262 ANNUAL REPORT SMITHSONIAN INSTITUTION, 194 7 



by other observers, and are comparable to the speed of 20 miles an 

 hour recorded in San Francisco Bay (C. K. Green, 1946, p. 492). 



The interval between the first and third wave crests, as recorded 

 on the Honolulu tide gage (fig. 2), was about 25 minutes, indicating 

 an average interval between early wave crests of approximately 12.5 

 minutes. The interval between the first wave crest and the succed- 

 ing trough was 7.5 minutes, however, indicating a wave period of 

 15 minutes at the beginning of the disturbance. This corresponds 

 with the mean wave period of 15.6 minutes found by Green (1946, 

 p. 499) at Honolulu and eight other stations on the coasts of 

 North and South America. At the mouth of Nuuanu Stream in 

 Honolulu, C. K. Wentworth observed an interval of approximately 

 15 minutes between successive bores ascending the stream, and a wave 

 period of about 15 minutes was observed by J. B. Cox and D. C. Cox 

 at Waikiki at about 7 : 45 a. m. Observations elsewhere were poor, 

 but in general indicated an interval not far from 15 minutes between 

 the early waves of the series. The interval between later waves at 

 Honolulu (fig. 2) and elsewhere was shorter and less regular, probably 

 because of the arrival of chains of waves traveling by somewhat 

 different routes, refracted around different sides of islands, and 

 reflected at various points, as well as traveling by the most direct 

 route. Probably contributing to the irregularity of later waves 

 were wind waves and also the free-period oscillations, in harbors 

 and channels, known as "seiches." If the period of the waves is 

 assumed to be 15 minutes, and the average speed to be about 490 miles 

 an hour, the average wave length from crest to crest was about 122 

 miles. 



Direct observations on the height of the waves in the open sea are 

 lacking, but theoretical considerations indicate that the height prob- 

 ably did not exceed 2 feet from crest to trough.* If so, the small 

 height combined with the very great wave length should have made 

 the waves imperceptible to ships at sea. That such was indeed the 

 case is indicated by the fact that the master of a ship lying offshore 

 near Hilo could feel no unusual waves, although he could see the 

 great waves breaking onshore. Crews of fishing boats in the Hawaiian 

 area also reported no unusual conditions at the time of the tsunami, 

 although heavy storm waves were running. The few reports of violent 

 waves of great height from ships at sea were probably occasioned by 

 storm waves, together with the knowledge that a tsunami was taking 

 place. 



The nature of the waves sweeping up onto Hawaiian shores varied 

 greatly from place to place. At some places the water rose gently, 



* Based on the assumption of a 10-foot wave In 10 feet of water, and the variation of 

 the wave height inversely as the fourth root of the depth. 



