A partly phenomenological theory and model are constructed of cyclically surging glaciers. During the after-surge portion of a surge cycle the lower portion of a glacier becomes increasingly stagnant. The upper part of the glacier gradually becomes more active as both its thickness and the magnitude of its basal shear stress increase. In the region between these two parts, called by us the trigger zone, the value of the derivative of the basal shear stress in the longitudinal direction of the glacier gradually increases with time. The pressure gradient in the water at the base of a glacier is related to the derivative of the basal shear stress. The pressure gradient decreases as the basal shear-stress gradient increases. The pressure gradient actually can take on negative values, a condition which produces “up-hill” water flow at the base of a glacier. A surge is started in the trigger zone when water is dammed there by a zero water-pressure gradient. The zone of fast-sliding velocities propagates up the glacier from the trigger zone with a velocity of the order of a surge velocity. The fast-sliding velocity zone also propagates down the glacier because of increased melt-water production.

Methods are developed for determining the distributions of stress and effective viscosity in a glacier, under the assumptions: the ice is quasi-viscous, the flow is time independent, and acceleration forces are negligible. Measurements of the three-dimensional distribution of velocity are needed for their application. The differential equations of mechanical equilibrium, expressed in terms of viscosity, strain-rate components, mean stress, and their gradients, are viewed as equations to be solved for viscosity and mean stress subject to boundary conditions at the free upper surface. For certain rectilinear flow patterns, unique distributions of stress and effective viscosity can always be derived. For more complicated flow this is not necessarily so. However, it is still possible to choose the best values of rheological parameters in any trial flow law based on the requirement that the residuals to the equations of equilibrium be minimized in a mean-square sense. The techniques are applied to measurements of internal deformation made in nine bore holes on the Athabasca Glacier. At the center line the magnitude of the surface-parallel shear stress increases with depth more slowly than would be expected from a standard shape factor correction or the theoretical distribution of Nye. Correspondingly the lateral distribution of lateral shear stress shows the opposite relationships. In the lower one- to two-thirds of the depth corresponding to a range in effective stress from about 0.5 to 1.2 bars, the gross rheology of the ice is not distinguishably different from the experimentally determined flow law of Glen (n = 4.2, T = 0.02° C) as generalized by Nye. The results do not support the conclusion that the effective viscosity is higher than would be expected from Glen’s experiments as indicated by the more limited measurements of Paterson and Savage. Power-law parameters derived for the different bore holes considered separately show a spread, which suggests some rheological inhomogeneity. However, no definite conclusions can be drawn, because of direct measurement errors at the bore holes and less definable uncertainty in the interpolated distribution of velocity between the holes. The upper one- to two-thirds of the glacier constitutes an anomalous zone in which there is either a strong effect from a complex distribution of stress arising from longitudinal stress gradients or more complicated rheology than in a homogeneous power-law material.

Budd’s expressions for strain-rate gradient along the centre line of a bounded ice shelf are shown to be applicable only to ice shelves with almost constant thickness and very small longitudinal strain-rates. A general expression is derived for creep in an ice shelf where the sole restriction is that of zero shear stresses in vertical planes. This is applied to the two special cases:

• (1) movement of an ice shelf restricted in at least one direction by sea-water pressure only;

• (2) movement of an ice shelf flowing between roughly parallel sides.

Available measurements of creep rates and dimensions of ice shelves are used, in conjunction with equations derived in a companion paper (Thomas, 1973), to evaluate the flow law parameters B and n for stresses down to 104 N m−2. The results show good agreement with laboratory work at higher stresses. Adoption of these values of B and n enables us to examine the restraining effects on an ice shelf of obstructions such as areas of grounding.

Uniaxial compressive creep tests were performed on polycrystalline samples of glacier ice at stresses ranging from 0.06 bar to 1.0 bar under conditions similar to those actually occurring in a temperate glacier. Tests were conducted in an ice tunnel on the Blue Glacier, Mt Olympus, Washington, U.S.A., thus ensuring that the temperature remained at the pressure melting point.

The flow law proposed as an appropriate one-dimensional flow law for temperate glacier ice is a polynomial expression containing linear, cubic and fifth-order terms. This law provides a good fit to the data and is also consistent with the quasi-viscous creep data of Glen (1955).

