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.
An ecosystem exposed
The cement road to Jebudo cuts across a vast tidal flat, known in Korean as a "getbol". These flats are an important ecosystem, supporting many benthic species like clams, crabs, sea snails, and mussels. When the road opens, the muddy expanse is exposed to the air, becomes a temporary feeding ground for millions of migratory shorebirds that travel along the East Asian-Australasian Flyway.
The road itself is a relatively recent structure. Until the 1980s, residents of the 0.98-square-kilometer island would wade through the water at low tide to reach the mainland. The first path was a simple stone road built by villagers. This was later paved with cement and, in the mid-1990s, expanded to two lanes to accommodate tourist traffic. The road's elevation has been raised several times, most recently in 2025, to increase accessibility, but it is intentionally kept low enough to be submerged. This preserves the island's unique tidal character, though it also ensures that those who miss the crossing window will be stranded until the next low tide.