The sea’s edge is always churning; sometimes covering treasures, sometimes exposing them.

In our part of the world, low tides uncover a bit of the sea floor twice a day, revealing tidepools.

The land side of our sea/land edge tends to be covered and revealed on a seasonal basis. Waves formed by the relatively gentle winds of summer push sand onto the face of the beach, forming a humped profile. Dried by summer sun, that sand is then blown inland a bit; there it is caught by plants, creating the foredune.

The larger, more powerful waves driven by winter storms scour the sand off the beach and deposit the sediment in sandbars just outside the surf zone, giving the beach a flatter, sometimes convex profile. With the summer sand out of the way, high winter surf can reach up into the foredune and slice it back.

And where do waves come from? Most waves at the beach are generated by wind blowing over the water. Winds right here create whitecaps and “chop” on the ocean surface (also called a “sea”); ocean swells, and the beach-lapping waves they become, are generated by winds far away — perhaps many thousands of miles away.

Swells reaching our beach at any given time often are generated by more than one wind or storm in different parts of the Pacific. Each storm generates a unique wave pattern, since the speed, duration, and fetch (area blown) of the winds are unique. Speed, duration, and fetch together determine the height, length, and period (time between crests) of the waves. Further, the swells from a given storm change as the storm evolves and ages.

As a pattern of waves approach the beach from one direction, the waves can interact with any waves arriving from other directions. Two crests of waves from two different patterns may overlap, combining to make one very large wave that runs high up the beach. These are the “sneaker waves” that soak shoes and knock the unwary into the water.

Watching a bird resting on the surface outside the surf zone, you’ll notice that it rises up and down with the passing wave. While the transfer of the wind’s energy travels though the water, the water itself doesn’t travel far in a wave until it reaches shore. As the wave enters shallower water, it trips on the bottom and creates a breaker. The breaker releases the distant wind’s energy on the beach, moving the sand.

Clearly, the seasonal on/off movement of beach sand is not uniform from year to year. The waves in some summers push more sand (and debris) onto the beach; the waves in some winters pull more sand (and debris) off the beach. A high erosion winter after a low accretion summer can take a significant bite out of the shoreline.

Even larger processes affect this interface, too. The Pacific Northwest jerks up and down as our continent moves westward, and sealevel changes with climate, resulting in significant sea level changes in geologically a short time. The flat tops of off-shore rocks like the one under the Cape Arago Lighthouse? That was sealevel 80,000 to 100,000 years ago; sealevel about 20,000 years ago was about 230 feet lower than it is today.

Over the last century, introduced European beach grass has very effectively trapped and held the summer sand, creating foredunes that are far higher than have formed on the Oregon Coast before. Heavy winter surf now often creates a tall escarpment as it cuts into this fortified foredune, presenting beach-walkers with a high cliff to negotiate where last summer they had only a gentle slope.

Stored inside the foredune is the beach debris from earlier years, from driftwood to treasure. Treasure, of course, like the George L. Olson, a schooner that was beached in 1944 and uncovered in recent weeks on the North Spit.

While waves can expose treasure on old beaches, currents can bring treasure to the shore. More on incoming treasure next time!

For information on how to arrange an exploration of our fascinating natural history, contact Marty at 541/267-4027, or e-mail mgiles@wavecrestdiscoveries.com. Questions and comments about local natural history are welcome.