Re: [Paddlewise] "Sneaker Waves"

There is a lot of energy in long waves. This energy can be concentrated in
several ways to create sneaker waves. Even if all the waves are uniform in
size and have arrived at the shore from a single distant storm, the
underwater topography off shore can bend the waves in such a way to focus
them onto an area. If that area is also shallow the slowing of the wave
front can create an even higher amplitude wave at the shallows. Combine that
with the focused waves crossing each other right at the shallows at the
right time and a much larger wave can result because the two wave amplitudes
are additive. A jetty (I forget where--somewhere on the west coast I think,
maybe CA) had stood for years until it was battered apart when long low
waves arrived from just the right direction to get them focused on the jetty
by the underwater topography further out. Recall that longer waves "feel the
bottom a lot deeper than shorter waves so this focusing of even one wave
trains energy can also happen out in somewhat deeper water than with shorter
waves.

If you have long waves coming from two or more different storms arriving at
the same time, out of phase, and from different directions you could get
even higher amplitude waves where the crests all add together at the same
time. If this large hump of water from combined wave crests also happened to
be shoaling at the same time they came together it will jump up far higher.
It would be rare to all come together at once but it happens and if you are
paddling there at the same time you will probably be lucky if all you have
to do is clean your shorts afterward.

My understanding is that a "Wave of Translation" or soliton is a wave that
moves water from one place to another. The most common one we are likely to
see clearly is the soup wave that runs up the beach after a wave enters
shallow enough water to destroy its normal orbital wave motion and break. If
you watch this for awhile you will also see waves formed in this near shore
zone that aren't breaking and aren't soups, but well up in a single smooth
steep wave (often somewhat crossing the breaking soups). Other instances of
Waves of translation could be the waves at the front of a tidal flow
entering a narrowing channel that focuses the energy such as the Bay of
Fundy, Turnigan Arm in AK, the mouth of the Amazon and several other river
mouths abound the world (known as tidal bores). The one example Russell
noticed from the suddenly stopped barge (my guess it grounded on shallows is
why it stopped) and wrote about can also be seen by kayakers entering very
shallow water on a dead calm day. The kayaks wake changes its usually
constant angle and the angle swings forward (making it more obtuse) until it
is going nearly straight out from the bow (or possibly just in front of the
bow) at each side of the bow. Try looking for it the next time you are
paddling fast into uniformly deep, roughly 6" to 8" deep, shallow water on a
calm day. Once I read about and knew what to look for I've noticed it many
times.

Matt Broze
www.marinerkayaks.com  
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