Weird Science of Tides Along Oregon / Washington Coast: Loosening the Moon

Published 11/17/20 at 4:55 PM PDT
By Oregon Coast Beach Connection staff

(Manzanita, Oregon) – What makes those crazy tides go along the Oregon and Washington coastline? Why the difference in tidal changes between places? And is it true our tides are pushing the moon away? (Above: Coos Bay's Shore Acres / courtesy Oregon's Adventure Coast)

The answer to the last one is definitely yes: the Pacific Northwest coast and the rest of the world are literally inching the moon away from the Earth. More on that in a bit.

All these questions have as much to do with astronomy and space as well as the Earth, its oceans and the beaches they slam against.

Tides are the direct result of gravity from the moon, with a dash of sun thrown in to the recipe. Really, we wouldn’t have tidal motion as we know it without our satellite.

Oregon Coast Beach Connection got the ultimate explanation from Dr. Bill Hanshumaker several years back, when he was with the Hatfield Marine Science Center. As he put it, the moon is essentially tugging at the oceans.

Looking at the graphic, gravity creates a bulge in the oceans on both sides of the planet (blue area). The moon pulls the oceans towards it, creating a bulge on the side closest to the moon and the opposite side. Hanshumaker said this creates a high tide on both sides of this world. The bulge on the other side happens because the Earth is being tugged at as well, but the oceans lag behind, creating that outward movement on the opposite side. Then, because of all that stretching and squishing of the Earth and the oceans, those two big bulges create a low point in between them, essentially. Those are the low tides, and sometimes the minus tides.

The sun also has a hand in tides, but not much.

“It has to do with the tilt of the Earth and the bulge of gravity on the water from the sun and the moon,” Hanshumaker said. “It depends on the geography of the place as well. It depends on where you are, and if that place is closest to the moon because of the tilt.”

Hanshumaker added the Oregon coast has a factor that separates it from the Washington coast as far as tides go as well: the state is in and around the 45th parallel, which is halfway between the pole and the equator. That can make a difference in low tides and high tides.

Yet it all gets much more complex from there. While the moon is moving the oceans around, there are land masses in the way, so the ocean doesn’t move uniformly. Currents can affect the tides along with topography of an area. Parts of the south Oregon coast, such as Gold Beach or Winchester Bay, will see sometimes vastly different tidal action than Long Beach or Westport in Washington, or the north coast’s Cannon Beach.

A low tide in Coos Bay could be hours different than one in Manzanita (about 180 miles away) or up around La Push, Washington. The height or depth of these can be quite different as well.

Why? It all comes down to the topography of the area and the shape or slope of the ocean floor nearby. This all comes back around to the land masses not letting the oceans move in a uniform manner.

The weirdest part of tides along either the Oregon or Washington coast is that they’re helping to shove the moon away from us. Really, this is all the oceans ganging up on the forces against the moon, not just the Pacific Northwest. The Earth’s crust is also helping these gravitational forces. The moon is scooting away from this planet at a rate of 1.48 inches per year.

How do they know this? Apollo astronauts set down reflective objects on the moon decades ago, and since then scientists have been beaming lasers on them to get exact measurements.

As an oddball side note, Oregon Coast Beach Connection has reached out to scientists to try and quantify how much Oregon’s coastline tides could be contributing to this, but there wasn’t really a way to estimate it.

According to astronomy icon Neil DeGrasse Tyson, the Earth's rotation is slowing by about 1/500 of a second every century. This means every 100 years, a day is 1/500 of a second longer. Tyson said in a 1995 article that a day will last some 1,000 hours in about one trillion years.

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