Climate studies using ice cores require knowledge of the ice deformation at a detailed level, obtainable only by integrated surveying and flow modelling. Field programs should consider model abilities and requirements at the planning stage. Strain and topographic surveys should enclose the flowlines to all boreholes and extend beyond. Only then is it possible to (1) calculate representative slopes at the drill sites and (2) use simple boundary conditions at locations where they do not affect the calculated flow near the holes. Mass conservation models, which may include a parameterized velocity field, estimate the imbalance between integrated accumulation and ice discharge. Momentum conservation models find the actual velocity field, and can reveal a more detailed flow history, but require detailed survey information for boundary conditions. A mass conservation model suggested that flow near core sites at Agassiz Ice Cap, Ellesmere Island, had been steady for more than 3000 years; however, a momentum conservation model showed that either the present transverse strain rate is much smaller than required by the mass conservation model, or the ice is much stiffer than accepted values. It also revealed transients in the flow and microclimate οf which the impact on the derived climate still needs to be assessed by integrated modelling and surveying.

A 1984 strain net on the Snowdome of Blue Glacier showed that the surface slope is a good estimator of ice flow direction and divide location. Topographic maps from 1939, 1952, 1957, 1979, and 1984 show that the flow divide migrates within a zone up to 350 m wide, in response to changes in east-west gradient in snowfall. This zone encloses 6% of the Blue Glacier accumulation area and up to 10% of the year-end residual snow. An ongoing 28-year mass-balance study has used an extreme, westerly divide, giving systematically high net balance estimates. The correct catchment area, for a given balance year calculation, depends on the future migration sequence of the ice divide, with a time constant of about 30 years.

Topographic sketch mapping of the whole ablation area of the Khumbu Glacier, East Nepal Himalaya, is performed, using a simple, stereo-photogrammetric method. This map shows that the surface morphology can be classified into 11 morphologic characteristics. Depending on their distribution and combination, the ablation area can be divided into four morphologic areas. Detailed maps, on a scale of 1:1000–2500, of these four areas indicate that the distribution and combination of these 11 morphologic characteristics result from thickness of the debris cover, supraglacial streams and ponds, and glacier dynamics. The irregularity in the ablation area of the Khumbu Glacier can be considered to be a consequence of the mass balance between rate of ice charge from upstream and irregular distribution of ablation rate, depending on debris-cover characteristics in situ.

Ice can become “hidden”, i.e. buried, by the superimposition of rock debris on a glacier or where rock debris may incorporate interstitial ice. Because it is obscured, problems result from a lack of understanding of the extent and continued activity of such ice. Landforms may be associated with this phenomenon and can be used as indirect evidence of its existence. A rock glacier can contain glacially-derived, buried ice as well as interstitial ice. We show, with examples, how such rock glaciers can be identified and provide information on the extent and possible volume of hidden ice in marginally glacierized and permafrost areas. In most cases, recognition of topography is sufficient, although time-separated aerial photographs may be necessary to locate the extent of ice. These are generally preferable to, and more cost effective than, most detailed on-site determinations of ice extent. It is possible to incorporate and extend knowledge of hidden ice in glacier mapping and inventory projects.

All sources of cartographic, aerial photographic, satellite image, and related data, from the 18th century to the present, for the eight geographic groups of Iceland’s glaciers, were evaluated for use in preparing a preliminary inventory of Iceland’s glaciers, based on information requirements of the Temporary Technical Secretariat for World Glacier Inventory. On the basis of an evaluation of all sources of historic and modern data for the Langjökull Group, the 1:50 000 scale U.S. Army Map Service Series C762 maps of Iceland were determined to be the best maps from which to derive information for a preliminary inventory, as long as the limitations of these maps are considered and accommodated. The fluctuations of Langjökull’s principal outlet glaciers on maps and Landsat images were found to be consistent with field observations at the International Hydrological Decade monitoring stations. Accumulation area ratios were calculated from late summer snow lines on 1973 Landsat images of Vatnajökull (0.70), Langjökull (0.78), and Mýrdalsjökull (0.35), Measurements of the area of the now stagnant glacier on Ok showed a rapid reduction in area (68 per cent) between 1910 and 1960, but a decline in rate of wastage since 1960 (73 per cent between 1910 and 1978). From 1910 and 1945 topographic maps, the volume of the glacier on Ok was found to be reduced by 0.62 km3.

