Matthias Kuhle

Reconstruction of the 2.4 million km2 late Pleistocene ice sheet on the Tibetan Plateau and its impact on the global climate

During 20 expeditions new data were obtained on the maximum extent of glaciation in Tibet and the surrounding mountains. Evidence was found of moraines at altitudes as low as 460 m on the southern flank of the Himalayas and 2300 m on the northern slope of the Tibetan Plateau, in the Qilian Shan. On the northern slopes of the Karakorum, Aghil and Kuen Lun, moraines occurred as far down as 1900 m. In southern Tibet radiographic analyses of erratics document former ice thicknesses of at least 1200 m. Glacial polishing and knobs in the Himalayas and Karakorum are proof of glaciers as thick as 1200–2000 m. On the basis of this evidence, a 1100–1600 m lower equilibrium (ELA) line was reconstructed for the Ice Age, which would mean 2–2.4 million km2 of ice covering almost all of Tibet, since the equilibrium (ELA) line was far below the average altitude of Tibet. On Mount Everest and K2, radiation was measured up to 6650 m, yielding values of 1200–1300 W/m2. Because of the subtropical latitude and the high altitude solar radiation in Tibet is 3–4 times greater than the energy intercepted between 60 and 70°N or S. With an area of 2–2.4 million km2 and an albedo of 90%, the Tibetan ice sheet caused the same heat loss on the earth as a 6–9.6 million km2 sized ice sheet at 60–70°N. Because of its proximity to the present-day equilibrium (ELA) line Tibet must have undergone large-scale glaciation earlier than other areas. Being subject to intensive radiation, the Tibetan ice must have performed an amplifying function during the onset of the Ice Age.

Würm glaciation of Lake Issyk-Kul area, Tian Shan Mts.: A case study in glacial history of Central Asia

Recent field research and modeling experiments by the authors suggest that Würm glaciation of Tian Shan Mountains had much larger extent than it was previously believed. Our reconstruction is based upon the following evidence: 1. a till blanket with buried glacier ice occurring on mountain plateaus at altitudes of 3700 to 4000 m asl; 2. trough valleys with U-shaped profiles breaching the border ridges and thus attesting to former outlet glaciers spreading outwards from the plateaus; 3. morphologically young moraines and ice-marginal ramps which mark termini of the outlet glaciers at 1600–1700 m asl (near Lake Issyk-Kul shores) and farther down to 1200 m asl (in Chu River valley); 4. clear evidence of impounding the Chu River by former glaciers and turning Lake Issyk-Kul into an ice-dammed and iceberg-infested basin; 5. radiocarbon dates attesting to the Late Pleistocene age of the whole set of glacial phenomena observed in the area.Our data on past glaciation provide a solution for the so called “paleogeographical puzzle of Lake Issyk-Kul”, in particular they account for the lake-level oscillations (by ice dam formations and destructions), for the origin of Boam Canyon (by impact of lake outbursts), and the deflection of Chu River from Lake Issyk-Kul (by incision of the canyon and build-up of an ice-raft delta near the lake outflow).The Würm depression of regional snowline was found to be in the range of 1150–1400 m. While todays snowline goes above the plateaus of Tian Shan touching only the higher ridges, the Würmian snowline dropped well below plateau surfaces making their glacierization inevitable. The same change in snowline/bedrock relationship was characteristic of the interglacial-to-glacial climate switches on the Tibetan Plateau resulting in similar changes of glaciation. The whole history of central Asian glaciations seems to be recorded in the Chinese loess sequences.A finite-element model was used to test two climate scenarios — one with a gradual and another with an abrupt change in snow-line elevation. The model predicted that an equilibrium ice cover would form in 19,000 (first scenario) or 15,000 (second scenario) years of growth. It also yielded ice thicknesses and ice-marginal positions which agreed well with the data of field observations.

The High Glacial (Last Ice Age and LGM) ice cover in High and Central Asia

Publisher Summary This chapter discusses ancient ice-marginal positions that are scattered throughout the high regions of Asia. This represents equilibrium line altitude (ELA) depressions of more than 1000m and indicates, locally, a glacial cover. It discusses that the field investigations to reconstruct the extent of Pleistocene glaciation in the mountains and highlands of central and south Asia have concentrated on identifying former glaciations and their spatial arrangements. This glacial gemorphological approach, on which the digital map is based, has also been discussed in the chapter. The enormous uplift rate of Tibet of approximately 10mm/a measured by triangulations since the 19th century have been confirmed by glacial geomorphological as well as seismological investigations of the uplift of the Himalaya. However, these amounts of uplift far exceed any conceivable primary tectonic uplift of the high plateau based on epirogenetic processes alone. Actually, they are much easier explained if a superimposed glacioisostatic compensation movement of Tibet, about 650m, is taken into account.

