Issyk-Kul Basin Research Articles

Concentration and correlation analysis of hydro-meteorological factors in the northern sub-basin of Lake Issyk-Kul in Central Asia

This paper, based on the non-parametric tests and wavelet analysis, analyzed monthly precipitation and runoff data of the small basin in the northern part of the Lake Issyk-Kull basin over the nearly 62-year period, the concentration and correlation of precipitation and runoff in the small bowl of the north Lake Issyk-Kull basin. The results indicated that (1) the Cholpon-Ata River runoff (runoff 1) and the Chong-Ak-Suu River runoff (runoff 2) in the small watershed in the northern part of Lake Issyk-Kull basin are from June to April, January, and from September to November showed a significant increasing trend. The significant abrupt growth change occurred in 1983, while the precipitation at the Cholpon-Ata station showed a significant increasing trend in February, with a sharp point around 1980. (2) The concentration degree (Cd) index of runoff 1 in the small watershed in the northern part of the Lake Issyk-Kull basin has increased but not significantly, and the Cd index of precipitation and runoff 2 showed an insignificant decrease. (3) The Cd index of runoff 1 in the small watershed in the northern part of Lake Issyk-Kull basin existed for 10 years and 18 years, and the Cd index of River 2 existed for 9 years and 13 years. In contrast, the precipitation Cd index was significant at 4- and 15-year cycles. (4) On multiple time scales, they have a significant negative correlation between the runoff and precipitation in the small watershed in the northern part of the Lake Issyk-Kul basin from May to September.

Geochemistry of lanthanides in thermal waters of Issyk-Kul Lake Basin

The distribution and abundance of lanthanides in thermal waters of the northern Tien Shan (Issyk-Kul lake basin) were studied. Waters are represented by three types: Na-Cl-SO4-HCO3, Na-Ca-Cl-SO4 and Na-Ca-Cl, demonstrates alkaline pH (7.3–9.7) and Eh from -260 to +98 mV. Discharge temperature varies from 15 to 50oC, and total dissolved solids from 0.2 to 13.0 g/l. It is established that lanthanides (or rare earth elements, REE) concentrations vary from 0.07 to 0.81 ppb, the maximal concentrations relate to a Na-Ca-Cl water type, which demonstrates the influence of reverse ion exchange. The total concentration of rare earth elements roughly increases as pH decreases, implying that the absolute abundance of REE is totally controlled by pH conditions. The ΣREE concentrations in groundwater exhibit a high positive correlation (R=0.8) with the total dissolved solids contents indicating that ΣREE are well related to the salinity of the thermal water samples. The major ions HCO3, SO4, Ca, K, and Mg have minor associations with REE. The geochemical and geological data suggest that the principal REE source of the thermal waters is bedrock mineralogy and lithology. The distribution and abundance of REE in thermal waters of Issyk-Kul basin were studied for the first time.

Assessing climate stability and greenhouse gas emissions in Issyk-Kul basin of Kyrgyzstan: A Focus on the tourist season

Assessing climate stability and greenhouse gas emissions in Issyk-Kul basin of Kyrgyzstan: A Focus on the tourist season

Changes in humus content on the territory of agricultural lands in the Issyk-Kul basin of Kyrgyzstan

The Issyk-Kul valley of Kyrgyzstan has very large diversity of soil types which is developed by complex of abiotic and biotic factors including mountain-valley landscapes and different climatic conditions. We found that there is a process of significant loss of humus content in almost all studied areas of the Issyk-Kul region, both in the upper and lower layers of the soil. The humus content has been significantly decreased in the upper layer of valley soils during the past four decades. Among them, mountain-valley chestnut and dark chestnut soils, represented in the Issyk-Kul region, showed themselves to be the most depleted. Here, the difference in humus content between the top arable and non-arable layers is 40%. More stable humus content is shown in the mountain light chestnut and mountain-valley light brown soils, presented in certain areas of the Ton, Ak-Suu and Tyup districts. Apparently significant decrease in the humus content in chestnut soils is associated with intensive long-term anthropogenic use, including non-compliance with agrotechnical standards.

