How are tsunami wave heights measured?
The wave height of a tsunami can be highly variable in a local area depending on the underwater topography, orientation to the oncoming wave, the tidal level, and the magnitude of the tsunami. Because direct physical measurement of a tsunami wave would be a life threatening event, a common method for determining tsunami wave height is by measuring the runup, the highest vertical point reached by the wave. Runup heights are measured by looking at the distance and extent of salt-killed vegetation, and the debris left once the wave has receded. This distance is referenced to a datum level, usually being the mean sea level or mean lower low water level. The reference to mean lower low water is more significant in areas with greater tidal ranges such as in Alaska where a smaller tsunami wave can be more devastating during a high tide than a larger wave at low tide. Tide gauges, found in most harbors, are the other tool for measuring tsunami wave height and period (wavelength).
