PARTICIPATING INSTITUTIONS • Centre for Inter-disciplinary Studies of Mountain & Hill Environment, University of Delhi, Delhi • Centre for Atmospheric Sciences, Indian Institute of Technology, Delhi • Centre for Himalayan Studies, University of North Bengal, Distt. Darjeeling • Department of Geography and Applied Geography, University of North Bengal, Distt. Darjeeling • Salim Ali Centre for Ornithology and Natural History, Anaikatti, Coimbatore • Water and Power Consultancy Services (India) Ltd., Gurgaon, Haryana • Food Microbiology Laboratory, Department of Botany, Sikkim Government College, Gangtok VOLUMES INDEX* Volume – I INTRODUCTORY VOLUME Volume – II LAND ENVIRONMENT - GEOPHYSICAL ENVIRONMENT Volume – III LAND ENVIRONMENT - SOIL Volume – IV WATER ENVIRONMENT Volume – V AIR ENVIRONMENT Volume – VI BIOLOGICAL ENVIRONMENT TERRESTRIAL AND AQUATIC RESOURCES Volume – VII BIOLOGICAL ENVIRONMENT - FAUNAL ELEMENTS Volume – VIII BIOLOGICAL ENVIRONMENT - FOOD RESOURCES Volume – IX SOCIO-ECONOMIC ENVIRONMENT Volume – X SOCIO-CULTURAL ENVIRONMENT EXECUTIVE SUMMARY AND RECOMMENDATIONS *For Volume-wise Detailed Index – Refer to the end of the report CONTENTS Page No. CHAPTER 1 GEOLOGY AND SEISMICITY 1.1 GEOLOGICAL FRAMEWORK 1 1.1.1 Sub-Himalayan Domain 3 1.1.2 The Lesser Himalayan Domain 3 1.1.3 Higher Himalayan Domain 3 1.1.4 The Tethyan Belt 3 1.2 STRATIGRAPHY 4 1.3 STRUCTURE, TECTONICS AND METAMORPHISM 8 1.3.1 The Rangit Tectonic Window 10 1.3.2 The Main Central Thrust Zone 11 1.3.3 Movement along the structural planes 15 1.4 GEOMORPHOLOGY 17 1.5 MINERAL RESOURCES 17 1.5.1 Mineral and Rock Resources 19 1.6 SEISMICITY 31 1.6.1 Seismic Zoning 33 1.6.2 Isoseismal Zones 35 1.6.3 Recent Earthquake in Sikkim 36 1.6.4 Microearthquake Surveys 37 1.7 GEOLOGICAL INVESTIGATIONS IN TEESTA BASIN IN SIKKIM 39 1.7.1 Bop Nala Region 39 1.7.2 Chakung Chhu- Teesta Confluence Region 40 1.7.3 Ralang region within Rangit Window 41 1.7.4 Geology around Rolep in East Sikkim 43 1.7.5 Geology along Teesta between Tong to Mangan 44 1.7.6 Geology along Teesta between Mangan to Rangpo 45 1.8 SPATIAL DISPOSITION OF STUDIED REGIONS ON THE 47 SEISMOTECTONIC MAP OF SIKKIM 1.9 GEOLOGICAL SENSITIVITY AND VULNERABILITY 49 CHAPTER 2 LANDSLIDES 2.1 INTRODUCTION 52 2.2 STATUS OF LANDSLIDES IN TEESTA BASIN 54 2.3 SOME EXISTING LANDSLIDES IN SIKKIM 56 2.3.1 District-wise Scenario 58 2.4 CASE HISTORIES OF SOME IMPORTANT LANDSLIDES 66 2.4.1 The Rangpo-Dikling Landslide Complex 66 2.4.2 Chandmari- Tathangchen Landslide Complex 68 2.4.3 Landslide Complex in the region between Mangan to Tong 71 2.4.4 B2 Slide Complex along Gangtok-Dikchu Road 74 2.4.5 Rangpo Slide 74 2.4.6 Lukhbir and Berrik Slides in West Bengal 75 2.4.7 Landslides along the Lachung Axis 75 2.4.8 Landslides along Teesta upstream of Chungthang 76 2.5 ENVIRONMENTAL IMPACT OF THESE SLIDES 77 2.6 REMEDIAL MEASURES TO PREVENT LANDSLIDES 80 2.6.1 Keeping soil free of moisture 80 2.6.2 