The Coriolis Effect | The Ocean, Beach and Changes to the Shoreline

By Athair Baer
If you’re anything like me, you see things and wonder, “what happened(?)” when things have been the same way for so long, but upon your next visit seem very… Changed.  This is the sort of thing that prompted my minor in Marine Biology. When I would see all the beautiful things on my beach one day and then a week later everything from the consistency of the sand to the color of the water would be so very different. 
  

photo: Heidi Grabowith

Well, it just so happens, that aside from how magical the ocean is, there’s a very routine mechanism to the changes of your shoreline. Out here, in Southern California, the cities annually shill out a heavy pant-load of cashola to keep the shape and depth of their beaches unchanged. This includes trucking in sand from other locations at times if you’re on one of the more ‘endangered’ coasts. This fantastic force is called the Coriolis Effect. First proposed by a scientific Frenchy named Gaspard-Gustave Coriolis, in 1835.

And it is the result of more than just the shape of your coast.  It’s the reason storms spiral the way they do – same with your toilet water direction. It affects our whole world and many different atmospheres.



We’ve all been on a merry-go-round as a kid. Right? Sitting in the middle while a friend grabs onto the rail and runs with it til he slips and drops or makes like one of the Dukes of Hazard and swings on-board. That centrifugal force is a big part of this Coriolis Effect, because if you think of it, in more ways than one, this wonderful planet of ours is just a big merry-go-round spinning on the axis of the north 'n south poles.



The spinning gets a lot more complicated when you add in other forces like billions of people, pushing winds, and the lopsided weight of continents and oceans of water – oh yeah, there’s a few reasons this planet tilts like a busted dreidel. None of which are what I just mentioned, but… Anyway. 



You see that picture of the storm system up there and you’ve probably got this mental image of a wind gust blowing the sand in your face on a global scale while there’s some giant toilet bowl flushing in your hemisphere’s appropriate direction in the middle of the Pacific and Atlantic Oceans — but I doubt this really hits the point of what’s happening when we’re talking about moving sand and reshaping your favorite surf spot.

You see, while the wind cells of our earth are doing this:

The oceans and landmasses are feeling this:

And when you zoom-in on the edge of one of these currents, it looks like this:

photo: CSU Pomona's Oceanography Program

Now, imagine the above as the edge of one of the spirals. That spinning current hits the sand and is forced to change direction – as things tend to go with inertia (something keeps going until something stops it or redirects the energy). Well the rest of the water from the spiral doesn’t stop coming just because the stuff on shore is ready to wash back.  What happens is a constant pushing down (or up if you’re in the southern hemisphere) of the sand. Thus, with all that pushing – like the boards on my rich neighbors’ surf rack, our beaches and coastlines are forever changing.