Science of Tsunami Hazards (Jan 2006)
MOMENTUM AS A USEFUL TSUNAMI DESCRIPTOR
Abstract
In looking at the videos of the Indonesian tsunami coming ashore at various locations, I thought, “That’s a lot of water with a lot of momentum, and that’s what does the damage.”Perhaps the momentum of a tsunami might be a physical quantity to focus on. Only external forces on the designated body of water create its momentum. Within the body of water, turbulence, internal friction and laminar flow involve internal forces and are not relevant.This could be particularly useful in the generating area. There could be external forces on a designated body of water from a landslide, a pyroclastic flow, an explosion, from steam generation and from chunks of matter falling into the ocean. The horizontal components of those forces result in horizontal momentums. Ultimately when the wave moves out from the generating area and the internal turbulence and laminar flow get dissipated by friction, in the remaining long wave motion the wave height is simply related to the horizontal momentum. The horizontal momentum contribution to the directionality of the wave would be narrower than that due only to the initial vertical displacement.Focusing on the momentum description of the tsunami introduces many new kinds of physical problems that are interesting in themselves.
