The Big Wave(1961)

Yukio, a farm boy, and Toru, a fisherboy, live in a small Japanese village that is periodically threatened by a volcano on one side and tidal waves on the other. Yukio's younger sister Setsu follows then and dreams of becoming a pearl diver. Toru is preparing to go fishing with his father when a bell tolls and a danger flag is hung high on the hill behind the village to warn of an impending tidal wave by the village patriarch, known as Old Gentleman.