Skip to main content
U.S. flag

An official website of the United States government

Electromagnetic methods for mapping freshwater lenses on Micronesian atoll islands

January 1, 1992

The overall shape of freshwater lenses can be determined by applying electromagnetic methods and inverse layered-earth modeling to the mapping of atoll island freshwater lenses. Conductivity profiles were run across the width of the inhabited islands at Mwoakilloa, Pingelap, and Sapwuahfik atolls of the Pohnpei State, Federated States of Micronesia using a dual-loop, frequency-domain, electromagnetic profiling system. Six values of apparent conductivity were recorded at each sounding station and were used to interpret layer conductivities and/or thicknesses. A three-layer model that includes the unsaturated, freshwater, and saltwater zones was used to simulate apparent-conductivity data measured in the field. Interpreted results were compared with chloride-concentration data from monitoring wells and indicate that the interface between freshwater and saltwater layers, defined from electromagnetic data, is located in the upper part of the transition zone, where the chloride-concentration profile shows a rapid increase with depth. The electromagnetic method can be used to interpret the thickness of the freshwater between monitoring wells, but can not be used to interpret the thickness of freshwater from monitoring wells to the margin of an island. ?? 1992.

Citation Information

Publication Year 1992
Title Electromagnetic methods for mapping freshwater lenses on Micronesian atoll islands
DOI
Authors S.S. Anthony
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Hydrology
Series Number
Index ID 70017165
Record Source USGS Publications Warehouse
USGS Organization