Two models based on standard observations of precipitation, temperature, and run-off at low-altitude weather and gaging stations have been devised to calculate annual glacier balances in the North Cascades of Washington. The predicted glacier balances of the Thunder Creek basin glaciers, determined by a run-off–precipitation (RP) model during the 1920–74 period, are compared with balances predicted by a precipitation–temperature (PT) model for the same period. Annual balances determined by the PT model are also compared with balances measured by field techniques at South Cascade Glacier since 1958. In the PT model, winter snow accumulation (winter balance) is determined by winter (October–April) precipitation observed at the Snoqualmie Falls weather station. Summer (May–September) ablation (summer balance) on the glaciers is estimated by a technique which utilizes maximum and minimum air temperatures, also observed at Snoqualmie Falls. Ablation calculations incorporate summer cloud cover as a variable by using a relationship between cloud cover and the range in daily maximum and minimum air temperatures.

Annual mass changes for the 1884–1974 period in both South Cascade Glacier and the Thunder Creek glaciers were reconstructed by utilizing the PT model. The fluctuations in glacier mass during this period generally agree with historical observations and show that a definite change in glacier activity from marked recession to stability or an advancing state occurred about 1945. During the 1900–45 period, South Cascade Glacier lost mass at a rate of 1.4 m per year and the Thunder Creek glaciers (which are at a higher altitude) at 1.1 m per year.

These models suggest that the relationship of glacier mass balance to precipitation and temperature is a very sensitive one. It appears from these studies that a decrease in summer air temperature of just over 0.5 deg or an increase in winter accumulation of slightly more than 10% (350 mm) from the 1920–74 average would cause these glaciers to grow continuously.

A high-resolution radio echo-sounder operating at a frequency of 840 MHz has been developed for airborne sounding of small and medium-sized polar glaciers and ice caps. The sounder uses a compact,, high-gain antenna which suppresses valley-wall echoes and simplifies operation from light aircraft, Successful field trials were carried out on Rusty, Trapridge, and Hazard Glaciers, Yukon Territory, Canada. Results compare well with ice depths obtained from earlier ground-based soundings on Rusty and Trapridge Glaciers. The maximum ice thickness encountered was 200 m on Hazard Glacier.

Owing to the high operating frequency, random scattering from inhomogeneities within the ice is a major cause of signal degradation. For this reason the sounder cannot penetrate great thicknesses of temperate or debris-rich ice. Spatial averaging, an immediate result of operating from a moving platform, reduces the effects of back-scattered “clutter”.

Profile surveys are presented of four ice rises on the east coast of the Antarctic Peninsula. On Butler Island velocity measurements were also made. The ice rises behave as miniature ice caps frozen to flat horizontal bedrock and provide a simple system for the study of laws of ice flow. Deformation is principally by shear through the ice mass. Velocity measurements provide a value of n = 3.13±0.52 for the flow law . Each ice rise is bounded on one side by ice shelf and on the other side by open sea. Towards open sea the profiles are found to agree well with steady-state theoretical profiles and they supply a value of for temperature – 13.5°C and stress range 0.5–1.3 bar. Towards ice shelf the profiles are elongated and they deviate from the theoretical profile. This may be due to compressive stress in the ice shelf causing migration of the grounding line down sloping bedrock. No significantly anomalous behaviour is found in the summit region.

Measurements of ice velocity, thickness, and surface topography on the large ice rise known as Roosevelt Island are consistent with Glen’s flow law, , for values of τ between 5 × 104 N m–2 and 1.4 × 105 N m–2, and there is no indication of a reduction in n at low stresses. If n = 3 there must be progressive softening of the ice towards the edge of the ice rise, and this probably represents the combined effects of warming and recrystallization leading to a fabric favoring shear. Assuming that near the centre of the ice rise, where the effects of recrystallization are probably negligible, the ice behaves in the same way as randomly-oriented polycrystalline ice, then the geothermal flux G in this area is approximately 0.06 W m–2. In the absence of measurements of deep-ice temperatures, the distribution of G across the ice rise cannot be determined. However, the simplest interpretation of the movement data requires:

• (1) a linear increase in G from 0.05 W m–2 on the north-east side of Roosevelt Island to 0.07 W m–2 in the south-west, and

• (2) strain-rate enhancement, due to recrystallization, that increases outward from the centre of the ice rise to reach a maximum value of approximately two near the edges.