Quantifying the impact of climate and vegetation changes on runoff based on the budyko framework in the Lake Issyk-Kul Basin, Kyrgyzstan

Identifying and quantifying the drivers of runoff (R) variability is fundamental to our understanding of the hydrologic cycle and necessary for decision makers to manage water resources. Climate variables and vegetation are the main factors influencing the R. However, the effects of climate and vegetation changes on R are still poorly understood, especially in arid regions with limited water resources. This study quantifies the contribution of precipitation (PRE), potential evapotranspiration (ET0), and Normalized Difference Vegetation Index (NDVI) to R in Lake Issyk-Kul Basin (LIKB) dryland Central Asia by using the Budyko model. The results showed that R, PRE, and ET0 decreased from 2000 to 2020, while the NDVI and underlying parameter (ω) showed a slightly increasing trend. By using the Mann-Kendall (M-K) statistical approach, divided the R series into a baseline period (2000–2010) and a change period (2011–2020) based on the breakthrough point (2011). In the baseline period, R showed a decreasing trend, while in the change period, R showed an increasing trend of 1.8 mm/yr. The sensitivity analysis shows that a 1 mm increase in PRE results in a 0.48 mm increase in R (sensitivity coefficient to R is 0.48). Conversely, a 1 mm increase in ET0 (sensitivity coefficient to R of −0.03) and a 1 unit increase in NDVI (sensitivity coefficient to R of −343.31) lead to R decreasing by 0.03 and 343.31 mm, respectively. The relative contributions of PRE, ET0 and NDVI were 33.98%, −3.17% and 3.67%, respectively, suggesting that changes in PRE and NDVI contributed to the decrease in R while the opposite for ET0. PRE dominated the decrease in R, which decreased by 26.58 mm, leading to a decrease in R of 12.76 mm. A decrease of 65.33 mm in ET0 and an increase of 0.003 in NDVI resulted in an increase and decrease of 1.96 and 1.18 mm in R, respectively. This study enhances the understanding of the response of the water cycle to climate and vegetation changes in arid regions and can provide theoretical support for water resource management and ecological restoration.

Crustal deformation of intermontane basins beneath Central Tien Shan revealed by full-wave ambient noise tomography

The Tien Shan is one of the highest, youngest, and most active orogenic belts at the southwestern margin of Central Asia. The topography of the Central Tien Shan is characterized by nearly parallel orogenic belts with interposing intermontane basins, providing an ideal site to investigate the formation and modification of the intermontane basins. Here we construct a high-resolution crustal velocity model of the Central Tien Shan using full-wave ambient noise tomography based on high-quality Rayleigh wave empirical Green's functions at periods of 5–50 s extracted from the dense seismic array during 1997–2000. Our new model reveals two high-velocity crustal anomalies beneath the Naryn Basin and Issyk-Kul Basin, respectively, and widespread low-velocity anomalies in the middle to lower crust beneath the mountain belts. We propose that the high-velocity crustal features of the Naryn Basin and Issyk-Kul Basin may be the remnant structures from the Palaeozoic collision. Widespread low-velocity anomalies reflect mantle upwelling and partial melting due to the Kazakh and Tarim lithosphere underthrusting, which have been consequently modifying the overlying crustal structures. High-resolution tomographic results reveal significant crustal heterogeneities beneath the Central Tien Shan, which shed new light on the continental growth mechanism and the crustal deformation of intermontane basins.

Identification of conservation priorities in the major basins of Central Asia: Using an integrated GIS-based ordered weighted averaging approach

Ecosystem services (ESs) provided by the major basins of Central Asia are critical to human well-being and have attracted the attention of the international community. The identification of conservation priorities is of great significance for the maintenance and protection of key ESs. In this study, we quantified the spatiotemporal changes of net primary productivity (NPP), soil conservation (SC), water yield (WY) and habitat quality (HQ) in the major basins of Central Asia from 1995 to 2015. In addition, a GIS-based ordered weighted averaging (OWA) multi-criterion valuation method was adopted to identify potential conservation areas under 11 scenarios. Conservation priorities were determined by comparing the conservation efficiency under each scenario. Then, a broad range of indicators were considered to distinguish the driving factors affecting ESs in conservation priorities. The results show that the average conservation efficiency in the Issyk-Kul Basin was the highest, followed by the Am Darya Basin, Ili-Balkhash Basin and Syr Darya Basin. We observed that the conservation efficiency of the four ESs declined continuously in the Ili-Balkhash Basin from 1995 to 2015, while it changed steadily in the other three basins. Correlation analysis indicated that natural factors (e.g., precipitation and topography) were the main driving factors of WY, SR and NPP in conservation priorities, while HQ was more affected by socio-economic factors (e.g., population density and both cropland and urban percentages). The identification of conservation priorities and their driving factors plays an important role in ensuring the ecological security of the lower reaches, regulating the regional water balance and stabilizing the climate pattern.

