Glacial Flooding & Disaster Risk Management Knowledge Exchange and Field Training July 11-24, 2013 in Huaraz, Peru HighMountains.org/workshop/peru-2013
GLOF and glacier-‐related hazards and risk in Tajikistan Tetsuya Komatsu and Teiji Watanabe Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan 1. Introduction Glaciers in high mountain regions not only give benefits to human activities in respect of water sources for drinking water, irrigation and energy generation, but also occasionally cause hazards such as glacial lake outburst floods (GLOFs) and ice avalanches. Accordingly, various assessments and mitigations to the glacier-‐related hazards have been undertaken worldwide (e.g. Quincy et al. 2007). The Pamir is one of the high mountain regions in Asia, where assessment investigations to glacier-‐related hazards are few (Schneider et al. 2010; Mergili & Schneider 2011) although glacier-‐related hazards and their threats have been recently reported (e.g. Shodomonov 2012). More activities for reducing the potential risks of glacial-‐related hazards should be required hereafter. This paper, focusing on the Tajik Pamir, aims to examine: (1) the contemporary glacial features, (2) characteristics of documented hazards associated with glaciers, and (3) the current status of the hazard assessment. 2. The Pamir, glaciers, and glacial lakes The terrain of the Tajik Pamir differs distinctly between the western and eastern areas. The western Tajik-‐Pamir (west from ca. 73°E) is distinguished as a combination of the predominantly west-‐east trending mountain ranges in altitudes from 5,000–7,000 m, and the deep, narrow valleys. In contrast, the eastern Tajik Pamir (east from ca. 73°E) comprises the broad valleys and basins bordered by the more subdued mountain ranges with altitudes of 5,000–6,000 m. The climate of the Pamir is represented by sub-‐continental and arid continental climate. The moisture delivered to the Pamir is mainly from the Westerlies: two-‐thirds of the annual precipitation occurs during the winter and spring seasons (Aizen 2011). The western Tajik Pamir generally receives greater amounts of the mean annual precipitation (200–2,000 mm/y) compared to the eastern Tajik Pamir (< 100–200 mm/y). The settlements in the Tajik Pamir are concentrated in the valley floors of the western Tajik Pamir, except for several eastern villages (e.g. Murgab); most residence, infrastructure and arable field in the western Tajik Pamir are situated on the alluvial fans/cones developing on the tributary mouths (Watanabe 2000). This situation makes the potential risk for geohazards (GLOF and flash flood) higher in the western Tajik Pamir. 1
In the Tajik Pamir, 6,730 glaciers, of which the total area attains 7,493 km2, have been identified by the Institute of Geography, the USSR Academy of Sciences (Kotlyakov et al. 2010a). Scattered cirques and small valley glaciers dominate in the western Tajik Pamir (west from ca. 73°E). Large glacier complexes comprising two or more individual valley-‐glaciers (e.g. the Fedchenko Glacier) can be often found in the northeastern most portion of the western Tajik Pamir. In contrast, smaller valley glaciers or slope niche glaciers largely occupy in the arid eastern Tajik Pamir. A notable feature of the Pamirian glaciers is that some of them show dynamic instability, which can be regarded as ‘surging’: 630 surge-‐type glaciers have been identified in total in the Tajik Pamir up until 1991 (Kotlyakov et al. 2010b). Systematic investigations to clarify the distribution, type and development of glacial lakes have been conducted only in the southwestern Tajik Pamir (the Gunt and Shakhdara valleys) by Mergili & Schneider (2011) and Mergili et al. (2012). These studies cover the period 1968–2009 using multitemporal satellite images: 172 glacial lakes (an area of ≥2,500 m2) have been identified in the 2007/2008 images. The 172 glacial lakes are mostly located at 4,400–4,700 m (Mergili et al. 2012). This altitudinal zone is significantly higher than the altitudes ranging from 3,810–4,000 m, which are calculated as lower boundary of discontinuous permafrost (permafrost probable) by Müllebner (2010). This situation in the southwestern Tajik Pamir is at least a favorable factor for the stability of the ice core (dead ice) underneath the lake-‐dammed moraines. 