This weekend I went to the Oregon Coast to experience the power of the ocean during a phenomenon called the “King Tide”, a time of an unusually high tide. To understand this phenomena, it is necessary to understand why we have high and low tides.
Why are there tides?
Ocean tides are a phenomenon caused by the gravitational pull of the Sun and Moon on the surface of the Earth. The Moon, since it is much closer to Earth than the Sun, has a greater gravitational effect than the Sun.
As the Moon circles the Earth, its gravitational force pulls the surface of the Earth towards itself. Although the deformation of the land is not visible without sensitive instruments, the effect this gravitational force can be directly observed on the ocean (and actually other bodies of water.) This gravitational force induces an egg-shaped bulge resulting in high tides on opposite sides of the Earth simultaneously (the opposing bulge is due to inertia, but we do not need to get into that). The bulge is greater on the side facing the Moon than on the opposing side. The gravitational pull of the Moon causes a reduction in amount of water roughly perpendicular to the high tide, or a low tide.
There are two high tides and two low tides per day. The amplitude difference between high and low tide varies with the phases of the Moon and also with geographical features around the world. Higher than normal tides typically occur during the new and full moon and when the Moon is at its perigee (when it is closest to the Earth in its monthly orbit.)
The Earth’s orbit around the Sun is elliptical, and it is closest to the Sun around early January. At this time, the gravitational force of the Sun on the Earth is at its greatest. When the Moon and Sun are closest to the Earth simultaneously, excessively large high tides occur. These tides have been termed, non-scientifically, King Tides (scientifically, Perigean Spring Tides). There are typically three King Tides per year. On the Oregon Coast, the first of these occurred this past weekend, November 5-7, 2021.
To observe this phenomenon, I went to the Smelt Sands State Recreation Site in Yachats, Oregon where I was able to watch the crashing waves from the Yachats 804 Trail. Smelt Sands is one of my favorite locations in the Newport, Oregon area. It possesses rocky shelves, the tops of which are maybe 10-20 feet above the surface of the ocean. Smelt Sands is not very aptly named since there is no sandy beach here! The rocks are great places for whale watching, and during normal low tides, there are wonderful tide pools on some of the lower outcroppings. Smelt Sands is one of the few localities on the Oregon Coast where smelt, 6-9” long silvery relatives to salmon, breed. This was a great place to watch the unusually high surf. The picture to the right shows the waves at high tide which were several feet higher than normal.
It was fun to watch the waves crashing onto the rocky shelves as seen in the photo to the left. This was a great place to view the action, although nothing was as impressive as my view of a King Tide from Shore Acres State Park on Cape Arago in November 2019 shown in the photo at the top of this article. A word of warning, if you are going to watch a King Tide, you must be very careful to stay away from cliff edges (unlike the person in the Cape Arago photo) and off beaches.
King Tides are of great interest to the scientific community because they may predict flooding and erosion patterns as sea levels rise with global-warming.
There will be two more King Tide events this winter – December 3-5 and January 1-3. King Tides are not only found on the Oregon Coast but also occur on the coast lines around the world. They are most impressive where there are high bluffs, cliffs, and offshore rock features. However, even manmade boardwalks and jetties can be good places for viewing.