The Qiantang Tidal Bore

During the autumnal equinox, when the moon's gravitational pull is at its peak, huge waves crash up the Qiantang River. Every year at this time, crowds gather at a safe distance to watch what begins as a distant line of white waves approaching. As it nears, it becomes a towering, thundering wall of water.

The phenomenon, known as a tidal bore, occurs when strong tides surge against the current of the river. The Qiantang Tidal Bore is the largest in the world, with recorded speeds of up to 25 miles an hour and heights of 30 feet. The Qiantang has the best conditions in the world to produce these tidal waves. Incoming tides are funneled into the shallow riverbed from the Gulf of Hangzhou and the bell shape narrows and concentrates the wave. People have been swept away in the past, so police now enforce a strict viewing distance.