Topography as a fundamental element of glacial systems: A new approach to ELA calculation and typological classification of paleo- and recent glaciations

The equilibrium line of glaciers as a climate-sensitive parameter is indispensable for the assessment of changes in climate through time. The methods previously developed for calculating the equilibrium line do not obtain, however, satisfactory accuracy. Using the statistical evaluation of data collected from 223 glaciers it is shown here that the inaccuracy of the prevailing methods results from the negligence of the specific glacier geometry.In calculating realistic ELAs glaciers must be understood as dynamic systems whose variables, climatic environment and topography, are linked through feedback. The accompanying transformation in this dynamic system, which is expressed by the difference between a mathematical index and the ELA, can be exactly determined with a regression line. The climatically induced change in glacier geometry is the controlling factor, i.e. operator. The behaviour of glacial systems in view of long-term climatic variations can first be understood when the details of the interdependency between topographical and climatic parameters are fully known, as will be demonstrated here.

New Findings concerning the Ice Age (Last Glacial Maximum) Glacier Cover of the East-Pamir, of the Nanga Parbat up to the Central Himalaya and of Tibet, as well as the Age of the Tibetan Inland Ice

The results presented on the glacio-geomorphological reconstruction of a maximum Ice Age (LGM = Last Glacial Maximum) glaciation in High-Asia concern five test-areas in and around Tibet (Figure 1, Nos. 14, 6, 17, 2, 9, 18, 16). For the E-Pamir plateau and its mountains a covering ice cap is proved; a snow-line (ELA)-depression of 820–1250 m in relation to the present relief has been calculated. The Ice Age snow-line ran at 3750–3950 m asl. In the Nanga Parbat-massif a glacial (LGM) ice-stream network with a snow-line altitude (ELA) at c. 3400– 3600 m has been reconstructed. This corresponds to an ELA-depression of at least 1200 m. The lowest ice margin site of the connected 1800–1900 m-thick Indus glacier flowed down to c. 800 m asl. From N-Tibet the author introduces further observations of ground moraines and erratics from a high plateau area he had already investigated in 1981. They provide evidence of a complete inland ice sheet in Tibet. From the S edge of Tibet six large outlet glacier systems i.e. lowest High Glacial ice margin sites of the Himalaya ice-stream network are reconstructed. This is a continuation of the investigations in 1977, 1978, 1982, 1984, 1988 and 1989 between Kangchendzönga in the E and Nanda Devi in the W. In this place probably the lowest glacial glacier end of the Himalaya-S-slope was found at c. 460 m asl at the Dumre settlement, S of the Manaslu. C14-datings from the Tsangpo valley on the S edge of Central Tibet classify the reconstructed Tibetan ice as being from the Last Glacial Maximum (LGM) between older than 48580 ± 4660–2930 and 9820 ± 350 YBP. From this empirical findings and inductive results on the Ice Age Tibetan glaciation are derived deductive conclusions on the interaction of the relief and the snow-line altitude with concern to the ice cover. Modelling by means of those snow-line depressions and estimations of the precipitation provide ideas about surface heights, ice thicknesses and flow behaviour of the ice sheet. The hypothesis of a global triggering of the ice age by the uplift of the subtropical Tibet up to above the snow-line motivates the investigations presented here.

The upper limit of glaciation in the Himalayas

On the slopes of Himalayan Mountains there is a reduction and culmination of glaciation at 7000–7200 m asl. The presumed cause for this is that the surface temperatures on these slopes are too low for glaciation. This working hypothesis was verified with temperature measurements using collected infra-red radiation. The regression analysis of the measurements taken in the Mt. Everest region during sunny weather conditions of the post-monsoon season resulted in a 0°C line at 7000–7200 m asl. The coincidence of the 0°C line with the upper limit of glaciation is causally definable with the copula between the function of temperature and snow metamorphism: since it is too cold above 7000–7200 m asl, metamorphism into perennial or galcial ice through settling or sintering is absent or simply too slow. High relief and drifting hinder here the processes of ice-formation through pressure compaction of the dry-snow accumulation caused by molecular diffusion and recrystallization. Above 7200 m only continuous leeward accumulations of shifting snow on wall sections with moderate inclination lead to the formation of seracs. However, glaciation generally ceases at this level. This additionally confirms another study. It has been proven that Himalayan glaciers with catchment areas over 7000 m do not extend further downward than those glaciers whose catchment areas just reach this altitude. A break in balance at 7100 m asl is thereby confirmed, and the upper glacial limit is proven. Above the glacial region a rocky zo ne adjoins with pergelic conditions even in the surface layer. This zone is covered by snow during monsoon season only. Here, the weathering processes take place in an arid environment without thawing and purely by means of temperature variations below 0°C. They could correspond to those occurring on a larger scale on the planets of our solar system.A lowering of the upper glacial limit by at least 660 or 1200 m respectively, analogous to the Pleistocene snow-line depression reconstructed in S Tibet and the Central Himalayas, is assumed during the Ice Age.

