Big Pacific

(boat horn blasts) -

Narrator

In china even humans are learning to make the most of the violent Pacific. (sonar bleeps) September and Hangzhou Bay waits for the annual return of an ancient sea monster. Temples were built to worship it and pagodas were built to placate it. For centuries it's been known as the Silver Dragon, a predictable yet potentially destructive wall of water that grows into the world's largest tidal wave. Unlike tsunamis which are triggered by earthquakes, this rare phenomenon is brought on by the lunar cycle and forms where the bay narrows and funnels the incoming tide continuously amplifying its size and speed. Building to 30 feet high and racing at 25 miles an hour it forces its way up the mouth of the Qiantang River. (dramatic music) Square in its path lies Hangzhou, population more than six million, one of China's biggest cities. It's an immovable object right in the way of an irresistible force. (waves crashing) The Chinese built seawalls to tame the Silver Dragon back in the 10th century. A Qing Dynasty wall from 1720 protects the city today yet five people a year still die. (waves crashing) (tranquil music) But a few brave souls now dare to ride the dragon. (lively music) The Qiantang River is home to one of the world's most daring competitions. In a sport where rides are usually measured in seconds, the dragon's back can challenge a surfer for a death-defying 20 minutes. Only the expert and the lucky will survive.