Geologic Implications of Magnetic Surveys — Malahoff and Woollard 295 
j I 56 ® 
Milts 
Fig. 20. Vents of the Hana, Kula, and Honolua volcanic series, and associated rift zones, island of Maui. 
(From Stearns and Macdonald, 1946.) 
netic surveys that the island of Kahoolawe lies 
on the Southwest Primary Rift Zone defined on 
Maui, the magnetic field relations to geology on 
Kahoolawe are considered along with those for 
Maui. 
Kahoolawe Island, according to Stearns 
(1940), is a shield-shaped, extinct volcano, 11 
miles long, 6 miles wide, and 1,491 ft high, 
lying 6% miles southwest of Maui. The island 
consists chiefly of tholeiite erupted from three 
rift zones and a vent at their intersection. The 
strike and position of these rift zones is defined 
by dike patterns in cliff faces and from the 
alignment of cinder cones present. 
THE MAGNETIC FIELD OVER THE ISLANDS OF 
MAUI AND KAHOOLAWE : From an inspection of 
the total force magnetic map (Fig. 2), it ap- 
pears that Maui was formed from eruptions on 
two east-west trending primary rift zones simi- 
lar to those described on the island of Hawaii. 
Geologic observations in Haleakala Crater show 
that the southwest primary anomaly trend on 
Maui parallels the geologic East Rift and South- 
west Rift of Steams and Macdonald (1942). 
The surface manifestations of the Southwest 
Maui Primary Rift Zone anomaly, therefore, 
appear to be these two rift zones. The analysis 
of this primary rift zone defines a belt of mag- 
netic rocks two miles wide. As elsewhere, the 
natural remanent magnetization of dike rocks 
collected in Haleakala Crater by Malahoff was 
approximately 10 times the intensity of the sur- 
rounding lavas, although the petrographic com- 
position of both the lavas and dike rocks was 
essentially the same. The direction of polariza- 
tion of these dike rocks from Haleakala was 
normal. 
Figure 21 shows that there are two principal 
centers of volcanism on the southwest primary 
rift zone anomaly, one marked as East Haleakala 
Volcanic Vent and the other as West Haleakala 
Volcanic Vent. Another volcanic vent zone is 
indicated on the same rift zone and has been 
named Kahoolawe Volcanic Vent, which is de- 
fined by a normally polarized dipole over the 
island of Kahoolawe (Figs. 22 and 23). 
Although the West Maui Primary Rift Zone 
anomaly strikes in the same general direction 
as does the southwest primary rift zone anom- 
aly, there is no connection between the two 
magnetic anomalies. It appears, therefore, that 
the two volcanic shields of East and West Maui 
originated along two separate primary rift zones. 
The isthmus between the two portions of Maui, 
