Reconnaissance by Submarine — Brock and Chamberlain 
377 
continental glaciation. The result of these posi- 
tive and negative shifts of sea level has been 
the formation of numerous marine terraces, 
reef horizons, and beaches, now found at vari- 
ous positions from several thousands of feet 
below to several hundreds of feet above the 
present sea level. 
Oahu, the center of population and site of 
the present investigations, is the third largest 
of the Hawaiian Islands with an area of 604 
square miles. The island was built up above sea 
level by the emergence and coalescing of two 
large volcanoes, the Koolau Volcano on the 
east and the Waianae Volcano on the west. 
Today the remnants of these two volcanoes 
form the Koolau and Waianae mountain ranges 
respectively, between which lies the Schofield 
Plateau, a flat, low plateau consisting of allu- 
vious and thinly-bedded lava flows. On the 
north and south flank of the island are wide 
coastal plains. 
Along western Oahu, the geology is com- 
pletely dominated by the deeply eroded rem- 
nants of the Waianae Volcano. The center of 
volcanic activity of this volcano was a caldera 
near Kolekole Pass at the head of Lualualei 
Valley. From this caldera and from the rift 
zones extending from it, large amounts of fluid 
lava were extruded over many millions of years. 
The older extrusions were thin, fluid, pahoehoe 
flows; the later flows were massive, adesitic aa. 
The main extrusive activity of the Waianae 
Volcano terminated several millions of years 
ago; the cessation of major eruptions was fol- 
lowed by deep erosion of the volcano and later 
by a few secondary eruptions of small magni- 
tude near the caldera. During the initial period 
of erosion the major valleys were formed; some, 
such as Lualualei, were graded to stands of the 
sea over 600 meters below the present sea level. 
With subsequent and continued subsidence of 
Oahu these major valleys were drowned, and 
eventually thick sections of reef, lagoonal, and 
beach sediments were deposited. 
The present geomorphology of the western 
coast of Oahu is dominated by the deeply 
eroded valleys described above. Between these 
valleys, sharp spurs extend down to the sea 
and offshore as submarine ridges. These spurs 
and their offshore extensions act as effective 
barriers to the alongshore transport of near- 
shore sand and other sediment. Consequently 
the nearshore environment is divided into lit- 
toral units or cells between which little exchange 
of sand occurs, and within which the amount 
of sand produced is in equilibrium with the 
amount of sediment lost from the cell. Con- 
tributions of littoral sand are from coastal 
streams and from the disintegration of calcium 
carbonate skeletal remains on the reef flats; 
losses of littoral sand are by offshore sedimenta- 
tion into deep water, and to a lesser extent by 
paralic deposition and by the landward migra- 
tion of beach dunes. 
The coastal zone between Kaena and Kepuhi 
points, the area of the present study, is essen- 
tially one large littoral cell; there appears to 
be very little nearshore sand transport around 
either point. The cell is dominated by the large 
Makua Valley located in the center of the cell; 
the major reservoir of beach sand is located at 
the mouth of this valley. Above sea level there 
are probably no fewer than four well-developed 
ancient sea level stands preserved, the most 
pronounced at — |— 8 meters. Below sea level there 
are at least five additionally preserved sea level 
stands, at — 18, —55, — 90, — 550, and 
— 1100 meters (Stearns, 1966:23). 
Biologic 
The nature of the sea floor in the area of 
investigation has been described elsewhere. As 
an environment it is a series of sand-covered 
terraces paralleling the trend of the coast and 
backed by discontinuous escarpments. In places, 
the sand covering on the terraces is thin and the 
epifauna scant, even where the rock is bare due 
possibly to sand scouring. This is most apparent 
in shallow water from 10 to 30 meters in 
depth. In depths of 30 meters or less there are 
some areas with a vigorous growth of herma- 
typic corals. There are extensive beds of the 
clam Pinna muricata on the sand-covered ter- 
races in depths between 35 and 100 meters, and 
occasionally on rocky areas numerous vasiform 
coral colonies, possibly a Montipora, are found 
in 60 to 80 meters of water. 
The sand-covered terraces, other than areas 
of Pinna beds, have little apparent life. Some 
dredging on the terraces resulted in the collec- 
tion of numerous heart urchins Brissus latecari- 
natus. There were also very few fishes over the 
