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Figure 2. Aeromagnetic profile (in gammas) and topographic profile and cross section taken along A-A' of fig. 1.

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References

Bull, C., E. Irving, and I. Willis. 1962. Further palaeo-magnetic results from south Victoria Land, Antarctica.Royal Astronomical Society. Geophysical Journal, 6(3):320-336.

McGinnis, L. D., T. Toni, and P. Webb. 1972. Dry ValleyDrilling Project. Antarctic Journal of the U.S., VII(3)53-56.

Robinson, E. E. 1964. Correlation of magnetic anomalieswith bedrock geology in the McMurdo Sound area, Antarc-tica. Journal of Geophysical Research, 69(20): 4319–43 26.

Seismic refraction and electricalresistivity investigations in

the dry valleysCLIFFORD C. CLARK

Department of GeologyNorthern Illinois University

Geophysical field work in the ice-free valleys ofVictoria Land, Antarci;ica, during the 1971-1972 aus-tral summer included both electrical depth sounding

and seismic refraction profiling. This ground explora-tion was conducted as part of the Dry Valley DrillingProject (McGinnis et al., 1972). Geophysical studieswere conducted to establish geologic control at bore-hole sites where drilling would provide relevant infor-mation concerning the history of the dry valleys. For adetailed description of electrical equipment and meth-ods, see McGinnis and Jensen (1971). An SIE port-able, 12-channel seismograph with an internal nickel-cadmium power supply was used for the 12 seismicstations of 366-meter geophone spread.

Some of the numerous lakes in the dry valleys aresuspected to be connected hydrologically to the sub-surface. In an area where the mean annual air tem-perature is —20° to — 25°C. (Horowitz et al., 1972),permafrost would be expected to restrict completelythe transfer of surface and subsurface water. Electricaland seismic measurements indicate that the occurrenceof "confining" permafrost (McGinnis and Jensen,1971) varies but is predictable. Temperatures at thebottom of some of these lakes are unexplicably high,and in some cases permafrost beneath the lakes is ab-sent. Drilling near these lakes will give us importantinformation concerning the hydrology of the area.

July-August 1972 91

One of these lakes, Don Juan Pond, in the southfork of Wright Valley, has been shown to be an areawhere there is no confining permafrost that could pro-hibit the upward migration of groundwater. The highsalinity of the water in the pond (more than 250,000parts per million of dissolved solids, principally cal-cium chloride) is probably what keeps it unfrozenyear-round. From seismic evidence, unfrozen sedi-ments and glacial debris in the basin are over 46meters thick on the western end of the pond and only20.5 meters thick on the eastern edge of the basin. Atime-distance curve is interpreted as indicating a faultzone striking north-south directly beneath the pond.P-wave velocities in the unfrozen sediments averageapproximately 1,800 meters per second, and typicalsurface resistivities are 7 to 10 ohm-meters, increasingto less than 300 ohm-meters at a depth of about 150meters. Relatively low resistivities, which continue wellinto the bedrock, suggest that the basement rock issaturated and the water is not frozen. Basement veloci-ties average 5,116 meters per second. Don QuixotePond, in the north fork of Wright Valley, is character-ized by low resistivities (less than 520-ohm-meters)and moderate high velocities (4,587 meters per sec-ond) at shallow depths, reflecting the thin drift coverand proximity to saturated basement.

Lake Vida, in Victoria Valley, has been shown tobe 38 to 40 meters deep from seismic measurements.Seismic profiles suggest that Lake Vida lies directly onbasement, whereas resistivities indicate that an un-frozen layer may exist at its base.

Lake Fryxell, in Taylor Valley, is another locationwhere permafrost varies extensively from place toplace, especially near the tongue of the CanadaGlacier.

Near Walcott Glacier, it was noticed that perrna-frost is very thin (less than 9 meters), probably asa result of recent volcanism. Other stations, not com-pletely analyzed, include those near Lake Miers, LakeBonney, and the shore of eastern Taylor Valley nearNew Harbor.

Conclusions. In general, it was assumed that wheresediments and bedrock had high resistivities (greaterthan 10,000 ohm-meters), confining permafrost wasdefinitely present. Where unfrozen surface materialwas present, especially near saline lakes, resistivitiesat depth were generally less than 500 ohm-meters.Compressional wave velocities ranged from below1,600 meters per second for unfrozen, unconsolidatedmaterial to over 6,000 meters per second, probablyindicating frozen granitic basement. Laboratory meas-urements of electrical and seismic properties of antarc-tic soils, rocks, and waters at various temperatures andpressures are in progress.

This work was supported by National ScienceFoundation contract C-642.

References

Horowitz, N. H., R. E. Cameron, and J . S. Hubbard. 1972.Microbiology of the dry valleys of Antarctica. Science,176(4032): 242-245.

McGinnis, L. D., and T. E. Jensen. 1971. Permafrost-hydrologic regimen in two ice-free valleys, Antarctica, fromelectrical depth sounding. Quaternary Research, 1(3)389-409.

McGinnis, L. D., T. Toni, and P. Webb. 1972. Dry ValleyDrilling Project. Antarctic Journal of the U.S., VII(3)53-56.

Monitoring of antarcticdry valley drilling sites

F. A. MORELLI, R. E. CAMERON, and D. R. GENSELBioscience and Planetology Section

Jet Propulsion LaboratoryCalifornia Institute of Technology

L. P. RANDALL

Department of Biological ScienceNorthern Illinois University

Increasing concern has been shown for the conser-vation and preservation of the Antarctic, which re-sulted in a recent colloquium (Parker, 1972). Man'srelatively recent permanent occupancy of the Conti-nent, his past, present, and anticipated activities andpractices, and a deeper appreciation for the environ-

This paper, presents the results of one phase of researchcarried out under National Aeronautics and Space Adminis-tration contract NAS 7-100. Logistic support and facilitiesfor the investigations in Antarctica and additional laboratorysupport at the Jet Propulsion Laboratory were providedunder National Science Foundation contract NSF-0585 forthe study of antarctic microbial ecology.

Figure 1. Dry Valley Drilling Project camp at Don Juan Pond,Wright Valley. Air samplers in foreground, left to right: Reynier,

Staplex, Andersen, and Roto-Rod.

92 ANTARCTIC JOURNAL