Natural hazards - their drivers, mechanisms and impacts in the Shyok-Nubra Valley, NW Himalaya, India

International Journal of Disaster Risk Reduction 35 (2019) 101094

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Natural hazards - their drivers, mechanisms and impacts in the Shyok-Nubra Valley, NW Himalaya, India

T

Naveen Hakhooa,∗, Ghulam Mohd. Bhata, Sundeep Panditab, Gulzar Hussainb, Ahsan Ul Haqb, Mateen Hafizc, Waquar Ahmeda, Yudhbir Singhb, Bindra Thusua,d a

Institute of Energy Research and Training (IERT), and Postgraduate Department of Geology, University of Jammu, Ambedkar Road, Jammu, Jammu and Kashmir, 180006, India b Postgraduate Department of Geology, University of Jammu, Ambedkar Road, Jammu, Jammu and Kashmir, 180006, India c Institute of Energy Research and Training (IERT), University of Jammu, and Govt. Maulana Azad Memorial (MAM) College, Ambedkar Road, Jammu, Jammu and Kashmir, 180006, India d Maghreb Petroleum Research Group (MPRG), Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, United Kingdom

ARTICLE INFO

ABSTRACT

Keywords: Natural hazards Shyok-Nubra valley Himalaya India

The Shyok-Nubra Valley situated in the NW Himalaya of India represents a dynamic environment where continuous tectonics has influenced the landscape, geologic and geomorphic processes. With existence of communities in such an environment it becomes very essential to document and understand the natural hazards. This paper provides a preliminary documentation and understanding of the natural hazards and their drivers, mechanisms and impacts in this region. Here, seismicity is poorly understood, and the earthquake hazards are primarily associated with collapse of building (Type-I and II) structures. Intense deformation has made the mountainous terrain very fragile, weak and highly susceptible to mass movements. The region is susceptible to floods and GLOFs, based on OSL dating, we report two flooding events (bracketed between 8.5 ± 0.4 and 7.5 ± 0.4 ka) and the increase in sedimentation rate over a period of 4.3 ka. Here, major settlements are on active fans that are highly vulnerable to numerous hazards. Fan hazard risk assessment in the Diskit area enabled identification of four hazard prone zones that should be avoided for any developmental work. Although the frequency of cloudburst and rain-storms has increased, very little is understood about the climate and its variability in this region. The region is prone to snow avalanche risk, but most of the settlements are located in the low susceptibility zone. The aeolian geomorphic processes are dominant in the region and desertification is prominent in some areas. This work provides a suitable context for resolving problems related to natural hazards susceptibility and developmental works in this region.

1. Introduction The Himalaya is one of the most prominent, youngest, highest and active mountain range that originated as a result of continent-continent collision c. 50–60 Ma ago [1–3]. This ongoing collision has influenced the Himalayan landscape, climate and geomorphic processes associated with numerous phenomena (e.g. earthquakes, mass movements and floods). Himalaya is divided by faults running along its entire length into distinct zones from the southernmost extremity of vast alluvial plains to the northern contact defined by the suture zones (Fig. 1) [4–13]. In the north-western Trans-Himalayan part of India, the ShyokNubra Valley, sandwiched between the Ladakh Batholith towards S-SW

and the Karakoram Batholith towards N-NE, represents such a region in a dynamic environment (Figs. 1 and 2), where natural and anthropogenic drivers of change have made communities highly vulnerable to natural hazards. This Trans-Himalayan region forms part of the main Himalayan arch under the ‘rain shadow zone’ [14]. The Indus River and its primary tributaries - the Shyok River and the Nubra River (Figs. 1 and 2) flow along major fault lines in the region [15,16]. In the Shyok-Nubra Valley Quaternary sedimentary accumulations (viz. loose/unconsolidated alluvium, glacial and fluvio-glacial sediments, lacustrine sediments, debris etc.) deposited in the hill slopes and valleys occur as vast expanse of loose veneer, debris flows, terraces and fans. Additionally, the

Corresponding author. E-mail addresses: [email protected] (N. Hakhoo), [email protected] (G.M. Bhat), [email protected] (S. Pandita), [email protected] (G. Hussain), [email protected] (A.U. Haq), [email protected] (M. Hafiz), [email protected] (W. Ahmed), [email protected] (Y. Singh), [email protected] (B. Thusu). ∗

https://doi.org/10.1016/j.ijdrr.2019.101094 Received 5 February 2019; Accepted 12 February 2019 Available online 02 March 2019 2212-4209/ © 2019 Elsevier Ltd. All rights reserved.

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Fig. 1. Geological map of the NW Himalayan region, showing the tectono-geomorphic zones, major tectonic boundaries, the location of the Ladakh and Karakoram batholiths and the intervening Shyok-Nubra region (Modified after [4]). KKH- Karakoram Highway.

The geology of the area (Fig. 3) is described in detail by [20,23–29] amongst others. The salient features of the geology are:

intense and abrupt climatic fluctuations, dynamic geological environment, fragile hill slopes, coupled with heterogeneous sediment accumulations has exacerbated erosion and transportation, mass wasting, land instabilities, melting of glaciers and floods [17]. With continuous tussle between the upliftment and denudation [18] and the existence of communities in such an environment it becomes very essential to document and understand the drivers of natural hazards (viz. earthquakes, mass movements, fan-hazards, floods, glacial lake outburst floods (GLOFs), cloudburst, snow-avalanches and desertification) in this region. A study of this nature is critical considering the safety and development in wake of very limited systematic documentation and understanding of the natural hazards in this region. Therefore, the present study is an attempt to elucidate various natural hazards, their drivers and mechanisms in this geo-politically sensitive region for the future disaster management and risk reduction policy framing and in resolving problems related to natural hazards susceptibility and developmental works in the Shyok-Nubra Valley.

1) The 700 km long dextral Karakoram Fault (KF) runs through the Nubra Valley. At the confluence of the Nubra and Shyok rivers, the KF separates rocks of the Ladakh terrain from those of the Karakoram terrain (batholiths) [30]. 2) Between the Ladakh and Karakoram batholiths, volcano-sedimentary rocks belonging to Shyok and Nubra groups are present [28]. The Shyok Group consists of slivers of ophiolite, chert, gabbro, peridotite and serpentinite interbedded with phyllite, slate, limestone and quartzite. The Nubra Group, cropping out along the Nubra River, consists of sandstone, conglomerates and shale interbedded with basic volcanics, serpentinite, pyroxenite and garnet-mica schist. 3) The Ladakh terrain lying towards the south of the KF is characterized by granitoids of the Ladakh Batholith that intrude older sequences of basalts and quartzites, i.e. the Early Cretaceous Shyok Formation [31] well exposed at Hundar, and overlain by pyroclastic flows of the Khardung Formation. The Ladakh granitoids, Shyok and Khardung formations exhibit extensive structural deformation from Khalsar to Diskit and Hundar (also in [20,29], and the rock-terrain is extremely sheared, jointed and fragile. 4) At the Shyok-Nubra confluence zone, west of the KF, wedge like Saltoro Block is present. The block consists of ophiolite, granitoids and greenschist facies metamorphic rocks [29], also exposed north of Khalsar at Tirith. Here, the rocks are intensely deformed and the shear (foliation) planes largely follow the trend of the Nubra Valley, and along the Karakoram Fault. 5) The Karakoram terrain consists of Nubra Formation [28], the Karakoram leucogranite batholith and the granitoid belt [32]. The Nubra Formation consisting of metavolcanic and metapilitic rocks (schists, andesites, dacites, pelites, marble) is ∼ 1.5 km wide and crops out along the foot of the Karakoram Range, where it is in sheared contact (defined by mylonites and breccia) with Karakoram Batholith. The Nubra Formation is extensively strained, deformed,

