ALBERT

Beschreibung: Although radio echo sounding equipment has been used with success for measuring the thickness of ice sheets in the Arctic and Antarctic, a valley glacier poses the additional problems of echoes from the valley walls, which may obscure the bottom echoes, and a high attenuation of radio waves in the ice. During July and August 1970, a study was carried out on Roslin Gletscher in Stauning Alper, East Greenland, to investigate the problems of radio echo sounding on a valley glacier. Results show that reflections from the valley walls are minimized by using sufficiently directional antennae, but attenuation of the signal in the ice is higher than that in polar ice at the same temperature. Water in and on the ice probably accounts for much of the attenuation, and the use of a lower frequency or measurements before the melt commences should give improved performance.

Beschreibung: Although radio echo sounding equipment has been used with success for measuring the thickness of ice sheets in the Arctic and Antarctic, a valley glacier poses the additional problems of echoes from the valley walls, which may obscure the bottom echoes, and a high attenuation of radio waves in the ice. During July and August 1970, a study was carried out on Roslin Gletscher in Stauning Alper, East Greenland, to investigate the problems of radio echo sounding on a valley glacier. Results show that reflections from the valley walls are minimized by using sufficiently directional antennae, but attenuation of the signal in the ice is higher than that in polar ice at the same temperature. Water in and on the ice probably accounts for much of the attenuation, and the use of a lower frequency or measurements before the melt commences should give improved performance.

Beschreibung: When rectangular single crystals of ice were subjected to uniaxial compression parallel to their Long axes and viewed between crossed polarizers, interference fringes were often observed. Some of these interference bands were associated with grain boundaries formed as a result of “kinking”. These can be explained in terms of the known anisotropic optical properties of ice and the change in the orientation of the optic axis across the boundary. This case has been analysed in detail with the aid of Jones’ calculus and good quantitative agreement exists between the theory and the experimental observations.Other interference bands were observed parallel to the trace of the basal plane on the surface of some deformed crystals. Alternative hypotheses for the explanation of this phenomenon have been considered and it seems probable that these bands are a result of slight random misorientations between adjacent slip lamellae. Applying Jones’ calculus to a simple model of such a deformed crystal indicates that the required misorientations are of the order of 1º If this explanation is correct, it implies that dislocations with non-basal Burgers vectors (probably c[0001]) make an active contribution to the deformation.

Beschreibung: Seasonal changes in the extent of snow cover and pack-ice were analysed in the satellite-derived maps of the Northern Hemisphere obtained during the last 5 yr. Two intervals were studied in detail: summer 1968 to summer 1969 and summer 1971 to summer 1972. These studies demonstrate that the variation in ground albedo as a result of changing snow and ice cover affects the Earth's energy budget to a far greater degree than any possible extraterrestrial mechanism could do on such a short time scale. However, the rapid expansion of snow cover between late September and November suggests possible feed-back process which could be speeded up or slowed down by minute changes in energy and moisture budget at the snow accretion area. These changes may be of any origin, natural or artificial, and on the time scales ranging from days to millenia.In this context, the close correspondence between the radiometrically dated gross climate changes within the past 150,000 yr and between the curve showing the rate of change in winter insolation for the middle latitudes of the Northern Hemisphere is conspicuous. The periodicity of about 20,000 yr is involved.An insolation chronology is introduced here, which is based entirely on astronomic factors (on the so called Milankovitch mechanism of Earth orbital elements). It is independent of any geologic or geochronologic dating systems. Two alternating units comprise the insolation chronology. The positive insolation regime (PIR) is an episode defined by progressively increasing winter irradiation in the Northern Hemisphere, whereas the negative insolation regime (NIR) is an episode of progressively decreasing winter irradiation. The PIR closely correlates with the generally warm intervals such as interglacials and temperate interstadials, the NIR with generally cold intervals. This basic pattern interferes with short-term oscillations which may retard or advance the climate response on the scale of centuries.It is observed that the positive insolation regime designated as PIR 110, which started at 11,000 YBP, has ended recently. The new negative insolation regime, NIR 0/ + 8, will last for the next 8000 yr. Inasmuch within the last radiometrically dated 150,000 yr no NIR is known to correlate with generally warm interval, the prognosis is for a long-lasting global cooling more severe than any experienced hitherto by civilized mankind.

