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posted Nov 17, 2012, 12:13 AM by Jennifer MacKinnon   [ updated Nov 17, 2012, 8:48 AM ]

As we sit here tonight there's a winter storm approaching, and the captain tells us the ship may be rocked by 20+ foot waves tomorrow. With strong winds too, some of these waves will break, producing white caps that will dot the ocean surface and walls of water that may wash over the back deck of the ship.  Dramatic as that sounds, the story unfolding underneath our feet is much much wilder. 

As the tide flows up and over the big mountain directly below us on the sea-floor it speeds up and crashes down the far side, rebounding in the form of huge breaking waves. It's pretty similar to what happens when wind flows over a big mountain range on land, which is why you often experience turbulence in an airplane as you cross the Rocky Mountains.  Think of a big wave breaking at the beach and you might picture a foaming wall of turbulent water  5, 10 or even 20 feet high.  The waves breaking below us are an astounding 1000 feet high!  That's as long as the Scripps Institution of Oceanography Pier, which I've included for reference :)  

The black lines in the Figure on the left show the locations of constant density, or temperature surfaces. Normally these are flat, as warm water sits quietly and happily on top of colder water. But here you can see them doing a crazy dance - places where they are vertical in the plot indicate times when the breaking internal wave has drawn cold deep water up to 1000 feet above it's normal depth. The color shows the strength of turbulence, which here is about 1000 times normal for the deep ocean!   

The other crazy thing about these breaking waves is that they're super slow-motion waves. Whereas a good surfing wave has a 10-15 second period, these waves take an hour or more to break.  It's a larger than life slow-motion ballet down there, and we're psyched we get to see it first hand.

- jen

Jennifer MacKinnon,
Nov 17, 2012, 12:13 AM