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



261 



place of origin was thus 2,241 miles N. 8.5" W. of Honolulu, and 2,375 

 miles N. 12° W. of Hilo (fig. 1) . 



The time of arrival of the waves in the Hawaiian Islands is known 

 with certainty only at Honolulu. The record of the Honolulu tide 

 gage (fig. 2) shows that the first rise started at about 6 : 33 a. m. (C. K. 

 Green, 1946, p. 491), though the exact time cannot be stated closer 

 than 2 or 3 minutes. The drum of the water-stage recorder at the 

 Waimea River, on Kauai, revolves too slowly to give an accurate in- 

 dication of time, but the first rise appears to have started there at 

 about 5 : 55. At Hilo, electric clocks were stopped at 7 : 06, and a 



HOURS 



HOURS 



Figure 2. — Record produced on the tide gage in Honolulu Harbor by the tsunami 



of April 1, 1946. 



brief power failure occurred at 7:18. These have been interpreted 

 by Powers (1946, p. 2), probably correctly, as the time of arrival of 

 two wave crests at Hilo. From other considerations, discussed briefly 

 elsewhere (Shepard, Macdonald, and Cox, in preparation), it ap- 

 pears probable, however, that the crest at 7 : 06 was the second wave 

 at Hilo, not the first. If so, allowing for the observed 15-minute 

 interval between later waves, the first rise at Hilo probably started at 

 about 6 : 45. Computed from these times of arrival, the approximate 

 average speed of the tsunami from its origin to Honolulu and Hilo 

 was, respectively, 490 and 498 miles an hour. On entering shallow 

 water the waves decreased greatly in speed. The waves moving up 

 Kawela Bay, on Oahu, were estimated by Shepard to be moving only 

 about 15 miles an hour. Similar low speeds near shore were reported 