The calculated values of G are larger than the world average, but this is consistent with the probably granitic core beneath Roosevelt Island. An increase in G of 0.02 W m–2 in a distance of 60 km would require an increase in granite thickness of about 5 km.

The purpose of this paper is to consider an ice-sheet model based on joint solution to the dynamic equations and equations of heat conductivity in which the surface relief is one of the unknown functions. The proposed model is applicable to calculations of the Antarctic ice sheet. Results of a numerical experiment for present values of the temperature of the ice surface and precipitation as well as for their separate and simultaneous increase by 2, 4, or 6 deg and 10, 20, or 30% are given.

Glaciological results of the continuing investigations of the Quelccaya ice cap located at lat. 13° 56’ S., long. 70° 50’ W., in the Cordillera Oriental of southern Peru are presented. Ice cores to a depth of 15 m have been retrieved from the summit dome (5650 m), middle dome (5543 m), and south dome (5480 m) and sampled in detail for microparticle, oxygen-isotope, and total-β-activity measurements. Results of these core analyses indicate that although the summit of this ice cap is only 300 m above the annual snow line and the firn is temperate, an interpretable stratigraphic record is preserved. The marked seasonal ice stratigraphy is produced by the marked seasonal variation in regional precipitation. High concentrations of microparticles and β- radioactive material occur during the dry season (May-August). Microparticles deposited during the rainy season are larger than those deposited during the dry season. On the Quelccaya ice cap the most negative δ18O values occur during the warmer rainy season (the opposite occurs in polar regions). The near-surface mean δ value of – 21‰ is remarkably low for this tropical site where the measured mean annual air temperature is – 3°C The seasonality of the microparticles, total β activity, and isotope ratios offers the prospect of a climatic ice-core record from this tropical ice cap.

The microwave emission from a half-space medium characterized by coordinate dependent scattering and absorbing centers has been calculated by numerically solving the radiative transfer equation by the method of invariant imbedding. A Mie scattering phase function and surface polarization have been included in the calculation. Also included are the physical temperature profile and the temperature variation of the index of refraction for ice. Using published values of grain-size and temperature-profile data of polar firn, the brightness temperature has been calculated for the 1.55 cm and 0.8 cm wavelengths. For selected regions in Greenland and Antarctica, the results of our calculations are in reasonable agreement with the observed Nimbus-5 and Nimbus-6 ESMR data.

The way free water is distributed around contact points of ice grains is recorded by measuring the dielectric constant of the porous system which constitutes snow. Within the saturation range of 11% to 15% of the pore volume, a transitional range from the “pendular” to the “funicular” mode of distribution of free water occurs. By measuring the drainage-flow of free water through snow, additional information as to the upper limit of the pendular distribution is obtained. This upper limit is reached at a saturation of approximately 14% of the pore volume.

A dynamic constitutive law is used to study the response of medium-density snow to shock waves. The results show good correlation between theory and experiment, except for low-intensity shocks which produce small permanent density changes. In this case the validity of the data is questioned, although further experimental work is needed to settle this question. The results of this work also partially explain why snow is so effective in absorbing energy associated with stress waves. This is felt to be due to the work-hardening characteristics of snow.

Nivation is a collective noun identifying a set of geomorphic processes, comprised of an indeterminate number of elements and of unknown relative importance, for which there is little likelihood of ever producing a precise definition. Instead, attention should first be directed towards the relationships between snow-packs and individual geomorphic processes. The relationship between freezing amplitude in the bedrock, snow cover, and aspect at an Arctic site in northern Norway and an alpine site in the Front Range, Colorado, U.S.A. is complex. Comparison of field data and laboratory criteria permit several conflicting interpretations. If oscillations across 0°C, regardless of freezing amplitude, are critical, the alpine site is potentially a more active freeze-thaw weathering regime, with a primary springtime peak and a secondary fall peak. If a freezing amplitude of –5°C is required for effective freeze-thaw weathering then the alpine site is largely inactive and the Arctic active (but with only a single fall peak). Chemical weathering is much more important at snow-patch sites than has traditionally been recognized. Mass wasting at colluvial sites subject to snow patches is dominated by interaction between overland flow and solifluction when the site is unvegetated, and by solifluction when it is vegetated. Given contemporary knowledge of snow and glacial geomorphology, there appears to be no threshold, only differences of intensity. Resolution of the disruptive mechanism associated with bedrock freezing and its constraining temperature and moisture requirements is the most pressing present problem in the field of snow geomorphology.

