The traditional story has its roots in a completely natural phenomenon that occurs every year around this time. The Jindo-Modo land bridge appears twice a year, in May and June when very low tides expose a 2.9 kilometer land bridge between the islands of Jindo and Modo. The land bridge appears for a little over an hour, allowing tourists and residents to walk across the sea from one island to the other.
The land bridge is not a miracle. It is a result of tidal harmonics. Tides are the rise and fall of sea levels caused by the gravity of the sun and moon pulling on the ocean surface. The sun and moon pull at the earth with different strengths at different times, depending on their relative positions. The earth’s rotation, shape and size of ocean basins, and local coastlines affect the magnitude and frequency of tides. Each of the contributions to the tides can be broken down into simpler components, or waves. The phase and size of each wave is unique to each location. Occasionally, these waves can line up in the same phase and create an extremely high or low tide. This is the case with the Jindo-Modo land bridge, when tidal harmonics line up to produce an extremely low tide in May and June, exposing a ridge of sediment between the two islands.
The exact date of the Jindo Sea land bridge crossing changes each year. Although the land bridge appears 2-3 times in the spring, the festival is celebrated only once.