A Visitor with Pull

By Henry H. Mitchell, December 14, 2008.

High Tide Mark in Dunes High Tide Mark in Dunes

Dark sand indicates the high tide mark among the dunes near the north end of Myrtle Beach State Park. Buildings of the Springmaid Beach Resort are in the background.

On a sunny 60-degree December afternoon in Myrtle Beach, South Carolina, we found a fairly calm surf, but wet sands all the way to the dunes. In some cases the high-water mark of four hours earlier was actually among the dunes, much higher than is typical.

With no evidence of a storm, past or present, close or distant, what could be causing this unusual encroachment? Only one culprit is possible: the moon! We're a little less than two days past full moon, and this month full moon coincided with the moon's being at its closest orbital point to the earth (perigee). Full moon occurs when the moon and sun are on opposite sides of the earth. That alignment (and the similar one at “new moon” (moon passes between earth and sun) always produces higher tides because of the increased gravitational pull. This time, it was enhanced by the moon's being a bit closer than usual.

For many years, as a planetarium operator, I tried different techniques of demonstrating to students the concepts of new moon, full moon, and the more extreme “spring tides” which happen at those two monthly events. I'm sure my instructional success was limited. If only I could have gathered up all those students and brought them to Myrtle Beach on a day like today! Unfortunately, we were 260 miles away — too far for a day trip.

The tidal reach will recede as the moon itself both recedes and orbits. Official charts predict that high tide will be two inches lower, elevation-wise, tomorrow.

Myrtle Beach has been known for generations as a vacation spot for “just regular folks.” From the evidence, this “visitor” had some real pull! — Not “just regular folks.”

See an example of receding high tides in the article “Moon Tracks on the Sands.”

This guide to Myrtle Beach is sponsored by Mitchells Publications.