Measurement of Short Period Motion On A Fast Moving Glacier and Analysis of Data (Abstract)

The investigation of glacier motion over short time periods for relatively long duration and over large longitudinal extent can yield valuable insight into the dynamics of glacier surging, basal sliding, ice stream development, and calving mechanisms. In this paper, we discuss techniques for monitoring short term horizontal and vertical motion employed on the often highly-fractured surface of Variegated Glacier, Alaska, prior to its recent surge (1980—84) and on the fast-moving outlet glacier — ice stream system of Jakobshavns Glacier, Greenland. The short period measurements described here were made continuously over one to several months, and, in many cases, encompass seasonal and longer term fluctuations as well. The positions of a relatively large number of surface markers (15-35) were followed as functions of time. Application of standard terrestrial surveying techniques and modern microwave and UHF positioning methods to these short period studies are discussed. We then describe methods of reduction and analysis on the resulting large data sets, which may be treated as quasi-stationary time series. Examples of correlation with other glacier variables, such as basal water pressure, seismicity, and stream discharge are given and the propagation of movement events discussed

Structure of ice III

[No abstract

A hot-water ice-coring drill

A new method of ice-core drilling uses an annulus of hot-water jets to melt out a cylindrical ice core. This lightweight device used in combination with a fast hot-water drill can quickly obtain ice cores from any depth

The Ice-Rock Interface and Basal Sliding Process as Revealed by Direct Observation in Bore Holes and Tunnels

The glacier bed, where basal sliding occurs, was reached by cable-tool drilling and sand-pump bailing in seven bore holes in Blue Glacier, Olympic National Park, Washington. Basal sliding velocities measured by bore-hole photography and confirmed by inclinometry are unexpectedly low, ranging from 0.3 to 3.0 cm/day and averaging 1.0 cm/day. This is much less than about half the surface velocity of 15 cm/day, which was the sliding-rate expected from earlier deformation measurements in bore holes made by thermal drilling alone

A direct optical method for the study of grain boundary melting

The structure and evolution of grain boundaries underlies the nature of polycrystalline materials. Here we describe an experimental apparatus and light reflection technique for measuring disorder at grain boundaries in optically clear material, in thermodynamic equilibrium. The approach is demonstrated on ice bicrystals. Crystallographic orientation is measured for each ice sample. The type and concentration of impurity in the liquid can be controlled and the temperature can be continuously recorded and controlled over a range near the melting point. The general methodology is appropriate for a wide variety of materials.Comment: 8 pages, 8 figures, updated with minor changes made to published versio

Observation of Basal Sliding of Variegated Glacier, Alaska

Variegated Glacier is a surge-type glacier in the St Elias mountain range in Alaska. The interval between surges is about 20 years; the last one occurred in 1964 to 1965. This glacier has been studied extensively since 1973 (Bindschadler and others, 1977). Thus far, measurements of ice velocities have been restricted to the surface. They have been analyzed using geophysically measured ice depths, in order to estimate ice velocities in the ice mass and at the base (Bindschadler and others, 1978). From 1973 to 1977 the distribution of annual ice velocities along most of the length of the glacier can be explained primarily by internal deformation without major contribution from sliding at the base. However, the variation of surface velocity with time gives definite indication that sliding occurs in summer and that the average summer rate is increasing progressively from summer to summer and that in a zone 5 to 7 km below the head of the glacier the summer-to-summer increase in inferred sliding rate is especially rapid. This is a notably distinguishing feature, which is probably indicative of a build-up toward the next surge. In order to obtain direct information about sliding-rates and water pressures at the base in this zone, a bore hole was drilled to the bottom of the glacier about 6 km below the glacier head. Observations in the hole started in June 1978 and were continued until 31 July 1978. The hole connected to an englacial water system at a depth of 204 m whereupon the water level dropped gradually to about 100 m below the surface. The last 6 m above-the base at 356 m could be drilled only by means of a cable tool because of the presence of debris-rich ice. Upon reaching the bottom, the water level increased rapidly to the firn water table at about 8 m below surface. Large variations in water level of about 200 m occurred during the following period of observation of 35 d. Major events such as audible icequakes, heavy rainfalls, and a period of unusually high ablation were associated with abrupt increases of water level up to the firn water table. High water pressure at the bottom drove a flow of muddy and sandy water upward in the hole. Consequently high freezing rates in the lower 150 m of the hole produced a very rough bore-hole wall covered with ledges, coral-reef-like features, grooves, and pockets filled with sand. Near the bottom, embedded rocks stuck out of the bore-hole wall. These features were recognized by bore-hole television. The bore-hole bottom consisted of sand which continuously proliferated and washed into the hole. Attempts to remove this sand by means of a sand pump failed, the bailed-out sand being replaced immediately. From bore-hole inclinometry an internal deformation of the ice mass of 0.22 m d^(−1) was obtained. Together with average surface velocity of 0.47 m d^(−1) we get a sliding velocity of 0.25 m d^(−1), averaged over the time of observation. This result confirms the sliding velocities inferred from surface velocity measurements. It also lies on the exponential trend line of increasing summer-to-summer velocities showing a doubling of sliding velocities about every two years (Bindschadler and others, unpublished). This strongly indicates that the next surge is likely to occur in the early eighties. Input of water from the surface probably will play a role in triggering the surge

Structure of ice III

[No abstract

Measurement of Short Period Motion On A Fast Moving Glacier and Analysis of Data (Abstract)

The investigation of glacier motion over short time periods for relatively long duration and over large longitudinal extent can yield valuable insight into the dynamics of glacier surging, basal sliding, ice stream development, and calving mechanisms. In this paper, we discuss techniques for monitoring short term horizontal and vertical motion employed on the often highly-fractured surface of Variegated Glacier, Alaska, prior to its recent surge (1980—84) and on the fast-moving outlet glacier — ice stream system of Jakobshavns Glacier, Greenland. The short period measurements described here were made continuously over one to several months, and, in many cases, encompass seasonal and longer term fluctuations as well. The positions of a relatively large number of surface markers (15-35) were followed as functions of time. Application of standard terrestrial surveying techniques and modern microwave and UHF positioning methods to these short period studies are discussed. We then describe methods of reduction and analysis on the resulting large data sets, which may be treated as quasi-stationary time series. Examples of correlation with other glacier variables, such as basal water pressure, seismicity, and stream discharge are given and the propagation of movement events discussed