GEOPHYSICAL INVESTIGATIONS.

(a) The suitability of first arrival seismic refraction apparatus for surface structure studies was investigated at sites in the Wright, Taylor, and Miers Valleys, and on Brown Peninsula. Results show that the apparatus provides a simple method of measuring the depth of moraine or loess above permafrost or rock, and the depth of weathering of exposed rock faces. It was also possible to measure the depth of firn above the brine layer in the Ross Ice Shelf, which is of interest in detailed studies of the latter. It was not found possible to distinguish between permafrost and ice on a velocity basis, and the above method could not therefore be used to detect ice-cored morains.

In addition to the above tests, seismic velocity data were accumulated for a wide variety of materials and should prove useful in evaluating future projects.

(b) Detailed temperature, light flux, and electrical conductivity measurements were taken in Lake Miers, which, together with water samples and the biological data of Mr Baker, will enable a full physical, chemical, and biological description of this lake. Preliminary results indicate marked differences from saline lakes of the Wright and Taylor Valleys.

Similar measurements undertaken in the upper levels of Lake Bonney revealed a hitherto unreported fine structure, the implications of which are still under consideration.

R. Bell

(c) Measurements on temperature density and electrical conductivity of Lake Vanda, made by R. Hoare with VUWAE8 in January 1964, indicated that the lake possessed a fairly complicated horizontally layered structure, the origin of which was not clear. Similar measurements were made by Hoare on this expedition, together with more sophisticated measurements on convection currents in the layers.

The two sets of observations made by the sane man using the same equipment have enabled unambiguous conclusions to be drawn about changes with time of the structure of Lake Vanda.

Other measurements provide additional support for the theory that most page 12 of the heat in the lake comes from solar radiation absorbed in the water. A qualitative explanation for the occurrence of the horizontal convecting layers has been proposed.

(d) The Ross Ice Shelf near Scott Base consists of fresh-water ice floating on sea water. It is permeable to salt water, which partly freezes to leave a brine occupying small interstices in the ice below sea level. Professor A. T. Wilson suggested that the brine should be more concentrated near the surface than further down, because of lower temperatures near the surface than at the bottom. This required an inversion of the normally stable density gradient, so it was decided to make a direct investigation of the density variation. It was found that samples of brine taken from a drill hole were denser near the top of the hole than at the bottom, thus verifying the hypothesis in an unexpectedly simple manner. It was anticipated that the brine would mix up in the hole, but this is apparently prevented by the viscosity of the brine-ice chips mixture in the hole.

R. Hoare.