[LWinters]

I am currently anchored in 15 feet of water at French Harbor on Roatan, Honduras. The night before last we had a major earthquake several miles offshore to the north of us. The strange vibration woke me from my sleep and extreme confusion set in. I recall asking the girl next to me, "what is that"? The look on her face instantly said, "holy hell if you don't know why in the hell are you asking me"?

After a few seconds the noise faded and I easily resumed my slumber seeing nothing out of place. It was only the next morning that we realized what had happened.

Tsunami. That was the fear that began welling up in myself and the other islanders. All ferry traffic was halted, but I kept thinking that staying put was crazy. Only a ship at sea is safe where tsunamis are not felt in the deep water. Close to shore they are sitting ducks for the massive waves.

About the time this was all registering the authorities lifted the warning with the statement that any potentially affected areas would have already been hit.

So, if you are on your boat and your region gets hit with a massive quake is proper protocol to haul ass to deep water?

 

[peptobysmol]

deep water or high ground. But i'm guessing if you felt the quake your in your boat... your best bet is to assume the "worship" position

 

[Noelex]

Given the threat of a Tsunami I would get myself into deep water and heave to, but despite all its destruction, the Tsunami wave is surprising small and I suspect the risk of damage from the wave when anchored in 15 feet of water is small. A greater risk may be from the water rapidly receding and grounding the boat. If tied to shore or pontoon I would defiantly move.

 

[TSOJOURNER]

It may help to remember that often before that actual wave hits, the water recedes.....looks like the tide just suddenly went out - way out.
So I'm thinking, yeah, if you suspect you just felt an earthquake, pull it up and motor out to sea.

 

[bacampbe]

I can't claim to know much about tsunami, but if one resulted from a quake that was centered only "several miles" from you, I think the wave would be on you before you could do much.

 

[TSOJOURNER]

I can't claim to know much about tsunami, but if one resulted from a quake that was centered only "several miles" from you, I think the wave would be on you before you could do much.

You're right. I got to looking around for tsunami information and a lot of what I found was surprising - at least to me. Here's the website:
Tsunami- EnchantedLearning.com

 

[LWinters]

Nice link Selkirk. The epicenter was less than 100 miles from here which means at a velocity of ~ 600 mph I would have just under 10 minutes from the time I felt (mostly heard) the quake to the time the wave was on us.

It's been blowing 20 - 25 every evening so I've got almost 10:1 scope out. With my old manual windless I'd have a nice view of the receding water and first run up from the bow of the boat as the last of the anchor chain and anchor were being secured.

Awww the risks we take to live the dream. Never read anything about that one in any of my books.

 

[Valiente]

Sailboats in the vicinity of the Christmas quake in Sumatra a few years back reported a slightly bigger swell, but we all know what happened near shore. Not all earthquakes cause tsunamis, and the worst tsunamis are sometimes not earthquake-related at all. A huge underwater landslip, like the one forecast to slide a chunk of a Canary Island down to the abyssal plain some day, could create a huge tsunami pointed at the east coast of North America. After the initial very impressive "splash", the sheer depth of the ocean would disguise the forces involved until the 150 foot rollers came ashore...eek!

Being so close and in just 15 feet of water, you got a "free ride" with no harm done, which was lucky indeed, as a tsunami at that depth would've likely put you ashore or capsized/crushed the boat.

I find it interesting that even on a boat you describe the same disorientation and confusion noted by people on land, even though the water must have mitigated somewhat the vibrations felt on land. Thanks for sharing this.

 

[mccary]

Being a Chesapeake Bay sailor I have never experienced an earthquake and never a tsunami, but my understanding of tsunamis is much like any large ocean wave breaking on the beach. In the open (read deep) ocean the wave energy extends down in the water but as the wave approaches shore the water depth becomes shallow and that energy has to go somewhere so it builds up high above the water and hence you have a breaking wave on the beach. The energy of a tsunami is much greater and hence makes a much taller wave breaking on the beach. And just like the normal surf wave breaking on the beach the water recedes just before the wave builds. So, if you want to get an understanding of a tsunami just shrink your perspective down and stand on the beach and watch the large ocean rollers building and breaking on the beach.

I don't think being anchored in 15' of water would have been sufficient to be safe from the effects of a tsunami, I think it would have taken off shore depths 150' + depth. But I am not an expert on this so I could be completely wrong.

