288 
PACIFIC SCIENCE, Vol. IX, July, 1955 
ondary features. The mean of these values is 
11°. In comparison, the maximum, mean, 
and minimum slopes of 6,000-foot height 
zones of the subaerial part of Mauna Loa 
were found to be 11°, 7°, and 3°, respectively. 
It is evident from these measurements as well 
as from inspection of the contour lines of 
Figure 1 and of the profiles of Figure 3 that 
the submarine slopes of this part of Hawaii 
are steeper than the subaerial slopes. 
Hawaiian Deep and Arch 
Beyond the foot of the lower slope of 
Hawaii is a broad depression that extends 
along most of the northeastern side of the 
entire chain and along part of the south- 
western side, as mentioned by Stocks (1950) 
and described more fully by Dietz and Me- 
nard (1953). The 18,000-foot contour of Fig- 
ure 1 shows the deepest part of the Hawaiian 
Deep; farther southwest the axis of the Deep 
shallows to 17,200 feet and its course is un- 
certain west of 155° 10' W. owing to its low 
relief and the low density of soundings. 
South and east of the axis of the Deep the 
bottom gradually becomes shallower until at 
the end of each long radial sounding traverse 
the depths are about 1,000 feet shallower than 
where the traverse crosses the Hawaiian Deep. 
This gentle northwestward-facing slope marks 
the inner side of the Hawaiian Arch, a 200- 
mile wide bulge that borders the Hawaiian 
Deep. The scarp that Dietz, Menard, and 
Hamilton (1954) found to border the outer 
edge of the Hawaiian Arch was not reached 
in this survey. In only a few places do the 
sounding traverses in the Hawaiian Deep and 
Arch have local depth variations that exceed 
100 feet, the probable limit of accuracy of 
reading the echo-sounder; accordingly, it is 
supposed that the bottom is mantled by a 
thick layer of sediment. 
The Hawaiian Deep is attributed by Dietz 
and Menard (1953) to crustal depression 
caused by the great load of the volcanic pile 
that comprises the Hawaiian Islands. The 
adjacent Hawaiian Arch they believed to be a 
related elastic bulge. 
Seamounts 
Five separate topographic highs were in- 
vestigated during the survey. For convenience 
all will be called seamounts though three of 
them approach the lower limit of size and 
isolation required for application of the term, 
seamount, by the International Committee on 
Nomenclature of Ocean Bottom Features 
(1953). 
Four of the seamounts were indicated by 
single soundings on previous charts (Table 1); 
however, the survey located new shallowest 
soundings as much as 4,100 feet shallower 
than the original ones (Table 1). One small 
deep seamount (Hohonu —" deep as a pit or 
TABLE 1 
Characteristics of the Fwe Seamounts 
Present Survey — 
Corrected Feet 
Previous Chart — 
Uncorrected Fathoms 
Previous Chart — 
Corrected Feet 
Height above 
Surroundings — Feet 
Diameter of Base — 
Statute Miles 
Mean Steepness of 
Slopes — Degrees 
Papa’u 
2490 
450 
2910 
3000 
6 
9? 
Loihi 
3222 
783 
4932 
9000 
14 
17 
Wini 
5346 
990 
6198 
12000 
20 
16 
’Apu’upu’u 
5832 
1600 
9924 
10500 
21 
18 
Hohonu 
11478 
5500 
6 
20 