2. Geological overview of the Shyok-Nubra region The Shyok-Nubra region is located between the two sutures (Indus Suture towards south and Shyok suture towards north) representing the remnants of collision between India and Asia. The Shyok-Nubra Valley consists of two strands, (i) the NW-SE running Shyok Valley occupied by the Lower Shyok River, and (ii) the NS running Nubra Valley occupied by the Nubra River. Both valleys exhibit characteristic structural control, primarily associated with the Karakoram Fault (KF) and the Shyok Suture Zone (SSZ), the major regional structural features in the region (Figs. 2 and 3) [20]. The Shyok-Nubra Valley and the adjacent Karakoram terrain are tectonically very active and comprised of sedimentary, metamorphic and magmatic rocks representing the remnants of an accretionary complex [21]. The basement (granitic and volcanic) rocks are overlain by unconsolidated to semi-consolidated Quaternary deposits of alluvium, glacial and fluvio-glacial sediments, lacustrine sediments and debris accumulations as moraines, terraces and fans [22]. 2

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Fig. 2. Satellite image of the NW Himalaya showing the Shyok-Nubra region (inset polygon), and the localities belonging to three domains, viz. Domain 1: 1. Panamik, 2. Tiggur, 3. Sumur; Domain 2: 4. Tsati, 5. Khalsar; and Domain 3: 6. Diskit, 7. Hunder, 8. Udmaru, 9. Changmar, 10. Bogdang, 11. Chalungkha, and 12. Turtuk. Leh is also seen in the lower inset rectangle. The extent of the palaeolake - Lake Gapshan (Yapchan) is also seen towards the NW, and the location of major glaciers is also shown (also see Table 2).

and also mylonitized at some places due to the proximity of the KF zone.

climatic fluctuations and extreme events (e.g. cloudburst) have given rise to intense erosion, sedimentation, debris flows, floods and numerous other hazards in this region.

The geology of the Shyok-Nubra region is very fragile as the rocks are highly fractured and deformation is very pronounced due to the tectonic activities and mountain building processes. Additionally, the rock types are highly variable in all directions, and such a diversified rock assemblage (as described above) along with considerable topographic changes have led to the intricate geological, hydro-geological and geomorphic processes in the region. These conditions coupled with

3. Hazards - their drivers and assessment 3.1. Earthquakes Himalaya is a well-established seismic zone highly prone to earthquakes and associated disasters resulting from the characteristic 3

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Fig. 3. Geological map of the Shyok, Nubra, Leh and Zanskar areas in Ladakh, NW Himalaya, of note is the complexity of rock variety between Ladakh and Karakoram batholiths (Modified after [19]).

seismotectonic features that have formed due to the collision between the Indian and Asian plates [33]; [3,34–36]. The Shyok-Nubra region is in the zone IV of the seismic zoning map of India, and seismotectonic atlas of India [37]. The tectonic activity in this region is due to proximity of the Karakoram Fault (KF), and various structural features like Shyok Suture Zone (SSZ), Karakorum Shear Zone (KSZ). Here, the seismicity associated mainly with the KF and the SSZ is poorly understood, and the seismic hazards have not been investigated thoroughly [38]. No major and detailed seismological observations have been undertaken in this region which is prone to earthquakes [39] and yet there is no record of a major earthquake experienced here till date. However micro, small and large magnitude earthquakes are frequently felt by the local population in this region (Fig. 4) [40]. The study by Parshad et al. [40] shows the presence of two seismic zones, sandwiching an aseismic zone at depths ranging from 12 to 40 km, where no stress is accumulating. The layer is suggestive of ‘partially melted crust’ present at this depth in the region [41]. The depth distribution of the earthquakes shows that the local earthquakes occur in the shallow crust where the stresses are being accumulated. Any large magnitude shallow crustal seismicity in this region may affect the building structures, fragile slopes, glaciers and lakes (if present), thereby posing an imminent threat of structure collapse, rock-fall/ landslides and flooding. The earthquake hazard in the Shyok-Nubra Valley will largely be determined by the strength of seismic activity, subsurface geology, local topography and the location of the settlements/communities. Here, a strong earthquake will generate a shaking intensity large enough to severely damage structures like bridges and buildings (Figs. 5 and 6). In

this region the seismic hazard risk is primarily associated with community location, building/construction standards and emergency preparedness. It is seen that the area has a number of settlements on the fans, perched fans, terraces and mountain slopes/ridges that may be devastated by ground shaking. The fans are largely unconsolidated and very mobile (also see the section 3.4 detailing the fans, fan formation and fan hazards in this region) and intense shaking can cause substantial damage to the building structures. The structures in the region primarily fall into three categories: (i) the traditional ones, based on vernacular construction; (ii) the building structures that initially were constructed traditionally, but are being modified and renovated using unreinforced masonry methods, and (iii) the structures based on unreinforced masonry dry-stone and random rubble concrete construction (Figs. 5 and 6) [42]. Broadly, these structures can be categorized as Type-I and Type-II. Type-I includes the structures with low workmanship standard, constructed of weak materials (rubble, mud blocks, mudmortar, soil etc.); soft structures (e.g. shops, temporary residential structures) made of masonry, weak reinforced concrete or composite materials (e.g. timber and brick) not well tied; and structures constructed entirely of timber. Type-II structures are constructed by ordinary workmanship with average quality mortar. Extreme weakness are avoided and the corners are bonded together, but the Type-II structures are not designed or reinforced to resist lateral forces. The Type-I structures are susceptible to cracking and slight damage by MM (Modified-Mercalli-Intensity) 5 earthquake and an MM5 or MM6 earthquake (∼Mw 5) can cause substantial damage to Type-I buildings and slight damage to Type-II buildings, which will be subjected to damage and possible collapse by MM 7 (> 5 to 5.9 Mw) and higher 4

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for landslide/debris flow occurrence in the Himalaya are local terrain conditions, slope-forming materials, topography, groundwater, and land cover [48]; in addition to these, strong winds, intense rainfall and earthquakes have become dominant triggers [49]. Intense structural deformation has rendered the mountainous terrain in the Shyok-Nubra region very fragile, weak and highly susceptible to debris flows and rock falls. The region comprising of Panamik, Sumur, Tiggur, Tsati, Khalsar, Diskit, Hunder, Udmaru, Changmar, Bogdang, Chalungka and Turtuk localities is susceptible to these hazards. (Also see section 4) (Fig. 7). These localities fall within three distinct tectonic domains [20] whose salient features are described as follows: Domain 1 (NE domain; Panamik, Tiggur and Sumur. Fig. 2) – in the Nubra Valley within the Karakoram fault zone (east of the Main Karakoram Fault following the Nubra River), up to the Karakoram Batholith (KB) piedmont zone in the east, consisting of numerous dissected/ deformed rock slopes and mixed fans (formed by combination of colluvial and alluvial processes). In Panamik, Sumur and Tiggur the mountain slopes facing towards W and SW (Fig. 8) have gentle to steep gradients ranging from 15° to 45° (Fig. 9), field investigations also reveal very steep slopes and slope gradients as observed in the proximity of the Karakoram Fault (KF) (Fig. 10). Here, the rocks depict three prominent and closely spaced joint sets dipping towards N, NW and NE. At Sumur and Tiggur some of the slopes depict S and N aspects just above the piedmont zone, where accumulation of large active fans with highly variable drainage has taken place (Fig. 10). Of note is the rapid elevation gain of ∼5500 m from the KF towards the high hinterland of the KB in the east over a horizontal distance of ∼ 6–7 km (Fig. 11). The topography in the area ranges from being highly immature to mature as evidenced by the stream-order ranging from 1 to 6 (Fig. 12). This indicates an evolving landscape with intense neotectonic activity also seen in the drainage behaviour within the fans (Fig. 10). Of note is the geothermal activity seen as thermal springs in Panamik along the KF contact zone (Fig. 10). In and along the fans towards the E of the KF in the Nubra Valley the drainage (channels, streams etc.) is shifting and veering towards north, opposite to the dextral movement along the KF towards south. The collective effect of the evolving landscape, coupled with geological and geomorphic processes has rendered the entire domain (ridges, slopes and valleys - strewn with thick and large scale accumulation of unconsolidated to semi-consolidated clay to boulder size sediment) very weak and susceptible to debris flow. During rain-storms and cloudbursts the fine clay-rich sediment forms slurry, this mixture makes the boulders hydrodynamic that wreck the structures coming in their path. With the frequent occurrences of cloudbursts and rain storms in the region the mass-movement episodes particularly debris flows have overwhelmed several localities, e.g. Tiggur and Sumur, which were severely effected in the cloudburst events of 2014 and 2015 (Figs. 10 and 13) and represent a very high risk areas in this domain. Domain 2 (SE domain; Tsati and Khalsar. Fig. 2) – towards the south of the Nubra Valley and further south-east of the confluence of the Shyok and Nubra rivers, where the KF exhibits a variation in its strike continuity [20], the Shyok River veers its course from north to west-northwest owing to subsurface structure control of the KF. This structurally deformed domain is in close proximity of the KB piedmont zone, where highly cleaved, jointed, sheared and gouged rocks, and dissected mixed fans are present (Fig. 14). In Tsati, the mountain slopes predominantly facing towards SW (with west and south facing slopes as well) are gentle to steep (slope gradient of 10° to 45°), very steep slopes (gradient of more than 45°) facing west and southwest are also present. In Khalsar, the mountain slopes facing predominantly N and also northeast and southeast are having gentle to steep gradients (15° to 35°), some of the slopes facing east and north have very steep gradients (Figs. 8 and 9). These steep slopes are present in the proximity of the fault planes, where the rocks are extensively deformed and highly susceptible to sliding and falling. One such fault continues from Tsati to

