Himalaya: Dynamics of a Giant, Tectonic Units and Structure of the Himalaya

The Himalaya is well known as the largest and highest mountain belt on Earth. Advances in geoscience over the past few decades have revealed a complex picture of the dynamics of this giant, opening up questions about the initial stages of Himalayan building, lateral variations in its structures, variations in tectonic forcing, tectonic-climate coupling and assessments of the natural hazards affecting this area.

In this three-volume book, we present the current knowledge on the building and present-day behavior of the Himalayan range. The objective is not to be exhaustive, but to provide some key elements used by researchers to unravel the many processes acting in the Himalayan dynamics.

Mountain environments are at the forefront of climate change with glacier retreat, landslides, flash floods and water availability. Understanding the delicate balance that controls the dynamics of the Himalayan giant is now, more than ever, a major challenge for the scientific community.

Rodolphe Cattin is a professor at the University of Montpellier, France. His activities performed in the Himalaya are on crustal structure imaging from ground and satellite observations, river dynamics and stress transfer associated with seismic events and surface processes.

Jean-Luc Epard obtained his PhD from the University of Lausanne, Switzerland (structural and Alpine geology) in 1990. He has been involved in 14 field expeditions in the Himalaya as participant or leader. His main area of expertise is the Mandi-Manali-Leh transect (India).

Tributes xi
Eduardo GARZANTI, Vincent GODARD, Rodolphe CATTIN, György HETÉNYI, Jean-Luc EPARD and Martin ROBYR

Foreword xvii
Rodolphe CATTIN and Jean-Luc EPARD

Preface From Research to Education: The Example of the Seismology at School in Nepal Program xix
György HETÉNYI and Shiba SUBEDI

Part 1 Surface Process 1

Chapter 1 Orogenesis and Climate 3
Frédéric FLUTEAU, Delphine TARDIF, Anta-Clarisse SARR, Guillaume LE HIR and Yannick DONNADIEU

1.1 Introduction 3

1.2.Climate in Asia: present and past 4

1.2.1.Present-dayclimate 4

1.2.2.Cenozoic climate evolution 7

1.3 Reconstructing the paleo-elevation of landforms 10

1.4.The contribution of climate modeling 12

1.4.1 Impact of orogenesis on the atmospheric circulation 13

1.4.2 Impact of orogenesis on the ocean circulation 18

1.4.3 Impact of orogenesis on the chemical composition of the atmosphere 20

1.5.Conclusion 21

1.6.References 23

Chapter 2 Eroding the Himalaya: Processes, Evolution, Implications 29
Vincent GODARD, Mikaël ATTAL, Saptarshi DEY, Maarten LUPKER and Rasmus C THIEDE

2.1 Introduction 29

2.2.Main process domains in the Himalaya 30

2.2.1.Himalayan rivers 30

2.2.2.The glaciated High Range 35

2.2.3 Critical hillslopes 36

2.3 Extreme events and their contribution to denudation 37

2.4 1-10 ka timescale and climatic oscillations 39

2.5 Impact of long-term tectonic and climatic evolution over several Ma 42

2.6 Out of the Himalaya: sediment transport and storage from the range to the sedimentary basin 45

2.7 Conclusion 48

2.8 References 49

Part 2 Natural Hazards 55

Chapter 3 Glaciers and Glacier Lake Outburst Floods in the Himalaya 57
Christoff ANDERMANN, Santosh NEPAL, Patrick WAGNON, Georg VEH, Sudan Bikash MAHARJAN, Mohd Farooq AZAM, Fanny BRUN and Wolfgang SCHWANGHART

3.1 Introduction 57

3.2 Glaciers and their future 61

3.2.1 The present state of glaciers at a regional scale 61

3.2.2 On the interest of monitoring glaciers 64

3.2.3.What will happen to the Himalayan glaciers and Karakoram glaciers? 65

3.3 Glacier lakes 66

3.3.1 Formation and present distribution of glacier lakes in the Himalaya 66

3.3.2 Historic changes of glacier lake abundance and size 69

3.3.3.Projections of future glacier lakes 71

3.4 Glacial lake outburst floods and downstream propagation 72

3.4.1.GLOF triggers 72

3.4.2 Dam breach 74

3.4.3.Flood propagation 75

3.4.4.Early warning 77

3.5.Consequences and impact 79

3.6.Role in landscape formation 81

3.7.Conclusion 83

3.8.References 83

Chapter 4 Landsliding in the Himalaya: Causes and Consequences 95
Odin MARC, Kaushal GNYAWALI, Wolfgang SCHWANGHART and Monique FORT

4.1 Introduction 95

4.2 Understanding landsliding and their links to the dynamics of the Himalayan range 96

4.2.1 Preliminary notions on the mechanics of landsliding 96

4.2.2 Seasonal landsliding caused by monsoons and extreme rainfall 99

4.2.3 Landslide induced by earthquakes and other exceptional perturbations 102

4.2.4.Giant and paleo-landslides 106

4.3.Landslides within Himalayan society 110

4.3.1 Hazard cascades and their societal impact 110

4.3.2 Human activities as an additional trigger of landslides 111

4.3.3 Potential for mitigation 114

4.3.4 Climate change and future landsliding 117

4.4 Conclusion 118

4.5 References 119

Chapter 5 Himalayan Surface Rupturing Earthquakes 131
Laurent BOLLINGER, Matthieu FERRY, Romain LE ROUX-MALLOUF, Jérôme VAN DER WOERD and Yann KLINGER