 

[sailak]

Lituya Bay Alaska, 1958 ---- 500m wave.

Biggest tsunami | Biggest Wave | Lituya Bay Tsunami

 

[LWinters]

I find it interesting that even on a boat you describe the same disorientation and confusion noted by people on land, even though the water must have mitigated somewhat the vibrations felt on land.

Hey Val. To be clear I definitely did not feel this quake. What woke me was a sound like I'd never heard before. The whole boat seemed to be humming although it wasn't moving a bit. My assumption is that the noise was created by the shock waves that emanated from the quake and were traveling through the land and water. They surely weren't able to move a boat in the water, but announced their presence audibly.

Years ago I got a grad degree in geology so the forces at work are not at all foreign to me, but how they impact a cruising boat wasn't a subject that came up much. The morning after the quake we had to make our way to the Port Captain and Customs/Immigration office to check into Honduras. There was no major damage visible, but things like ceiling tiles and light fixtures were down all over the place.

Mother nature is an awesome force, but after Hurricane IKE and now this I am just fine sticking to the less powerful side of her nature. Remind me not to anchor up near any active volcanoes.

 

[sailak]

It's quite common to hear an earthquake before you feel it -- and it seems the shakes you hear are more violent than the one you don't hear.

 

[dacap06]

Tsunami Mechanics

my understanding of tsunamis is much like any large ocean wave breaking on the beach. In the open (read deep) ocean the wave energy extends down in the water but as the wave approaches shore the water depth becomes shallow and that energy has to go somewhere so it builds up high above the water and hence you have a breaking wave on the beach.

Here's what I learned years ago in Naval Science. The tsunami wave is spread out, not down. Because they originate with the displacement of seabed through earthquake, underwater land slide, or meteor strike, the volume of water involved in the displacement is enormous, but they typically start out only one to three feet tall with a wavelength of a hundred miles or more.

The speed of travel is affected by the depth of the water. In really deep water tsunamis travel very fast - on the order of 500 mph. One can pass by a ship and no one aboard would even notice. That stands to reason. It would take 10 minutes to go by, so call it a 3 foot rise over 5 minutes followed by a three foot fall over 5 minutes. When a tsunami travels over a depth gradient as it does when it approaches land, the front of the wave slows down more than the rear does since the rear is in deeper water than the front. The wave length shortens and the height increases as the water piles up on itself since momentum is conserved.

A tsunami hitting land does not look like the wall of water crashing down on the beach you see at the cinema. Rather, the period shortens to a mile or three (or 10) and it appears that the sea level simply rises astoundingly within a few minutes, and the flooding can proceed many miles inland as the moving water dissipates its momentum by friction and climbing the land.

So I've been told. In all my years at sea, I never saw one for myself.

DaCAP

 

[TSOJOURNER]

.............Remind me not to anchor up near any active volcanoes.

Hey, might be perfectly safe NOW! I mean what are the chances of the same person experiencing an earthquake and then a volcanic eruption?:laugher

It'd be like being mugged by the same guy in two different locations.
But still, you never know......

 

[Valiente]

Hey Val. To be clear I definitely did not feel this quake. What woke me was a sound like I'd never heard before.

Maybe the weird physiological effects were from the sound. I believe much of an earthquake's "sound" is sub-sonic, but very powerfully so. Others on land have reported disorientation and even nausea without feeling "the shake" of an earthquake to any great degree.

Some biologists attribute the seemingly predictive behaviour of animals to precursor earthquake activity before a big tremor hits: They are, on some level, "hearing" the earth starting to creak.

 

[capttb]

Thankfully I keep my boat in a harbor that is "tsunami ready", they have sirens and signs pointing uphill when they tested the siren no one paid any attention.
DANA POINT, Calif. (AP) ―
The harbor town of Dana Point is the first Southern California city to be certified as "tsunami ready" by the National Weather Service.
To receive the designation city officials had to draw up a response plan, identify evacuation routes, post tsunami-warning signs and conduct a public education program.
So far, more than 30 signs have been posted in the low-lying harbor area, telling people they are in a tsunami-hazard zone.
Two other California areas have been dubbed "tsunami ready:" Crescent City in Northern California and the coastal campus of the University of California.