Fig. 4. Map of the Shyok-Nubra region showing the distribution of earthquakes occurring from 2008 to 2013 in this region, the orange balls depict the epicenters (Modified after [40]). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

intensity earthquakes [42–44]. The vernacular construction is undoubtedly beneficial and time-tested, having unique construction and earthquake resistant ability [45], but these are being replaced by poorly designed concrete buildings that are less resistant to ground shaking. Small magnitude earthquakes (Mw less than 3) are frequent in the Shyok-Nubra region, and from 2008 to 2013 nearly 200 events have been recorded, among them 20 are ∼ Mw 4 magnitude, and one Mw 4.5 earthquake was recorded on 09-09-2010 [40]. The Ground shaking (also experienced by local populace) due to earthquakes is very common in this region, at many places the repeated shaking has destabilised the steep slopes and cliffs that can lead to debris-flows and rock-falls – a potential hazard in the Shyok-Nubra Valley, particularly in Turtuk area where significant hazard risk to life and property exists (Fig. 6). In the Bogdang area ∼23 km SE of Turtuk, the local settlements are situated on terraces where the risk of the rock fall and destabilisation is very high. Here, it is seen that huge boulders move downslope on shaking caused by the movement of heavy locomotives (Fig. 6), and serious damage will be caused by ground shaking due to a medium intensity earthquake. In addition to this, heavy rain and unconsolidated or fractured rock will exacerbate the aforesaid hazardous effects of earthquakes in the area, particularly in Turtuk and Tyakshi where the poorly designed building structures on semi-unconsolidated terraces and steep slopes and ridges are under greater earthquake hazard risk (Fig. 6). What we have observed is that greater risk to people in the Shyok-Nubra Valley is from the collapse of the building structures during an earthquake, apart from flood hazard associated with a broken dam or embankment, and rock-fall/landslide. 3.2. Mass movements Mass movements are one of the most important geomorphic hazard in the Himalaya where the damage caused by the landslides/debris flows is ∼ 30% of the total damage caused by landslides globally [46]. The human population explosion and urban expansion has exacerbated the landslide threat in Himalaya [47]. The primary factors responsible 5

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Fig. 5. Earthquake hazard in Shyok-Nubra Valley is primarily associated with location of settlements/communities and collapse of building structures, as can be exemplified here: (a) The Diskit Monastery - a vernacular construction developed with an objective to provide protection against harsh climate and calamities. But, weak geological conditions, e.g. fractures as seen in the bed-rock have increased its vulnerability, of note is the tree line following water seepage along a major fracture, that may slip during an earthquake. (b) Unreinforced masonry renovation and random rubble construction (bottom foreground) within the Monastery, highly susceptible to ground-shaking and collapse. (c) High ridges and steep slopes on top of the Monastery laden with loose rubble and carsized boulders, very susceptible to rock-fall and sliding. (d) Building structure (Type-I) in Hunder area based on unreinforced masonry dry-stone and random rubble construction. (e) Highly fractured and deformed steep ridges and vertical mountain faces precariously rising above the bridges. (f) Construction (Type-I) of residential structures in Turtuk area based on unreinforced random rubble construction, a complete opposite of the rich vernacular heritage of the region, and an extremely risk prone area.

Khalsar with a NW-SE strike continuity, this fault has also been traced to Diskit further west (Fig. 14). With an average elevation of ∼3000 m that ranges from ∼2500 m in the Shyok valley to ∼7400 m (Fig. 11) in the high mountains, the drainage in this domain is highly variable. The stream order ranges from 1 to 6 (Fig. 12), as observed in domain 1, which suggest that the area is tectonically very active.

In addition to geologic and geomorphic influence, this domain straddling between the Karakoram and Ladakh terrain exhibits intense deformation due to the proximity of the fault. Here also, the mountain slopes surrounding the Khalsar area are covered with a very thick accumulation of unconsolidated to semi-consolidated clay to boulder size sediment. During 2010, 2014 and 2015 cloudbursts huge debris flow 6

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Fig. 6. Earthquake hazard risk: (a) Mushrooming of masonry dry-stone building structures (Type-I and II) in Turtuk, and the general absence of vernacular design. (b) Structures (Type-I) juxtaposed with steep/vertical scarps highly susceptible to collapse, fall and sliding. (c) A random rubble/dry-stone structure (Type-I) complete destroyed in the Bogdang area. (d) Some of the older building in the Turtuk area still retain vernacular design and architecture. (e) Building structures (TypeII) in Thang area based on modern masonry column and slab construction, and additional parameters (e.g. wall ties, bands, buttresses, lintel/sill bands, prescribed height, length and joints etc.) are ignored.

had completely destroyed the structures in Khaslar which is a very high risk area (Fig. 15). Domain 3 (NW domain; Diskit, Hunder, Udmaru, Bogdang, Chalunka and Turtuk. Fig. 2) – towards the west-northwest of the confluence of the Shyok and Nubra rivers, and south of the Saltoro ridge and the Shyok Suture Zone (SSZ), and north of the Ladakh Batholith in the Shyok Valley. In Diskit and Hunder, the slopes primarily facing towards N and NE have gentle to steep gradients of 15° to 35°, some of the slopes are very steep with gradient of more than 45° (Figs. 8 and 9). With an average elevation of ∼2700 m, that ranges from 2540 m to 7400 m (Fig. 11), the stream order ranges from 1 to 6 (Fig. 12),

reflecting a mature but evolving landscape that is in accordance with the regional topography. The fault continuing form Tsati and Khalsar makes a surficial expression in Diskit [20], the fault movement has rendered the rocks intensely fractured. In Diskit, a monastery has been built on this deformed bedrock where the deformation/discontinuity planes are very prominent. The expressions of this tectonic deformation are also seen in some of the rock blocks at the base of the Monastery (Figs. 5 and 16). Further 35 km NW of Hunder in Udmaru, gentle to steep mountain slopes (gradient of 15° to 45°) facing S and SW are highly deformed in the proximity of the suture zone north of the Shyok River (Figs. 8 and 9). The relief follows regional elevation ranging from 7

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Fig. 7. Potential hazard map of the Shyok-Nubra region depicting the geomorphology and the hazard zones, the major settlements and fault locations are also shown.

