Friday, March 11, 2011

The tsunami tango in Sidney

I can’t claim credit for that title but its such a good one that I just had to use it and it seemed appropriate.  The title comes from an account of a cruiser who got caught in the Sumatran tsunami in 2009.  It’s a harrowing tale of death, survival and the fragility of human existence.   I bookmarked the site and I’ve read the story a couple of times.  Once you start reading it is hard to pull yourself away from it.  (I just read it again and noted that it’s a little hard to find the link to the 2nd page but if you look at the top of the page that I linked you’ll see the link to the rest of the story)

I was lying awake at around 6:00 this morning, as I often am, thinking about whether I should go back to sleep or whether I should get up and finish coating the deckbox lids.  The cat clearly thought I should get up and feed him.  My phone started ringing and when I checked the incoming number it was Marilyn.  I immediately assumed a catastrophe and answered by asking her what was wrong.  For some reason she was awake before me and had been watching the news of the earthquake in Japan.  Her sister and family live in Tokyo so we have an immediate interest in anything that happens on that side of the world.  By the time she called me her sister had already sent word via another sister that they were OK.  Marilyn was calling me to tell me that there was a tsunami warning in effect for the BC coast.

If you read Wayne’s account of the impact of the tsunami on American Samoa then you will know that his advice is to get your boat out of the marina immediately when you get the warning.  The energy of a wave is determined by its amplitude (height) and speed.  So a very big wave (like the one in Perfect Storm) travelling relatively slowly can do a lot of damage but conversely a relatively small wave travelling extremely rapidly also carries a lot of destructive energy.  In deep water a 3 foot wave travelling at several hundred miles per hour would pass harmlessly under Gray Hawk and we might not even notice it.  Its only when the speed of the wave impacts the shallow coastal waters and turns its speed into amplitude that the problems start.  So Wayne’s overwhelming advice to get the hell out of the marina was ringing in my ears as I hung up the phone this morning.

Tsunami waves travel roughly at the speed of a 747.  Anyone who has sat through a long airline flight knows that no matter how fast the plane is travelling, it still takes time to get from here to there or there to here.  So I knew the tsunami would take some time to arrive on the BC coast, I just didn’t know how long it had been on its way.  I turned the radio on and turned the volume up so I could hear it as I frantically started getting the boat ready to get underway.  Once I had the engine room battened down and the start pins pushed I felt I could relax a bit because I could leave in minutes if it turned out that was all the time I had.  By that time Marilyn had called back to tell me that she had maybe over-reacted and that even if I needed to leave I had about two hours before I needed to do so.

When I balanced the risk of leaving the marina in the dark alone against what appeared to be the negligible risk that anything was going to happen I eventually decided to stay tied up.  We’re now past the time when the tsunami should have hit here if it was going to so I guess maybe I got lucky this time. 

I’m really glad I was here to make the decision.  It would have been agonizing to be away from the boat listening to the news and helpless to deal with it directly.  At least on the boat I was occupied and felt like I was in control of my own destiny.  CBC news has interviewed a couple of harbourmasters on the west coast of the island.  Their advice to their tenants has been uniformly to leave their boat and go inland.  I guess that’s all they can advise.  Telling the marina tenants to get their boats the hell out would cause a panic and could easily create more damage from the panic than the tsunami would have.  That doesn’t change how I would react – given the choice I still think I would get the hell out, single-handed if necessary. 

When it looked like I would have to leave this morning my only concern was how I would get tied up again when I came back.  In hindsight that was pretty silly because, if I had really needed to leave, there might not have been anything to come back to.  If there were any docks left floating there would have been lots of open space cleared by the boats that would have been sitting in the parking lot.  Needless to say I’m glad it didn’t come to that.

(added later)

I’ve been listening to the news all day & I’ve synthesized a better understanding of why tsunamis are so powerful from what I knew and what I’ve learned.  I thought I had a pretty good understanding before this but maybe I didn’t.  Maybe I still don’t for that matter.

Wind waves that we normally encounter affect a relatively small portion of the water column.  If you dive below the surface of a wind torn body of water the water underneath is calm.  That’s not the case with a tsunami wave.  Its hard to imagine the impossibly great forces that initially cause the wave.  The floor of the ocean shifts such that a bulge is created on the surface of the ocean however many hundreds or thousands of meters above.  The ocean floor literally lifts that entire column of water abruptly.  The amount of energy necessary to do that is hard to imagine and that’s what makes the resulting wave so deadly. 

1 comment:

Reluctant Cowboy said...

Glad this ended up a non-event for you and the rest of the family ok.

I guess this was one way to get your heart a pumping. I think I'd rather make a strong pot of coffee and sit on deck watching the sun come up.