Geologic Implications of Magnetic Surveys — Malahoff and Woollard 
293 
the magnetic computations were corrected for 
terrain at the flight level at which the magnetic 
readings were recorded. 
The largest topographic effect was produced 
by the peak of Mauna Kea, where the aeromag- 
netic profiles, out of necessity with the light 
plane used, were taken at an elevation of only 
300 ft above the highest point. The maximum 
effect of terrain above this point was — |— 600 
gammas (Fig. 19). As seen from Figure 19, 
the terrain correction here changed the magnetic 
profile to a textbook-type symmetrical dipole 
profile. The magnetic effect of the flank of 
Mauna Loa on the same profile was 190 
gammas. The reason for this relatively low ter- 
rain effect on Mauna Loa lies in the greater 
height of the level of observation above ground 
surface. The terrain effect of Kohala Mountain 
was -|— 100 gammas, and that of Hualalai Moun- 
tain, on the same profile, was — )— 1 30 gammas. 
As indicated, a magnetic susceptibility of 10.0 
X 10“ 3 was used in computing all of the effects 
of terrain. It should be noted that, because the 
topographic slope of the terrain was considerably 
less than 35°, the inclination of the earth’s 
magnetic field in Hawaii, the topographic terrain 
correction in every case produced only a posi- 
tive effect. 
Because the magnetic terrain corrections did 
not alter the shape of the magnetic anomalies 
to any great extent even over Mauna Kea, it was 
not essential to correct the total magnetic force 
anomaly map of Hawaii (Fig. 13) for topo- 
graphic effects on the magnetic field. 
Islands of Maui and Kahoolawe 
geology of maui: Maui is the second largest 
island in the Hawaiian group and was formed 
by two volcanoes. East Maui contains the 
10,025-ft high Haleakala Volcano and West 
Maui contains a deeply dissected volcano 5,788 
ft high. 
The flat isthmus connecting the two volcanoes 
was made by lavas from East Maui banking 
against the flows from West Maui. The oldest 
rocks on East Maui are the Honomanu basalts, 
which were extruded in the Pliocene or early 
Pleistocene period along three rift zones 
(Stearns and Macdonald, 1942) to form a shield 
about 8,000 ft high. Covering this dome are 
the Kula volcanics extruded in early or middle 
Pleistocene time. These consist of hawaiites, 
ankaramites, and related alkalic basalts. Vol- 
canic activity was renewed in the middle to 
late Pleistocene and continued at least until 
about 1750 A.D., when the Hana lavas were 
deposited. During early Pleistocene time, it is 
probable that Maui, Kahoolawe, Lanai, and 
Molokai were joined as one island. 
West Maui is composed of the older tholeiitic 
Wailuku basalts extruded in the Pliocene or 
early Pleistocene along two rifts and a set of 
radial fissures. The basalts form a shield 5,600 
ft high. Iao Valley marks the center of the 
Fig. 18. Magnetic anomalies of Kilauea Volcano, island of Hawaii, flown at an elevation of 10,000 ft. 
Contour interval at 10 gammas. 