Increasing soil strength 82 2.6.3 Toe protection works 82 2.6.4 River Training 83 2.7 TYPICAL LANDSLIDE PROBLEM 84 2.7.1 Features 84 2.7.2 Mechanism 85 2.7.3 Treatment Measures 85 2.7.4 Variuos forces to be considered 86 2.8 FLOOD PROBLEM 91 2.9 SOCIO-ECONOMIC IMPLICATION OF FLOODS AND LAND EROSION/SLIDES 93 2.9.1 Flood Management works in Vogue 93 2.9.2 Performance of Flood Management Works 95 2.9.3 Formulation and Implementation of Schemes 96 2.9.4 Evaluation of Flood Management Works 97 CHAPTER 3 GLACIERS 3.1 HIMALAYA AND GLACIERS 109 3.1.1 Glaciers 110 3.1.2 Glacial Movement 110 3.1.3 Glacial Erosion 112 3.1.4 Classification of Glaciers 113 3.2 RECESSION OF GLACIERS 114 3.3 GLACIAL STUDIES IN SIKKIM 116 3.4 OBJECTIVE OF THE STUDY 117 3.5 GLACIERS 117 3.6 GLACIAL LAKES 118 3.7 DATA USE AND METHODOLOGY 119 3.7.1 Topographic Maps 120 3.7.2 Satellite Images 120 3.8 INVENTORY OF GLACIERS 121 3.8.1 Area of the glacier 121 3.9 INVENTORY OF GLACIAL LAKES 123 3.9.1 Classification of lakes 124 3.9.2 Stability Analysis 125 3.9.3 Types of Glaciers 126 3.10 GLACIERS OF SIKKIM HIMALAYA 127 3.10.1 Zemu Glacier 131 3.10.2 Glacial Lakes of Sikkim Himalaya 132 3.10.3 Erosion lakes 133 3.10.4 Trough valley lakes 133 3.10.5 Cirque lakes 134 3.10.6 Blocked lakes 134 3.10.7 Supra-glacial lakes 134 3.10.8 Moraine-dammed lakes 135 3.10.9 Ice-dammed lakes 136 3.10.10 Inventory and Characteristics 136 3.11 MAJOR LAKES 139 3.11.1 Glacial Lakes Outburst Floods 141 3.11.2 Causes of Lakes Creation 142 3.11.3 Causes of Glacial Lakes Water Level Rise 143 3.11.4 Bursting Mechanisms 144 3.11.5 Mechanism of Ice Core-Dammed Lakes failure 144 3.11.6 Mechanisms of Moraine-Dammed Lakes failure 146 3.11.7 Surge Propagation 146 3.11.8 Sediment Processes during a Glacial Lakes Outburst Flood 147 3.11.9 Socio-economic effects of Glacial Lakes Outburst Floods 147 3.11.10 Potentially Dangerous Glacial Lakes 148 3.11.11 Criteria for Identification 149 3.11.12 Major Glacial Lakes Associated with the Glaciers 153 3.11.13 Potentially Dangerous Glacial Lakes 156 3.11.14 Glacial lake outburst flood mitigation measures, monitoring and early warning systems 158 3.11.15 Reducing the Volume of Lakes Water 158 3.11.16 Preventative Measures around the Lakes Area 159 3.11.17 Protecting infrastructure against the destructive forces of the surge 159 3.11.18 Monitoring and early warning systems 160 Bibliography 163 Annexure LIST OF TABLES Table 1.1 Tectonostratigraphic Succession along South-North Darjeeling-Sikkim Himalayan Section Table 1.2 Mineral deposits in Sikkim Table 1.3 Chronological Listing of some Earthquakes of Magnitude > 4.5 for Sikkim Table 1.4 Seismic zones of India with corresponding MM (or MSK) scale intensity, Richter magnitude and horizontal force Table 1.5 Effects of Bihar-Nepal Earthquake (1988) in Sikkim Table 1.6 Focal Mechanism Solutions Table 2.1 Some of the important landslides in different districts of Sikkim Table 2.2 Landslides