, 2 min, 351 words
Tags: alaska how-stuff-works kayak-adventures
Out on the water, waves are kind of a big deal. And there's one type of wave that takes the cake in terms of consistency and impact: tides. The tidal cycle is the sloshing of water around the Earth caused by the combined gravitational attraction of the Moon (2/3 of the effect) and the Sun (1/3 of the effect).
We spent a delightful few hours discussing tides, including causes, effects, and local variation. One of my favorite tidbits has to do with the frequency of tides in the Gulf of Mexico. Most of the time, we think about having two low and two high tides per day. That's because there are two tidal bulges: one caused by the Moon and the other caused by inertia. See here, for instance. (You can also view this as "centrifugal force" if you're in the rotating reference frame of the Earth-Moon system.) Over the course of one day, the Earth completes one full rotation and rotates under both bulges.
It turns out, however, that ocean bathymetry (the underwater equivalent of topography) affects tides rather dramatically. In Seward, this means the two high tides in a day may be very different heights. See, for instance, this abstract. Even wilder, in some places, like the Gulf of Mexico, bathymetry causes the usual twice-per-day tidal cycle to morph into a once-per-day, or diurnal, cycle. This is caused by the resonance of tides in basins in and around the Gulf, as discussed in this paper.
It totally blew my mind that some places might get only one tidal cycle per day. I definitely want to learn more about this once I have a bit more time on my hands.
I owe a huge thanks to Emily, who gave a fabulous, multifaceted, interactive presentation on tides this morning. She's an experienced guide, so she's excellent at interpretation and engaged many parts of our brains. I had a fabulous time learning from her.