Chapter 68 – The High Glacial (Last Ice Age and Last Glacial Maximum) Ice Cover of High and Central Asia, with a Critical Review of Some Recent OSL and TCN Dates

The existence of a former Tibetan ice sheet is confirmed by glacial geological and glacial geomorphological observations collected throughout High Asia by the author since 1973. Non‐calibrated terrestrial cosmogenic nuclide dates presented by other authors apparently conflict with this evidence, whereas conventional radiocarbon dates and an independently acquired glacial chronology support the evidence given for an extended LGP (LGM) glaciation.

The pleistocene glaciation in the Karakoram-mountains: Reconstruction of past glacier extensions and ice thicknesses

Geomorphological and Quaternarygeological field- and laboratory data (Fig.1) are introduced and interpreted with regard to the maximum Ice Age (LGM) glaciation of the Central-and South Karakoram in the Braldu-, Basna-, Shigar-and Indus valley system as well as on the Deosai plateau between the Skardu Basin and the Astor valley (Fig.2). These data result from two research expeditions in the years 1997 and 2000. They show that between c. 60 and 20 Ka the Central Karakorum and its south slope were covered by a continuous c. 125,000 km2 sized ice stream network. This ice stream network flowed together to a joint parent glacier, the Indus glacier. The tongue end of the Indus glacier reached down to 850 ∼ 800 m a.s.l. In its centre the surface of this Indus ice stream network reached a height of a good 6000 m. Its most important ice thicknesses amounted to c. 2400 ∼ 2900 m.

Glacier-Induced Hazards as a Consequence of Glacigenic Mountain Landscapes, in Particular Glacier- and Moraine-Dammed Lake Outbursts and Holocene Debris Production

With the help of representative examples this paper attempts to infer the damaging effects, induced by glaciers, not only — as is normally the case (cf. amongst others, Hewitt 1982, 1988, 1995) — from the geomorphodynamics, observed directly on the spot, but from the entire glacigenic character of the high mountain landscape. Accordingly, not only the current changes of the glacier, which produce damage — as for instance the shifting of the glacier termination (cf. 3.) — are on the focus of interest, but also the development of the glacigenic relief during the High- to Late Glacial (cf. 2.). From the mountain shaping through prehistorical glaciation, partly filling up the relief, a transformation of the valleys resulted, which was not stable during the Interglacials. Characteristics of the glacial relief, such as U-shaped valleys, subsequently crumbled away on their typically over-steepened valley flanks and collapsed as soon as, following deglaciation, the abutment of the ice filling was absent in the valley. This is a process which, in the Interglacials, the preglacial U-shaped valley relief — depending on the length of time passed since deglaciation and according to resistance of the valley flanks — more or less quickly reestablishes. Through the processes proceeding as a result, i.e. wet and dry mass self-movements such as rockfall, rock slide, landslide etc., debris bodies are built up on the valley floors. These directly or indirectly result in or induce in the form of fans, cones and screes numerous damaging effects (cf. 4.).

The Last Glacial Maximum (LGM) glacier cover of the Aconcagua group and adjacent massifs in the Mendoza Andes (South America)

Publisher Summary This chapter discusses the glacial limit that investigates in four months glacial geological and geomorphological mapping project and fieldwork from January to May 1980. It has been carried out in three adjacent massifs of the Mendoza Andes; the Cerro Aconcagua, the Cerro Tupungato and the Cerro Juncal that reach 7021 m, c. 6800 m, and 6180 m a.s.l. Three deals with the reconstruction of glaciers— namely, the extension, the thickness of the valley glaciers, and the remainder are concerned with Pleistocene moraines formed under semi-arid conditions. The reconstructed Last Glacial Maximum (LGM) glacial limits are discussed together with the positions of erratics, striated debris, moraines, and glacial polish of the valley flanks, 12 valley- and glaciercross-profiles of the Mendoza glacier system as well as te photographs, providing evidence by the arrangement of the positions. The chapter also provides an overview on the Rio Mendoza valley in which a glacier terminus is represented by moraines with striated boulders at 1870 m a.s.1. On the eastern flank of the Cerros del Chacay, a glacier reached down to 2060 m a.s.l. Thus, in the Cerro Aconcagua and adjacent massifs, that is, the Cerro Tupungato and the Cerro Juncal, an ice stream network exist that comprised ice streams up to 112.5 km long and vertical ranges of up to 5150 m.