Experimental surveys were made in two test areas using a recently developed airborne technique by which several parameters, including wave tilt, of very-low-frequency (VLF) radio waves from distant transmitters are measured. Ground measurements were made using direct-current resistivity sounding and horizontal profiling methods, the slingram method, and an electromagnetic depth sounding method in which variations in the coupling between 2 horizontal loops is measured as a function of frequency. In each test area--one near Glennallen in the Copper River basin and the other near the Yukon River--at least 1 ice-free locality was located using the airborne VLF data and was corroborated by resistivity measurements. The airborne data appear to reflect the presence of gravel dep sits near some of the large rivers near Glennallen, but the data are complicated by topographic effects. In the Yukon River test area the airborne data indicate differences in resistivity between deeply weathered and relatively fresh bedrock.

Good quality resistivity depth soundings, which are not seriously affected by lateral effects, were obtained in both areas. Near Glennallen typical resistivities for fine-grained sediments are 40-80 ohm-meters in the active layer, greater than 2,000 ohm-meters in the frozen layer, and 150 ohm-meters in the underlying sediments except in localities where the presence of saline water reduces the resistivity to 10-20 ohm-meters. Resistivities of wet unfrozen gravel are about 200-500 ohm-meters. The depth to the top of the frozen layer can be determined quite accurately; determination of the depth to the bottom cannot be determined as closely. Similar resistivity data were obtained in the Yukon River test area except that the resistivity of the unfrozen material was found to be more varia le. Where bedrock is near the surface, the resistivity appears to be inversely proportional to the degree of weathering. The electromagnetic depth soundings substantiate the resistivity results and for some geoelectric sections the electromagnetic data add supplementary information.

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