Exploring the relationship between key ecosystem services and socioecological drivers in alpine basins: A case of Issyk-Kul Basin in Central Asia

Natural changes and human disturbance have far-reaching influences on ecosystem services (ESs) in arid alpine basins. In this paper, the Issyk-Kul Basin (IKB) is taken as a case study to systematically quantify 5 ES distributions and determine ES hotspots/coldspots. We used Spearman correlation analysis to explore trade-offs and synergies between ESs. Then, ES bundles and socioecological drivers of ESs were identified by utilizing K-means clustering and redundancy analysis (RDA). The results revealed that the water yield (WY) and soil retention (SR) in the IKB increased significantly from 1992 to 2015, but food production (FP) and habitat quality (HQ) exhibited decreasing trends. Correlation analysis indicated a synergistic relationship between SR and WY/NPP (R = 0.34/R = 0.68; p < 0.001), and a trade-off relationship between FP and HQ (r = −0.35; p < 0.01). Based on cluster analysis, three ES bundles were identified, including the “Agriculture bundle”, “Soil & vegetation bundle” and “Habit quality bundle”. Redundancy analysis (RDA) indicated that WY and SR were mainly affected by natural factors (i.e., precipitation, slope and vegetation coverage), while FP and HQ were more sensitive to human factors (i.e., population density, percentage of cropland and percentage of urban). Our findings promote a better understanding of the complex relationship between ESs, and provide a reference for developing win-win management strategies for socioeconomic development and ecological protection in alpine basins.

Active Tectonics and Paleoseismicity of the Eastern Issyk-Kul Basin (Kyrgyzstan, Tien Shan)

Abstract—The Malyi Orgochor, Orgochor, Birbash, Sukhoi Ridge, Ichketosma, and Tosma uplifts in the eastern Issyk-Kul basin are fault-related anticlinal folds composed of Neogene and Quaternary sediments involved in tectonic movements. The folds have asymmetric transversal profiles, with low-angle southern limbs and steep northern limbs cut by segments of the South Issyk-Kul and Karkara reverse faults reactivated in the late Quaternary. The location and geometry of the two faults, which both show reverse and left-lateral strike slip components, correspond to neotectonic propagation of deformation from the Terskey-Ala-Too Range over almost the whole eastern Issyk-Kul basin. Judging by primary and secondary coseismic surface deformation in the area, the South Issyk-Kul and Karkara faults repeatedly generated large earthquakes (M ≥ 7, I ≥ 9) in the Late Pleistocene and Holocene. According to trenching results, the historical earthquakes that occurred in the first and 10–11th centuries accommodated motions on the South Issyk-Kul fault. The new seismotectonic and paleoseismicity data from the eastern Issyk-Kul basin provide updates to its seismic potential.

Trend Analysis of Annual and Seasonal River Runoff by Using Innovative Trend Analysis with Significant Test

This study investigated the temporal patterns of annual and seasonal river runoff data at 13 hydrological stations in the Lake Issyk-Kul basin, Central Asia. The temporal trends were analyzed using the innovative trend analysis (ITA) method with significance testing. The ITA method results were compared with the Mann-Kendall (MK) trend test at a 95% confidence level. The comparison results revealed that the ITA method could effectively identify the trends detected by the MK trend test. Specifically, the MK test found that the time series percentage decreased from 46.15% in the north to 25.64% in the south, while the ITA method revealed a similar rate of decrease, from 39.2% to 29.4%. According to the temporal distribution of the MK test, significantly increasing (decreasing) trends were observed in 5 (0), 6 (2), 4 (3), 8 (0), and 8 (1) time series in annual, spring, summer, autumn, and winter river runoff data. At the same time, the ITA method detected significant trends in 7 (1), 9 (3), 6(3), 9 (3), and 8 (2) time series in the study area. As for the ITA method, the “peak” values of 24 time series (26.97%) exhibited increasing patterns, 25 time series (28.09%) displayed increasing patterns for “low” values, and 40 time series (44.94%) showed increasing patterns for “medium” values. According to the “low”, “medium”, and “peak” values, five time series (33.33%), seven time series (46.67%), and three time series (20%) manifested decreasing trends, respectively. These results detailed the patterns of annual and seasonal river runoff data series by evaluating “low”, “medium”, and “peak” values.

