Part II—Geophysical investigations in the Hawaiian Islands

Abstract

During 1938 and 1939, an extensive series of geophysical surveys, employing both resistivity and magnetic methods, have been carried on in the Hawaiian Islands by the Section of Geophysics of the United States Geological Survey in cooperation with the Division of Ground‐Water of the Survey and the Division of Hydrography of the Territorial Government (see Fig. 1). During this time, surveys have been conducted on the islands of Oahu, Molokai, and Maul. Two distinct types of ground‐water occurrence are being investigated: (1) The basal fresh‐water lens floating on underlying salt water in obedience to the Ghyben‐Herzberg principle (Fig. 2); and (2) perched ground‐water (Fig. 3) .

Geohydrology of the Central Oahu, Hawaii, ground-water flow system and numerical simulation of the effects of additional pumping

“…Swartz did not attempt to delineate the dams beyond his resistivity survey area. Although presumably based on the same data, the boundaries presented by Swartz (1940) differ slightly from those of Swartz (1939). Dale and Takasaki (1976), utilizing information from wells drilled since the study of Swartz (1939), refined the boundaries of the Schofield ground-water area and the associated ground-water dams ( fig.…”

“…Shettigara's boundaries presented in figure 8 are based on figure 7.25 of Shettigara (1985). The northern boundary of Shettigara (1985), Shettigara and Peterson (1985), and Shettigara and Adams (1989) is about 5,200 ft north of the transition-zone limit of Swartz (1939). No attempt was made to extend the dams beyond the area of the geophysical survey.…”

“…Palmer (1955) interpreted several low mounds on the Schofield Plateau as "small lava shields" which may have been supplied with lava from dikes striking transverse to the main Koolau rift zone. Shettigara and Peterson (1985), using one-and two-dimen- Dale and Takasaki, 1976Swartz, 1939Broadbent, 1980Shettigara, 1985Mink and Lau, 1990 TOPOGRAPHIC DIVIDE sional models to interpret their resistivity sounding and profile data, concluded that the ground-water dams were shallow dikes. The dikes making up the northern dam were estimated to be within 100 ft of the ground surface.…”

“…Within the Schofield area, the resistivity measurements failed to detect underlying saltwater because of the great thickness of the freshwater zone. Swartz (1939) estimated the locations of the northern and southern boundaries of the Schofield ground-water area ( fig. 8) using the geophysical survey results.…”

“…In 1938, an electrical resistivity survey using the Lee Partitioning Method was conducted to determine the extent of the high-level water in the Schofield area (Swartz, 1939(Swartz, ,1940. This method was found to be suitable for detecting the transition between freshwater and underlying saltwater.…”