Among the observers of the 1946 tsunami at Hilo was Francis P. Shepard of the Scripps Institution of Oceanography, one of the world's foremost marine geologists. He was able to make a detailed inspection of the waves. Their onrush and retreat, he reported, was accompanied by a great hissing, roaring and rattling. The third and fourth waves seemed to be the highest. On some of the islands' beaches the waves came in gently; they were steepest on the shores facing the direction of the seaquake from which the waves had come. In Hilo Bay they were from 21 to 26 feet high. The highest waves, 55 feet, occurred at Pololu Valley.

Scientists and fishermen have occasionally seen strange by-products of the phenomenon. During a 1933 tsunami in Japan the sea glowed brilliantly at night. The luminosity of the water is now believed to have been caused by the stimulation of vast numbers of the luminescent organism Noctiluca miliaris by the turbulence of the sea. Japanese fishermen have sometimes observed that sardines hauled up in their nets during a tsunami have enormously swollen stomachs; the fish have swallowed vast numbers of bottom living diatoms, raised to the surface by the disturbance. The waves of a 1923 tsunami in Sagami Bay brought to the surface and battered to death huge numbers of fishes that normally live at a depth of 3000 feet. Gratified fishermen hauled them in by the thousands.