Glacier mapping is steadily developing, along with the continuous expansion of glaciological research, in China. In the last 20 years we have made surveys and drawn up glacial topographic maps on large scales, of various study areas in Tianshan and the Qinghai-Xizang Plateau. This paper discusses the cartographic techniques, in the form of points, lines, symbols, brush-shading, colours, etc., used to create a vivid reproduction of the special natural landscape of glaciers on maps for the use of glaciologists and other scientists. For example, variations in rock symbols may be used to show the exposed bedrock, the glacial abrasion and the cryogenetic weathering. Different colours and points are used to indicate the various depositional landforms which are also enhanced by the method of brush-shading and the use of differently coloured contour lines. In addition, the paper discusses the technical and theoretical problems of glacier mapping.

A map of the surface elevation for the southern half of the Greenland ice sheet has been produced from data gathered by the radar altimeter on board the SEASAT satellite. From June 1978 until September 1978, useful data were collected during most passes over the ice sheet, but data was not collected continuously along each pass. Over 85 000 separate ranges were obtained from the satellite to the surface at points spaced 662 m apart along each orbital pass.

Techniques required for the reduction of the recorded return waveforms to surface elevations have previously been described in a series of papers (Martin and others, 1983; Brenner and others, 1983; and Zwally and others, 1983). Once all corrections have been applied to the range data due to atmospheric effects, ocean and earth tides, and orbital perturbations, the set of ranges at orbital crossing points (where ascending orbits crossed descending orbits) had a mean relative error of 2.9 m, with a standard deviation of ±2.9 m. Elevations over the flatter and smoother portions of the ice sheet have a precision as small as ±0.25 m, while data over sloping and rough areas are of lower quality. Along each orbital track, the data are corrected for the slope-induced error.

The reduced set of surface elevations has been interpolated to assigned elevation values at the nodal points of a regular grid with a 10 km spacing (polar stereographic projection). This grid was then contoured at intervals of 50 m above 2400 m altitude and 100 m at lower elevations. Similar grids of slope-induced error corrections were contoured to provide some measure of its effect on the data. Ancillary plots of parameters of the fitting and gridding process are included to help in estimating the quality of the derived surface topography in different regions.

The surface elevation contour map shows the existence of distinct drainage basins within the ice sheet — most notably in the southern and eastern areas. This detail will prove most useful in the delineation of these basins for hydrological or glaciological studies. In combination with ice-thickness data, these elevation data permit a more accurate measurement of the bedrock elevation. The corrected altimeter data in orbital-pass and map format have been provided to the National Space Science Data Center at Goddard Space Flight Center and to the World Data Center-A, Glaciology, as a source of information to be used by other scientific investigators. These data have already been used to produce detailed maps of the topography in more localized areas (e.g. Figure 2, from Zwally and others, 1983 and Figure 2 of Bindschadler, 1984).

A comprehensive, airborne survey of the Vanderford and Adams glaciers was started in January 1983, continued through the austral summer season 1984/5, and completed in February 1985.

Ice-thickness and surface-elevation data were collected over some 4500 square kilometres, on a grid spacing of approximately 5 kilometres.

The measurement system was based on a Bell 206 helicopter, fitted with ANARE 100 MHz ice radar, Motorola Mini-Ranger navigation equipment, and a digital, pressure altimeter. A JMR, satellite, doppler receiver was used to position the navigation ground stations precisely. Gravity measurements were used to fill in ice-thickness coverage, where the ice radar failed to produce an echo and also to help determine where the glacier was floating.

Ice-movement profiles were measured across the front sections of the glaciers and additional spot values were obtained further upstream by utilizing the 3 m accuracy of the navigation equipment to locate markers quickly at both the beginning and end of the season’s work.

A data logger in the helicopter recorded time, navigation distances, aircraft to ground clearance, and air pressure, at 10 second intervals. These data were later merged with manually-scaled, ice-thickness values, for computer processing.

The results show that the Vanderford glacier dominates the system and drains about 5 cubic kilometres of ice per annum, mainly from the inland ice sheet to the south. Ice flowing into the Adams Glacier tends to come from nearer the coast and to the south and west of the glacier. Bedrock topography beneath the Vanderford shows that the deep, inland trench, similar to that found below other outlet glaciers, drops to 2500 m below sea level, 60 kilometres from the front. The trench has steep sides to the east and gives a clearly-defined edge to the fast glacier flow. The western side, however, is much more complicated, particularly further inland, where the flow is not clearly separate from that of the Adams glacier.

