From the beach it seems waves come in a dependable pattern. Beneath the surf, though, it can be a different story.

The unpredictable interaction of one wave against another, or against a rocky shoreline, occasionally produces a sudden 'sneaker wave' that surges onto the sand – potentially overwhelming those on the beach.

That's what Steve Raplee caught on video in Charleston, south of Coos Bay, according to Seattle TV station KING 5. Raplee, who owns the High Tide Café, pulled out a camera to film the surf and people strolling on the sand. A boy and a dog walk straight toward the water.

Then, roiling waves pour out from around a rocky barrier and flood the beach where Raplee and others were walking.

"Uh oh. Time to go here," Raplee says with growing anxiety. "Get out of the way!"

Reaching a grassy area above the waves, Raplee takes a deep breath and watches the water churn.

"I just got out of the way. It would have taken anybody in its path," he says.

Sneaker waves are a perennial concern on the Oregon coast and a phenomenon still not fully understood.

"When you get into the beach, especially when you get into complicated areas like the rocks, you can get feedback – the previous wave changes the condition for the next wave," Oregon State University oceanographer Robert Holman told The Oregonian in 2011. "If you had a previous wave that washed down at just the right time, that would reinforce the next wave. That can produce things that truly are dangerous and not expected."

-- Mike Rogoway

mrogoway@oregonian.com

503-294-7699

@rogoway