Visiting Maine beaches in the summer is a rare treat and soon there will be throngs of beachgoers heading to places like Popham and Reid State Parks to splash around in a very different intertidal than we have in Brunswick. Rather than craggy tide pool-filled shorelines or silty squishy mud flats, these coastal parks feature beaches that are wide open and sandy. Sandy beaches are somewhat of a rarity along this part of the coast — hence their popularity in the summer. Their open-facing shoreline also means that they often have large waves that break along their shores.

On a recent visit to Reid State Park, I watched a perfect wave come ashore and thought about what makes it form that way rather than being uneven or collapsing on itself. There are a lot of different factors that determine what a wave looks like. The biggest one, perhaps, on this visit, was the direction of the wind. There are offshore breezes and onshore breezes, each of which are determined in part by the difference in the temperature between the land and the sea.

In the spring and the fall, when that difference is the greatest, these winds are often quite strong. This was the case recently when an offshore breeze helped to make the waves exceptionally clean and crisp at their break. An offshore breeze is when the wind blows “off of the shore” towards the sea. An onshore breeze is just the opposite — when the breeze blows from the sea “on to the shore.”

Another factor determining what each wave ends up looking like is the strength of the wind. Following on from the previous directional theme, if you have ever been by the shore in the spring or fall, the strength of the wind can be quite impressive. That’s particularly true if you are in a place where there are not bits of land to interrupt the wind’s path as it drives its energy into the water.

In spots with open beaches like Reid and Popham, this strength can be particularly impressive in the shoulder seasons. The cumulative build-up of the wind, and thus the waves, when there is no land and when the wind starts far offshore, is called “fetch.” The bigger the fetch, the bigger the waves.

All of this can be dissected in the anatomy of a wave. A wave is composed of a few basic parts — there is the very uppermost part, the crest, and the very bottom part is the trough. The height between the two of them is called the face. The measurement of a wave’s length is the distance between either two crests or two troughs. That distance is determined, for the most part, by how much resistance the wave meets.


As it gets closer to the shore, for example, it meets the bottom of the sea floor, and it starts to lose its energy more quickly, thus breaking more frequently and spilling into a pile of waves that break on the land. That gets to the other measurement of a wave which is wave frequency or wave period. That is the measure of how many waves pass by during a certain period of time. A fun way to measure this is to stand at a fixed point on the edge of the shore and count how many waves pass it for 30 seconds or so.

The odd thing about watching waves come in, whatever their form, size, and frequency, is that you aren’t really watching the movement of water at all. You’re really watching the movement of energy. The water basically just goes around in a circle and that’s why some waves look like a tube.

Those perfect clean waves that surfers seek out — where energy is transferred, but the water essentially stays in place — allow a surfer to stay on the same wave, riding up and down fueled by the wave’s energy. That’s more the case in deeper water than in shallow water since there is less resistance from the bottom, hence less slowing down of the energy.

This is an oversimplified explanation of waves and there is much more to be learned from both the oceanographic world and the surfing one.

Regardless, as we head into official summer and the forces on the water begin to equalize, it’s neat to look carefully at a wave and think of what goes into its formation and how that energy translates into the unsettled feeling of a season of transition or, by contrast, a season of a bit more relaxation and calm on the water.

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