Tsunami Awareness

October-November 2005

This is an article from WaveLength Magazine, available in print in North America and globally on the web.
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by John Gray

Whether hurricanes or tsunami, we need to be prepared for natural disaster.

Last year’s Indian Ocean Tsunami brought worldwide attention to tsunami, but savvy sea kayakers from Alaska to New Zealand know tsunami awareness is basic to paddle plans and campsite selections.

The last well-known Pacific Northwest tsunami was in Prince William Sound, Alaska in 1964, from a quake with a magnitude of between 8.4 and 9.2 on the Richter Scale. Only six years earlier, the highest-ever recorded tsunami reached 1,720 feet in Lituya Bay, Alaska.

The Queen Charlotte Islands were the site of Canada’s largest recorded quake back in 1949. The 8.1 magnitude quake knocked cows off their feet, but the ‘tsunami’ that hit British Columbia shores was only one foot high, unnoticeable on a choppy day.

If Alaska and the Queen Charlottes don’t catch your attention, consider the Cascadia fault. This megathrust fault runs north-south 100 miles west of Vancouver Island, all the way to Crescent City, California. But don’t cancel your West Coast paddle just yet—Cascadia is on a 600-year average cycle with quakes as frequent as 200 years and as infrequent as 800 years.

BC’s Inside Passage is well protected, but perhaps not immune to a tsunami. While there is no record of a megathrust tsunami down the Inside Passage, local tsunami are possible. And don’t trivialize the ‘local’ label. Lituya Bay was a ‘local’ tsunami and New Guinea’s 1999 ‘local’ tsunami killed 2,000 people.

Hawaiians learned the hard way after pre-contact tsunami devastated north shore valleys from Kauai to the Big Island. If you’ve paddled Kauai’s Na Pali coast, did you hike to Kalalau Valley’s waterslide pool? The trail passes through the stone ruins of an ancient Hawaiian village on high ground well back from the sea. Ancient Hawaiians understood big waves.

Next to harming royalty, a major ‘Kapu’ in Hawaiian culture was turning your back on the sea. Today, we know that violating this basic taboo is unwise, so remember the safe camping lessons of Kalalau.

Not all submarine earthquakes generate tsunami, so the big waves are even less predictable than the earthquakes spawning them. When conditions are perfect, a giant oceanic bubble is uplifted when a ‘locked’ subducting plate pops like a spring, releasing the pressures of continental drift. The shallow-slope wave is unnoticeable at sea, but 100+ miles thick, with concentric rings spreading at the speed of a 747.

As the tsunami hits shore and slows to highway speeds, backwaters keep coming. Floods behind the first waves often exceed the height of the original tsunami. This ‘run-up’ goes inland to the ground elevation equal to their height. Khao Lak, where 5,000 people died December 26, 2004, flooded inland more than two miles—to 38 feet of elevation.

Run-ups remain inland up to an hour, then wash back to sea, taking everything they missed the first time.

So how do we paddle with tsunami awareness? Early warning is the most important factor in tsunami survival. When you camp in a state or national park, a helicopter sweep may bring a warning, but in remote wilderness you are on your own. So tune your marine radio to tsunami alerts every few hours.

Radio alerts are late and redundant if you already feel the ground shake, but they are vital warnings for long-range tsunami spawned in Alaska, Japan, Chile or California. On Hawai’i trips, we organized a tsunami watch with a local radio station. Alaska tsunami can hit Hawai’i in five or six hours, so we did a check at midnight and 4 am on every Moloka’i trip for seven years.

Actually feeling the quake is always the best early warning. Close to the epicenter, you might feel a rapidly arriving noise— thousands of windows rattling in the city, displaced rocks and trees in the wilderness. There is no doubt of an earthquake when the shake is sharp and defined. If it’s difficult to stand, or the shaking lasts more than 15 seconds, that’s warning enough. As soon as you can, run for high ground.

The second style of shake, usually associated with a megathrust quake, is more insidious. It may be almost unnoticeable, with low frequency rumbling vibrations lasting several minutes. The low frequency indicates the quake is a long way off—if you feel it, it’s a biggie—and the tsunami it spawned is approaching at 500–600 miles per hour.

Five hundred miles from the epicenter, we felt a subtle shake from the Sumatra quake and immediately knew from length and frequency that it was tsunami time. That faint shake was a non-technical 90-minute warning before the 38 foot wave swamped Khao Lak, plenty of time to run for the hills —if you have tsunami awareness.

The tusnami wrapped this boat around trees, but note the trees are still standing!

If the sea drops unusually fast, it’s a sure sign a tsunami is imminent, no more than five to twenty minutes away. When you observe seabed which is never exposed to the air, it’s time to run. Don’t stop for your toothbrush.

Avoid camping on beaches fronted by flat sand or mudflats. Floodplains with flat beaches and low-lying seabeds create the worst run-ups. Core samples show that repeated tsunami over the eons often help to create coastal floodplains. Coastal river valleys with flat floors are even more receptive to tsunami run-ups, which level the floodplain every few hundred years.