3. Glacier-‐related hazards in the Tajik Pamir The report published from the Department of Hydrometeorology in Tajikistan (Makhmadaliev et al. 2008) indicates that 9 GLOFs and 1 glacier-‐related debris-‐flow have occurred in the western Tajik Pamir. On the other hand, 7 GLOFs are confirmed from the website of the MNV Consulting Ltd., which shows the historical records of the major floods in Tajikistan during the period 1894–2000. The detailed information about cause and occurrence location of such glacier-‐related hazards has been obtained from only five events. These hazardous events are closely associated with either glacier surge or glacial lake on moraines. 3.1. Hazard related to glacier surge A well-‐known case of the surge-‐related hazard in the Tajik Pamir is the outburst of the glacial-‐dammed lake, which occurs as a consequence that the tributary glacier advances into the ice-‐free trunk valley and blocks the main river. For instance, such a hazardous surge took place at the Medvezhiy (Bear) Glacier (N38°39’, E72°09’37”), located in the upper reaches of the Vanch Valley, the western Tajik Pamir. Surges of this glacier have been identified six times (1951, 1963, 1973, 1989, 2001, and 2011) (Kotlyakov et al. 2010b). Among these surges, the events in 1963, 1973, 1989, and 2011 have induced the glacier terminus to block the main valley, and close the Abdukagor River.
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3.2. Hazard related to glacial lake on moraines Only one event has been recognized as a hazard related to a glacial lake on moraines in the Tajik Pamir up to now, i.e., a debris flow named ‘the Dasht 2002 event’, which occurred in the tributary headwaters of the Shakhdara valley (the southwestern Tajik Pamir) on 7 August 2002. This hazardous debris flow originated from a glacial lake (the Dasht Lake; N37°13’12”, E71°44’03”, 4,400 m), which had formed on the ice-‐cored end moraine and gained its size to an area of 32,000 m2. The volume of the released water from this lake and that of the entrained debris into the water were estimated to be 32,000 m3 and 1.0–1.5 million m3, respectively (Mergili & Schneider 2011). This debris flow traveled 10.5 km downstream the valley, and attacked the Dasht village (2,620—2,600 m) situated on the alluvial fan; its travel time to the village was considered to be at least 45 minutes based on the voice of the local people (Mergili & Schneider 2011). Eventually, this event destroyed a large part of the village and killed approx. 25 local people. The changes of the Dasht Lake before and after the event can be traced from the observation of the multitemporal satellite images covering the years of 1968, 1973, 1992, 2000, 2002 and 2008, and a 1:50,000 Russian map compiled in 1983–84. The development history of the Dasht Lake suggests that the lake is characterized by the ‘no surface outlet’, ‘repeatedly appeared’, ‘rapidly enlarged’, and ‘short-‐lived’ lake on the ice-‐cored end moraine. Considering these characteristics, the appearance and expansion of this glacial lake are most likely attributed to the temporal blockage of the drainage channel through or beneath the dead-‐ice/till complex, caused by the ice deformation and/or ice-‐debris collapses into the channel, which was observed in Tien Shan (Narama et al. 2010); the sudden discharge (outburst) from the lake is probably due to the blockage failure assigned to the increasing water pressure and/or the atmospheric warming in summer. 