TSUNAMI OF APRIL 1, 1946 — MACDONALD, ET AL. 263 



flooding over the coastal lands without the development of any steep 

 wave front. At such places most of the damage resulted from the 

 violent run-back of the water to the sea. At some localities, although 

 the general water surface rose gently, ordinary storm waves moved in 

 over the top of the broad swells of the tsunami, and there at least part 

 of the damage was caused by the storm waves. At most places, 

 however, the waves of the tsunami swept toward shore with steep 

 fronts and great turbulence, causing a loud roaring and hissing noise. 

 Locally, the wave closely resembled a tidal bore, the steep front rolling 

 in over comparatively quiet water in front of it. Behind the steep 

 front, the wave crest was broad and nearly flat, with smaller storm 

 waves superimposed upon it. Such bores were best developed in 

 bays and estuaries, but waves of closely similar form were observed 

 crossing shallowly submerged reefs upon otherwise open coasts. 



At many places the violence of the waves moving shoreward was 

 sufficiently great to tear loose heads of coral and algae, up to 4 feet 

 across, and toss them onto the beach as much as 15 feet above sea 

 level. Locally, blocks of reef rock weighing several tons were quarried 

 at the outer edge of the reef and thrown onto the reef surface. 



Between crests, the water withdrew from shore, exposing reefs, 

 coastal mud flats, and harbor bottoms for distances up to 500 feet or 

 more from the normal strand line. The outflow of the water was 

 rapid and turbulent, making a loud hissing, roaring, and rattling noise. 

 At several places houses were carried out to sea, and in some areas even 

 large rocks and blocks of concrete were carried out onto the reefs. 

 Sand beaches were strongly eroded by the outgoing water. People 

 and their belongings were swept to sea, some being rescued hours later 

 by boats and life rafts dropped from planes. 



At a few places, generally but not exclusively on the sides of the 

 islands away from the wave origin, the first wave was reported to 

 have been the highest. At those places, the rise was generally of the 

 quiet sort. There are, however, no instrumental records showing the 

 first wave to have been the highest, and it is possible that at places 

 reporting the first wave as the highest, earlier waves may have been 

 overlooked. Much more generallj; the third or fourth w^ave was re- 

 ported to have been the highest and most violent. The third crest was 

 the largest at the Honolulu tide gage (fig. 2) . At other localities the 

 sixth, seventh, or eighth waves were said to have been the highest. At 

 Waimea Kivcr, Kauai, the sixth crest was higher than any other, both 

 in absolute level and in its height above the preceding and succeeding 

 troughs. 



In general, if not everywhere, the size and violence of the waves 

 increased to a maximum with the third to eighth waves. The oscilla- 

 tions then gradually decreased in amplitude over a period of at least 



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