∼2500 m in the valley to 7400 m (Fig. 11) in the high mountains towards north and south. High relief is also observed along the fans underlain by terraces undergoing rapid uplift (Fig. 11). In Udmaru the fore-slopes close to the piedmont zone are deformed and highly unstable, with disjunct cleavage and vertical fractures (Figs. 16 and 17). West of Udmaru, at Changmar the mountain slopes exhibit quaversal slopes towards N, S, E and W, with steep to very steep gradients of 30° to more than 45° (Figs. 8 and 9). The fault can be traced from Diskit to Changmar, although the faults seems to have been cut by tear/transfer faults, along which the sense of movement is dextral. In Changmar three distinct intersecting joint sets striking SW-NE, NW-SE and E-W are seen in a rock face dipping 25◦towards SE (Fig. 17). These fractures exhibit a structural control of a fault striking NW-SE and exhibiting lateral continuity but an opposite sinistral movement towards Bogdang. About 7 km before Bogdang at 38° 48.815′ N, 77° 5.542′E a 500 m wide cataclasite/fault gouge is seen that can be traced for ∼2 km towards Bogdang. In Bogdang the valley is very narrow, and the gentle to steep mountain slopes (gradient of 15° to 45°) are facing S and SW, very steep slopes (scarps) are seen in proximity of the fault. The relief is very steep with maximum slope and height gain observed in the entire Shyok Valley (Figs. 8 and 9). The immature fans resting on top of thick boulder terraces in proximity of the faults pose a serious debris flow/rock-fall threat in Bogdang (Figs. 16 and 17). In this area and up to Turtuk, the drainage exhibits stream order from 1 to 6 (Fig. 12), indicative of mature to immature, i.e. evolving landscape. From Bogdang to Chalungkha and Turtuk (also see section 4) the mountain slopes facing N, NE, S and SW exhibit gentle to very steep gradients (Fig. 8), and the rock deformation is complex. This complexity can be attributed to the narrowing of the valley, and the juxtaposition of different deformation structures in the piedmont zone exacerbating the hazards, particularly

debris flow in dissected/deformed rock slopes (Figs. 16 and 17). This entire domain is covered with intensely fractured and deformed brittle rocks, and very loose eroded (clay to boulder size) material that is highly susceptible to debris flow. In this domain Diskit, Hunder, Bogdang and Turtuk are very high risk areas. Diskit and Turtuk (due to large community size and population) are particularly vulnerable, as evidenced by 2006, 2010, 2014 and 2015 cloudburst and debris flow events (Fig. 18), still fresh in the memory of the local people (as narrated by them). Being surrounded by steep and fragile slopes and glacial melt rivers, flooding, rock fall and debris flow frequently hit this domain. The south-eastern zones covered by dissected, deformed and fractured rock slopes are categorized as highly vulnerable to mass movements. Most of the households are located in these two zones and are highly vulnerable to above-mentioned hazards particularly in Turtuk area, which sets the ideal context for understanding and investigating environmental hazards and their effects on the mountain communities. Being surrounded by high altitude mountains and glacial melt rivers, flooding, rock fall and landslides frequently hit Turtuk. The region is also vulnerable to earthquakes [39,50]. As narrated by the local people, Turtuk was severely damaged during the 2010 and 2015 flash floods [50]. In Turtuk, the geological and geomorphic processes have given rise to numerous hazards viz. earthquakes, down-slope movements and debris flows and floods, and anthropogenic activities have exacerbated their risk [50]. In this domain, a detailed hazard analysis and mapping is required for micro-zonation of mass movement hazards to delineate the safer zones. Flat terrain in the Shyok-Nubra region is rare (except along the river flood plains), and it is very important to identify and classify the slopes that make most of the terrain. In the Shyok-Nubra Valley, the slopes that are susceptible to these hazards occur regionally with every 8

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Fig. 8. Aspect map of the Shyok-Nubra region, showing that the mountain faces and slopes predominantly towards east, southeast, west and southwest – the directions facing the major settlements in region and hence increasing the risk of mass movements.

Fig. 9. Slope gradient map of the Shyok-Nubra region, depicting moderate to steep slopes in the proximity of the major settlements in region.

possible orientation, and the slope angle varies at an average from 30 to 45°, i.e. steep to very steep (Figs. 8 and 9). Additionally, the factors including the distance from the fault; proximity of piedmont zone, flood

plain, dissected/deformed rock slopes, distance from the drainage; relief; rock type (as discussed in the geology section); and dip slope relationship suggest that the mountainous terrain in the Shyok-Nubra 9

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Fig. 10. Field relationships observed in Domain 1 (NE domain comprising Panamik, Tiggur and Sumur). (a) Fan in Panamik depicting boulder accumulations at three distinct levels associated with three flooding events. The blue arrow shows the primary channel avulsion towards north. (b) Highly deformed, jointed and cleaved rock slopes on top of the Panamik fan. (c) Fragile and Friable east facing slopes in Panamik on top of the hot water spring in proximity of the Karakoram Fault. (d) West facing slopes prone to debris flow on top of the newly constructed structure at cloudburst and debris flow prone locality Tiggur. (e) Mud slide and debris flow prone west facing slopes at Sumur, white painted chortans (religious structures) are also seen. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Valley is very fragile, weak and highly susceptible to mass movements. It is also seen regionally that the drainages particularly the first order drainages develop along fracture planes which become pathways for the rain and melt water. It has been found that there is a fair concomitance between the mass movements and drainage, also reflected by the distance of ∼50–300 m between the two, suggestive of river entrenchment due to upliftment of the surrounding mountains in the Shyok-Nubra Valley.

cloudbursts, besides melting of snow/ice, and the bursting of glacial dams [53–55]. Additionally, encroachment of the natural water ways and the change in land use patterns etc. have intensified the impacts of floods in this region, as evidenced during 2010, 2014 and 2015 events. With the alarming change in climate, the frequency of flooding events is expected to intensify in the entire Hindu Kush-Himalaya (HKH region) [56] of which Shyok-Nubra Valley forms a part. Intergovernmental Panel on Climate Change (IPCC) has warned about the increasing trends of glacier melting in the HKH and Karakoram regions, which will further accelerate flooding events in the future, particularly the GLOFs [57–59]. Hazardous glacial lakes have been widely reported in the Himalaya [60–63], and GLOFs are among the most dangerous natural hazards here [64]. Being highly unpredictable and extremely catastrophic, the GLOFs have the potential to destroy settlements and

3.3. Floods and glacial lake outburst floods (GLOFs) Floods are a major hazard globally [51] and are caused by different factors (e.g. Ref. [52]), however in the Shyok-Nubra region, in the recent years floods have been largely attributed to rain-storms and 10

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Fig. 11. Digital elevation model (DEM) of the Shyok-Nubra region, of note is the rapid elevation gain of ∼5500 m from the Karakoram Fault (KF) towards the high hinterland of the KB in the east over a horizontal distance of ∼ 6–7 km.

Fig. 12. Drainage map of the Shyok-Nubra region. The stream-order ranging from 1 to 6 shows that the topography in the area ranges from being highly immature to mature indicative of an active and evolving landscape.

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Fig. 13. The aftermath of the debris-flow caused by the cloudburst of 2014 and 2015 in Sumur (Nubra region). The debris flow direction is towards south-southwest, the debris-flow sediment accumulation profile is also shown.

Fig. 14. Field relationships observed in Domain 2 (SE domain comprising Tsati and Khalsar). (a) Fan in Tsati showing the shifting of the primary channel toward north, and highly deformed south-west facing rock slopes. Dissected fan is seen towards far left. (b) Surficial expression of the Tsati-Khalsar Thrust in the highly cleaved, jointed, sheared and gouged rocks. (c) Photograph of the fault zone showing drag and kinematics. (d) North and northeast facing slopes having gentle to steep gradients at Khalsar. The camp is seen at the bottom piedmont zone, and Tsati fan towards extreme mid-bottom left.

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Fig. 15. Extensive destruction caused by the debris-flow accompanying cloudburst in Khalsar (Domain 2), this area is highly susceptible to cloudburst and debrisflow hazard risk.

