300 
PACIFIC SCIENCE, Vol. XX, July 1966 
Fig. 26. Sketch of the primary rift zones and volcanic pipe zones of the island of Lanai. 
omalies on East Molokai. The smaller anomalies 
appear to represent shallower sources which are 
superimposed upon the broad anomalies asso- 
ciated with the volcanic vent zone. These in 
turn are superimposed upon the primary rift 
trends believed to result from intrusions in 
crustal rifts. It appears, therefore, that East 
Molokai was formed by volcanic eruptions 
originating from at least two centers, and that 
West Molokai was formed by eruptions origi- 
nating from at least three centers. The results 
for the analyses of the four principal magnetic 
anomalies are listed in Table 4. 
In connection with the Southwest Molokai 
Volcanic Vent Zone, it is to be noted that the 
associated anomaly is inversely polarized. As 
explained in connection with relations on Maui, 
this can be explained as being due either to a 
reversal of the earth’s magnetic field during the 
period of solidification of magma within the 
vent, or to a filling of the vent with possibly 
olivine-rich rock which is less magnetic than 
the surrounding basalts. The computed mag- 
netization contrast of 7.7 X 10 -3 cgs units 
between the pipe zone rocks and the surround- 
ing basalts is well within the range of possible 
magnetization contrast between olivine-rich ba- 
salt and tholeiitic basalt. 
Island of Lanai 
geology: Lanai consists of a single shield- 
shaped volcano. According to Stearns (1940&), 
outpouring of lava has taken place from three 
sets of fissures that form three rift zones (Fig. 
26), a northwest rift zone, a southwest rift 
zone, and a faulted south rift zone. Numerous 
dikes and faults occupy these rift zones. Basaltic 
flows erupted from these fissures and formed the 