Glaciers can be separated into two classes according to their flow behaviour: normal (relatively steady, annually-averaged, flow rates) and surge-type (pronounced non-annual fluctuations in flow rates). Using glacier inventory data, we compared the population statistics of 1637 normal and surge-type glaciers in the St. Elias Mountains, Yukon Territory, Canada. Within the 38 drainage basins analysed, there is a pronounced spatial variation in the concentration of surge-type glaciers, but no obvious environmental control can be evinced. Analysis of the length distribution function for surge-type glaciers reveals that long glaciers (length exceeding 15 km) have a greater tendency to be surge-type than short glaciers.

The mass balance and sensitivity of calculated mass balance to uncertainties in the data and in the model for the variation of ice velocity with depth are addressed, using data from the EGIG transect and from the OSU transect in south Greenland (Drew and Whillans, 1984). The calculation uses a non-steady continuity model with allowances for three-dimensional flow and horizontal velocity variation with depth. Depth variation in horizontal velocity is obtained, using the constitutive relation for ice with calculated temperature profiles and with full allowance for longitudinal stresses and enhancement of flow due to ice anistrophy and texture. Separate calculations are made for different thickening or thinning rates, until a match between observed and calculated surface velocities is obtained.

For the EGIG transect, our mass-balance results are in the range reported by Mälzer and Seckel (1975) and Bindschadler (1984). Results for the OSU transect, just south of the Arctic Circle on the south dome, are also reported.

Of particular interest is the sensitivity study, which is designed to determine which aspects of the data and flow behavior are most critical to the calculations. Data that are comparatively well-constrained are flow-line definition, surface velocity and thickness. The flow lines and lateral spreading are obtained from satellite radar altimetry (Zwally and others, 1983) and checked against velocity data along the OSU profile. Thicknesses are from aerial radar sounding (Overgaard, personal communication). Surface velocities along the EGIG transect are corrected in a manner similar to that suggested by Robin (1983, figure 2.17b) and possible errors are not critical. Along the OSU transect the surface velocities are well-determined by Doppler satellite tracking in short-arc translocation mode.

Accumulation rates are not well-determined and show substantial scatter for reasons that are not understood. Along the OSU transect, accumulation rates were obtained by augering for the nuclear bomb horizons. As reported earlier (Mock, 1967), the accumulation rates in this region show no clear pattern with elevation or slope. Similar, but less severe, problems exist in the EGIG area. The lack of a good model describing the geographic variation in accumulation rate results in calculated surface velocity uncertainties of 9% for the OSU and 6% for the EGIG transect.

The calculated results are comparatively insensitive to parameters affecting the temperature profile. This is because, in this model, the mean velocity is determined by continuity and temperature affects only the ratio of horizontal velocity at a given depth to the mean velocity for the entire profile.

Longitudinal stresses are included because they affect the viscosity through the effective shear stress. Neglecting this would lead to a 30% error in calculated surface velocity near the ice divide and about 6% away from the divide. Provided longitudinal stresses are included, uncertainties in these stresses are not critical.

Enhancement factors are, however, important. Most authors believe that ice fabric, texture, and impurity content can affect strain rates by 100% to 1200% (Shoji and Langway, 1984). As with the temperature profile, this problem does not affect calculated mean velocities, which are based on continuity, but it does affect the ratio of surface to mean velocity. Enhancement factors are more critical than temperature uncertainties and therefore failure to include depth-variable flow enhancement alters calculated surface velocities by 5 to 10%.

In summary, the mass balance along two transects has been investigated by comparing measured and calculated surface velocities. The most critical problems are (1) understanding the geographic distribution in accumulation rate and (2) correctly allowing for enhanced shearing due to structural variations with depth.

Landsats 4 & 5 have acquired approximately one thousand images of Antarctica in 1984 and 1985, including a few thematic mapper images. I will show, on two maps, where these images have been acquired and give a preliminary evaluation of their quality.

In 1984-85, airborne radar soundings were carried out over West Antarctic ice streams A, B, and C, the neighboring parts of the Ross Ice Shelf, and Crary Ice Rise. Here we use the radar data to map the boundaries of the ice streams, to calculate surface elevations, and to measure ice thicknesses. Lee thicknesses and surface elevations have been used together to map the grounding zones and ice rises (Figure 1).