4. Applied hazards assessment: A review 4-‐1. Assessment by Schneider and Mergili (2010) Schneider et al. (2010) focused on the potential risk rating of geohazards to each of the selected 209 villages in the Jirgital and Gorno-‐Badakhshan Autonomous Oblast (GBAO) areas, as well in the Zarafshan range, and to provide the proper hazard mitigation recommendations to the respective villages by (1) remote sensing survey, (2) field observation at several key areas including observations from helicopter, and (3) estimates of hazard impacts using computer modeling. The potential hazard risk to the villages is rated to be either of six classes (1: very low hazard to 6: very high hazard), depending on the calculated score; and the confidence level (A: vey high confidence to E: no information) is given to each of such rating results. They showed that 34 villages in the Tajik Pamir (the GBAO and Jirgital area) were rated as over ‘medium hazard (Class 4)’. Regarding the significant glacier-‐related hazards, the following three cases can be extracted from their assessment: (1) ice avalanches caused by glacier 3
detachment, (2) GLOFs, and (3) compounded-‐GLOFs induced by cascade effect. The potentiality of (1) was detected in a hanging-‐glacier (N38°01’, E71°55’), which occupies uppermost reaches of a tributary valley in the Bartnag valley. Both of Bartang and Ravivd villages, located near the mouth of the tributary, were rated ‘medium hazard (Class 4)’. The risks of (2) have been pointed out particularly in the following glacial lakes: (a) glacial lakes proximal to glacier snouts (e.g. supraglacial lakes and moraine-‐dammed lakes) (N37°42’26”, E72°12’34”) and Shadzud village (N37°42’45”, E72°21’40”) in the Gunt valley; (b) the distal glacial lake named Nimatskul (N37°40’30”, E72°04’07”), located in a tributary of the Gunt valley; and (c) the lake dammed by rock-‐glacierized glacier-‐terminus (N38°34’, E72°36’30”), located in the headwaters of Pasor village, the upper Bartang valley. Villages in the downstream of these glacial lakes were assigned to the rate up to the ‘medium hazard (Class 4)’. The case of (3) can occur when a GLOF triggers one or more cascading outburst floods of the downstream lakes. Such cases have been assumed in two glacial lakes in the headwater of Varshedz village (N37°42’, E72°20’50”) and the landslide-‐dammed lake named Rivakkul (N37°36’55”, E72°04’40”) and the glacial lakes in its upstream. In particular, the former lakes have been assessed as the most hazardous glacial lakes in the GBAO, and therefore the Varshedz village, located at the valley mouth, was rated ‘high hazard (Class 5)’. 4-‐2. Assessment by Mergili and Schneider (2011) Mergili & Schneider (2011), based on the GIS and Remote Sensing approaches, focused on assessment of each of the identified alpine lakes about the potentiality and impact of lake outburst hazard. The study area of this assessment covers the Gunt and Shakhdara valleys only. In their assessment, 408 alpine lakes were firstly identified in the study area. Secondary, both of the potentially hazardous lakes and possible hazard-‐impact areas were evaluated thorough the rating and scouring systems. Their results show that 122 lakes were identified as ‘negligible (Class 0)’, 35 lakes as ‘low hazard (Class 1)’, 124 lakes as ‘moderate hazard (Class 2)’, 87 lakes as ‘medium hazard (Class 3)’, 34 lakes as ‘high hazard (Class 4)’, 6 lakes as ‘very high hazard (Class 5)’, and no lakes as ‘extremely high hazard (Class 6)’. Moreover, three lakes were highlighted as the potentially worst hazardous lakes, based on overlaying the possible impact areas of lake outburst floods with the areas of settlements and agriculture/pasture fields. All of these lakes, mentioned also in Schneider et al. (2010), were found in the upper reaches of the tributaries of the Gunt valley: Lake V1 (N37°37’39”, E72°16’16”) ranked as ‘very high hazard’, V2 (N37°36’40”, E72°16’45”) ranked as ‘high hazard’, and N1 (Nimatskul) ranked as ‘high hazard’. The Dasht Lake in 2002 (just before causing the GLOF) was ranked as ‘medium hazard (Class 3)’, which is considered to be underestimation against the actual impact to the downstream.