Fig. 16. Field relationships observed in Domain 3 (NW domain comprising Diskit, Hunder, Udmaru, Bogdang, Chalunka and Turtuk). (a) Panoramic view of the Shyok Valley (upfront and left), confluence zone (near Saltoro ridge), and Nubra Valley (extreme right) from Diskit Monastery. (b) Diskit monastery built on these deformed (jointed, sheared and cleaved) bedrock in which deformation/discontinuity planes are very prominent. (c) Fragile, boulder ridden north facing slopes on top of the Diskit Monastery, deep narrow and steep east facing scarp following the trend of Tsati-Khalsar thrust are also seen. (d) Steep southeast facing fragile and highly jointed mountain slopes at Udmaru. (e) Steep southeast facing slopes highly prone to rock fall at Changmar, where Shyok River veers off course from west to north. (f) Boulder terrace (Fanglomerate), highly susceptible to rock fall forming a very high risk zone at Changmar. (g) Perched terraces/mixed fans, and the built up of the fan-on-fan system in Bogdang in proximity of the highly deformed north facing slopes. A fault scarp is also seen towards far left. (h) Panoramic view of Turtuk showing potential hazards.

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Fig. 17. Field photographs depicting deformation structures associated with regional and local faulting. (a) Trace of the thrust continuing form Tsati and Khalsar at Diskit. (b) Fracture relationship at Changmar as observed on a steep rock slope with five distinct fracture sets. This intense fracturing is regionally present but distinctly seen here. (c) Cataclasite/Fault Gouge in granite. The gouge is ∼100 m thick and is traceable for nearly 2 km near Bogdang. (d), (e), (f) and (g) Deformational structural features associated with intersecting faults in Turtuk. The vergence and field kinematics shows the presence of north dipping reverse faults.

infrastructure hundreds of kilometers downstream from the outburst location. Since the year 1553, a total of 21 GLOFs have occurred in the Shyok-Nubra Valley (Table 1) [53–55,65,66]. These GLOFs were associated with the glacial surge dams formed mainly by the ChongKhumdan glacier (and smaller glaciers, e.g., Kichik Khumdan, Aqtash and Sultan Chussku) in the Upper Shyok region (Table 2; Figs. 2 and 19). These glaciers are notorious for exhibiting abrupt advances, and an increase in glacial surge activities in Karakoram terrain as observed after the year 1990 [67]. Chong-Khumdan glacier in particular has exhibited periodic advances and blocked the Shyok River forming

glacially dammed lakes many times in the past. The bursting of such dams has created serious GLOFs in the downstream areas [53,54]. One of the largest glacial lakes (Yapchan/Gapshan Lake) formed in the year 1928, with first reported sighting of the glacial dam and lake in the late spring of 1927 [54]. The lake was 12 km long, wide at the northern end and narrowing at the south, the average width being 915 m, and Depth 25 m (maximum 137 m) (Figs. 2 and 19) [53]. In 1929, when the outburst occurred, the lake had reached a length of 18 km, with an estimated volume of 1.5 × 109 m3 [68]. The flooding devastated the downstream areas, including Attock District (now in Pakistan). These GLOFs have ranged in their intensity from small to major and great, and 14

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Fig. 18. Cloudburst aftermath in Diskit, and building structures under the risk of debris-flow. These structures are occupying the natural water ways, and it is seen that after a disastrous event the buildings are constructed on top of the buried structures (inset) at the same spot.

Table 2 Inventory of the major glaciers (and surging glaciers) in the Karakoram with history of glacial damming and GLOFs (From Ref. [65], also see Figs. 2 and 19). Data From [53,54,65].

Table 1 Glacial Lake Outburst Floods (GLOFs) events in the Shyok Valley (From Ref. [65]). Data From [53,54,65]. S. No.

Year

Glacier

Dammed River

Consequence

S. No.

Glacier

Gradient (m/km)

Length (km)

Area (km2)

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21

1533 1780 1826 1833 1835 1839 1842 1855a 1855b 1871 1879 1882 1898 1901 1903 1905 1926 1929 1932 1933 1940∗

Khumdan Khumdan Khumdan Khumdan Sultan Chussku Khumdan Chong Khumdan Khumdan Khumdan Khumdan Khumdan Khumdan Khumdan Khumdan Kichik Khumdan Kichik Khumdan Chong Khumdan Chong Khumdan Chong Khumdan Chong Khumdan Khumdan

Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok Shyok

No Information No Information Serious Flooding No Flooding Extensive Floods Minor Flooding Small Flood Local Flooding Major Flood Large Flood Great Flood Large Flood Large Flood Major Flood Local Flooding Small Flood Great Flooding Great Flooding Major Flooding Major Flooding Major Flooding

01 02 03 04

Chong Khumdan Kichik Khumdan Aqtash Sultan Chussku

135 143 165 153

21 20 13 14

151 86 35 33

length of time. Soft sediment deformation structures are also distinctly seen in these sediments (Fig. 21). One such discontinuous (∼5 m thick) outcrop of ponded sediments can be traced for ∼2 km in Changmar (Fig. 22). These accumulations are dominantly present on the right bank (towards the west) of the Shyok River on east facing slopes, and a small outcrop is also present on the left bank (north-west facing slopes) close to the Changmar Village. The west facing slopes towards the eastern bank of the Shyok River are devoid of the ponded sediments that have been completely eroded. We sampled these sediments and analysed them by Optically Stimulated Luminescence (OSL) dating (e.g. [70–74] from the Birbal Sahni Institute of Palaeosceinces (Lucknow, India) to get the approximate time-span for the existence of these palaeo-lakes, and the timing and cyclicity of associated flooding events (e.g. [75–78] (Table 3). The sediments were sampled at three levels covering the entire thickness from two locations, viz. 1 (34° 47′ 55.70″N; 77° 06′ 31.55″E) and 2 (34° 46′ 04.06″N; 77° 06′ 59.18″E) with a vertical separation of ∼15 m at present (Fig. 22). We obtained a basal and top OSL date of 12.8 ± 0.5 ka and 8.5 ± 0.4 ka at location 1. This suggests the existence of a palaeolake that was established 12.8 ± 0.5 ka ago in this area, which sustained for c. 4.3 ka and breached c. 8.5 ka ago possibly causing a flooding event. At location 2, a basal OSL date of 8.7 ± 0.4 ka and a top OSL date of 7.5 ± 0.4 ka was obtained, suggesting the existence of the palaeo-lake that was sustained for c.1 ka and was breached c. 7 ka ago (Fig. 22). In this area, at least two palaeo-lakes and two flooding events (which could be more) can be bracketed between 8.5 ± 0.4 and 7.5 ± 0.4 ka. However, the ages from additional outcrops must be determined regionally to establish the occurrences of damming of the Shyok River, formation

some of them have caused severe flooding. In the year 1929 GLOF event, the water level rose to 26 m in 4 h in Saser-Brangsa (Upper Shyok) and to 19 m over 24 h in Diskit (Lower Shyok) [53] (Fig. 20). Presently very limited work has been done to assess the occurrence and distribution of the glacial lakes in this part of HKH-Karakoram region in India. However, in the HKH-Karakoram region of Pakistan 2410 glacial lakes have been identified in 10 river basins, out of which 1328 are major lakes and 52 are GLOF lakes. In the Shyok river basin of Pakistan 31 major lakes and 6 GLOFs have been identified [69]. In the Shyok-Nubra Valley (India), palaeolake (ponded) sediments and palaeo-shorelines are distinctly seen in Tsati, Khalsar, Changmar and Turtuk, among other places (Fig. 21). This indicates the existence of palaeo-lakes (formed by the damming/blocking of the Shyok River) that would have inundated large parts of this region over a considerable 15

