The principles that underlie the analysis of aerial photographs using the coherent light from a laser are summarized, and then a study of such a filtering technique applied to an aerial photograph of Jakobshavn Isbræ is given as an example.

Two systems of crevasses, respectively parallel and perpendicular to the direction of flow of the southern lobe of the glacier can be detected after filtering. These two crevasse systems were not apparent at first sight on the original photograph as they were obliterated by a network of curved crevasses. It appears that this latter network are not true crevasses, but surface undulations formed by differential ablation of bands of black (or blue) and white ice.

All available mean annual accumulation data on the Greenland ice sheet (excluding the Thule peninsula) have been collected and analyzed using multiple regression techniques to develop equations capable of predicting mean annual accumulation. The analysis was carried out for north Greenland, south Greenland, and for the transition zone between the two major regions. The resulting equations show that mean annual accumulation can be predicted from the independent parameters latitude, longitude and elevation. The patterns of accumulation are shown in a series of isohyetal (contours of accumulation in terms of water) maps. The major feature shown is a well defined asymmetry in accumulation; a pronounced east-slope maximum in south Greenland and an equally pronounced west-slope maximum in north Greenland. Poleward of lat. 69° N., isohyets decrease in elevation to the north. Mean annual accumulation ranges from >90 g./cm.2 in south-east Greenland to <15 g./cm.2 in north-east Greenland. A brief discussion of mass balance estimates of the Greenland ice sheet and of the relevance of this study to them is included.

Observations in and around natural caves beneath the glacier Østerdalsisen in 1961 and 1962 indicated that, within the marginal zone, basal sliding played a major part in the movement measured at the upper surface. Sliding rates apparently were influenced by the availability of water at the glacier. The contribution of differential movement within the ice, which was unimportant within the outermost part (about 10 m.) of the glacier, increased with distance from the edge. Movement at the bottom was free from macroscopic irregularities, except where local conditions at the bed influenced the mode of flow. Air temperatures within the innermost parts of subglacial caves were almost constant, below 0°C. Studies indicated that large gaps are unlikely to exist between the glacier and its bed when the ice is more than 50 m. thick.

A lichen-growth curve has been developed for dating Recent glacial and periglacial deposits in the Indian Peaks area of the Colorado Front Range. Rhizocarpon geographicum was selected for the study because of its long life span and consistent size-age relationship. The species grows at different rates in different micro-environments, with moisture, stability of substrate and length of snow-free growing season having the greatest effect. Growth rates were determined indirectly, by measuring the maximum diameters of circular or nearly circular thalli growing on surfaces of known exposure age. Measurements were made on 24 historically dated surfaces, ranging in age from 25 to 69 yr., and on three radiocarbon-dated surfaces, including (1) mudflow levees younger than 180 yr., (2) a rock wall built by prehistoric Indians about 970 yr. ago, and (3) ground moraine deposited by a retreating valley glacier about 2,460 radiocarbon years ago. R. geographicurrz grows very rapidly (14. mm./100 yr.) during the First 100 yr. of its life. Growth then slows to an average rate of 3.3 mm./100 yr. The completed growth curve is believed to be suitable for dating deposits at least as old as 3,000 yr.

Unlike the other large lakes in the ice-free valleys of southern Victoria Land, Antarctica, Lake Vida, in Victoria Valley, is probably frozen to its base. Sand layers in the uppermost 11 m. of ice on Lake Vida may indicate that this lake has a different history from the others. Summer-time ablation is about 50 cm. of ice.

An analysis of the margin of the ice sheet in the upper Ferrar Glacier area of south Victoria Land, Antarctica, shows that the shear hypothesis and the theory of Weertman are both of value if an attempt is made to explain the formation of the morainic deposits of this area.

Three types of debris layer have been observed within the glacier:

• i. Silty and sandy layers, with a slight dip towards the interior of the glacier, are separated from one another by white bubbly ice and blue dense ice at the edge of the glacier. They have resulted from a freezing-in process due to the formation of segregation ice and upwarping near the margin of the ice sheet.

• ii. Fault planes in the glacier, filled with slabs and gravel, are the result of shearing which has occurred along and transformed thermal-contraction fissures. The debris has been scraped from the glacier bed, carried into the ice and ultimately transported along these planes.

• iii. Three coarse debris layers of different ages associated with major shear zones at the boundary between stagnant and active ice.

Due to favourable circumstances, the debris layers of Weertman have been observed to be faulted by shear planes of the second type.

Salinity profiles of young sea ice are presented which show salinity differences of the order of 2‰ to 3‰ within a ~3 cm. distance, horizontally as well as vertically. This ice is also shown, by use of a penetrating dye, to be very permeable which encumbers any attempt to explain such pronounced salinity variations. Two generations of brine-drainage features are described; the first is inherited from the liquid and the later-generation channels develop from brine-pocket and Tyndall-figure migration.

It is proposed that at least part of the brine contained in the ice mass migrates downward in the following way: cold dense brine cascades from higher levels, causing the more dilute, warmer brine at lower levels to partially freeze. This would also account for some of the local variations in salinity.