The first set of sequential measurements by two different sets of satellite altimetry data indicate that the Greenland ice sheet, south of 65.1° north latitude, thickened at the rate of 35 ± 17 cm a−1 during 1975 to 1978. The average change in surface elevation was calculated from the elevation differences determined at 525 locations observed by both GEOS-3 and Seasat radar altimeters. The observed thickening is consistent with the 8 cm a−1 thickening previously measured in the accumulation zone, approximately 900 km farther north, during conventional, surface, survey methods. The increase in ice thickness suggests a higher precipitation than the long-term average, which is one possible result of a warmer climate in polar regions. The excess ice accumulation, in the 10 % of the Greenland ice sheet observed, is estimated to be 53 km3 a−1, which is equivalent to a sea-level reduction of 0.15 mm a−1. Additional, high-precision, sequential, altimetric measurements could be used to determine the overall mass balance of the Greenland and Antarctic ice sheets.

The margins of many ice sheets and ice caps are marked by the presence of alternating layers of debris-laden and clean ice. The role of this ice in flow and sediment transport near the margins of glaciers has been the subject of considerable controversy between glacial geologists and glaciologists for over three decades.

Glacial geologists (Goldthwait, 1951, 1960, 1971, 1975; Bishop, 1957; Souchez, 1967, Boulton, 1970, 1972; Hambrey, 1976) commonly refer to the debris-bearing ice bands as “thrust planes” or “shear planes”, apparently seeing them as reverse faults which transport rock debris from the glacier bed to the surface in a “conveyor-belt-like” manner (Goldthwait, 1975, p. 192). As supporting evidence for the shear-plane mechanism, glacial geologists have offered only qualitative observations and none seem to have actually observed it in action. Glaciologists on the other hand, particularly Weertman (1961), Hooke (1968; 1973), and Hooke and Hudleston (1978), have objected to this concept on physical grounds and have presented convincing arguments for doubting that it is mechanically sound. In spite of the controversy surrounding it, the shear-plane mechanism has gained wide acceptance among geologists and physical geographers and has been perpetuated in recent years through a number of popular introductory geology and physical geography textbooks (e.g. Embleton and King, 1975; Judson, Deffeyes, and Hargraves, 1976; Leet, Judson, and Kauffman, 1978; Press and Siever, 1982; Hamblin; 1982).

The recent availability of high resolution (greater than 250 Hz) seismic recording equipment in the Antarctic field environment has allowed the acoustical mapping of a previously unobserved subglacial phenomenon. This phenomenon is a thin (less than 10 m), yet continuous, layer at the base of Ice Stream B in West Antarctica. Discovery of this layer came during the 1983–84 austral summer in a seismic reflection survey that covered approximately 10 km2 near the Upstream B field camp (83°31’S, 138°05’W). Although analysis of the seismic data is at a preliminary stage, there is the possibility that this feature could be a basal “lubricating” layer; some sort of lubrication is of course necessary to explain the very large horizontal velocities of these ice streams.

During the seismic reflection survey on Ice Stream B, a new digital seismic recording system, developed by the Geophysical and Polar Research Center, was used for the first time under field conditions. Resolution of such a thin layer was possible only because of the very large bandwidth (0–600 Hz) and dynamic range (84 dB) of this device; this bandwidth is about twice that possessed by commercially available seismic recorders. In addition, a new level of portability (i.e. a weight of 40 kg and a power requirement of 90 watts), which should make this device usable in virtually any Antarctic field situation, has been achieved by the application of advanced recording technologies. The portability of this digital seismic recorder, when combined with its large bandwidth and dynamic range, should result in the resolution of a whole new class of intra- and subglacial phenomena, of which the thin basal layer of Ice Stream B is the first example.

The terminus position of Shoestring Glacier, Mount St. Helens, has pulsated over the last few centuries, generally following local climate trends, but the pattern of advance and retreat has been strongly modulated by effects of local volcanic activity. In this paper, I discuss the techniques employed to map and survey fluctuations in ice velocity, thickness, and terminus position of Shoestring Glacier. Solutions to major problems in acquiring and interpreting data peculiar to an active volcano are also explained. Results show that this steep mountain glacier responds quickly and dramatically to local environmental changes. The effects of volcanic activity are distinguished from internal instabilities and local climate change by combining information obtained using a variety of techniques, including field surveying, contour-mapping using stereo-aerial photographs, photo-documentation, and published historical accounts, In this paper I will focus attention on surveying and mapping conducted since 1979 at Shoestring Glacier, but will also discuss methods used to identify historic and “prehistoric” glacier fluctuations back to the early 1800s.

