112 
PACIFIC SCIENCE, Vol. XVII, January 1963 
5. Hurricane: Waves from tropical storms, 
usually approaching from the southeast through 
southwest. They are most likely to occur in Au- 
gust and September, although occurrence may 
be between June and December. 
Of the five classes of waves, those generated 
by the northeast trades are by far the most per- 
sistent source of wave energy for the east and 
northeast shores of the island. Undoubtedly these 
waves account for the greater abundance of cal- 
careous reefs on the windward side of the island. 
Waves from Aleutian lows are probably the 
dominant agent responsible for recent erosion 
along the Napali Cliffs on the northwest coast 
of the island. These waves produce a southwest- 
erly drift of littoral sediment from the Napali 
Cliffs towards Nohili Point and have been a 
major influence in the formation of the straight 
coast line near Barking Sands (between sample 
stations 1 to 7, Fig. 11). The meteorological 
conditions giving rise to unusually high waves 
of this type in January 1947 are described by 
Arthur ( 1948). Waves of this type, with break- 
ers estimated to be 20 ft high and periods of 
14-16 sec, were observed on the north coast of 
Kauai on 30 November 1935. 
Southern swell is the most common type of 
wave on the south and lee sides of the island. 
Although these waves are low, they are almost 
continuous during the summer months and pro- 
duce a westerly transport of sand from the Wai- 
mea River toward the Mana Coastal Plain. Hur- 
ricanes, although infrequent, are important, and 
the local residents attribute some recent erosion 
to the combined effects of the hurricane of 1957 
and the tsunami of the same year. Kauai is ex- 
posed to tsunami waves accompanying seismic 
activity in the vicinity of the Aleutian and Ku- 
rile Trenches in the northern hemisphere, and, 
to a lesser degree, from tsunami waves generated 
off the coast of Chile in the southern hemis- 
phere. These catastrophic waves cause considera- 
ble coastal erosion and, at times, transport large 
blocks of reef material inland (Shepard, Mac- 
donald, and Cox, 1950). 
SEDIMENTS 
Eighty-three sand samples and five beach and 
dune rock samples were collected from the near- 
shore zone along the coasts of the island. Exami- 
nation of the sediment showed that it could 
easily be divided on the basis of origin into: ( 1 ) 
biogenous material derived from the skeletons 
of molluscs, coral, calcareous algae, and fora- 
minifera; and (2) terrigenous material derived 
from erosion of the island’s volcanic formations. 
These two sediment types were characterized by 
important differences in color, density, and solu- 
bility in dilute hydrochloric acid. In general, the 
biogenous material appeared to constitute the 
predominant sediment in the nearshore region 
of the island. On the windward coast, the per- 
centage of biogenous material was so high that 
the terrigenous fraction was rarely visible to 
the unaided eye. 
Most samples were composed of medium and 
coarse grain sand containing 80% to 95% cal- 
cium carbonate of biogenous origin. Analysis by 
X-ray diffraction showed that, mineralogically, 
the biogenous material was composed of three 
components: aragonite, magnesium-rich calcite, ! 
and magnesium-poor calcite. Terrigenous sedi- 
ments were common only on the lee coasts of 
the island, especially in the vicinity of and down 
current from river mouths. The terrigenous ma- 
terial consisted mainly of olivine grains and 
sand-size, partially-weathered feldspathic rock 
fragments, plus a small percentage of opaque 
iron oxides. 
A brief description of the size distributions of 
the sands follows, together with their biological, 
chemical, and mineralogical analyses. Detailed 
data on each sample are listed in Table 2. 
Size Distribution 
The size distributions of all the sediments ; 
were determined by the Emery settling tube 
(Poole et al., 1951), and some, especially the 
coarsest, were also analyzed by sieving. The me- 
dian diameter of the particle size distribution 
is expressed in microns, and measures of the 
standard deviation (sorting) and skewness are 
given in the graphic phi notation of Inman i 
(1952). Sieving was necessary in order to obtain 
the parameters for the coarser samples. Since 
sieve and settling tube analyses are based on 
different properties of the sediment, the para- 
meters obtained by the two methods are only 
roughly comparable. For example, the partly 
hollow tests of foraminifera are retained in a 