If practical, check your charts for campsites fronted by deep water and/or a reef, and then camp high. The deep water creates a collapsing shoulder wave that forms close to shore, devastating the impact zone, but not running inland very far. The dramatic high wave looks like impending doom—and it is if you are walking the beach. However, run-up floods are the most devastating form of tsunami.

Funnel-effect run-ups in river valleys and estuaries can have serious consequences far from the sea. In wide-open Khao Lak, the run-up went two miles inland. In Sumatra, tsunami run-ups almost 200 feet above sea level filled funnel-shaped valleys starting two miles from the sea.

Camping high avoids the run-up, but how high is high? The 1964 Prince William Sound Great Quake generated over 200 foot wave heights in the Sound.

Tsunami can travel far up channels and estuaries, intensifying in energy and height as they run down the funnel. You may be safer camping on a 30 to 60 foot rise overlooking the beach than pitching your tent a couple of miles up an estuary or river valley. Thanks to the funnel effect, the end of a long, winding estuary or bay might be the most dangerous place.

If you’re out on a boat on the open sea with a deep bottom, keep your bow pointed to sea. Mariners head for sea with the first tsunami warning because deep water is the safest place. Anchoring in shallow onshore waters or mooring in a harbor are the worst possible spots to ride out a tsunami. But what about kayakers?

Paddling to deep water is a safe bet if you can make it, but many factors influence your decision. Bottom configuration is most important. Hawai’i’s deep drop-offs bring safety a few hundred yards from shore, and a few minutes in a kayak should get you to water deep enough for the tsunami to pass beneath you safely.

However, gradually sloping bottoms don’t work if there’s a long paddle to the hundred yard depth contour line. Videos from Khao Lak show the tsunami wall approaching from over a mile across the exposed mud bank. The Big Island’s Waipio Valley has a flat sand beach, so run-ups swamped the entire valley, while Kalalau Beach is steep and drops rapidly, protecting the village from run-ups.

When you stay on land, follow your pre-planned route to high ground. Go as high as you can, as fast as you can. If a tsunami does hit, move higher. Tsunamis are usually a series of waves, sometimes as much as an hour apart. The first wave is often the smallest, as with Port Alberni in 1964. In Phuket, there were three waves; the second, the biggest, arrived 15 minutes after the first.

We lost a good friend who returned to her house after the first wave, only to be killed by the second, far larger wave. The house sat between two mountains on a small 100-yard beach with a steep road fifty yards in either direction. Safety was seconds away, but sitting at the mouth of the funnel, our friend’s house was flattened. She came to rest almost half a mile up the valley.

Stay high. In Khao Lak and Bang Tao the run-up pushed so far inland it lasted an hour. Then the backwash drained, taking everything that wasn’t chained down back to the sea.

Your last resort is to climb a tree—or whatever it takes to get elevation. Tree climbers survived both the 1960 Chile and 2004 Indian Ocean tsunamis. Those branches may not be comfortable and the experience may be harrowing, but large trees generally make it through the run-up and the backwash. Stay in the tree. Don’t try swimming for safety when the flooding stops. Be patient and wait for the backwash to totally recede, and then make your escape.

For the Pacific Northwest, a big one could come anytime in the next five centuries. However, Alaska is so complicated we can expect a tsunami at any time. It’s forty years since Prince William Sound.

Finally, enjoy your paddling and don’t be obsessed with tsunami. Odds are there won’t be a big one in your lifetime. Incorporate tsunami awareness into your paddle plans. When you are properly prepared, relax about tsunami—at least until the ground starts shaking.

© John ‘Caveman’ Gray lives in Thailand where he’s known as Ling Yai (Thai for Big Monkey). He pioneered tropical kayaking in Hawai’i in the early 80s. His 1985 sea kayaking documentary ‘Moloka’i’s Forgotten Frontier’ won an Emmy award and a Teddy as the year’s best environmental education production. Later relocating in Phuket, Thailand he began exploring the limestone islands of South Thailand by kayak, founding a rural development demonstration project which won six ecotourism awards. He’s now teaching a course in Sustainable Tourism for the Thai Foreign Ministry to regional tourism bureaucrats, and doing a series of one-off Ecotourism survey expeditions. Participants are limited to serious ecotourists who want to contribute to the pro bono ecotourism audits and plans for the different countries, and who want to be in documentaries on the adventures. Having turned 60 this year, John calls this his ‘Golden Series’:

• February: Indigenous Tagbanua Tribe on Coron Island, Palawan, Philippines

• April: Palawan Ecotoursim Survey for Mayor Ed Hagedown of Puerto Princessa

• June: Timor-Leste Ecotourism Audit and potential World Heritage Site survey

• August: Hawai’i for Local Boy Secret’s trip

• September: Marine National Parks of Korea

• October: Halong Bay, Vietnam.

For more information, you can email John at info@johngray-seacanoe.com. See www.extremescience.com/BiggestWave.htm for info on the Lituya Bay tsunami which was caused by a landslide.