Destruction of Medieval Archaeological Monuments by Strong Earthquakes in the Southwestern Issyk-Kul Basin, Tien Shan

The destruction of a major archaeological site in the 7th–9th centuries clearly demonstrates a lack of seismic knowledge of the region and, as a result, the neglected and underestimated seismic hazard assessment in the Alabash-Konur-Oleng Depression region near the southern border of the Issyk-Kul basin on the map of the Kyrgyz Republic. The aim of the field studies was to assess the consequences of a seismic event, to identify damage to the integrity of archaeological structures, and to estimate the strength of an earthquake in a given region. To search for archaeological sites, aerial photography of the site along the Akterek River was carried out—from the coast to the elevation of the Duvana Mountains. Field studies in the southern Issyk-Kul basin and the Alabash-Konur-Oleng Depression led to the discovery of an ancient destroyed complex on the southern slope of the Duvana Mountains. This structure, located on a seismotectonic scarp, was destroyed by it and absorbed by a seismotectonic graben. Most likely, a strong (I0 ≥ 9) earthquake occurred during the complex’s existence, the 7th–9th centuries (?). There are other archaeological sites of various age in the Alabash-Konuroleng depression, bearing traces of the strongest seismic impacts, the study of which can help extend the seismic catalog for centuries and contribute to a more accurate seismic hazard assessment of the area of currently rising uplifts—the Adyrs (foothills) of the Terskey Ala-Too Range.

Changes in intra-annual runoff and its response to climate variability and anthropogenic activity in the Lake Issyk-Kul Basin, Kyrgyzstan

An attribute study of the runoff changes due to climate change and anthropogenic activities is of great value to determining the best response to runoff changes. This study investigates the evolution of the intra-annual runoff and evaluates the effects of changes in climate and anthropogenic activities on runoff variations in the Lake Issyk-Kul Basin (LIKB). The monotonic trend test and wavelet transform analysis were used to characterize the trends and periods of the hydro-meteorological variables in the LIKB. In addition, the periodicity-trend superposition model and double-mass curves were used to assess the contributions of climate change and anthropogenic activities to runoff variations. The analyses were conducted using regional climate data combined with runoff data derived from 13 different river stations in the LIKB for the period between 1943 and 2012. The results indicate the following. (1) The monthly runoff trends in the three groups of tributaries (northern, southeastern, and southern tributaries) exhibit distinct differences, and the percentage of the data sets with no pattern gradually increased (from 26% to 38%) from north to south. There is a positive trend, with a similar decrease (from 50% to 24%) from north to south. (2) The air temperature, precipitation, and runoff in the LIKB increased throughout the low and high flow periods. The statistical index of the runoff concentration degree (RCD) decreased at most stations (Chong-Koi-Suu, Chong-Ak-Suu, Chong-Urykty, Pzhergalan, Ak-Sai, Tossor, Ton, Chong-Kyzyl-Suu, Tamga, and Karakol), except for the Cholpon-Ata, Ak-Suu, and Dzhuuku stations. (3) In addition, the periodic characteristics of the RCD show that the RCD has a 12-year significant period over the low flow period, which is similar to that for precipitation but varies from that for air temperature. (4) Climate variability and anthropogenic activities are two different contributors to runoff reduction in the LIKB. The respective contributions of anthropogenic activities to the runoff determined using the two methods were 35.3% and 18%, whereas the climate change contributions were 64.7% and 82%, respectively. Climate change was the main reason for the runoff variations. These results provide a basis for the scientific management and sustainable allocation of water resources in the LIKB.

