376 
PACIFIC SCIENCE, VoL XXII, July 1968 
meteorological conditions within the Pacific 
Basin: 
(1) Kona Wind Waves: Generated by local 
westerly storms; period 7 seconds, direction of 
approach SSW, height 2.4 meters, frequency of 
occurrence 3 9-5%, generally during the winter 
months. 
(2) North Pacific Swell: Generated by the 
passage of low pressure areas across the North- 
ern Pacific Basin; period 13 seconds, direction 
of approach NNW, height 3.4 meters, frequency 
of occurrence 89%, generally during the winter 
months. 
(3) Southern Hemisphere Swell: Generated 
by low pressure areas in the Southern Hemi- 
sphere; period 15 seconds, direction of ap- 
proach S, height 0.9 meters, frequency of occur- 
rence 53%, entirely during the summer months. 
(4) Trade wind Waves: Generated by the 
easterly tradewinds; period 8 seconds, direction 
of approach E and NE, height 2.4 meters, fre- 
quency of occurrence nearly 100% but, due to 
the sheltering effect of Oahu, of minor im- 
portance in the area of investigation. 
The currents that lie within the breaker zone, 
and which are of prime importance in the along- 
shore transport of littoral sand, are dependent 
upon the wave regime and consequently vary 
greatly in direction and speed. Waves from the 
northwest quadrant (generally North Pacific 
Swell) create southeastwardly flowing currents; 
waves approaching from the southwest quadrant 
(generally Southern Hemisphere Swell and 
Kona Wind Waves) produce currents flowing 
toward the northwest. Current speeds vary 
from less than Vio knot to about % knot. 
thermal structure: The island of Oahu 
centered at 21°30' north latitude is in tropical 
water with a permanent surface isothermal 
layer. The long term (1936-1956) average 
temperatures within a 250-mile radius of Oahu 
are given in Table 1, together with the range 
for depths from the surface to 2000 meters. 
It will be noted from Table 1 that the greatest 
range in temperature occurs between 200 and 
300 meters. These are the depths where the 
thermocline is ordinarily found. However, the 
thermocline fluctuates in depth depending upon 
3 Per cent of the year during which each wave type 
occurs. 
TABLE 1 
Average Temperature Data for an Area Within 
a 250-Mile Radius of Oahu, Hawaii* 
DEPTH in 
METERS. 
TEMPERATURE 
(degrees c) 
TEMPERATURE 
RANGE 
(DEGREES C) 
+ OR — 
0 
24.6 
2.2 
50 
24.1 
2.5 
100 
22.3 
2,3 
200 
16.7 
4.7 
300 
12.4 
3.7 
500 
8.2 
2.7 
800 
4.8 
0.6 
1000 
4.2 
0.7 
1500 
2.8 
0.2 
2000 
2.1 
0.2 
* From Dr. B. C. Heezen. 
the stirring effects of the wind or lack thereof, 
and the depths through which it fluctuates will 
show a greater temperature range than depths 
above or below. A protected lee area such as 
the Waianae coast of Oahu, because of reduced 
strength of the prevailing tradewinds, may have 
a shallower mixed layer. During the "Asherah” 
dives in this area, the location of the thermo- 
cline was inferred by noting the depth at 
which both visual ranges were minimal and the 
greatest apparent concentration of particulate 
matter occurred. On this basis the thermocline 
was between 70 and 100 meters. No vertical 
temperature profiles were obtained at the time 
of the diving operations. 
Geologic 
The main Hawaiian islands lie toward the 
southeastern limit of the Hawaiian Ridge, a 
large, positive, geomorphic feature built up of 
shield-shaped basaltic domes along a 1,600-mile 
fissure in the north-central Pacific Ocean. 
Neither the age nor the geologic history of the 
Hawaiian Ridge is well known, but recent 
investigations have indicated a Tertiary age for 
most of the Ridge, with a developmental 
sequence starting in the northwest and pro- 
ceeding to the southeast. The growth of the 
Ridge has been accompanied by large scale 
subsidence; superimposed upon this subsidence 
have been major Tertiary and Quaternary 
eustatic sea level fluctuations due to tectonic 
deformation of the Pacific Basin and intense 
