Jindo Sea Parting – Tidal Harmonics

Would you walk through the sea if it parted? Would you? Really?  In South Korea, at the southern tip of the Korean Peninsula, a natural phenomenon takes place in the Jindo Sea in which the northern portion of the East China Sea opens up just wide enough to expose and reveal a 1.8-mile long stretch of sand, connecting South Korea’s Jindo Island to the nearby island of Modo.  This phenomenon ONLY happens TWICE a year lasting long enough for people to walk across to the other island in the middle of the sea.

Commonly known as tidal harmonics, this predictable phenomenon is caused by the gravitational attraction of the moon and the sun acting on the oceans of the rotating Earth. We can observe tides in our seas and oceans resulting from the gravitational forces that exist between the Earth, the Moon and the Sun – gravitational forces refer to the gravity of the sun and the moon tugging at the surface of the Earth’s water, which causes the periodic rising and falling of the sea level or tides. The complex movements within the Earth-Moon-Sun system generate forces on the oceans that can vary over time. For example, the distance between the moon and the earth varies over 27½ days thereby making the magnitude of the force vary over the same period. 

Depending on the relative position and motions of each body, both the sun and the moon pull with different strengths and at different times, causing high tides in some areas and low tides in others. The two most important ones being: 

• The spring-neap cycle – a 14.77 day cycle resulting from the tidal influence of the sun and moon either reinforcing each other (called spring tides, although this has nothing to do with the season) or partially cancelling each other (neap tides). 

• The equinoctial cycle – a half yearly cycle caused by the tilt of the earth, and its orbit around the Sun which leads to higher than average spring tides around the time of the equinoxes (March and September) and lower than average spring tides in June and December. On average, the spring tidal currents are around twice as fast as the neap currents. This means that a spring tidal current can generate around 8 times the power of a neap tidal current. Spring tides usually occur 1½ to 2½ days after full and new moon, with neap tides experienced just after the first and third quarter (when half the moon is visible). Information on lunar phases is easily found on the internet.

In the case of the Jindo Sea phenomenon, numerous tidal harmonics line up just right to generate extreme low tides. So, what seems to be a biblical-like parting of the waters is, in reality, a lowering of the entire sea.  The visible 40-to-60-meter-wide ridge of land, is most likely the result of the sediment depositing in one spot over time due to relatively calmer water along the line between the islands of Jindo and Modo.