The predictable miracle
Twice a day, the Yellow Sea pulls back from the coast of Hwaseong, South Korea, to reveal a 2.3-kilometer causeway. This paved, two-lane road connects the mainland to the small island of Jebudo, allowing cars and pedestrians to cross what is, for most of the day, the seafloor. This event, often called the "Moses Miracle," is not a miracle, but a predictable result of gravitational forces.
The phenomenon is a product of semidiurnal tides—two high and two low tides of roughly equal size every lunar day. The gravitational pull of the Moon, and to a lesser degree the Sun, creates bulges of water on opposite sides of the Earth. As the planet rotates, coastlines pass through these bulges. The West Coast of Korea, where Jebudo is located, experiences a particularly large tidal range. When the water level drops sufficiently, the S-shaped road emerges and remains accessible for about six hours before the tide returns. The exact timing of the road's opening and closing changes daily, a direct consequence of the Moon's 28-day orbit around the Earth. Local authorities post daily schedules, but miscalculations are common, and vehicles are frequently caught by the rapidly rising water.