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PACIFIC SCIENCE, Vol. XX, July 1966 
Fig. 31. Total force magnetic map of the island of Kauai, based on aeromagnetic profiles flown at 8,000 
ft. Contour interval at 50 gammas. 
at 5 km. Rocks within the vent zone appear to 
have a magnetization contrast of 5.5 X 10 -3 
cgs units with the surrounding basalts. 
The Koloa Volcanic Vent Zone is approxi- 
mately 11 km long and 9-5 km wide. The top 
of the anomalous body is buried about 2.1 km 
beneath the surface. Rocks within the pipe zone 
appear to have a magnetization contrast of 
70 X 10~ 3 cgs units with the surrounding 
basalts. 
The North Kauai Volcanic Vent Zone, 
though defined by a distinct magnetic anomaly, 
appears to be unrelated to any major center of 
volcanism. The vent zone is approximately 21 
km long and 9-5 km wide. No quantitative 
analysis of this anomaly was attempted because 
the magnetic coverage off the north shore of 
the island was insufficient to define the position 
of the negative pole of the anomaly’s dipole 
pair. 
Island of Niihau 
geology: The geology of Niihau is rela- 
tively simple. According to Stearns (1947) the 
mass of the island is composed of a deeply 
weathered remanent of a basalt shield of 
Tertiary age, cut by a dike complex trending 
northeast-southwest. Stearns placed the vent 
two miles out to sea from the eastern shore of 
the island (Fig. 32). 
magnetic relations: Analysis of the total 
intensity magnetic map of Niihau (Fig. 33) 
shows that one primary rift zone anomaly 
strikes northeast-southwest along the island and 
one distinct volcanic vent zone anomaly is 
located on this trend in the middle of the 
island (Fig. 32). The magnetic map places the 
center of the Niihau Volcanic Vent Zone about 
l/ 2 mile inland from the eastern coast of the 
island. This vent zone probably marks the 
central vent from which the lavas that formed 
