Hawaii as a Site for the Moho Hole— Woollard 
281 
on to provide not only moral support but also 
possibly some financial aid for support facili- 
ties and any legal assistance or legislative ac- 
tion required to facilitate the operation. 
Scientific benefits to be obtained 
The principal scientific advantages in drill- 
ing the Moho Hole in the Hawaiian area are 
briefly as follows: 
L The mean mantle velocity in the area 
north of Maui (8.27 ± 2 km/sec) is normal 
for the Pacific Ocean, and agrees closely with 
the mean of all measurements in the Pacific 
(8.25 km/sec). The mantle rock sampled, 
therefore, can be expected to be representative 
for the Pacific area as a whole. 
2. The mantle material, on the basis of the 
seismic velocity measurements in the proposed 
site area, is truly anisotropic in that the spreads 
oriented north to south show a velocity of 
approximately 8.0 ±0.1 km/sec, whereas those 
oriented east to west show a velocity of 8.55 
± .2 km/sec. Cores here, therefore, should per- 
mit the determination of the cause of aniso- 
tropic transmission and identify the minerals 
causing it. 
3. The crustal structure at the NSF-recom- 
mended site shows not only a local thinning 
of the crust, but also a somewhat subnormal 
thickness of the basal crustal layer, which has 
a higher than normal velocity (6.96 km/sec) 
as compared to 6.84 km/sec for the area as a 
whole. In addition, the overlying intermediate 
crustal layer has a somewhat greater than nor- 
mal thickness and lower than normal velocity 
of about 5.8 km/sec. It appears, therefore, that 
this thickening of the second crustal layer has 
been made at the expense of the underlying 
basal layer. There also may have been attrition 
of the basal layer from below, as evidenced by 
the rise in the crust-mantle interface. The alter- 
nate interpretation for the rise in the M dis- 
continuity is that it is caused by domal uplift 
due to outward flow of mantle material from 
beneath the Hawaiian Ridge caused by crustal 
subsidence. The upper crustal layer having a 
velocity of about 4.2 km/sec is normal for the 
area with a thickness of about 1 km. 
As the crustal structure is not strictly nor- 
mal, one might argue that this is not the 
place to drill to the mantle. Conversely, one 
can also argue that it is the place to drill 
in that a significant physical-chemical process 
involving both the mantle and crust and two 
seismic discontinuities appears to be active 
and can be studied here. If Hess is right, 
and serpentinization of olivine-rich mantle rock 
determines the location of the Moho; and if 
the crust is really serpentinite, as Hess postu- 
lates, with a thin veneer of extruded basalt on 
top, here is an opportunity to study an area 
where serpentinization appears to be migrating 
as a wave front through the crust, with a fol- 
lowing wave front of deserpentinization. What- 
ever the mechanism that will explain the ob- 
served structure, it appears to be of fundamental 
importance and one that might well have a 
bearing on the whole problem of the develop- 
ment of crustal structure, the thickness of the 
crust, the depth of the Moho, and how isostasy 
is maintained. A drill hole here, therefore, 
would provide auxiliary scientific information 
of considerable importance. 
4. Auxiliary considerations are: 
a. The U.S. Geological Survey and the Uni- 
versity of Hawaii are conducting continuing 
and extensive petrological, geochemical, and 
geophysical studies in the present active vol- 
cano at Kilauea, which is drawing material 
from a depth of 40-45 km below the mantle- 
crust boundary. Thus, there will be a con- 
tinuing scientific program related to the Moho 
Hole operation. 
b. The Hawaiian primary lavas are tho- 
leiitic and, because of their depth of origin, can 
be related directly to the composition of the 
underlying mantle. Knowing the chemical com- 
position and mineralogy of the mantle, the 
process of differentiation leading to tholeiitic 
and alkalic basalts can be realistically studied. 
c. The high velocity, high density pipe fill- 
ing on Oahu, at a depth of less than 6000 ft, 
can be drilled at relatively low expense to deter- 
mine the chemical and petrologic nature of re- 
crystallized mantle material which appears to 
have undergone very little change in physical 
properties, but which may represent an impor- 
tant phase in the chain of transformations from 
mantle material to tholeiitic basalt. 
d. The existing wealth of geophysical, geo- 