The field survey was conducted at the glacier from mid-1979 to late 1983, during several eruptive episodes, major earthquakes, and covering winter and summer velocity and thickness changes. (Brugman and Post, 1980; Brugman and Meier, 1981). Coordinates of glacier velocity markers and the survey reference net were monitored with several different theodolites and electronic distance meters. In addition, topographic maps of Shoestring Glacier and vicinity were made for the years between 1979 and 1982, for the purpose of characterizing the drastic changes which occurred during the volcanic eruption of Mount St. Helens of May 18, 1980. The maps were constructed with 2 m contour intervals, using three sets of vertical aerial photographs. The difference between maps results in two plots showing the surficial changes caused by the volcanic field-checked against ground survey data on thickness change, using standard techniques. Overall, this study included monitoring glacier flow, configuration, and thickness changes at Shoestring Glacier since mid-1979, and also monitoring any changes in the local survey net due to ground deformation associated with nearby volcanic activity.

In addition, photographic and written documentation of recent glacier fluctuations at Mount St. Helens was compiled from a variety of sources, which included local explorers, scientists, mountaineers, aviators, and historians. From this information, I was able to obtain the general pattern of Shoestring Glacier terminus fluctuations since the early 1900s.

To extend the study further back in time, I also mapped the local surficial geology surrounding Shoestring Glacier using aerial photographs and ground studies. Because Mount St. Helens is a highly active, young volcano, a major problem was to distinguish glacier moraines, built during a recent ice advance, from volcanic levees built during passage of a recent lahar. Both lahar levees and glacier moraines exist along the glacier margin and most have been dissected and scoured by later mudflows. This study required the separate identification of glacial lag-till, from mudflow and rock avalanche debris. Comparison of depositional and erosional features generated by the several major lahars which decended over the Shoestring Glacier during the 1980 eruptions to pre-1980 surficial geology shows that glacier and lahar deposits are closely intermingled, but they can be distinguished on the basis of surface morphology obtained from aerial photographs, supported by field mapping of sedimentary structures. The dominant pre-1980 surficial deposits were laid down during a time of intense volcanism dating from 1800-1857, when the Shoestring Glacier was initially at its most advanced terminus position in its limited geologic record. During the early 1900s, several minor historic eruptions deposited ash and debris as distinctive englacial debris layers, which were well preserved within the glaciers on Mount St. Helens. Rock material deposited in the early to mid-1800s from glacier advances and volcanic eruptions can be distinguished from volcanic material deposited during the early 1900s because of the minor effect these later eruptions had on the glaciers of Mount St. Helens.

This study shows that, over the last few centuries, repeated eruptions of Mount St. Helens have caused important changes in the mass balance of Shoestring Glacier. During several volcanic eruptions since 1800, the Shoestring and nearby glaciers have been deeply blanketed with rock ejecta and avalanche and mudflow debris, which could have increased the glacier mass balances. In contrast, the dominant effect of major volcanic eruptions on the Shoestring Glacier has led to strongly negative mass balances due to scouring, melting, and blasting away of glacier snow and ice. Deep incision of the glacier and its surrounding topography is clearly evident from the maps produced during this study, both during and before 1980. This melting and scouring occurred as pyroclastic flows and lahars swept down the glacier-filled canyon from the summit of the volcano and has probably occurred repeatedly since the canyon holding the Shoestring Glacier was first cut, approximately two thousand years ago. The eruption of Mount St. Helens on May 18, 1980, when the Shoestring Glacier was beheaded, deeply incised, and covered by volcanic ejecta and mudflow debris, is the most recent example of the highly variable environment in which the glacier continues to survive.

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.

The meaning of the term ‘short period’ is relative to the size and mean velocity of an ice mass. On a small, fast-moving glacier, such as Variegated, close to the time of surge, speeds of 0.5 to 65 m/day allow accurate measurement of surface velocity, uplift, and strain over hourly time intervals. Motion studies over similar time periods may be accurately performed on lower Jakobshavns Glacier, where average speeds of 20 m/day are present. On the other hand, 50—70 km from terra firma on upper Jakobshavns Glacier, speeds are much reduced and stable control is difficult to establish. In a region such as this short period becomes daily to weekly, or even longer if absolute velocities are required.

Several factors are critical in the planning and successful completion of comprehensive short period motion study with a minimum of manpower. Choice of instrument type, location of control, marker construction and size, placement of markers on a highly-crevassed surface, and accuracy requirements all require careful consideration and are described in detail in this paper.

On Variegated and lower Jakobshavns Glaciers standard theodolites and electronic distance meters (EDM) were used to determine the horizontal and vertical position of a surface marker from either the glacier margin or from a moving control point, on the ice itself, whose location was simultaneously monitored. Mean flow azimuth and plunge were determined by complete surveys made daily or weekly. Shorter period surveys were often limited to the measurement of either distances only or angles only, depending on the component of motion along the line of measurement. Interpolation among these data sets for a given point yields accurate velocity, strain-rate, and vertical motion. The motion of a larger number of points could be determined from a few survey stations in this manner - for example, up to 30 markers were surveyed from 2 stations continuously over a three month period, covering a longitudinal distance of 15 km along the glacier.

Markers, consisting of poles drilled into the surface, metal and plastic tetrahedron, cloth drapes and dye bombs, were emplaced on foot, when feasible. At other times, however, the highly-fractured surface of these fast moving glaciers required deployment from a hovering helicopter. Many of the markers were equipped with fixed retro-reflecting prisms to facilitate EDM measurement. Remote light systems on control points allowed surveying during periods of darkness (when, invariably, interesting events tended to occur).

On upper Jakobshavns Glacier, markers were located using a microwave, or UHF, positioning system installed on board a helicopter. The decrease in accuracy of such measurements relative to standard methods required longer time periods between positioning, but, even at these lower frequencies, significant fluctuations were observed. Guidance capabilities of the positioning systems allowed rapid reoccupation of marker sites on the vast ice surface and also allowed rapid mapping of surface topography and terminus position,

Results show several interesting features of glacier dynamics: large fluctuations in velocity over periods of hours to days, rapid and substantial uplift of the surface, and the subsequent propagation of these movement events and kinematic-type waves along the surface; large seasonal DC shifts in velocity and interesting development of marginal and medial shear zones. Digitization and time-series analysis of the resulting data sets allow identification of significant periods of oscillation in glacier motion and quantitative description of the propagation of high-frequency disturbances. Correlation with continuous records of other variables on Variegated Glacier, observed by various investigators from University of Alaska and Washington and Caltech, such as borehole water level, seismicity, stream discharge, and small-scale strain and tilt, enables the first detailed observational description of a surging glacier to be made, and a detailed comparison with theoretical ideas.

A new amendment to Murphy’s Law regarding such short period motion studies is also presented.

Chinese Glacier Inventory is part of International Glacier Inventory, and glacier maps are important components of the glacier inventory.

Since 1979, we have completed glacier maps for Qilianshan, Altaishan, Tianshan and Pamier mountain systems one after another, about 40% of the whole work.

In order to improve the quality and accuracy of the maps, we fully considered the principles for the compilation of the International Glacier Inventory with due respect to the specific conditions in China as follows;

1. 1. Materials and data.

   Newly published aerial topographic maps of 1:50 000 and 1:100 000 are used as basic maps with aerial photographs as supplementary data for checking and correction.

2. 2. Scale and projection.

   According to the use of the glacial maps, the shape and size of the surveyed area and base data, the scale of the maps of drainage basins is fixed at 1:250 000 and 1:400 000, with Gauss projection. For the distribution maps of glaciers and their geographic landscape and characteristics, and for coding key maps, scales of 1:1 000 000 and 1:2000 000 are used, respectively, and their projection is the normal, minimum-error, conformal, conical projection, with two standard parallels.

3. 3. Synthesis and presentational method.

   To show the location, type, shape, direction of movement and dependent drainage basin of glaciers is the most important task for the compilation of glacier inventory. Therefore, it is very necessary to carry out scientific summarization during compilation and to decide the acceptance or rejection of the surveyed features. In addition, the key elements of drainage basins, ridges, etc. are also given in detail.

   The glacier map is a basic skeleton for the glacier inventory, giving important basic data for glaciological research and exploitation, as well as the utilization of the ice-snow resources, etc.

In the period from 1982 to 1984, the Silesian University Expeditions investigated the annual cycle of the Hans Glacier velocity and front fluctuations. They also analysed the factors influencing these processes (J.Jania, L.Kolondra, E. Bukowska-Jania 1983).

Surrounding the Hans Glacier frontal zone, permanent tripods had been installed (by cementation in monolithic rocks) for the photo-theodolite, to establish three stereo-photogrammetric bases. While two of the three bases were used for surveying the fluctuations of the glacier front along the entire width (ca. 2.5 km), the remaining one was installed to record the velocity of the glacier by the time-parallactic method. Photogrammetric pictures were reiterated approximately every 10 days during August in 1982, 1983 and 1984. During the polar winters of 1982/83 and 1983/84, the oscillations of the glacier front were recorded at one base only. Pictures were taken once a month (also by moonlight). Using a Gornik-type seismograph, natural micro-tremors coming from the glacier were recorded continually, The seismograph works at the nearby Polish Polar Station, which operates a meteorological station.

The application of permanent metal tripods with an auto-centering disc made it possible to take successive pictures at the same external orientation of the camera on one hand, while, on the other hand, improving the convergent photographs (a similar approach was reported by U. Voigt 1966). On the glacier surface, ground points of control were signalled with a Maltese cross. The investigators made use of natural reference points, i.e. some characteristic features of the glacier surface. Maximum errors of the photogrammetric survey were mxy = ±0.3 m, mz = ±0.1 m.

The results of glacier tongue velocity measurements (ca 50 ma−1), as well as the results of measuring the fluctuations of the glacier front position enabled the rate of calving to be calculated. Thus, the calving velocity amounts to ca 100 ma−1 and the mass loss at the contact with sea water approaches ca 20% of the annual mass loss due to ablation.

The calving speed and the velocity of the glacier undergo variations in different periods of the year and the maxima of the processes do not overlap. While the glacier velocity reaches its maximum value at the beginning of the summer season (July), maximum calving speed is recorded in autumn (September-October). However, there may appear a shift in the time at which these maxima occur. It depends on the meteorological conditions and the thermal state of the sea in the given year. The effect produced by the two “antagonistic” glacial processes is the change in position of the glacier front in the sea. Its maximum and minimum extension appears by the end of July and in October, respectively. The amplitude of the Hans Glacier front fluctuations, measured for the period of August, 1982 to August, 1983, amounted to 60 ma−1 on the centre line. The results of photogrammetric surveying by C. Lipert, from 1957 to 1959, have shown that the maximum changes in the extension of the glacier front amount to 250 ma−1. These fluctuations display regularities similar to those reported for the Columbia Glacier, Alaska by C.S. Brown, M.F. Meier and A. Post (1982).

Analyses of micro-tremors coming from the glacier involved their variability in scale and frequency from one day to the next and throughout the year, as well as photogrammetric survey. Attempts were also made to find the englacial source of those micro-tremors. Source location was attempted in the summer of 1980, by using three geophones situated in the frontal part of the glacier. Thus, the majority of the micro-tremors owe their origin to the zone situated at a distance of 200 to 300 m from the front line and not to the ice cliff, as had been expected (A. Cichowicz, personal communication). It is worth noting that there exists an overlap of the annual distribution of the frequency of micro-tremor occurrence with the curve of glacier velocity variations. This enabled the investigator to determine the glacier dynamics by tremor recording.

In a study of the Rutford Ice Stream, strain rates were measured on a transverse section. Magnitudes ranged up to 40 × 10−3 a−1 but were typically in the order of 3 × 10−3 a−1 with an error of 0.1 χ 10−3 a−1. Variations in the strain rate between adjacent stakes of 0.2 χ 10−3 a−1 to 2 × 10−3 a−1 were matched to the thickness variations on the glacier.

For each set of three adjacent stakes, the velocity gradient components of the surface strain rate tensor were calculated by assuming that the gradients were linear over the distance between adjacent stakes. When plotted against distance across the ice stream, each strain rate component revealed different aspects of the flow field. The longitudinal strain rate was compressive, with an almost constant magnitude of 10−3 a−1. The lateral strain rate is extensive, with an average value of 1.1 × 10−3 a−1 which agreed with the angle between the divergent flow lines observed on a Landsat image. Peaks in the lateral strain rate, corresponding to longitudinal bands of thicker ice, showed that these thicker bands were spreading more rapidly at the expense of thinner areas. The two velocity gradient components of the shear rate tensor also reflected differences in ice thickness.