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Fig. 19. Map of the Upper Shyok region published in Ref. [53] and presented as such to carry forward this historically important documentation of the formation of glacial lakes in this region. The location of the major surge glaciers and Gapshan (Yapchan) Lake, yellow inset is also shown. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

of palaeo-lakes and their bursting (e.g. [22,79]), especially given the uncertainty associated with using few data points. Additionally, by taking into account the sediment thickness (∼5 m) and age range between the oldest and the youngest layers at two locations, i.e. c. 4.3 ka at location 1 and c. 1.2 ka at location 2. It is seen that sedimentation rate has considerably increased from 1.2 mm/year (in palaeo-lake at location 1) to 4.2 mm/year (in palaeo-lake at location 2), that can primarily be attributed to the increased erosional rates and sediment transport by glacial, fluvial and aeolian processes. The increased sediment transport suggests more pronounced uplift of the terrain due to the activity of KF and/or some subsidiary faults [80]. The Flood hazards in the Shyok-Nubra region have not been usually considered a threat owing to dry conditions, and wandering watercourses in the mountains. But, the rainstorms and accompanying floods (of 2006, 2010, 2014 and 2015) have proven that conditions are there for powerful and severe floods to occur. These floods can cause considerable erosion in some areas while depositing large amounts of sediment and debris in others. Presently the glaciers in Upper Shyok region (in Karakoram) are away from the valley wall, and the glacial lakes are absent. But, with increase in glacial surge activities post 1990 [67] there is an increased risk of glacial lake formation. Once established the outburst from such a lake will likely destroy the settlements on the fans in the Shyok-Nubra Valley, particularly Tsati, Khalsar, Diskit and

Hunder (as in 1929 GLOF event [53,54,68], which have become populated over the years. Therefore, it is important to perform GLOFs risk assessment and understand the mechanism of outburst, accompanied with continuous monitoring of glaciers in the region. 3.4. Fan hazards In the Shyok-Nubra Valley communities are settled and building structures are constructed usually on slopes, flood plains and piedmont zones and particularly on fans which represent the attractive sites for developmental purposes because of their gentle surface, local drainage and fertile soil. (Fig. 7). The fans are gently-sloping triangular (fanshaped) landforms on which hazards are significant and difficult to manage, and the communities are always in great danger [81,82]. Numerous fans made of boulders, sand, gravel and silt built up by debris flows and streams (colluvium and alluvium) occur in the ShyokNubra Valley [83] (Fig. 7). These fans have been formed by the downslope movement of debris by gravity and erosion, which accumulates the sediments in the piedmont zone. The entire fan surface is prone to flood, sediment and debris flow, scour and erosion, and is a dangerous location for the establishment of communities [81,82]. All the major settlements (e.g. Diskit, Hunder, Hundri, Udmaru, Bogdang, Turtuk, Khalsar, Tiggur, Tsati and Panamik) in this region are situated 16

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narrow channel of the canyon carries the debris downslope which accumulate below the slope-drop and at the piedmont zone forming fans, and the flow progressively moves towards the flat valley below. 2. The flow from the ‘Apex’ moves on the topmost surface of the alluvial fan forming a single (primary) channel which may follow the previously formed flow direction or may as well form a new flow direction for itself, thus creating a ‘Channelized Zone’ in the upper fan region which is highly prone to high velocity flood hazards. 3. Further down, the primary channel becomes wide, shallow and very slow, depositing sediments and debris in the ‘Mid-fan Area’. The deposition of the debris in the existing channels, backfills them causing sudden and unexpected channel formation by avulsion. In this area, frequent detachment and rejoining of the channels by different sedimentary processes (e.g. accumulation and erosion of sediments) forms the ‘Braided Zone’ where very erratic, random and unpredictable flow paths exist. 4. The base of the fan represents a uniform and gentle surface which is called as the ‘Toe’ where the ‘Sheet Flow’ (shallow overland flow with high velocity) is very common. Additionally, at the basal part, the adjacent fans converge and coalesce producing alluvial ‘Aprons’. 3.4.2. Flood hazards on the fans During a flood event, the path that the flood water takes on the fan as it moves from the apex to the toe mainly depends on sediment content and velocity of flowing water, the fan's slope, soil and vegetative cover, and the type and extent of fan development [81,82,84]. All these factors vary significantly from one fan to another in the ShyokNubra Valley, and this makes the behaviour of the floods on the fans highly unpredictable. The flows on the fans are characteristically subjected to lateral migration, relocation, and the flood water may not follow the same path during subsequent floods. However, it is seen that some zones on the fans are more prone to flood hazards, and it is important to identify such zones on fans in the Shyok-Nubra Valley. The full range of hazards that may be encountered on fans are given in FEMA-1989, 1990 [84,85], and the most potent fan hazards in the Shyok-Nubra Valley are, (i) high -velocity flow, producing significant force (pressure against building structures caused by the movement of flowing water); (ii) erosion/undercutting, scour; (iii) debris/sediment flow and their deposition; (iv) flash flooding (without any warning). The fans in the Shyok-Nubra Valley are young and very active and the entire fan surface represents a potential site for flood, sediment and debris deposition and scour, and is a dangerous location for settling the communities. Usually it is seen that, as the time progresses in the older regions of the fans, the hazards, e.g. the floods follow a predictable pattern, and flood flows may remain within defined channels [81,82, 84]. But, in Shyok-Nubra Valley the landscape is ever evolving and tectonically very active, therefore, the fans or portions of fans which are considered stable and seem inactive may exhibit rejuvenation. Regardless of whether a fan is active, inactive, or both, there is always some degree of unpredictability of the flood hazard on all fans [84–86]. Additionally, the fans in Shyok-Nubra Valley are very close to the colluvial foot slopes where an extremely large accumulation of unconsolidated material (silt, sand, gravel and boulders) is seen (Figs. 23 and 24). These fans are highly vulnerable to ‘debris flows’ that can result from the presence of tons of fine sediment such as silt and clay in fast-flowing flood during a rainstorm or a cloudburst. During such an extreme event the slurry will transport sand, gravel, boulders from the mountain onto the fan [84–86].

Fig. 20. Top, the 1929 Glacial Lake Outburst Flooding (GLOF) in Shyok River that caused inundation of Diskit where the water level rose to ∼19 m over a period of 24 h (Photograph by Ref. [53]). Bottom, present day water level in the Shyok River, Diskit towards far left.

on such fans (Fig. 7). We undertook field-investigations in Shyok-Nubra Valley (with detailed study in Diskit, Figs. 23 and 24) to build an example to understand the fan formation and fan hazards (their occurrences and zonation) based on [81,82]. 3.4.1. Formation of fans in the Shyok-Nubra Valley In the Shyok-Nubra Valley, colluvial/alluvial and mixed fans are typically found along the piedmont zone. Here, the cold semi-arid high altitude desert like climate in combination with abrupt topographic variation has created conditions conducive for the fan formation. The active tectonics primarily associated with the Karakoram Fault (KF) has produced mostly active fans in areas towards the east of the KF up to the slope break along the Karakoram terrain. These young active fans exhibit characteristic morphology of braided channels and erratic flowpaths (Figs. 7 and 23). In the Shyok-Nubra Valley the evolution and the growth of the fans has followed a general sequence of events as observed throughout the world in tectonically active areas also described in [81,82] (on which this work is primarily based), and given as follows (Figs. 23 and 24):

3.4.3. Fan hazard risk assessment and zonation in Diskit A detailed study of the fan in Diskit was done in order to determine the severity and location of hazards expected here (Figs. 23 and 24). The active and inactive portions of the fans were mapped, and the locations of previous and potential debris flow paths were determined. In Diskit, two fans growing along a coalescing cone (CZ) are seen, and the

1. All the fans have a highest point called the ‘Apex’ which forms the outlet of the narrow canyon higher up in the mountain. During rainstorms/cloudbursts the turbulent flow emanating from the 17

