The evidence for the existence of small glaciers in the cwms of the Caernarvonshire mountains during the Late-glacial Period is presented, and by an analysis of their distribution some of the factors responsible for their formation are deduced. These were primarily protection from insolation, drifting of snow into the cirques by wind and the distribution of precipitation.

The acoustic televiewer is a geophysical logging instrument that is deployed in a water-filled borehole and operated while trolling. It generates a digital, magnetically oriented image of the borehole wall that is developed from the amplitudes and transit times of acoustic waves emitted from the tool and reflected at the water–wall interface. The transit-time data are also converted to radial distances, from which cross-sectional views of the borehole shape can be constructed. Because the televiewer is equipped with both a three-component magnetometer and a two-component inclinometer, the borehole’s trajectory in space is continuously recorded as well. This instrument is routinely used in mining and hydrogeologic applications, but in this investigation it was deployed in two boreholes drilled into Upper Fremont Glacier, Wyoming, U.S.A. The acoustic images recorded in this glacial setting are not as clear as those typically obtained in rocks, due to a lower reflection coefficient for water and ice than for water and rock. Results indicate that the depth and orientation of features intersecting the boreholes can be determined, but that interpreting their physical nature is problematic and requires corroborating information from inspection of cores. Nevertheless, these data can provide some insight into englacial structural characteristics. Additional information derived from the cross-sectional geometry of the borehole, as well as from its trajectory, may also be useful in studies concerned with stress patterns and deformation processes.

Measurements of the event rate of natural, small-amplitude displacement accelerations in potential fracture zones of avalanches prove to be good indications for decrease of stability.

No single flow model can simulate all possible glaciers and ice sheets without violating fundamental tenets of computational science. The root cause is not one of numerical sophistication, precision or accurate initial conditions. Instead, using flow and transport as data transmission, glaciers inadvertently function as information processors. This computational capability confers a level of complexity that inherently limits our ability to accurately and efficiently predict glacier flow and therefore, for example, to forecast those aspects of climate systems that depend on glaciers. In particular, even with considerable future advancements in glacier physics, computational theory shows that no dramatic improvements in numerical speed are likely when compared to today’s glacier models. Therefore, to increase speed and resolution, the next generation of climate and sea-level models must rely on simulations tailored to specific ice-sheet geometries rather than general-purpose glacier flow models. However, because glaciers process information, entirely new computation-theoretic advances in glaciology are possible, and concepts from information entropy may help to define new glacier scaling relationships and identify which geometries will be most problematic for modeling.

Results of determinations of proton magnetic relaxation time (T1) in the liquid phase of frozen sea water at temperatures between −2°C and −38°C, with variable rate and direction of temperature change, are presented. Temperature hysteresis corresponding to the crystallization range of certain sea-water salts, mainly NaCl which partially precipitates as the crystalline hydrate NaCl.°2H2O at temperatures below −23°C, is detected in the temperature dependence of T1, as in the analogous dependence of brine content. It is shown that formation of crystalline hydrates in brine is preceded by complete solvation of ions at −5 to −6°C. The main causes of hysteresis in temperature dependence of T1 and the extension of loop limits compared with the analogous loop for liquid brine content are indicated. Additional potentialities of using the nuclear magnetic resonance method for investigating sea-ice properties are presented.

By 1969 considerable data had been collected over Law Dome from surface measurements. These included surface elevation, ice thickness, accumulation rates, ice movement and strain-rates, surface mean temperatures, and several temperature-depth gradients. Since then core drilling up to 380 m in depth has been carried out from the summit to the coast where the cores reached close to the bed. The bore holes have been concentrated on two main flow lines: one to Cape Folger and the other to Cape Poinsett. The bore-hole temperatures give a clear indication of the temperature distribution throughout the ice cap.

Numerical modelling shows that the measured deep temperatures closely match the steady-state temperature distribution calculated from the present regime. The variations in the temperature profiles over the dome are primarily associated with the flow regime.

The Cape Folger line has low accumulation rates and low velocities which results in positive surface temperature-depth gradients increasing towards the coast. By contrast the Cape Poinsett line has high accumulation rates and high velocities which result in a large negative temperature-depth gradient there. The profile at the Dome summit is close to isothermal primarily due to the high accumulation rates and lack of horizontal motion.

In order to determine the effect of basal debris drag as a component in a sliding law, it is necessary to know the basal debris concentration. Does, for example, this debris concentration exhibit uniformity, in an average sense, across a valley? What effect does a localized region of high quarryability have on basal debris concentration down-stream? The analysis presented here suggests that, for the case of sparse debris, debris concentration tends to be uniform over the entire bed. Consequently, the debris-drag term in a sliding law will also tend to be uniform.

In order to reach the above conclusions, it is necessary to consider debris balance, the balance of the quarrying, abrasion, and debris-flushing rates. This entails proposing and testing quarrying and flushing laws, since these laws have not been previously proposed. It is concluded that the quarrying, flushing, and erosion rates depend weakly on the sliding velocity. Furthermore, the abrasion rate is negligible compared to the quarrying rate. (This conclusion depends partially on the definition of abrasion.) The quarrying rate also depends on other factors such as the effective pressure_pressure-fluctuation mechanism; the cross-valley dependency of this mechanism is investigated. The flushing rate is found to depend on the ratio, N-channel area/bed area, and on average N-channel diameter.

