32 
PACIFIC SCIENCE, January, 1947 
forded by the zone of small heights along 
the northwestern shore of Kauai (Fig. 3), at 
the head of a broad swale extending outward 
to oceanic depths. The broad valley-like de¬ 
pression off the eastern coast of Hawaii south 
of Hilo Bay probably also was somewhat 
effective in reducing the heights reached by 
the water along that coast. Although fairly 
great, ranging from 16 to 19 feet, the 
heights there are not much greater than those 
reached by ordinary storm waves. 
Presence or absence of reefs.—The presence 
of a well-developed fringing reef appears 
to have had a decided effect in reducing the 
intensity of wave onslaught. Along the reef- 
protected northern coast of Oahu the heights 
reached on shore by the waves were on the 
average decidedly less than on the unpro¬ 
tected northern coasts of Molokai and Ha¬ 
waii, or on the less protected northern coast 
of Kauai. The best-developed coral reef in 
the Hawaiian Islands fills Kaneohe Bay on 
Oahu, where it has a width of about 3 miles. 
Despite the fact that the broad mouth of 
Kaneohe Bay is open to the north and north¬ 
east, the tsunami produced a rise in water 
level at the bay head which was so small as 
to be hardly perceptible to observers, and, so 
far as could be determined, nowhere ex¬ 
ceeded 2 feet. Along the shore north of the 
bay the heights ranged from 4 to 10 feet, 
and on the end of Mokapu Peninsula south¬ 
east of the bay the heights reached more than 
20 feet (Fig. 4). 
The lesser heights along the southern 
shore of Molokai were probably partly due 
to the wide protecting reef. The effect of the 
reef in reducing wave violence along that 
shore is well shown at places where channels 
cross the reef. There the waves striking the 
shore at the heads of the channels were dis¬ 
tinctly larger than those reaching shore on 
each side of the channel. Thus at the- head 
of a small channel which crosses the reef 
just west of the mouth of Kainalu Stream the 
water rose 11 feet, damaging houses, where¬ 
as just east and west of this channel the 
water rose only 7 to 8 feet. 
Configuration of the coast line .—It is gen¬ 
erally considered that the effects of tsunamis 
should be intensified near the heads of V- 
shaped embayments. Such embayments great¬ 
ly increase tidal fluctuations, as in the Bay 
of Fundy, and might be expected to act like¬ 
wise on the similarly long waves of a 
tsunami. Imamura (1937: 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, special 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 funneling, 
but measurements around its shores show no 
systematic increase in heights toward its head 
(Fig. 7 and Plate 1). 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 ex¬ 
treme height of 54 feet at Waikolu Valley, 
on the northern shore of Molokai, may have 
been partly the result of funneling between 
Kalaupapa Peninsula and the point and small 
islands just east of the mouth of the valley. 
At both Pololu Valley on Hawaii and Pele- 
kunu 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, 