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Fig. 21. Regional presence of palaeolake (ponding) and inundation related signatures in the Shyok Valley. (a) Palaeo-shorelines seen (shown in the photograph by white stippled lines) that can be traced from Khalsar to Agham, photograph clicked from Tsati. (b) Soft sediment deformation structures in palaeolake sediments at Khalsar. (c) Palaeolake sediments ∼5–10 m thick, traceable from Changmar towards Bogdang. (d) Finely laminated, typically yellow coloured palaeolake sediments preserved at Changmar. (e) Palaeolake sediments, ∼5–10 m thick at Turtuk. (f) Small scale soft sediment deformation structures observed in palaeolake sediments at Turtuk. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

fans are mixed-type with major colluvial growth. The fans can be classified (after [81,82] into distinct parts, which include – 1. Apex (geomorphic and hydrodynamic); 2. Channelized Zone; 3. Braided Zone; 4. Apron and 5. Sheet Flow Zone. The source of the colluvium is primarily the fall face and transportational mid-slope. These colluvial accumulations also form prominent Colluvial Foot-Slope (CFS), and the alluvial interactions form the Alluvial Toe-Slope (ATS) (Figs. 23 and 24) (After [81,82,84–86]). This fan can be classified into eight zones based on fan hazard risk assessment (following [81,82,84]), and these zones are: A. The old entrenched fan surface which presently receives minimal sediment supply through debris flows from the source area, viz. mountain fall face and the transportational mid-slope. This surface is free from being undermined. B. and C. The boulder and coarse grained sediment accumulation zone and natural levees formed by the debris flows within and along the channels. D. The entrenched surface highly susceptible to floods, if the primary channel becomes blocked by debris flows or sediment accumulation. E. The distributary (secondary) channels that do not show any evidence of major scour, deposition, migration, or avulsion during recent floods triggered by cloudbursts and rainstorms. F. The areas that are susceptible and subjected to sheet flooding. G. The

channels that are prone to migration with an unpredictable and uncertain behaviour. H. The surface that is prone to overbank flooding, channel shifting, or invasion from a distributary/secondary channel that might originate from primary channel (G). Cloudburst events of the year 2010 and 2015, and the locations most severely affected have also been shown. It is seen the entire fan surface is hazard prone, and the older stable surfaces in and close to zone A. are less vulnerable, in addition to surfaces close to relatively stable zone E. that is not completely free from hazards. The zones D., F., G., H. and the fan edge in proximity of the fall-face and transportational mid-slope are highly susceptible to fan hazards as evidenced by the 2010 and 2015 cloudburst events (Fig. 24). In the inhabited fans in Shyok-Nubra Valley particularly in Diskit, additional development activities on the active portion of the fans and into the channels (e.g. Fig. 18) will disrupt and adversely affect the natural processes, and subject any structure situated on the fan to severe hazards during the flood events. 3.5. Cloudbursts The Cloudbursts and associated flash-floods and debris flows are 18

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Fig. 22. The location (1 and 2) of the outcrops of the ponded sediments which can be traced for ∼2 km in Changmar area. These accumulations are dominantly present towards east facing slopes, and have been completely eroded from the west facing slopes. The OSL dates from the ponded sediments at two locations are also shown in the insets.

one of the strongest, quickest and unexpected disasters whose frequency of occurrence has increased during the last ten years in the Shyok-Nubra Valley. The cold-arid to semi-arid high altitude desert type climate, barren landscape and sparse vegetation, coupled with the deposition and accumulation of very loose eroded material (sand-gravel to boulder size) regionally on the mountain slopes has exposed the habitable areas to the cloudburst hazards. These cloudburst events have repeatedly occurred over the Ladakh Himalaya in the past (e.g. 1907, 1930 events) and recently in the years 1995, 2005 (23–24 June; 06 July), 2006 (30–31 July; 01 August), 2008 (09 August), 2010 (04–06 August), 2013, 2014 and 2015 [87,88]. One such cloudburst event on 6th August 2010 followed by flash flood resulted in considerable and widespread destruction to life and property from Leh to Zagok in the east and Turtuk in the northwest. The flashfloods affected 52 villages in the area, covering around 1420 ha of land and destroyed 1749 houses. The National Highway was washed off at many places, and the road link got snapped for days [89–92]. Extensive damage was reported from Khalsar, Tiggur, Sumur, Turtuk and Tyakshi in the Shyok-Nubra Valley. The extent of damage can still be seen in all these areas (Fig. 25). In order to minimize the risk of future disasters, it is necessary to monitor climate change and build climatic/simulation models (e.g. Ref. [93]) with a conservation plan in place.

Meager climate studies conducted over Ladakh Himalaya [94] show that the temperature has increased over a period from 1901 to 1989, with a greater increase noted after the 1960s [95]. Precipitation is decreasing during winter and summer periods with a significant change seen after the 1990s [96]. In this region cloudbursts invariably occur along the remote mountain slopes, and the flash-floods and debris flows have not been evaluated scientifically. These events are largely unreported and known only if there is damage and loss of life and property. So the nature, occurrence and repetition of these events has largely remained elusive. Thus, there is an urgent need to understand the climate over Shyok-Nubra Valley, and to further study in this context. 3.6. Snow avalanches Himalaya holds true to its name, meaning ‘abode of snow’, due to severe cold climate (average minimum temperature −40 °C) and high annual average snow accumulation of ∼10 m at high altitudes [97]. It is estimated that at the intersection of the Hindu-Kush, Karakoram and Western Himalaya a total annual precipitation of 2650–3000 mm occurs in the form of snow (with no liquid precipitation) [98,99]. This gives rise to intense avalanche activity in this region, particularly in the Greater (Higher) and Trans Himalaya. From 1995 to 2006 the largest

Table 3 Luminescence dose rate and calculated OSL dates of the samples. Samples

Dose Rate (Gy/Ka)

De (Gy)

2c 2b 2a 1c 1b 1a

3.998 4.261 3.872 4.408 4.511 4.247

25.1 27.4 26 31.8 36.4 43.8

0.151 0.164 0.148 0.167 0.171 0.161

Age (Ka) 0.4 0.4 0.4 0.4 0.7 0.7

6.278 6.431 6.716 7.213 8.068 10.313

0.257 0.265 0.277 0.288 0.344 0.423

19

Fading Corrected Age (Ka)

a-value

7.5 ± 0.4 7.6 ± 0.4 8.7 ± 0.4 8.5 ± 0.4 9.2 ± 0.3 12.8 ± 0.5

0.034 0.033 0.038 0.037 0.043 0.038

g-value (%/decade) 0.001 0.001 0.001 0.001 0.001 0.001

3.60 3.43 4.70 3.31 2.65 4.05

0.90 0.99 1.05 0.95 0.94 0.89

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Fig. 23. Google image of coalescing fans in Diskit, showing different parts, viz. 1. Apex, 2. Channelized Zone, 3. Braided Zone, 4. Apron and 5. Sheet Flow Zone, and typical fan morphology (After [81,82]). Of note is the braided zone in the active fan towards right.

number of avalanche related incidents and deaths occurred in Indian part of Himalaya [98]. In the Shyok-Nubra region, ∼37% area of Nubra Basin and ∼20% of Shyok Basin is covered with glaciers. The climatic conditions of the Nubra-Shyok are very harsh during the winters that are very similar to continental snow conditions [100,101]. The Shyok-Nubra basin has

very cold temperature during winters. The precipitation is mainly in the form of snow, however rainfall does occur in the low lying areas during the summers. High relief and steep slopes has led to a number of large slope failures in the region, and increased avalanche incidents ([100] and references therein). There are multiple risk areas, particularly the high passes. Here, Fig. 24. Sketch illustration - fans along a coalescing zone in Diskit. The fans can be classified into distinct hazard zones, viz. Old fan surface (A); boulder accumulations and levees (B, C); flood prone entrenched surface (D); distributary channels (E); areas prone to sheet flooding (F). G is the migrating channel with uncertain behaviour. H is a surface prone to overbank flooding (also see section 3.4.3).

