Hawaiian Wave Patterns — Emery 
259 
Fig. 3. Wave pattern based upon aerial observation at positions indicated by circles on 31 August and 1 
September 1961. The wide lines show changing directions of crest lines of each of three different trains of 
7- sec waves. The narrow lines show the same for several trains of short-period (about 1-sec) waves. 
this material has been deposited to form sandy 
shores chiefly in the immediate lee of prominent 
rocky headlands where the intensity of wave 
attack and of longshore currents is sharply re- 
duced. Generally this lee is west of headlands, 
but on Lanai it is on the east side because 
that side is sheltered by nearby Maui. Muddy 
shores are not common, but those which do 
exist are in areas which have the greatest pro- 
tection from waves, well into the lee of the 
islands or of headlands. 
In recent years there has been erosion of 
certain sand beaches, particularly those on the 
east side of Kauai, the north side of Oahu, and 
the north side of Maui. In part, this erosion has 
probably resulted from man’s activities. How- 
ever, the close relationship between shore type 
and degree of exposure exhibited by Figure 4 
suggests another cause. As shown by Wentworth 
(1949), there may have been a directional 
change of trade winds at Honolulu from a mean 
of 050° in 1908 to 085° between 1925 and 
1939 to 063° in 1943. If the trend is real and 
if it continued into recent years, the average 
wind direction would again have been about 
050° sometime between 1950 and I960. Al- 
though the wind direction at Honolulu may not 
correspond exactly with the direction of the 
winds at sea because of the deflecting effects of 
nearby mountains, the changes in wind direction 
at Honolulu may well reflect changes at sea. 
Such a change of wind direction at sea would 
have produced a corresponding change of wave 
approach. Possibly the beaches are being shifted 
somewhat as weather vanes in response to this 
change in direction of wave approach. 
SUMMARY AND CONCLUSIONS 
Mapping of surface winds and wave patterns 
from the air is a simple procedure. A 2 -day 
survey in the Hawaiian Islands showed that the 
wind was from the east, but was subject to 
Fig. 4. Relationship of type of shore to degree of 
exposure to dominant waves. Radiating lines at upper 
right-hand corner show common azimuths of wave 
crests and directions of wave approach. 