Innovative Trend Analysis of Precipitation in the Lake Issyk-Kul Basin, Kyrgyzstan

The analysis of various characteristics and trends of precipitation is an essential task to improve the utilization of water resources. Lake Issyk-Kul basin is an upper alpine catchment, which is more susceptible to the effects of climate variability, and identifying rainfall variations has vital importance for water resource planning and management in the lake basin. The well-known approaches linear regression, Şen’s slope, Spearman’s rho, and Mann-Kendall trend tests are applied frequently to try to identify trend variations, especially in rainfall, in most literature around the world. Recently, a newly developed method of Şen-innovative trend analysis (ITA) provides some advantages of visual-graphical illustrations and the identification of trends, which is one of the main focuses in this article. This study obtained the monthly precipitation data (between 1951 and 2012) from three meteorological stations (Balykchy, Cholpon-Ata, and Kyzyl-Suu) surrounding the Lake Issyk-Kul, and investigated the trends of precipitation variability by applying the ITA method. For comparison purposes, the traditional Mann–Kendall trend test also used the same time series. The main results of this study include the following. (1) According to the Mann-Kendall trend test, the precipitation of all months at the Balykchy station showed a positive trend (except in January (Zc = −0.784) and July (Zc = 0.079)). At the Cholpon-Ata and Kyzyl-Suu stations, monthly precipitation (with the same month of multiple years averaged) indicated a decreasing trend in January, June, August, and November. At the monthly scale, significant increasing trends (Zc &gt; Z0.10 = 1.645) were detected in February and October for three stations. (2) The ITA method indicated that the rising trends were seen in 16 out of 36 months at the three stations, while six months showed decreasing patterns for “high” monthly precipitation. According to the “low” monthly precipitations, 14 months had an increasing trend, and four months showed a decreasing trend. Through the application of the ITA method (January, March, and August at Balykchy; December at Cholpon-Ata; and July and December at Kyzyl-Suu), there were some significant increasing trends, but the Mann-Kendall test found no significant trends. The significant trend occupies 19.4% in the Mann-Kendall test and 36.1% in the ITA method, which indicates that the ITA method displays more positive significant trends than Mann–Kendall Zc. (3) Compared with the classical Mann-Kendall trend results, the ITA method has some advantages. This approach allows more detailed interpretations about trend detection, which has benefits for identifying hidden variation trends of precipitation and the graphical illustration of the trend variability of extreme events, such as “high” and “low” values of monthly precipitation. In contrast, these cannot be discovered by applying traditional methods.

МОРФОГЕНЕТИЧЕСКИЕ ТИПЫ И ДИНАМИКА РЕЧНЫХ ДЕЛЬТ ГОРНЫХ ОЗЕР

Based on the analysis of published sources, topographic maps, and satellite images, new data were obtained on the hydrological regime, morphology, size and dynamics of river deltas in the lakes inthe mountains of southern Russia and Mongolia. For high mountain lakes (Baikal, Issyk-Kul, Son-Kul, Chatyr-Kul, Sevan, lakes of Mongolia), most small rivers form alluvial fans with numerous channels. Large rivers flowing into the valley bays form multi-arm lobed padded deltas (Issyk-Kul Lake). Less common are blocked estuaries, deltas filling estuarine lagoons and prograding deltas on the open coasts (Lake Baikal, some lakes of Mongolia). The most studied are the river deltas flowing into Lake Baikal and Issyk-Kul. During the Pleistocene, River Selenga formed three alluvial fans with a total area of 1.8 thousand km 2 : 1) the Middle Pleistocene fan at 12–13 m above the level of Lake Baikal (457 m a.s.l.); 2) the Late Pleistocene fan at 8–12 m, and 3) the Holocene fan at 0.5–2 m. Over the past 78 thousand years, the Selenga River has prograded its delta by about 20 km into the lake. For the period 1980–2013 no delta growth has been observed. Lake Issyk-Kuls level fluctuations had a strong influence on the formation of the hydrographic network of the Issyk-Kul basin and on the dynamics of river mouths. Deep regression at the end of the Upper Pleistocene led to a lake area reduction by 2000 km 2 , incision of the rivers of the Issyk-Kul basin into lacustrine shelf deposits and the development of erosive river valleys along the entire perimeter of the lake, preserved to date in the form of flooded underwater valleys. In the recent epoch, most of the rivers of the Issyk-Kul basin have cut through mouth estuaries and over the past 150 years have formed various morphodynamic types of deltas (from the open-coast alluvial fans to multi-branch deltas filling ingression gulfs). One to three km elongation of the high-discharge rivers occurred during this period. The increase in the area of river deltas over the past 30 years (the total effect of the decrease of the lake level and accumulation of alluvium) ranged from 0.01 to 0.07 km 2 . Several large rivers of Russia (Upper Angara, Selenga) and Mongolia (Teysin-Gol, KobdoGol) have delta areas from 200 to 500 km 2 , the remaining deltas do not exceed 50 km 2 . The current progradaion rate of most lake deltas over the past 30 years is very low due to an extremely insignificant load of suspended sediment, with the exception of some large rivers.