To study the dynamics of ice sheets and glaciers, velocities at the bed of a glacier must be measured directly or calculated using data gathered from boreholes and surface surveys. Boreholes to the bed are expensive and time-consuming to drill, so the determination of basal velocity is almost exclusively by numerical inversion of velocities observed at the surface. For non-linearly viscous glaciers, a perturbation analysis demonstrates that inversions for englacial velocities will magnify measurement errors at an exponential rate with depth. The rate at which calculation errors grow is proportional to a Lyapunov exponent, a measure of “information loss” which is shown to be a simple linear function of spatial frequency with a coefficient depending on Glen’s flow-law exponent, n. The coefficient decreases with increasing non-linearity, demonstrating that inversions with non-linearly viscous ice have smaller calculation errors than inversions with linearly viscous ice. In both the linear and nonlinear cases, the Lyapunov exponent (and rate of error growth) increases with decreasing wavelength, which limits velocity calculations at the bed to wavelengths on the order of one ice thickness or greater. This limitation is theoretical and cannot be countered by more accurate survey data or special numerical techniques.

By comparing the recorded run-off from a precipitation district, about 55 per cent of which is covered by glaciers, to the run-off from a neighbouring district without glaciers it has been possible to determine the changes in the glacier mass of Jostedalsbreen. In the period 1900 to 1940 the annual decrease of the glacier mass was equivalent to 0.4 m. of water times the glaciated area. A close relationship is established between the change of the glacier mass and the length of one of the outflow glaciers, Brikadalsbreen. It is shown that the change in the glacier mass is related to the summer temperature and, to a minor extent, to the amount of winter snowfall.

An electrodynamic containment system has been used to study the freeezing behaviour of supercooled water drops, of radius range 25 to 90 μm. The drops were freozen at temperatures between 0 and — 29°C in an environment whose relative humidity was approximately 90% with respect to ice. Freezing events were observed visually and photographically, and measurements were mager of the accompanying freactional mass loss Δm/m.

The most common moger of freeezing (70% of the drops studied) resulted in an apparently spherical ice particle. However, 18% exhibited spikes or other protuberances and the freeezing of 3% was accompanied by the ejection of numerous ice particles. In each of these situations values of Δm/m ranged freom about 5 to 15%. A further 9% of the drops exhibited one or more secondary mass-loss events, occurring several seconds after the freeezing process was complete; these were thus indicative of the ejection of ice particles.

Almost all of the values of Δm/m were significantly in excess of those predicted on the basis of evaporation during freeezing, suggesting that an additional mechanism of mass loss was also present. The measured freeezing times were consigerrably shorter than the classical values—at least, for the larger drops freeezing at warmer temperatures. Some visual observations were consistent with the “supersaturation wave” around a freeezing drop, which has been predicted by Nix and Fukuta (1974).

As part of the feasibility study for the development of an open-pit mine at the edge of the Greenland ice sheet, a study is made of the ice flow toward the proposed pit. The flow is analyzed by considering the two-dimensional flow along seven cross-sections. The most favorable profile is determined for each cross-section and its flow calculated. The excavation necessary to expose the ore is 106 × 106 m3 of ice. 66 × 106 m3 of ice will have to be removed in order to establish favorable profiles and an additional 7.9 × 106 m3 of ice will have to be removed each year in order to prevent the glacier from thickening and advancing into the mine. Many other glaciological problems must be considered, and field work continues in order to provide more information about the area.

A newly discovered pothole field in the White Mountains, N.H., is described, and is attributed to action of melt water from the last continental glacier. Discordance of pothole orientation with slope direction is explained by inferring the presence of a retaining wall of ice which controlled stream flow direction during the period of pothole formation. The potholes constitute the highest evidence of continental glacial drainage yet known in New England.

Radio-echo returns from internal reflectors were monitored for three weeks during surge motion on Variegated Glacier, Alaska in July 1982. A monopulse transmitter with 3 MHz center frequency was fixed on the glacier surface near the equilibrium line. Data were recorded on magnetic tape approximately three times daily and contain both amplitude and phase information. The frequency spectrum of returned radiation from englacial scatterers shows peaks in the 12 to 30 MHz range which places constraints on the size and geometry of the scatterers. Timing of variations in the amplitude and frequency of returned radiation were found to coincide with changes in glacier velocity, basal water pressure, and surface melt rate. These changes in the echo pattern are interpreted in terms of the redistribution of water in englacial channels and cavities connected to the bed some distance down-glacier. This connection has large hydraulic resistance compared to a bore hole connected vertically to the bed. The inflow of water to the cavities from surface melt and rain and the drainage are generally in equilibrium except in times of changed surface input and during surge pulses. In the latter case, water may fill these cavities due to increased pressure at the bed associated with the motion pulse. The information obtained is therefore complementary to bore-hole water pressure levels but cannot duplicate it. This is apparently due to fundamental differences in the hydraulics of the natural cavity and conduit system, and a bore hole connected vertically to the bed.