Beschreibung: A new method of electromagnetic sounding in resistive electrical environments has been developed for use in lunar exploration. It is applicable to the study of terrestrial glaciers and ice sheets. A horizontal electric dipole antenna on the ground is used to transmit power at frequencies of 1, 2, 4, 8, 16 and 32 MHz. A set of orthogonal receiving coils is mounted on a vehicle which traverses away from the transmitter. Field strength is recorded as a function of distance. Waves which travel above the surface interfere with waves from the subsurface, generating interference patterns which can be used to determine the dielectric constant, the loss tangent, and depth to reflecting horizons.The technique was tested on the Athabasca Glacier in western Canada. At 1, 2 and 4 MHz the ice was found to have a dielectric constant of about 3.3, a loss tangent (tan δ) which is roughly inversely proportional to frequency giving values off tanδ in the range 0.25 to 0.35 (wherefis in MHz). These values correspond well with the known properties of ice near 0° C, which is a temperature typical of temperate glaciers. It has been possible to determine the depth of the ice but results are not always consistent with previous seismic and gravity surveys and with drilling. At frequencies of 16 and 32 MHz, scattering is the dominant feature of the results. At 8 MHz there is a transition from clear-cut interference patterns to the scattering patterns. From these findings, we suggest that the Athabasca Glacier has a large number of dielectric scatterers with dimensions less than about 35 m, probably due in large part to crevasses.

Beschreibung: The two medial moraines of the Glacier de Tsidjiore Nouve are nourished by rock debris revealed at the surface by progressive ablation down-glacier. The sources of the moraine appear to be rock outcrops marginal to or above the Pigne d’Arolla ice fall, much of the detritus entering the glacier via crevasses either at the summit or the base of the ice fall. The role of differential ablation in the emergence of the moraines as relief features is illuminated by measurements made in the late summers of 1971 and 1972. The eventual decline of the moraines down-glacier is related to factors of reducing debris supply, lateral sliding and accelerated ablation due to attenuation of the detrital cover to a mean thickness of 1 cm or less. A model of moraine development, different in several respects from that proposed by Loomis (1970) for the Kaskawulsh Glacier, Alaska, is outlined.

Beschreibung: Measurements were made of the vertical electric field Strength around snow cornices on Bridger Ridge (2 590 m a.s.l.) in the Bridger Range, South-western Montana. The fields were considerably enhanced, owing to the exposed position of the cornices, but were nevertheless appreciably lower than those shown by Latham and Saunders (1970[b]) to be necessary in order to provide significant additional bonding when ice crystals collide with an ice surface. However, measurements made on Bridger Ridge and neighbouring Bangtail Ridge showed that the charges carried on snow crystals saltating over the surface of cornices were close to their limiting values.Rough calculations indicated that pressure melting is unlikely to be of importance in the development of snow cornices formed from granular crystals, that frictional melting is probably significant only at fairly low temperatures and moderately high wind velocities, and that strong electrostatic forces between highly charged snow crystals saltating over the surface of a cornice may be sufficient to provide bonding where the crystal velocities are comparatively low.

Beschreibung: Measurements were made of the vertical electric field Strength around snow cornices on Bridger Ridge (2 590 m a.s.l.) in the Bridger Range, South-western Montana. The fields were considerably enhanced, owing to the exposed position of the cornices, but were nevertheless appreciably lower than those shown by Latham and Saunders (1970[b]) to be necessary in order to provide significant additional bonding when ice crystals collide with an ice surface. However, measurements made on Bridger Ridge and neighbouring Bangtail Ridge showed that the charges carried on snow crystals saltating over the surface of cornices were close to their limiting values.Rough calculations indicated that pressure melting is unlikely to be of importance in the development of snow cornices formed from granular crystals, that frictional melting is probably significant only at fairly low temperatures and moderately high wind velocities, and that strong electrostatic forces between highly charged snow crystals saltating over the surface of a cornice may be sufficient to provide bonding where the crystal velocities are comparatively low.