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5. Remarks on the Tajik-‐Pamirian glacial-‐related hazards 5-‐1. Assumed glacial-‐related hazards Considering both of the past hazardous events (Chapter 3) and the assessment results (Chapter 4), the following three matters: (1) detached glacier, (2) surge glacier, and (3) glacial lake (in particular ‘guerrilla glacial lake’), should be responsible for the major hazards in the Tajik Pamir, especially in the GBAO area. (1) Detached glacier: A hanging glacier, located in a tributary of the Bartang valley, shows the sign of glacier detachment along the transverse crack (Schneider et al. 2010). Ice avalanche by the falling ice bodies may cause serious damage to the downstream villages when the detachment occurs. (2) Surge glacier: Some of the surge glaciers terminate their snouts at the valley confluence to potentially block the ice-‐free main valley after the surge-‐induced advance, and subsequently to form a temporary lake, which is prone to cause outburst floods (e.g. Medvezhiy Glacier). Further, it is reported that a collapsed glacier-‐tongue itself by the surge movement causes an ice-‐water debris flow. Surging behaviors of such glaciers should become a potential disastrous threat in the area. (3) Glacial lake (in particular ‘guerrilla glacial lake’): Potentially hazardous glacial lakes were screened out through the hazard assessment studies (Schneider et al. 2010; Mergili & Schneider 2011) in the most areas of the Tajik Pamir (chapter 4). It should be noted that although an outburst flood from the relatively small-‐size glacial lake (e.g. 32, 000 m2) can cause serious damage to downstream, as exemplified by the Dasht 2002 event, its potential risk could not be appropriately evaluated by these hazard assessment studies. To analyze the case of the Dasht 2002 event, this type of glacial lake should be distinguished as a ‘repeatedly appeared’, ‘rapidly enlarged (within less than one year)’, ‘short-‐lived (within less than two years)’, ‘superficially closed’, and ‘relatively small size’ glacial lake on the ice-‐cored moraine, being appropriate to be designated as a guerrilla glacial lake. Such guerrilla glacial lakes would be discharged unexpectedly, when the blockage to the drainage channels beneath/through the ice-‐cored moraine is failed (e.g. Narama et al. 2010). Because both of the blockage and its failure likely occur depending on the invisible factors in the sub/intra-‐moraine conditions, it is impossible to predict the timing of not only the lake outburst, but also the lake appearance. 5-‐2. Recommended mitigation activity to glacier-‐related hazards Not only glacial lakes assessed as the dangerous lakes, but also those displaying similar features to a guerilla glacial lake, should be assumed to cause a serious hazard to downstream in the Tajik Pamir. In addition, it must be taken into consideration that the early detection of the emergence of the guerrilla glacial lakes should be a key to reducing the GLOF hazards in this area, because unpredicted outburst discharge from such lakes can potentially occur within less than one or more years after its appearance. Regular monitoring of identified 5
hazard factors should be required to prepare appropriate hazard-‐mitigation activities. In other words, a frequent and routine monitoring to all of the glaciers and glacial lakes should be conducted continuously to fulfill these demands. In terms of the cost and efficiency, one of the most suitable ways to such monitoring is to use the earth observation satellite images. In near future, observation of a certain area with frequent repetitions may be practicable by launching many sets of microsatellites such as a 50-‐kg class microsatellites. The observation requests to the microsatellites must be worth considering. Further, the risk assessments to glacier-‐related hazards in the Tajik Pamir have been accomplished in different two ways (Schneider et al. 2010; Mergili & Schneider 2011) at present; however, the assessment areas of these two hardly overlap each other, and do not cover the whole Tajik Pamir. Therefore, the