Ice temperatures were measured on the ice plateau at Mawson, Antarctica, for one year down to depths of 11 m. and through a floating sea-ice cover for six months. The plateau data were examined by harmonic analysis and the thermal diffusivity of the ice was obtained from the classical model of heat diffusion. An improved model of heat diffusion proposed by Lettau (1954) was also used to derive the diffusivity. The results show that absorbed radiation affects the computed diffusivity values down to 6–8 in. depth and a model is put forward to explain these apparent changes with depth. Data on the extinction of radiation in the ice have been published elsewhere (Weller and Schwerdtfeger, in press). The diffusivity of the ice is determined for periods with no radiation in winter and the value of 0.011 cm2. sec−1 agrees well with values at 8 m. depth where the effect of radiation becomes negligible.

Heat-flux plates embedded in the ice were used to determine the diffusivity independently and also to give numerical values of the heat flux at any moment. The geometry and characteristics of these flux plates are discussed elsewhere (Schwerdtfeger and Weller, 1967). They are also used to derive the diffusivity of sea ice and enable a detailed analysis of the diurnal heat flux in such complex substances as sea ice to be made.

A theoretical expression is derived for the rate of increase in the density of a compact of uniform ice spheres due to volume diffusion in the ice. The diffusion occurs due to the existence of high concentrations of vacancies in the ice just beneath the concave surfaces of the necks which grow between the ice spheres. Accurate measurements on the densification of a compact of ice spheres as a function of time, temperature, and particle size are found to be in excellent agreement with the theory The importance of this process in the metamorphism of dry snow at a uniform temperature is discussed.

A linear relationship between strength and density is a characteristic feature of deposited snow. This relationship is explained theoretically in the case of old dry snow in ternis of the theory of sintering. The discontinuity in the relationship at a density of about 0.4 g./cm3 is considered to mark a transition point below which the snow densifies primarily by rearranement of the grains and the strength increases by the growth of existing bonds, and above which densification occurs by volume diffusion and the strength increases primarily by the creation of new bonds. Experimental evidence to support these ideas is presented.

The dielectric relaxation of névé and glacial ice has been studied on two temperate glaciers in Greenland and France. Measurement of the capacitance and loss tangent in the audio-frequency range of thin parallel wires placed on the surface of a glacier gave ϵ′, the relative permittivity, and ϵ″, the loss factor of the névé. The relaxation time can be expressed in terms of the frequency fm at the maximum ϵ″ value of the Cole-Cole ϵ″−ϵ′ diagram, and its variation with depth was derived from the Cole-Cole diagrams obtained for different wire separations.

For wet 0°C. surface snow in Greenland, fm ≈ 4 kHz. and decreased with the increase in density and form factor at greater depths, while for the low-density, cold surface névé in France fm ≈ 2 kHz. and increased with the increase in temperature at greater depths. All Cole-Cole diagrams showed both impurity-ion losses at low frequencies below 6 kHz., and a spreading factor of the distribution in relaxation times caused by the changes in the physical properties of the glacier with depth. Although the method could not measure temperatures absolutely, relative temperature differences and the position of the 0°C. isotherm were detected when a temperature gradient existed in a glacier.

The activation energy ϵe1 of polar firn samples determined by D.C. resistivity measurements is a function of temperature and density. In the temperature range −2° C. to −10° C. ϵe1 decreases with decreasing temperature reaching a nearly constant value for temperatures colder than −10°C.; in the temperature range −10°C. to −21°C. ϵe1 was found to decrease with increasing density and to lie between 0.7 eV. and 0.4 eV.

Stereophotogrammetric techniques were used for a study of snow avalanches. The contour lines of the avalanche slope were mapped from stereo-photographs taken before and after the occurrence of the avalanche. The outline of the avalanche front at certain time intervals and the contours of the snow cloud were also plotted. A relative accuracy for the different maps of 0.7 m. on the terrain was established.

The volume of the snow cloud at four different stages of the avalanche was determined from the maps. These volumes were also computed independently from coordinate readings that were made in the stereo models. The standard errors of both methods of volume determination were estimated to be 450 m.3 and 290 m.3 respectively, representing errors of 5 per cent and 3 per cent of the average cloud volume.

The photographs were taken with an accurately determined time interval. Therefore, the velocity of the avalanche front could be determined from the photogrammetric measurements.

A new concept of attitude stabilization for thermal probes or coring drills in ice eliminates instability. The center of support is placed above the center of gravity. A lower and an upper hot point produce melt penetration. The ratio of their power levels is the basis for stabilization. This is provided by the automatic control of the heater in the upper hot point.

A new down bore-hole instrument to extract atmospheric gases entrapped in glacier ice was designed, developed and tested in a Greenland ice tunnel. Using this ice and a 7.5 kW. source, about 30 hr. are required to melt the approximately 1 metric ton sample, extract the gases, and to separate and collect with molecular sieves the minimum of 100 cm.3 of CO2 necessary for the 14C measurements made later using special low-level counters. Age results using the down bore-hole CO2 samples agree with results obtained earlier from CO2 samples collected at the same tunnel location using a vacuum-vessel melting technique. A mean value of 5,120±200 yr. b.p. is obtained for the seven samples measured using both collection systems, making this the oldest natural polar glacier ice measured to date.

Brine volume of sea ice is a function of the salinity and temperature of the ice, and it is related to its strength. This paper gives three equations which can be used to compute the brine volume for three temperature ranges from −0.5° to −22.9°C. A less accurate equation covering the total range is also presented.