The King Tides are coming!

Photo caption: When extreme high tides coincide with storms, waves 100 feet and taller can crash into the cliffs below Cape Disappointment Lighthouse. Photo by Aaron Webster.

How the sun and the moon affect the motion of the ocean

by Aaron Webster, Interpretive Specialist, Cape Disappointment

The earth, moon and sun are locked in a complex but predictable dance that helps produce the tides. These tides change from day to day, but in patterns that repeat in monthly and yearly cycles. In the beginning of January, these celestial bodies conspire to bring the biggest tides of the year – the king tides.

For a few days on either side of Jan. 21, we will have the chance to see these king tides.

Photo caption: Anchor Island at Cape Disappointment is only an island at high tide. During low tide, it sits in a salt marsh. Photos by Aaron Webster.

What causes tides?

The moon revolves around the earth once every month, causing monthly patterns in the tides. The earth revolves once around the sun every year, causing yearly patterns in the tides. King tides happen when these monthly and yearly patterns coincide to produce the highest (and lowest) tides of the year, typically in January and July.

Gravitational attraction between the sun, earth and moon pulls the ocean water up, which creates two bulges in the ocean surface, one on either side of the earth.

Consider: Why would there be a bulge on BOTH sides?

Photo caption: The moon’s gravity pulls on the earth, causing the oceans to rise. CC.BY 2.0

Over the course of the day, the sun and moon don’t move much, but the earth spins once around. So, the bulges are mostly stationary and as we pass through them and we usually only experience two high and two low tides per day. In Washington, these two high tides are usually unequal, but as you move toward the equator, they become more equal.

Consider: Why are the two high tides unequal in our area?

Let’s take a closer look at these monthly and yearly cycles.

As seen below, these bulges sometimes line up, creating extra high tides called spring tides. Spring tides are named as such because the water "springs up.” These happen twice a month at the full and new moon.

Spring tide bulges vary in size depending on how close the earth is to the sun or moon.

What makes a king tide?

In January, the earth makes its closest approach to the sun. This makes January’s spring tides extra high, creating what we call king tides. Other things can affect the height of tides including the shape of the ocean floor, latitude, atmospheric pressure, and even the tilt of the earth.

Consider: Why do we have King Tides in July, when the earth is furthest from the sun?

The diagram at left shows the tidal bulges created by the moon and sun, leading to spring tides.

Washington’s tides

Tides vary widely across the globe, even on the same day. Our king tides are higher than Hawaii’s, but lower than in parts of Alaska. When these tides approach the shore, they “feel” the sea floor of the in the same ways that regular waves do.

Each wave or tide has a sort of imaginary circle underneath it. The size of the circle depends on the size of the wave. An ocean wave has a circle that's anywhere from a foot in diameter to 100 feet in diameter. When this circle touches the sea floor, the wave changes shape, in part, because of friction. The wave will continue to change shape as it travels through even shallower water.

When a regular wave approaches shore, it grows taller in height, but gets shorter in length because of the way the “bottom” of the wave drags on the bottom of the ocean.

Tides work the same way. The tide is like a giant wave with a huge circle beneath it. So, our relatively wide and shallow continental shelf amplifies the height of the tide and creates the opportunity for massive king tides to hit the shore.

Consider: What other ways are tides like waves?

The tides also affect river currents. For example, high tide acts like a dam at the mouth of the Columbia – the river backs up behind the dam and even flows backward for a short distance.

Seeing the king tides

Even on a calm day, King tides can be dramatic, but when king tides combine with large ocean swells the effects can be spectacular!

It’s important to watch from a safe distance and respect any closures you may encounter.

One of the best places for wave watching is Cape Disappointment State Park in the southwest corner of the state. When the tide is high (over 8 feet), huge waves crash into the cliffs.

The Lewis & Clark Interpretive Center at Cape Disappointment is a great wave watching spot because it’s perched high on a cliff overlooking the Columbia River Bar.

Beware of sneaker waves and stay off beaches during winter storm events. Sneaker waves are much bigger than normal waves and they “sneak up on you” because they are infrequent. You might see 10 or 20 minutes of “regular” waves and then all of the sudden - WHAM - here comes a double-size wave that washes all the way up the beach, carrying driftwood logs and other dangers. For the best wave watching experience, follow the weather and wave forecasts and look for a day when big waves, high tides, and sunny skies combine.

Stay safe, have fun!

As I began to write this piece, providing a solid explanation in such a short space seemed impossible. But I hope this entry into the science of king tides provided answers, generated questions and ultimately leads to more research among those of you interested in this fascinating topic.

I hope you’ll go out to one of our beautiful State Parks to view the upcoming King tides. This time around they’re bound to coincide with some sizeable waves, so be careful and stay off the beaches. These events don’t just produce great pictures, they also provide a glimpse into the future of rising sea levels.

Today’s King tides are the regular high tides of tomorrow!