TSUNAMI OF APRIL 1, 1946 — MACDONALD, ET AL. 271 



where channels cross the reef. There the waves striking the shore at 

 the heads of the channels were distinctly larger than those reaching 

 shore on each side of the channel. Thus at the head of a small chan- 

 nel which crosses the reef just west of the mouth of Kainalu Stream 

 the water rose 11 feet, damaging houses, whereas just east and west 

 of this channel the water rose only 7 to 8 feet. 



Configuration of the coast line. — It is generally considered that 

 the effects of tsunamis should be intensiHed near the heads of V- 

 shaped embayments. Such embayments greatly increase tidal fluc- 

 tuations, as in the Bay of Fundy, and might be expected to act like- 

 wise on the similarly long waves of a tsunami. Imamura (1937, 

 pp. 125-127) states that as such a wave rolls up a V-shaped em- 

 bayment its height increases in inverse ratio to the width and depth 

 of the bay, and cites examples of such increases in height of the waves 

 toward the bay head during Japanese tsunamis. Consequently, spe- 

 cial search was made for this phenomenon in funnel-shaped bays on 

 Hawaiian shores. No good examples could be found. Hilo Bay would 

 appear to be an almost ideal site for such f unneling, but measurements 

 around its shores show no systematic increase in heights toward its 

 head (fig. 7 and 8) . Similarly there was a lack of increase in heights 

 toward the head of the broad V-shaped embayment on the northern 

 coast of Maui. Possibly the extreme height of 54 feet at Waikolu 

 Valley, on the northern shore of Molokai, may have been partly the 

 result of f unneling between Kalaupapa Peninsula and the point and 

 small islands just east of the mouth of the valley. At both Pololu 

 Valley on Hawaii and Pelekunu Valley on Molokai, the water level 

 was higher at the bay head than on the walls of the bay part way out. 

 However, at Pololu Valley, and probably also at Pelekunu, this level 

 was the result of a local upsurge where the waves crossed the beach. 

 Conversely, several bays were found in which the heights reached by 

 the water were less at the bay head than near its mouth. 



Several small steep valleys, debouching into small bays, were found 

 in which the water rose to appreciably greater heights along the valley 

 axis than on the sides near the bay mouth or opposite the beach. Thus, 

 in the small bay just south of Hanamaula Bay, on the eastern shore of 

 Kauai, the water rose only 25 feet on the bay sides, but swept up the 

 small valley at its head to a height of 40 feet. At Moloaa, on Kauai, the 

 water reached an altitude of 40 feet in the axis of the valley, but only 

 30 to 35 feet on the bay walls. Again, at Honouliwai, on Molokai, the 

 water reached a height of 27 feet opposite the beach, but went 6 feet 

 higher up the valley. These are merely si)ecialized examples of effect, 

 upon the rush of water up on shore, of a topography above sea level 

 which served to concentrate the inrushing water. 



Merging of waves frovn different directions. — Wave crests traveling 

 by different routes may arrive at a given locality simultaneously 