Surface textures and angularity–roundness characteristics of quartz sand grains of till from the base of the Greenland ice sheet at Camp Century were examined with a scanning electron microscope. Two basic populations are revealed; an angular component, which shows grains with edge abrasion and attrition indicative of subglacial grinding, and a well-rounded component with the characteristics of aeolian transport. It is suggested that these two populations were mixed subglacially, the aeolian fraction having been produced at some stage before the ice sheet encroached over the area of their deposition.

A model of dislocation glide in ice Ih was recently proposed. This model was developed on certain assumptions, namely that transitions occur through cooperative movements of H2O molecules in the non-crystalline core of dislocations. A relation between the velocity vd of linear defects and shear stress τ or temperature T is obtained. This relation shows that vd varies linearly with τ at low values of τ and (or) T but varies more rapidly at higher stresses; this non-linearity is more pronounced the higher the temperature. Such an analysis is extended in order to take into account doping effects. The case of HF-doped ice is considered: it is shown that there is a strong accumulation effect of HF molecules in the dislocation cores, which induces an increase of the rate of transitions. The results are in agreement with experimental data concerning both the velocity of dislocations and high-temperature internal friction in HF-doped ice.

Uniaxial compression creep tests were performed on artificial and natural polycrystalline ices at temperatures near –7°C. The grain-size range investigated was from 1 to 10 mm. Contrary to previous results, the permanent creep-rate was not found to increase with crystal size. Only the transient creep appears to be sensitive to variations in crystal size.

Brillouin spectroscopy has been used to measure the adiabatic elastic constants of laboratory-grown pure monocrystalline ice Ih at – 3°C. The values obtained were (in units of 108 N/m2): c11 = 136.96 ±0.60, c12 = 69.66± 0.45, c13 = 56.28±0.31, c33 = 147.02±0.68, c44 = 29.59±0.15. Comparison of these values with ultrasonic measurements quoted in the literature reveals no significant acoustic dispersion in ice over frequencies ranging to 1010 Hz. However, the results suggest that the elastic constants of ice may depend on the precise crystal quality and age of a given sample. The low experimental error in the values obtained, along with the inherent versatility of the method, indicate that Brillouin spectroscopy is an effective technique for systematically investigating the elastic properties of ice samples formed under natural conditions.

A core drill capable of drilling to more than 100 m depth in cold ice is described. It is designed with a view to fast operation and easy transport, core handling, and maintenance.

Increasing interest is being directed toward studies involving measurement of strain and strain-rates in sea and glacier ice. A number of techniques for obtaining these data over gauge lengths ranging from 1 m to several kilometers have been reported, but there has been little experience with shorter lengths. Use of commercially available electrical resistance strain-gauges (length 5–20 cm) intended for embedment in concrete offers a new approach in which multiple gauge, two- and three-dimensional arrays can be installed in ice with minimum effort and monitored with portable equipment. This report describes a pilot study designed to demonstrate the use of three types of electrical resistance strain gauges in sea ice under exposed field conditions. Results include detection of variations in strain fields related to tidal currents.

We discuss the possibility of the occurrence of thermal instability in ice sheets and glaciers. This may arise from the non-linear viscous heating term, which could provide for the existence of multiple steady states in the flow and temperature fields: a word of warning is given about the applicability of these ideas.

An approximate calculation is made of the rate at which a bottom crevasse in a cold ice shelf or tabular iceberg can close shut by freezing of water and can creep open through the creep deformation of ice. In all but the thickest ice shelves and icebergs, those with a thickness greater than about 400 m, the freezing process is the more important mechanism if the ice is cold (< – 10°C). Consequently in a cold iceberg or ice shelf a bottom crevasse, once formed, will freeze shut.