Paleoseismicity of Adyr Faults: The Kokonadyr–Tegerek Fault, Southwestern Issyk-Kul Region, the Tien Shan

We have studied paleoseismicity along the adyr (piedmont) Kokonadyr–Tegerek fault zone in the SW Issyk-Kul region. We have shown that although earthquake slip continues in the tectonic contact zone between the Paleozoic rocks of the Kokonadyr–Tegerek uplift and the Quaternary deposits of the Alabash–Konuroleng trough, still most earthquake-generating ruptures visible at the surface are moving for some hundreds of meters southward from the abovementioned adyr fault. This process leads to the formation of multislip earthquake scarps and compensation grabens behind them. Radiocarbon dating identified four large Holocene earthquakes along the Kokonadyr–Tegerek fault zone that occurred during the following time spans: 1771‒1785, 1440‒1515, as well as probably 2310–745 B.C. and 6400–5300 B.C. Judging from the parameters of these ruptures, or earthquake scarps, their magnitudes were greater than or equal to 7 and the intensity of shaking was Io ≥ IX. Vigorous seismic activity has gone on along the Kokonadyr–Tegerek fault zone since at least the Middle Quaternary. The relevant evidence includes uplifted and abandoned valleys of this age in the eponymous uplift and considerable accumulations of lacustrine deposits in the northern Alabash–Konuroleng depression. The thick sedimentary sequence was caused by glacier melting on the northern slope of the Terskei Ala-Too mountain range, while the abandoned valleys indicate considerable tectonic damming. The most suitable model to explain the formation of adyrs (piedmont areas or foothills) in the southern Issyk-Kul basin seems to be a model that envisages a low-angle northward propogating or southward dipping main fault that is complicated with reverse movements. All the materials acquired in this study can be used to develop a new Earthquake Hazard Map for the Republic of Kyrgyzstan.

BRONZE PLAQUES FROM NORTHERN KYRGYZSTAN WITH REPRESENTATIONS OF HORSEMEN

We describe bronze plaques representing armed horsemen, found in the Issyk-Kul Basin and in the Chuya valley, northern Kyrgyzstan, and owned by public and private museums in Bishkek. Similar plaques from southern Siberia and Central Asia were described by many Russian, Kazakh, Kirghiz, and Mongolian historians and archaeologists. A formal classifi cation of plaques is proposed, and their chronology, cultural attribution, and function are assessed. Such items, associated with early medieval Turkicspeaking nomads of Tian Shan and Semirechye, are similar to those worn by the Yenisei Kyrgyz of the Minusinsk Basin in southern Siberia, by the Kimek of the steppe Altai and the upper Irtysh in Kazakhstan, by the Qarluq of southwestern Central Asia, and by other Turkic tribes inhabiting areas from the Ural to Mongolia.

Large ancient earthquakes in the western Issyk-Kul basin (Kyrgyzstan, northern Tien Shan)

New paleoseismological and archaeoseismological data from the western Issyk-Kul basin of Kyrgyzstan (northern Tien Shan) provide new insights on active fault in the actively-deforming, basement-involved thrust system of Central Asia. Newly discovered fault scarps follow south-and north-dipping thrust faults which delineate the Kyrgyz and Kungey ranges bordering the Issyk-Kul basin. Motion on these faults generated earthquakes with magnitudes 6.2–7.6 and MSK-64 shaking intensities VIII-XI. Deformation observed in the zone of the Toguz-Bulak fault results from two Holocene earthquakes and another event that occurred about 8000 yr BP. Two more events, at 13,000 and 3000 yr BP, deformed the northeastern periphery of the Kyzyl-Ompul Uplift. Archaeoseismological research in the Northern Sary-Bulun settlement in the western periphery of the Boz-Barmak Uplift, revealed traces of another earthquake of MSK-64 shaking intensity I ≥ VIII dating back to the 12th Century. The obtained data correlates well with results of previous paleoseismological and archeoseismological studies. They show that in the northern Tien Shan there were clusters of strong earthquakes with ages of 14–13, 8, 4–3 ka ago and in the 11–12th centuries AD divided by periods of 4–5 ka. We infer that coseismic slip on these faults may have formed a tectonic dam at the edge of the basin through growth of the Boz-Barmak Uplift, and this dam ultimately deflected the Chu River into its modern channel which bypasses the lake. Lacustrine sediments in the northeastern periclinal segment of the Boz-Barmak Uplift bear signatures of soft-sediment deformation structures (seismites) corresponding to seven M ≥ 5–5.5 (I ≥ VI-VII) earthquakes timed at about 20,000 yr BP.

