Submarine Topography — Emery 
287 
ship speed and offsetting of the course by the 
wind and sea. 
About 2,430 two-minute interval soundings 
resulted from the survey. These soundings 
were plotted on U. S. Coast and Geodetic 
Survey Chart No. 4115 (1951 edition) which 
also contains 380 soundings in the area of 
interest. An additional 220 useful soundings 
were transferred to the plotting chart from a 
compilation made by Dietz and Menard 
(1953) for their general map of the Hawaiian 
region. A few additional old soundings were 
omitted because they differed markedly from 
others in the vicinity and were considered 
erroneous in position. The total of 3,030 
soundings served as the basis for the sea floor 
contour lines of Figure 1. 
Corrections for true sound velocity in the 
water were made using data from the Marshall 
Islands (Emery, Tracey, and Ladd, 1954) so 
that the contour lines would indicate actual 
depths. Contour lines of land topography at 
the same interval of 1,500 feet (250 fathoms) 
were added to the chart from the geological 
map of Hawaii (Stearns and Macdonald, 
1946).* 
RESULTS 
The survey shows the presence of three 
main physiographic units: lower slopes of 
Hawaii, Hawaiian Deep, and Hawaiian Arch 
(Figures 1 and 2). Superimposed on these 
units are five seamounts. 
Lower Slope of Hawaii 
The lower slope of the island of Hawaii 
extends a distance of between 10 and 20 miles 
from shore to a depth of more than 15,000 
feet. Instead of being a simple smooth surface 
the slope has been made somewhat irregular 
by four kinds of secondary features. One such 
feature is volcanic cones, two of which are 
located directly south of Kilauea. These cones 
will be discussed in the section on seamounts. 
A second irregularity is that of elongate 
ridges that extend seaward off both South 
Cape and Cape Kumukahi. Both ridges are 
probably the result of vulcanism along rifts 
or zones of weakness, extensions of which 
have been recognized on land (Stearns and 
Macdonald, 1946, p. 25) and are exemplified 
by a row of many small craters between Cape 
Kumukahi and Kilauea Crater. As would be 
expected of volcanic activity, at least one hill 
rises above the general level of the outer end 
of the ridge off Cape Kumukahi. A second 
hill is shown on U. S. Coast and Geodetic 
Survey Chart No. 4115 to rise from depths 
of more than 1,800 feet to within 210 feet of 
the sea surface (35 fathoms —Existence Doubt- 
ful) at a point 5 miles off Cape Kumukahi, 
but detailed sounding traverses made in this 
area failed to reveal depths shallower than 
1,800 feet. The ridges bear a striking resem- 
blance to similar features of guyots in the 
Marshall Islands, particularly Sylvania Guyot 
near Bikini Atoll (Emery, Tracy, and Ladd, 
1954). 
The third kind of irregularity of the slope 
is a greater than usual steepness near the shore 
from south of Kilauea Crater northeastward 
to near Cape Kumukahi; this steepness is 
believed to result from the presence of a 
normal fault that is parallel to shore and is 
en echelon with faults of the Hilina zone on 
land. The latter is marked by two scarps 1,000 
to 1,500 feet high and the scarp on the sea 
floor is nearly as high. The fourth and last 
kind of irregularity on the slope is a long 
broad low ridge that extends eastward from 
the northernmost parasitic cone. This area is 
one in which 4,553 earthquakes were detected 
in a six-week period of 1952 (Macdonald, 
1952). Whether this low ridge is of volcanic 
or structural origin is unknown. The sub- 
marine slope appears to be free of a fifth kind 
of secondary land form, submerged wave- 
formed terraces, unlike the northeastern coast 
where Dietz and Menard (1953) reported an 
extensive terrace at a depth of 1,080 feet. 
The steepness of the lower slopes was 
measured along 11 of the sounding traverses, 
using for each measurement the gradient of 
the steepest 6,000-foot depth zone and avoid- 
ing as much as possible the influence of sec- 
