#tidal harmonics

“Parting” of the Jindo Sea

Here’s a story about a lady and a tiger. According to a Korean legend, tigers were once abundant on the island of Jindo in the Jindo Sea, just off the southwest corner of the Korean peninsula. Tigers began to invade villages on the island, so the people fled to neighboring Modo island. Unfortunately, a woman named Bbyong was left behind. She prayed to the ocean god daily and was finally told in a dream that a rainbow would appear in the sea the next day to let her cross to her family. When she walked out to the shore the next day, a rainbow road magically appeared, and Bbyong’s family crossed the sea on the road to finally meet up with her again. The event is celebrated every year during the Jindo Yeongdeung Festival, or Sea-Parting Festival.

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.

-Amy

References:

http://noc.ac.uk/f/content/using-science/Intro_to_Tides_and_Tidal_Numerical_Modelling.pdf

http://news.nationalgeographic.com/news/2013/13/130426-jindo-sea-parting-festival-korea-red-tides-science-moses/

http://www.holidaysia.com/events/jindo-sea-festival/