alongside the roads in Sikkim Table 3.1 Database used for landuse/ landcover mapping of Teesta basin Table 3.2 List of used topographic maps published by the Survey of India Table 3.3 Glacier cover area inventory in Sikkim Himalaya Table 3.4 Types of Glacier in the Sikkim Himalaya Table 3.5 Number and area of glaciers in the Sikkim Himalaya as Published by the Geological Survey of India, 1999 Table 3.6 Types of glacial lakes in the Sikkim Himalaya Table 3.7 Distribution of number and area with respect to the aspect of the lakes Table 3.8 Major glacial lakes of Teesta basin in Sikkim Table 3.9 Potentially dangerous glacial lakes requiring further studies and monitoring in different watersheds of Teesta basin in Sikkim LIST OF FIGURES Figure.1.1 Geology and Stratigraphy of Teesta basin in Sikkim Figure. 1.2 Geological section along A-B (see Fig. 1.1) in Sikkim Himalaya. MBT: Main Boundary Thrust, MCT: Main Central Thrust Figure.1.3 Barrovian zones in MCT zone along SW-NE traverse Figure. 1.4 Seismotectonic map of Sikkim and adjacent regions Figure. 1.5 Seismic zoning map of India (Source : BIS, 2001, New Delhi) Figure. 1.6 North-south depth section of earthquakes along P-Q traverse (Fig. 1.4) in Sikkim Figure. 2.1 Old and new landslides in Sikkim Himalaya with locations of some of the important landslides. Figure 2.2 Frequency of old and new landslides in various watersheds in Teesta Basin in Sikkim. Figure. 2.3 Planimetric area of the watersheds (shown as bars) and the area covered by landslides (lines with dots) given in percent of the watershed area Figure. 2.4 Geology around Rangpo-Dikling Landslide Complex Figure. 2.5 Chandmari-Tathangchen Landslide Complex Figure. 2.6 Geology of the area around Gangtok with location of Chandmari- Tathangchen Slide Complex and 9th mile side Figure. 2.7 Geology around Mangan-Tong landslide complex Figure. 2.8 B2 slides lies in the MCT zone Figure. 2.9 Site plan of 7th mile slide on Gangtok-Kupup road Figure. 3.1 Different bands of Landsat-7 (ETM+) December, 2000 Figure. 3.2 Bands 5,7 and 8 of Landsat-7 (ETM+) of December, 2000 Figure. 3.3 Subset of the satellite image of landsat-7 7 ETM+ Panchromatic mode of Dec. 2000 covering Teesta basin in Sikkim for the mapping of glaciers and glacial lakes. Figure. 3.4 Subset and colour composite bands 9 (R) and 2(B) of Landsat-7 ETM+ of 26 Dec. 2000 to show the ice cover in the Zemu glacier Figure. 3.5 Subset and colour composite bands 9 (R), 8(G) and 2(B) of Landsat-7 EYM+ of 26 Dec. 2000 to show the debris an clean glacier including the supraglacial lakes in gthe Zemu glacier. Figure. 3.6 False colour composite (bands 4, 3 and 2 of the Landsat-7 ETC+) of Teesta river basin in Sikkim. Figure. 3.7 Three-dimensional (3D) view, digital elevation model draped over the satellite image of Teesta basin in Sikkim. Figure. 3.8 Subset and colour composite bands 9(R), 8(G) and 2(B) of Landsat-7 ETM+ of 26 December, 2000 of the Sikkim.