The entire event was captured on China’s Central Television and ended when the wave finally crashed against a dam down river almost three hours later.
The waves can be as tall as 3.5 metres, and the ‘trumpet-shaped’ mouth of the river helps generate the monster tidal. Temperatures, quantity of water and wind also influence the wave size.
Although this phenomenon can be seen in several locations around the world where sea water is funneled by a river, the Qiantang river bore is one of the largest.
Their post includes Chinese news footage of the event, in which the scale of the waves is helpfully demonstrated by life-sized dummies placed along the water’s edge to warn tourists away. For further illustration, see the American surfers who were allowed to ride the bore for 10 kilometres in 2008: