Air temperature and precipitation data have been obtained from the Geladandong region at the headwaters of the Yangtze River. At the equilibrium line altitude of the glaciers, mean annual and summer air temperatures are –10 to –12.0°C and 1.0 to –1.0°C, respectively. Accumulation on the glaciers on the south side of the Tanggula mountains depends mainly on water vapour transported from the south and southeast. The moisture source for the glaciers on the north side is from the east. Precipitation increases with altitude in the glaciated areas. An estimated annual accumulation in the firn areas is about 400 to 600 mm of water equivalent. The Geladandon region has a cold, dry climate and the glaciers in the region can be classified as continental. The present climatic conditions result in a negative mass budget for most glaciers.

The seasonal snow cover in the Tien Shan mountains is characterized by low density, low liquid-water content and low temperature. It is known as typical dry snow. Large temperature gradients in the basal layer of the snow cover exist throughout the entire period of snow accumulation, and depth hoar is therefore extremely well-developed. Full-depth depth-hoar avalanches, however, seldom occur. Avalanches in the Tien Shan mountains are mostly loose snow avalanches. Although normally not large in size, they are the most dangerous type. The occurrence of hazardous avalanches shows cycles of about ten years because of periodic climatic variations.

Since the Little Ice Age, most glaciers in the Tien Shan mountains have been retreating. Owing to an increase in precipitation in most parts of the mountains during the late 1950s to early 1970s, the percentage of receding glaciers and the speed of retreat have tended to decrease in the 1970s. However, the general trend of continuous glacier retreat remains unchanged, in part because the summer air temperature shows no tendency to decrease.

In the Tien Shan mountains, as the degree of climatic continentality increases the mass balance becomes more dependent on summer temperature, and accumulation and ablation tend to be lower. Therefore, the responses of glaciers to climatic fluctuations in more continental areas are not synchronous with those in less continental areas, and the amplitude of the glacier variations becomes smaller.

About 80% of the glaciers in China have been inventoried. Based on the inventory and an estimate of the area that has not been inventoried, there are about 45 375 glaciers in China, with a total area of 58 735 km2 and an ice volume of about 5.31 × 1012 m3. These glaciers are widespread in high mountains and in highland areas in western China, between 27°06′ to 49°09′N and 71°32′ to 103°54′E. The glacierized area in China comprises about 16% of the alpine glacier area in the world, and 47% of that in Asia. There are about 230 large glaciers, with areas exceeding 100 km2, in the world outside Antarctica and Greenland. Among them, 65 (28%) are in Asia and 31 (13%) in China.

Α δ18O record from Dunde Ice Cap, located in the Qilian mountains on the northeastern margin of the Tibetan Plateau, has been analyzed and interpreted. With an ice temperature of –7.3°C at a depth of 10 m and –4.7°C at the bottom of the ice cap, and an accumulation rate of 400 mm a−1, the Dunde core has provided interesting results. The upper part of this core, core D-l, can be easily dated by a combination of δ18O, microparticle concentration and conductivity. It can also be dated as far back as 4550 BP by counting dust layers in ice. Based on the time scale established by the above methods and on the δ18O–temperature relation, the δ18O fluctuations in the upper 120 m of the core can be interpreted as mainly due to climatic changes during the past ~ 5000 years. The warmest periods in the past ~ 5000 years in the core were found to be centered on the present, 3000, and 4100 BP, and the colder periods center around 500, 1200, 4000, and 4500 BP. It is clear from the ice-core record that the Little Ice Age was only one of many cold periods in the past, although it was the coldest period in the past 500 years.

Research on the sources and spatial variation of the chemical content of snow was conducted in four headwater basins of the eastern Tien Shan, China. The mean SO42- concentration of 16.2 μeq L-1 was three-fold greater than background concentrations from other remote areas of the world. About 80% of the SO42- in snow was deposited in association with Ca2+ and Mg2+ , partially accounting for the relatively high pH of 6.34 in new snow. The variance of individualions in the snowpack ranged from 24 to 46%, measured as the standard deviation divided by the mean and based on 59 samples. Analysis of variance tests showed that solute concentrations varied significantly among sites within an individual basin and that the mean solute concentrations did not vary significantly among basins. Aeolian dust in the snowpack resulted in significant post-depositional alterations in the solute content of snow. Mineral weathering of the dust in the snowpack of the Tien Shan mproduced alkalinity and Ca2+, increasing conductance and buffering H+ .

Mid -winter flooding of the Drift River was caused by melting of snow and glacier ice during the 1989–90 eruption of Redoubt Volcano. “Drift” Glacier (unofficial name) was beheaded when 110 to 120 × 106 m3 of perennial snow and ice were mechanically entrained by the four largest volcanically initiated flows. The flow volumes were increased by incorporation of the seasonal snowpack on the lower glacier surface and in the flooded river valley. The seasonal snow contributed a volume equivalent to about 35 × 106 m3 of water to the flows, increasing the cumulative flood volume by almost 30%. No large amounts of meltwater were stored on or under the glacier before any of the flows took place. The threat of flooding was significantly reduced after the second major eruption removed the remainder of the easily erodible snow and ice.

Beneath Ürümqi Glacier Νo. 1, there is an ice-laden till layer which is more than 10 m thick near the terminus. The 0°C isotherm is generally at some depth below the glacier sole and lies within the bedrock below the ice-laden till layer near the terminus. Thus the glacier is entirely cold and impermeable, except for a thin snow-firn layer at its surface and some crevassed areas. Meltwater drains off mainly by surface channels, assisted by subglacial conduits. Four flow mechanisms have been identified in the glacier. They are ice deformation, bed deformation, shear faulting, and sliding over the bed. At the terminus and along the margins, bed deformation can provide a significant contribution to the overall surface motion. Bed deformation consists of creep and discontinuous slip. However, creep experiments on samples taken from the ice-laden till layer provide no positive indication that this layer deforms more easily than clean ice. Discontinuous slip thus may provide the major contribution to bed deformation.

Snow samples were collected from a 0.5 m snowpack at Glacier No. 1 and near Bogda Feng, eastern Tien Shan, northwest China. Samples that were melted in the field were analyzed for chloride, nitrate, sulfate, sodium, potassium, magnesium, calcium, and microparticles. Eight samples were returned frozen and were analyzed for the above ions plus ammonium, acetate, formate, methylsulfonate, and hydrogen peroxide. There was no significant difference in measured major ion concentrations between the melted and frozen samples. Measured cations in both sets of samples were two to three times greater than measured anions. Calcium and sodium are the dominant cations while sulfate is the dominant measured anion. High ion burdens are associated with dusty layers in the snowpack, indicating that dust from the vast arid regions of central Asia is the dominant source for major ions in Tien Shan snow. The significant increase in sulfate and decrease in the cation : anion ratio in Bogda Feng snow relative to Glacier No. 1 snow suggest that anthropogenic emissions from Ürümqi are an important source of sulfate to precipitation downwind from the city.

In the source area of the Ürümqi River, during the glacier ablation season, net radiation is the only heat input to the tundra, averaging 119W m−2 in July and August, more than twice that to the glacier, where additional heat input is contributed by sensible heat. The heat input to the tundra is mostly lost by evaporation, which accounts for 86%, while the input to the glacier is mostly lost by melting. The relatively small heat input to the glacier and the large evaporation rate of its surroundings favour the glacier’s existence. Most precipitation occurs between June and August, accounting for 66% of the annual total. Precipitation increases with altitude in average conditions during the ablation season; the annual precipitation is estimated to be about 650 mm at the mean equilibrium line altitude of 4030 m. This amount is considerably larger than that of the surrounding area. Evaporation is estimated at 270 mm a−1 on the tundra, reducing the runofTin a rather large proportion, and 120 mm a−1 on the glacier. Almost all runoff takes place between May and September, and is mostly concentrated in July and August when the glacier melt is the most intense. When air temperature is high during the ablation period, although the precipitation is less, runoff could peak because of the glacier melt. Based on the measured runoff and estimated regional precipitation and evaporation, the glacier mass balance is calculated and discussed.

Measurement of wind velocity, wind direction, air temperature, precipitation and humidity were obtained at various altitudes in order to describe micrometeorological conditions on the north slope of Mount Qogir (K2). Meteorological elements were monitored above the moraine surface in the proglacial area and over the ice surface in the ablation area and snow surface in the firn area of K2 glacier. Precipitation increases quickly with altitude from the dry valley to the firn area. Relative humidity also increases with elevation. In the K2 glacier area, the highest absolute humidity occurs over the glacier tongue. The effects of melting and freezing of the surface of the glacier in the ablation area on diurnal and day-to-day changes in air temperature influence air temperature in ablation areas, decreasing diurnal range by comparison with the firn areas. On clear days, a down-valley wind blows from the firn area before sunrise and an up-valley wind after sunrise. On days with precipitation, an up-valley wind predominates in the night-time and a down-valley wind in the day-time.

The energy-balance approach was used to calculate snowmelt at a site in the mid-mountain zone of the western Tien Shan mountains. During a 19-day snowmelt period, the results showed that net radiation and sensible heat fluxes accounted for 76.9 and 23.1% of the incoming energy, while snowmelt and evaporation consumed 97.1 and 2.9% of the energy, respectively. Snowmelt calculated from the energy balance compares favourably with measured values, indicating the suitability of the energy-balance approach for estimating the rate of snowmelt in the mountain environment of the western Tien Shan.

There appear to have been several important glacial advances on the southern slope of the west Kunlun mountains, Tibetan Plateau, since 45 000 a BP. Based on the record of alternating till and lacustrine sediments and 14C determinations, these advances are dated to 23 000–16 000, 8500–8000, and 4000–2500 a BP, and to the 16th–19th century AD, with regional variations occurring during each of the advances. The glaciation of 23 000–16 000 a BP is equivalent to the last glacial maximum (LGM) and its scope and scale were much larger than any of the others.

Lake changes are a response to both tectonic uplift of the plateau and global climatic change. With regard to the latter, both changes in precipitation and changes in the extent of glaciation can affect lake levels. High lake levels occurred during interstadial conditions between 40 000 and 30 000 a BP, when the area experienced a relatively warm and humid climate, and during the LGM, between 21 000 and 15 000 a BP. During the Holocene, lakes have been shrinking gradually, coincident with the dry climate of this period of time.

Hydrological records of Kunmalike River in the southern Tien Shan show that jökulhlaups have occurred about once a year since 1956 from the glacier-dammed Lake Mertsbacher. The maximum peak discharge of the jökulhlaups is 1920 m3 s−1 and the maximum total volume is 3.275 × 108 m3. The release mechanism of the glacier-dammed lake is not a mechanical failure of the glacier dam, but drainage of pressurized water through a subglacial tunnel which is enlarged due to melting by frictional heat in the flowing water and advective heat from the lake. There is no relationship between the size of the jökulhlaups and the mean summer air temperature. The seasonal flood peaks in Kunmalike River have become larger and the flood periods have been prolonged both in spring and winter because of the draining of the lake. Once a jökulhlaup has started, its discharge is forecast hour by hour by extrapolating the measured hydrograph as exponential curves.

Annual mass exchange differs between maritime and continental glaciers. A common characteristic of these glaciers in Asian high-mountain areas is that most of the annual accumulation occurs in summer. Since variations in mass balance of a summer-accumulation type of glacier are quite sensitive to variations in summer air temperature, shrinkages of such glaciers due to climate warming are predicted by the use of simplified experimental relations between air temperature and mass balance, disregarding variation of other climatic variables such as cloudiness and precipitation. The results predict that both small and large maritime glaciers are more sensitive to warming than a continental ice cap. A small glacier would disappear in a few decades if the air temperature persisted a few degrees above that of an equilibrium state of mass balance.

Jökulhlaups drain regularly from six subglacial geothermal areas in Iceland. From Grímsvötn in Vatnajökull, jökulhlaups have occurred at 4 to 6 yearly-intervals since the 1940s with peak discharges of 600 to 10000 m3s−1, durations of 2 to 3 weeks and total volumes of 0.5 to 3.0 km3. Prior to that, about one jökulhlaup occurred per decade, with an estimated discharge of 5 km of water and a peak discharge of approximately 30000 m3s−1. Clarke’s (1982) modification of Nye’s (1976) general model of discharge of jökulhlaups gives, in many respects, satisfactory simulations for jökulhlaups from Grímsvötn the best fit being obtained for Manning roughness coefficients n = 0.08 to 0.09 m−1/3s and a constant lake temperature of 0.2°C (which is the present lake temperature). The rapid ascent of the exceptional jökulhlaup of 1938, which accompanied a volcanic eruption, can only be simulated by a lake temperature of the order of 4°C.

Jökulhlaups originating at geothermal areas beneath ice cauldrons located 10 to 15 km northwest of Grímsvötn have a peak discharge of 200 to 1500 m3s−1 in 1 to 3 days, with total volume of 50 to 350 × 106m3, and they recede slowly in 1 to 2 weeks. The form of the hydrograph has reversed asymmetry to that of a typical Grímsvötn hydrograph. The reservoir water temperature must be well above the melting point (10 to 20°C) and the flowing water seems not to be confined to a tunnel but to spread out beneath the glacier and later gradually to collect back to conduits.

Since the time of the settlement of Iceland (870 AD), at least 80 subglacial volcanic eruptions have been reported, many of them causing tremendous jökulhlaups with dramatic impact on inhabited areas and landforms. The peak discharges of the largest floods (from Katla) have been estimated at the order of 100 000 to 300 000 m3 s−1, with durations of 3 to 5 days and total volume of the order of 1 km3. It is now apparent that the potentially largest and most catastrophic jökulhlaups may be caused by eruptions in the voluminous ice-filled calderas in northern Vatnajökull (of Bárdharbunga and Kverkfjöll). They may be the source of prehistoric jökulhlaups, with estimated peak discharge of 400 000 m3 s−1.

At present, jökulhlaups originate from some 15 marginal ice-dammed lakes in Iceland. Typical values for peak discharges are 1000 to 3000 m3s−1, with durations of 2 to 5 days and total volumes of 2000 × 106 m3. Hydrographs for jökulhlaups from marginal lakes have a shape similar to those of the typical Grímsvötn jökulhlaup. Simulations describe reasonably well the ascending phase of the hydrographs assuming a constant lake temperature of about 1°C; but they fail to describe the recession. Some floods from marginal lakes, however, have reached their peaks exceptionally rapidly, in a single day. Such rapid ascent can be simulated by assuming drainage of lake water at 4 to 8°C.

An empirical power-law relationship is obtained between peak discharge, Qmax, and total volume Vt of the jökulhlaups from Grímsvötn: Qmax = KVtb, where Qmax is measured in m3s−1, Vt in 106m3, Κ = 4.15 × 10−3s−1 m2 and b = 1.84. In general, the jökulhlaups (excepting those caused by eruptions) occur when the lake has risen to a critical level, but before a lake level required for simple flotation of the ice dam is reached. The difference between the hydrostatic water pressure maintained by the lake and the ice overburden pressure of the ice dam is of the order 2 to 6 bar.

The annual evaporation of a continental-type glacier (43°05’ Ν, 86°48’ E) in the Chinese Tien Shan is estimated, based on data derived from four field observations carried out between summer 1987 and spring 1988, and data from a permanent weather station near the glacier. The evaporation during the melting and non-melting seasons is estimated as 81 mm and negligible, respectively. Assuming that the ablation is equivalent to the annual precipitation (650 mm) in 1987, estimated annual evaporation of 81 mm is 12% of the ablation and consumes 54% of the energy which causes the ablation. It can be said that evaporation suppresses ablation by 50% in comparison with the condition in which there is no evaporation.

The influence of fluctuations of air temperature and humidity on the ablation of the glacier were evaluated. Changes in temperature and humidity cause larger changes in ablation of glaciers in a cold and dry climate. The influence of humidity change is very important to glaciers located in a relatively warm environment.

Scale-dependent atmosphere-glacier interactions operate over a glacier surface as the surface has different thermal and radiative characteristics from those of the surrounding ground. In order to evaluate heat supply to the glacier surface in the main ablation period, three main interaction processes are considered: advection, glacier wind, and multiple reflection of solar radiation. The amount of heat supply was calculated for the equilibrium line altitude (ELA) by assuming a simple rectangular-shaped glacier, and by applying meteorological and glaciological data for four different glaciated regions (Tien Shan, Patagonia, west Kunlun and Nepal Himalaya). The total heat supply due to the above three processes had the common tendency of being smallest for glaciers of 1 to several kilometres in length, and largest at 16 km, which was the maximum length considered in this study. Among the cases, the Tien Shan showed a daytime heat supply higher by 2.3 MJ m−2 for a 16km-long glacier compared with a small glacier 2 km in length. Relating this difference directly to ELA, an ELA approximately 300 m higher might be expected for a long glacier than a short one, assuming the same amount of solid precipitation. Glacier inventory data for China support this tendency, but the calculated value is slightly larger than that observed. The results show that there is a possibility that responses in glacier variation to climate change may be modified considerably through scale-dependent atmosphere-glacier interactions.

Basal deformation was studied in tunnel 2 in the east tributary of Ürümqi Glacier No. 1, Tien Shan mountains. Beneath the tunnel there is an ice-laden till layer, about 11 m thick and at a sub-freezing temperature. This layer is deformable and provides a significant part of the overall surface motion. The basal velocity in the tunnel gradually decreases from the back wall towards the entrance, with a compressive strain rate ranging from −0.579 to −5.739 × 10−2 a−1. The inclination of the principal strain rate to the horizontal gradually decreases from the back wall towards the tunnel entrance. The study provides data on the longitudinal compression and vertical uplift in the basal ice and ice-laden till layer resulting from interaction of glacier with recently exposed proglacial deposits.