5.1 Introduction 131

5.2 The large devastating earthquakes in the Himalaya 133

5.2.1 Historical chronicles and earthquakes 133

5.2.2 Strong instrumental earthquakes 135

5.3 Surface expression of the seismic deformation in the landscape and within paleoseismological excavations 138

5.3.1 In the mesoseismal trace of the 1934 earthquake 138

5.3.2 In the mesoseismal trace of the 1714 earthquake in Bhutan 142

5.3.3 In the mesoseismal trace of the 1950 earthquake 145

5.4 Overview of the paleoseismological excavations along the Himalayanarc 147

5.5 Abandoned alluvial terraces, an archive of the paleoearthquakes 149

5.6.Conclusion 151

5.7.References 151

Chapter 6 Seismic Coupling and Hazard Assessment of the Himalaya 155
Sylvain MICHEL, Victoria STEVENS, Luca DAL ZILIO and Romain JOLIVET

6.1 Introduction 155

6.2 From current ground motion to the buildup of slip deficit at depth 158

6.2.1 Geodetic observations of the interseismic period 160

6.2.2 Inferring coupling along the MHT with a Bayesian analysis 160

6.2.3 Interseismic coupling distribution 162

6.2.4 Discussion 164

6.3 Seismic potential of the MHT 167

6.3.1 Conservation of the seismicmoment 167

6.3.2 Magnitude-frequency distribution in the Himalaya 169

6.3.3 Including the physics of fault slip in seismic hazard 172

6.3.4.Seismic potential of the MHT 173

6.4 Seismic hazard in the Himalaya 175

6.4.1 Ground motion prediction equations and Vs30 176

6.4.2 Modeling scenario events 177

6.4.3 Probabilistic seismic hazard assessment 180

6.4.4 From hazard to risk 183

6.5 Conclusion 184

6.6 References 184

Part 3 Focus 191

Chapter 7 Recent and Present Deformation of the Western Himalaya 193
François JOUANNE, Jean-Louis MUGNIER, Riccardo VASSALLO, Naveed MUNAWAR, Awais AHMED, Adnan Alam AWAN, Manzoor A MALIK and Ramperu JAYANGONDAPERUMAL

7.1 Introduction 193

7.2.Structural styles and tectonic prismmodel 195

7.2.1.The main structural zones 195

7.2.2 The Himalaya in the west of the syntax 195

7.2.3 The Himalaya of the Jammu-Kashmir area 198

7.2.4 A structural evolution in agreement with the tectonic prismmodel 199

7.3 Out-of-sequence deformation in the western Himalayan syntax 201

7.3.1 Quaternary out-of-sequence activity of the NW Himalayan thrusts 201

7.3.2 Out-of-sequence seismological and paleoseismological activity in the NW Himalaya 205

7.4 Deformation associated with a ductile décollement, not always aseismic 208

7.4.1 Seismic coupling assessment along the MHT 208

7.4.2 Occurrence of ruptures on asperities 209

7.4.3 Transition between thin-skin and thick-skin tectonics 211

7.5.Conclusion 212

7.6.References 213

Chapter 8 The 2015 April 25 Gorkha Earthquake 217
Laurent BOLLINGER, Lok Bijaya ADHIKARI, Jérôme VERGNE, György HETÉNYI and Shiba SUBEDI

8.1 Introduction 217

8.2 The main shock and its effects on the ground 219

8.2.1 Overview description of the main shock 219

8.2.2 Ground motion and deformation 221

8.3 Investigating the seismic source at depth 222

8.4.Aftershock activity and post-seismic relaxation 225

8.4.1 Early aftershocks and the occurrence of the Kodari earthquake 225

8.4.2 Seismicity monitored by denser, dedicated temporary networks 226

8.4.3 Post-seismic relaxation monitored by geodetic and seismological networks 229

8.5 A more earthquake-informed and earthquake-resilient local community in the aftermath of the earthquake 231

8.6.Conclusion 232

8.7.References 233

Chapter 9 Crustal Fluids in the Nepal Himalaya and Sensitivity to the Earthquake Cycle 239
Frédéric GIRAULT, Christian FRANCE-LANORD, Lok Bijaya ADHIKARI, Bishal Nath UPRETI, Kabi Raj PAUDYAL, Ananta Prasad GAJUREL, Pierre AGRINIER, Rémi LOSNO, Chiara GROPPO, Franco ROLFO, Sandeep THAPA, Shashi TAMANG and Frédéric PERRIER

9.1 Introduction 239

9.2 Overview of thermal springs geochemistry in Nepal 240

9.3 Overview of gaseous emission zones in Nepal 249

9.4.Spatial organization of crustal fluid release 253

9.5 Temporal variations of crustal fluid release: a tectonic control 256

9.6 Conclusion 260

9.7 References 261

Conclusion 267
Rodolphe CATTIN and Jean-Luc EPARD

List of Authors 269

Index 275

Summaries of other volumes 279

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