3/29/12
The shoreline is the most vulnerable place to be when a tsunami strikes. In deep water, a tsunami is a series of low, broad bulges hundreds of miles long that won’t be noticed by people in boats.
As the ocean shallows near the coast, the tsunami slows down, allowing the water to build and the height to grow. A major tsunami may be only a few feet high in deep water, but can grow to a towering 30 feet or more at the coast.
The trick to being safe from a tsunami is to be on high ground out of the tsunami zone, or in very deep water where the tsunami height is still small.
Commercial fishermen have the most to lose when a tsunami strikes. Lives and livelihoods are at stake.
Crescent City learned the hard way what can happen when you don’t have a plan to deal with a tsunami. In 2006, three docks were destroyed by a moderate tsunami from the Kuril Islands north of Japan.
As a result, the county, harbor district, and city worked together to develop a notification plan for fishermen. They got to practice that plan on March 11 of 2011, notifying boat owners that a tsunami was expected and to consider getting their boats out of the harbor.
From 2 a.m. to 6 a.m. a steady stream of boats made it safely to deep water.
The system didn’t work perfectly. Some owners couldn’t be reached because contact information wasn’t up to date. A few others were out of town and at least one boat was having engine repairs. But most of the boats in the commercial fleet made it safely out.
The waters offshore of the North Coast can be hazardous with rough seas and bad weather. Exiting Humboldt Bay can be dangerous even without a tsunami on the horizon. Make sure you fully understand the hazards of our offshore environment before heading out to sea.
Regardless of experience, last year many boat owners took their boats offshore without adequate supplies or knowledge of how long they would need to stay offshore. As a result, boaters tried to reenter harbors too early, while dangerous tsunami conditions still existed. They put themselves and their boats at risk.
Much of our recreational water use is in much smaller craft — fishing, sail, and row boats, kayaks, and surfboards. If you fall in this group, I suggest you add the Tsunami Warning Center to the weather, tide, and other sites you probably already check before you leave.
If a tsunami advisory or warning is in place, postpone your water plans for another day. If you are already out on the water, your best way to find out about a tsunami warning is by monitoring VHF channel 16 on your marine radio. There’s also a good chance you can hear one of the coastal sirens, or an announcement from the air. Take these warnings seriously and get off the water as soon as you can.
You can’t surf a tsunami so don’t try — look at the Japan videos if you don’t believe me. I heard someone describing the surges coming up the Mad River as “totally surfable”. He didn’t notice the large log rolling in the waves at the same time. It is rare for a tsunami to have a face and without a face there is nothing for your board to grip.
And if you happen to be sitting on your board offshore when you feel an earthquake, get to shore as quickly as you can.
What happens if the tsunami source is nearby? The first tsunami surges from a Cascadia earthquake could arrive in minutes. If you are onshore or in the harbor when this earthquake hits, you will know it. The shaking will probably last for more than a minute. I know your boats are valuable, but your life is more so. Look at the videos from Japan again. The only prudent behavior is to forget about your boat and immediately head to higher ground. You will also feel the earthquake if you are at sea.
The earthquake may feel like a series of strong bumps as if you are hitting the bottom. It is your warning to get to deeper water, if you are able.
Be prepared to stay offshore for many hours. Monitor your marine VHS radio for information and what harbors you can safely return to. Don’t let your concerns about a possible tsunami ruin your enjoyment of the ocean and the beach. But always pay attention. If an earthquake occurs, get out of the water and off the beach.
If you hear a siren or other warning, get off the beach.
And don’t forget other coastal hazards — we’re much more likely to be visited by large sneaker waves before the next tsunami arrives.
The State Tsunami Program has just released a new tsunami brochure for boaters.
Lori Dengler is professor and chair of the Geology Department at Humboldt State University and an expert on tsunami education and mitigation.