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.

Conical mounds of ice have been observed to form in a few hours during violent winter storms along the edge of shore-fast ice near Dunkirk, New York. They occur in lines which parallel depth contours, and are evenly spaced in the manner of beach cusps. The height and spacing of mounds and number of rows vary from year to year depending on such factors as storm duration and intensity, and the position of the edge of the shore-fast ice at the beginning of the storm.

The evenly sloping conical mounds have central channels which increase in width lakeward. The ice between the channels forms headlands above the lake surface. Spray-formed levees develop along the headlands and slope gently away from the lake margin. Lake marginal walls of ice are usually vertical.

Spray, slush and ice blocks are ejected over the cone as each successive wave is focused by the converging channel walls. Ice blocks, interlayered with frozen slush and dirt, form bedding paralleling the sloping surface of cones, headlands and levees. These features are here termed “ice volcanoes” because their origin is in so many ways analogous to that of true volcanoes.

Seismic refraction and reflection shooting was carried out along three profiles about 10 km long, angled 60° to one another, near “Byrd” station, Antarctica, during the 1970–71 field season. No dependence of velocity upon azimuth was found, but velocities at 200 or 300 m depth were slightly greater than at a site 30 km away where measurements were made in 1958. The difference can probably be attributed to different ice fabrics arising from a 50% difference in snow accumulation rates at the two sites. The velocity depth and density–velocity functions at the two sites are also significantly different, but close agreement was found at each site between the depths to significant changes in the velocity gradient and the depths of fundamental change in the densification process. Such agreement may permit density–depth curves, and consequently accumulation rates, to be measured by seismic refraction shooting alone.

The reflection shooting on a common reflection-point profile led to a good determination of mean velocity through the ice as a function of angle of incidence. The results agree closely with similar measurements at the 1958 site, and with an anisotropic model based on glaciological and sonic logging observations in the deep drill hole. The mean vertical velocity of 3.90–3.93 km/s through the solid ice is about 2% higher than has commonly been used for determinations of ice thickness from seismic reflection shooting.

A study of Hoseason Glacier was made to test whether photogrammetry could yield meaningful glaciological information from repeated series of air photographs without ground control. Three maps indicate that large time differences, different camera systems, and the use of sea ice as a level datum do not present insurmountable difficulties in photogrammetric reduction. Surface horizontal movement was determined and level profiles were compiled. Hoseason Glacier is probably in equilibrium.

The mass transfer on an ice surface was measured using a groove decay technique on (0001) plane and <1010> direction at −10° C. The evaporation–condensation and viscous flow terms in Mullins’ theory were deduced from the change of decay constant as a function of groove wavelength between 16 and 80 μm. A viscous flow term contributes the most to groove decay while an evaporation–condensation term contributes up to 31.5% of the mass transfer for the shortest wavelength measured and other terms were found to be negligible. Large discrepancies between the decay constants obtained from the measurements and constants calculated from theory indicate that other mechanisms not considered in Mullins’ theory may be responsible for the groove decay.

A 51 mm diameter bore-hole camera allows observation of subglacial conditions, measurement of basal sliding rates, and study of internal structure and debris in ice at depth. The camera is simple in construction, field operation and maintenance. Water turbidity is a significant problem but it can be overcome by pumping.

“Postglacial”, with a capital “P”, is a chrono-stratigraphical unit starting with the Preboreal at 10 000 B.P. De Geer used the same name for a period covering approximately the last 8 900 years. The same word “postglacial”, with a small “p”, is a genetic facies term telling us that the sediments were deposited without influence of the receding ice (in contrast to glacial deposits).

An abrupt change in radio echo sounding travel time was observed on the ice shelf near McMurdo station, Antarctica, and was mapped by a zig-zag traverse. This boundary corresponds to the horizontal extent of brine penetration into the edge of the ice shelf.

Acoustic emissions in the audio spectrum are reported from observations of laboratory experiments conducted on snow samples in uniaxial compression. A number of tests show the pattern of acoustic emissions to be a function of the rate of deformation. Over the frequency range 20 to 7 000 Hz acoustic emissions are associated with rates of deformation corresponding to brittle fracture of the snow sample. Though probably present, no acoustic emissions were detected from samples deforming plastically.