assessment investigation using both of the two approaches should be pursued urgently to diminishing the missing areas such as the Vanch valley. References Aizen, V. 2011. Pamirs. In: Singh, V.P. et al. (eds.) Encyclopedia of Snow, Ice and Glaciers, Dordrecht, Springer, 813–815. Kotlyakov, V.M. et al. 2010a. Glaciers of the former Soviet Union. In: Williams, R.S.Jr., Ferrigno, J.G. (eds.) Glaciers of Asia, U.S. Geological Survey Professional Paper 1386–F–1. Kotlyakov, V.M. et al. 2010b. Investigations of the fluctuations of surge-‐type glaciers in the Pamir based on observations from space. In: Williams, R.S.Jr., Ferrigno, J.G. (eds.) Glaciers of Asia, U.S. Geological Survey Professional Paper 1386–F–1, pp.77–93. Makhmadaliev, B. et al. 2008. The second national communication of the Republic of Tajikistan under the United Nations Framework Convention on Climate Change. State Agency for Hydrometeorology of the Committee for Environmental Protection, Dushanbe, Tajikistan, http://unfccc.int/resource/docs/natc/tainc2.pdf (Accessed May 25, 2012). Mergili, M., Schneider, J.F. 2011. Regional-‐scale analysis of lake outburst hazards in the southwestern Pamir, Tajikistan, based on remote sensing and GIS. Natural Hazards and Earth System Sciences, 11, 1447–1462. Mergili, M. et al. 2012. Changes of the cryosphere and related geohazards in the high-‐mountain areas of Tajikistan and Austria: a comparison. Geografiska Annaler, Series A, 93, 79–96. Müllebner, B. 2010. Modelling of potential permafrost areas in the Pamirs and Alai mountains (Tajikistan) using remote sensing and GIS techniques. Master’s thesis, BOKU University. Narama, C. et al. 2010. The 24 July 2008 outburst flood at the western Zyndan glacier lake and recent regional changes in glacier lakes of the Teskey Ala-‐Too range, Tien Shan, Kyrgyzstan. Natural Hazards and Earth System Sciences, 10, 647–659. Quincy, D.J. et al. 2007. Early recognition of glacial lake hazards in the Himalaya using remote sensing datasets. Global and Planetary Changes, 56, 137–152. 6
Schneider, J.F. 2005. Glacier retreat, glacial lake outburst and surging glaciers in the Pamir, Tajikistan. Geophysical Research Abstracts, Vol. 7, 08129. Schneider, J. F. et al. 2010. Remote geohazards in high mountain areas of Tajikistan. Assessment of hazards connected to lake outburst floods and large landslide dams in selected areas of the Pamir and Alai mountains. Report of the TajHaz-‐Project by the BOKU University Vienna and FOCUS Humanitarian Assistance. Shodomonov, M. 2012. Remote geohazards in Tajikistan: Assessment of the hazards connected to lake outburst floods and large landslides in selected areas of the Pamir and Alai mountains. Andean-‐Asian Mountain Global Knowledge Exchange on Glaciers, Glacial Lakes, Water and Hazard Management, An Adaption Partnership Workshop, 131–132. Watanabe, T. 2000. Environmental impact assessment: geomorphology of the Bartang and Kudara valleys. In: Alford, D., Schuster, R. (eds.) Usoi Landslide Dam and Lake Sarez—An Assessment of Hazard and Risk in the Pamir Mountains, Tajikistan: Geneva, Switzerland, United Nations, ISDR Prevention Series No. 1, pp. 53-‐58. Dr. Tetsuya Komatsu is a research student at the Faculty of Environmental Earth Science, Hokkaido University, Japan. He received his PhD from Hokkaido University in 2010 for his doctoral thesis entitled “Late Quaternary lake-‐glacier interaction in the Karakul closed-‐basin, eastern Pamir.” His major fields of study are Geomorphology and Quaternary Science. Since 2006, he has focused his research largely on Quaternary landscape reconstruction and hazard assessment study in the Pamir. Dr. Teiji Watanabe is a professor, Faculty of Environmental Earth Science, Hokkaido University, Japan. His first visit to Tajikistan was 1999 as a member of the Lake Sarez assessment team sent by the UN-‐ISDR. He has been involved in GLOF and landscape change research in the Nepal Himalaya since 1987, and has been leading a team to the Tajik and Kyrgyz Pamir since 2005 for establishing sustainable mountain society.
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