Regional Geomorphological Conditions Related to Recent Changes of Glacial Lakes in the Issyk-Kul Basin, Northern Tien Shan

To assess the current state of glacial lakes, we examine the seasonal lake-area changes of 339 glacial lakes in the Teskey and Kungoy Ranges of the Issyk-Kul Basin, Kyrgyzstan, during 2013–2016 based on optical satellite images (Landsat7/ETM+ and 8/OLI). The glacial lakes are classified into six types based on their seasonal variations in area: stable, increasing, decreasing, appearing, vanishing, and short-lived. We then track the number of each type in a given year and examine how each number changes from one year to the next. We find that many appearing, vanishing, and short-lived types occurred in both mountain ranges, having a large variability in number that is not directly related to the local short-term summer temperature anomaly, nor to precipitation or glacier recession. However, those in the Teskey Range vary significantly more than those in the Kungoy Range. To determine if the changing number and distribution of the various lake types may be due to changes in ground ice, we apply differential interferometric synthetic aperture radar (DInSAR) analysis using ALOS-2/PALSAR-2 for the debris landforms behind which glacial lakes appear. In the Teskey Range, ground ice occurs in 413 out of a total of 930 debris landforms, whereas in the Kungoy Range, ground ice occurs in 71 out of 180. In zones with predominant glacier-retreat during 1971–2010 (from Corona KH-4B and ALOS/PRISM), the Teskey Range had 180 new lake depressions as potential lake-basins, whereas the Kungoy Range had just 22. Existing depressions also expanded when melting ice produced subsidence. Such subsidence, together with debris landforms containing ground ice and ice tunnels, appear to cause the observed large number variability. In particular, the deposition of ice and debris by tunnel collapse or the freezing of storage water in a debris landform may close-off an ice tunnel, causing a lake to appear. Subsequent re-opening via melting of such blockage would produce either a vanishing or a short-lived type. In this way, the large variability in the number of each lake type and the distribution of types over this four-year period arises from regional geomorphological conditions and not directly from the local short-term summer temperature anomaly and precipitation or glacier recession.

Spatial differentiation in stable isotope compositions of surface waters and its environmental significance in the Issyk-Kul Lake region of Central Asia

Stable isotope values of oxygen (18O) and hydrogen (2H) of surface waters were used to study the origin and environmental significances in the Issyk-Kul basin of Kyrgyzstan in Central Asia, which is the most important intermountain basin in the modern Tien Shan orogen. This study is the first analysis of hydrochemical spatial differentiation in the stable isotopes of surface waters in this watershed. 75 samples were collected from rivers, springs, lakes, rain and snow during the rainy season in July and August of 2016. Stable isotopes of 18O and 2H were studied for all samples, and cation ratios (Sr/Ca and Mg/Ca) were also determined for lake water samples. Stable isotope values from precipitation scattered around the Local Meteoric Water Line (determined from Urumqi Station of the global network of isotopes in precipitation (GNIP)), together with values of the Deuterium excess parameter (d) from 15.3‰ to 30.5‰, with an average of 19.8‰, indicating that the moisture sources are primarily from regions with low relative humidity. The δ18O and δ2H values were significantly different between the river and lake samples, indicating that regional evaporation caused the isotopic enrichment of lake water. Geospatial autocorrelation, measured by Moran’s I coefficient, indicated weak spatial autocorrelation within stable isotopes of oxygen and hydrogen in the surface waters of the studied area, which is primarily an effect of climate during the water chemistry evolution. The cation ratios Sr/Ca and Mg/Ca in lake water samples were not correlated with the concentration of total dissolved solids, but did show correlation with stable isotopic values, which is significant for paleoenvironmental reconstruction.

天山北部地域，イシク・クル湖流域における氷河湖の面積変動と地形環境

天山北部地域，イシク・クル湖流域における氷河湖の面積変動と地形環境