expert, Dr. Emile Okal, preparing and planning for these gigantic, powerful waves cannot be discussed enough.

For four decades, Dr. Okal saw many examples of widespread damage left by tsunamis. As a member of dozens of international survey teams investigating tsunami disaster zones, Dr. Okal helped collect eye-witness accounts, runup, and inundation data—the maximum heights waves reached on shore and the distances inland that the waters stretched.

Using this data, Dr. Okal has been instrumental in advising communities how best to limit the destruction of tsunamis and save lives. In 1999, for example, relying on this data, the remote village primary school in Omoa on the Marquesas Islands in the Pacific Ocean was moved and rebuilt a kilometer (around 1,093 yards) inland after the original beachfront schoolhouse was destroyed.

The reasons people in Japan risk settling below the tsunami stones—or people anywhere build in tsunami zones—are basically the same: The coastlines are alluring, and people have a tendency to forget previous disasters, says Dr. Okal, now professor emeritus at the Department of Earth & Planetary Sciences at Northwestern University in Evanston, Illinois.

“Japan is a heavily populated country where most of the areas that are easy to live and build on are close to the sea,” he explains. As the world’s population has grown, he adds, people need more space to live and will naturally migrate towards the shore.

“Coastal communities have always been attractive places to live because of economic activity. It’s very difficult to tell a fisherman, ‘Go and live in the mountain at the back of the valley.’ Furthermore, most of the trade in global economic activity around the world goes by sea, and so you have to have boats and big harbors to accommodate these ships—obviously, you can’t just locate them inland.”

It is the population spreading seawards—not increased frequency or strength of tsunamis—that has led to greater death and destruction.

It is the population spreading seawards—not increased frequency or strength of tsunamis, which has remained the same for probably tens of thousands of years—that has led to greater death and destruction.

“We are really confident when we say the Sumatra tsunami of 2004 was the largest such event in terms of fatalities in the history of mankind, because the population has increased so much,” Dr. Okal says, referring the December 26 tsunami that killed nearly 228,000 people in Indonesia and surrounding areas. The disaster’s extraordinarily massive waves, some reaching 167 feet high, were triggered by a nearby Indian Ocean earthquake that registered a 9.1 magnitude or higher.

Education is Crucial

The infrequency of tsunamis allows new generations of coastal dwellers to forget their sudden and overwhelming powers of destruction.

According to Dr. Okal, people must personally and regularly hear about tsunamis to take the risk seriously. “This is why coastal fishing communities in many countries, such as Peru, have acquired a certain resilience because they learned these things happened and your grandfather had to run away.”

But in places where ancestral education has disappeared, classroom instruction and other forms of instruction about tsunamis are crucial.

“The best thing to do is to educate people,” Dr. Okal says. “A tsunami is something you have to live with—it will come back in the future.”

And if people “lose awareness, they don’t evacuate.”

Even the simplest forms of information can make a difference.

In 2009, the Samoan islands, comprising American and independent Samoa, were hit with a nighttime “doublet” of earthquakes. The tsunamis they launched—with waves higher than 70 feet tall—annihilated villages and killed almost 200 people. Experts believe one of the reasons many islanders escaped the deadly waters was because of a basic form of advertising—roadside signs saying “Tsunami Zone: Caution.” Another reason was public education on both islands about evacuating instantly whenever earthquakes are felt.

Japan—Roadside tsunami warning.  ©Alexandar Vujodinovic/Wikimedia (CC BY-SA 4.0)
Japan—Roadside tsunami warning. ©Alexandar Vujodinovic/Wikimedia (CC BY-SA 4.0)

Japan’s highways also have similar warning signs, pointing the direction people should drive towards safety. Leaflets distributed to the population say “Keep moving to the highest ground possible,” and every Japanese schoolchild knows a red-and-white checkered flag on the beach means evacuate immediately in the event of a tsunami. The first day of September is known in Japan as Disaster Prevention Day. This public holiday—in which the public practices emergency evacuation drills—coincides with the anniversary of the Great Kantō earthquake a century ago.

Despite these best measures, when the Great Tōhoku Earthquake and tsunami struck Japan in the afternoon of March 11, 2011, 18,000 people lost their lives.

The tragedy could have been worse—social scientists estimated 200,000 people were living or working in the area where the tsunami inundated the shore. To Dr. Okal, the public response to this natural disaster showed the benefits of regular training about evacuation.

People survived “because they had these drills, because everywhere you go in Japan you have these little symbols that tell you to run away in that direction, and they knew exactly what to do,” he says.

Tsunami Defense Innovations

There are, of course, efforts to find more reliable ways to save lives than evacuating to higher ground.

Sea walls have long been a traditional coastal defense, but they are useless against waves of water travelling up to thirty miles an hour.

Sea walls have long been a traditional coastal defense, but they are useless against waves of water travelling up to thirty miles an hour.

One idea has been to replace sea walls with waterfront parks featuring rolling hills that dramatically reduce the amount of kinetic energy from the water. These “tsunami mitigation parks” are currently being developed in Chile, Indonesia, and Japan. So far, none have been tested by a real-life emergency.

Pillars helped this mosque survive the 2004 tsunami in Aceh.  ©USGS/Wikimedia. Public Domain
Pillars helped this mosque survive the 2004 tsunami in Aceh. ©USGS/Wikimedia. Public Domain

Buildings in tsunami zones are now being constructed to survive the onslaughts of water.

Some buildings resemble traditional housing built on stanchions above the water. “It turns out a bridge is better than a dam at resisting a tsunami. There has been a push in certain communities, including Hawaii, to build structures where the first floor is open, essentially built on pillars, and this has proved to be quite efficient,” says Dr. Okal.

Another method has been to utilize fluid dynamics through examining a city map and discovering how many people are in each building. During an evacuation procedure, the evacuation modelers create pathways to maximize the flow of people safely from each area of the city to pre-existing shelters.

Early Warnings and the Basics

Earthquake and tsunami early warning systems are improving with time, and wave-detection devices on the ocean floor are opening a new avenue of research. “We have made great progress in detecting the early stages of generation and propagation of the tsunamis because we have made progress in monitoring the earthquakes responsible for a tsunami,” Dr. Okal says.

However, closer to shore, he admits that the basic response remains the same: “If you feel the Earth shaking, that is a warning. If you are close to a beach, you evacuate without thinking, without waiting for any order from the authorities. You take your life in your own hands, and you run.”


*Gordon Cairns is a freelance journalist and teacher of English and Forest Schools based in Scotland.


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