Not for surfing: Tsunamis
The waves we are used to seeing (perhaps jousting with) at our favourite beach have wavelengths of order 100 m and travel at speeds of order 1 ms-1. Tsunami’s are rather different. They have wavelengths of order 100 km and speeds of 200 ms-1 (or over 400 mph!). They arise from some large scale impulsive disturbance to the ocean, such as an earthquake, a landlside, or a meteor. A Quicktime Movie of this can be accessed below.