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Fig. 25. Extensive damage caused by cloudburst in Shyok-Nubra Valley. (a) and (b) Devastation and destruction at Khalsar. (d) Cloudburst caused debris-flow overwhelming residential house in Tiggur. (c) Cloudburst aftermath at Sumur. (d) Cloudburst aftermath in Garadi, Turtuk (Shyok Valley). Notice huge car-sized boulders carried by torrential flow, one of the boulders is very close to the primary school building.

failures occur due to the melting of a layer of the snow acting as lubricant forming a slip surface, accumulation of a large snow mass following heavy snowfall, and excessive loading and movement of vehicles. Parshad et al. [100] have divided the Shyok-Nubra basin into five zones on the basis of avalanche susceptibility, viz. (I) Very High, (II) Moderate-to- High, (III) Moderate, (IV) Low, and (V) Very Low. In the Shyok-Nubra basin 27.5% of total area is in very high susceptibility zone and only 4.8% of the total area is in very low susceptibility zone [100]. Most of the settlements are located in the low susceptibility zone, except for the inhabited areas in the proximity of the steep slopes, as in Turtuk [50].

obstacle and barchans dunes, and desert rock varnish (brown coloured with greasy luster) occur at particular places along the courses of the Nubra and Shyok rivers. The formation of sand dunes in the area is controlled by rock type, flowing water, glaciers and particularly the aeolian processes (Fig. 26). These dunes may or may not represent the role of climate parameters and cannot be always equated with phases of extreme aridity [102]. Although the aeolian geomorphic processes are dominating the landscape and have led to desert like conditions in the Shyok-Nubra Valley, these processes have not been well-studied. Most of these aeolian deposits are not permanent features, are frequently mobilized and replenished, and highly prone to being blown and washed away by intense wind activity [102,103]. The local populace in the Shyok-Nubra Valley is largely dependent on the produce from the agricultural patches in the proximity of the aeolian deposits. With the increase in the extent of these deposits and their irregular behaviour, the agricultural practices are under constant threat in the region, and there is a pressing need to provide scientific means for the mitigation of the desertification hazard in the area.

3.7. Desertification In Shyok-Nubra Valley the climate is cold-arid high altitude desert type, rainfall is scanty, and precipitation is mainly as snow that melts and brings water to low lying areas. There is plenty of water in the region, however desert like conditions are observed in some areas, e.g. Hunder (Shyok Valley), where large Quaternary sand-dune fields are seen (Fig. 26). Interestingly, no Quaternary deposits are observed downstream of the Shyok River. In the Nubra Valley, the bed of the Nubra River is also occupied with small to moderate size sand-dunes separated by depressions. The sand-and-dust storms triggered by cold winds storming down from the Siachen Glacier occur daily during the afternoon in the Nubra Basin (Fig. 26) [22]. So the wind activity is very intense that has strengthened the aeolian geomorphic processes leading to desert like conditions. Although this region has surplus water, due to the overall arid climate, vegetation cover is scarce and limited to the areas proximal to glacial-fed streams [102]. The decrease in moisture is reflected in the cold desert like conditions, and geomorphic features like cluster,

4. Summary and conclusions 4.1. Summary The Shyok-Nubra Valley represents one of the most dynamic environments in the HKH region where continuous geological and geomorphic processes have driven the natural hazards that are interacting with one another in complex ways which are not understood completely. These processes have resulted in a very diverse range of geomorphic hazards throughout the Shyok-Nubra Valley, viz. Earthquakes, mass movements, fan-hazards, floods and glacial lake outburst floods 21

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Fig. 26. Cold-arid desert like conditions in Shyok-Nubra Valley. (a) Quaternary dunes (like cluster, obstacle and barchans dunes) field at Hunder. (b) Camel safari at the Hunder sand dunes, Diskit Monastery is seen in the background (top right). (c) Sandstorms due to cold gravity winds in Nubra Valley. (d) Bed of the Nubra River occupied by moderate dunes separated by depressions.

cloudbursts (e.g. in 2006, 2010, 2014 and 2015). GLOFs in the region are associated with glacial surge activities that have increased significantly since 1990 [67]. We report the presence of at least two palaeo-lakes (close to Turtuk) that formed within a very short time span, and two flooding events that can be bracketed between 8.5 ± 0.4 and 7.5 ± 0.4 ka. We also report the increase in sedimentation rate from 1.2 mm/year to 4.2 mm/year over a time span of 4 ka (from Changmar area), suggesting increased erosional rates and sediment transport by intensifying glacial, fluvial, aeolian processes and pronounced uplift of the terrain due to the activity of the regional and local/subsidiary faults. In the Shyok-Nubra Valley all the major settlements are confined to the fans which are attractive sites for developmental activities, but at the same time are dangerous locations to settle because of being hazard prone. The fans in this region are very active and highly susceptible to debris flows in particular. We conducted a detailed study of the fan in Diskit to determine its mode of formation and structure (based on [81,82,84–86]), out of the eight zones identified, four zones D, F, G, H and the fan edges are highly susceptible to hazards as evidenced by the 2010 and 2015 cloudburst events. Any additional developmental activities on the active portion of the fans and into the channels will disrupt and adversely affect the natural processes exacerbating the hazards during the flood events. The frequency of occurrence of cloudbursts has increased over the last decade in the Shyok-Nubra Valley. Extensive damage and its aftermath is seen in Khalsar, Tiggur, Sumur, Turtuk and Tyakshi in the Shyok-Nubra Valley. It is important to understand the climate over Shyok-Nubra Valley, and to further study in this context keeping in view the alarming increase in the frequency of cloudburst events in this region. In the Shyok-Nubra region, ∼37% area of Nubra Basin and ∼20% of Shyok Basin is covered with glaciers. High relief and steep slopes has led to a large number of slope failures in the region, and increased avalanche incidents. There are multiple risk areas, particularly the high passes [100]. Most of the settlements are located in the low susceptibility zone, except for the inhabited areas in the proximity of the steep slopes, as in Turtuk. The aeolian geomorphic processes dominate the landscape of the Shyok-Nubra Valley, and have led to desert like conditions here. Most of these aeolian deposits (sand-dunes) are temporary, frequently mobilized and replenished by intense wind activity [102,103]. With the increase in the extent of these sand-dunes and their irregular behaviour, the agricultural lands are under constant

(GLOFs), cloudburst, snow-avalanches and desertification. Geology of the Shyok-Nubra region is very fragile as the variable rock types are highly fractured and deformation is very pronounced due to the tectonic and mountain building activities, that have led to the intricate geological, hydro-geological and geomorphic processes in the region. These geological conditions coupled with extreme climatic events have given rise to intense erosion, sedimentation, debris flows, floods and numerous other hazards in this region. In the Shyok-Nubra region the earthquake hazard is primarily associated with community location and building/construction standards. The structures in the region primarily fall into three categories: (i) the vernacular construction; (ii) the vernacular/traditional building structures modified and renovated by unreinforced masonry methods, and (iii) the structures based on unreinforced masonry dry-stone and random rubble concrete construction. These structures can be assigned the category of Building Type-I and Type-II. The ∼ Mw 5 earthquake can cause substantial damage to Type-I structures, and slight damage to Type-II buildings, which will be subjected to damage and possible collapse by > 5 to 5.9 Mw (or greater Mw) earthquakes [42–44]. We have observed that greater hazard to people in the Shyok-Nubra Valley can come from the collapse of the man-made structures during an earthquake, apart from flood hazard associated with a broken dam or embankment, and rock-fall. The evolving landscape, coupled with geological and geomorphic processes has rendered the entire region (consisting of ridges, slopes and valleys covered with massive accumulation of unconsolidated clay to boulder size sediment) very weak and susceptible to mass movements. The frequent occurrences of cloudbursts and rain-storms in the region have resulted in severe debris flows that have overwhelmed several localities. Diskit and Turtuk are particularly vulnerable, as evidenced by 2006, 2010, 2014 and 2015 cloudburst and debris flow events. Being surrounded by steep and fragile slopes and glacial melt rivers, flooding, rock fall and debris flow frequently hit all the three domains (Domain 1- Panamik, Tiggur and Sumur; Domain 2- Tsati and Khalsar; Domain 3- Diskit, Hunder, Udmaru, Bogdang, Chalunka and Turtuk (Fig. 2)) in the region, and a detailed hazard analysis and mapping is required for the micro-zonation of mass movement hazards to delineate the safer zones. A number of floods, and at least 21 GLOFs have occurred in the Shyok-Nubra Valley (and many have gone unreported). Powerful and severe floods have occurred in the region due to rainstorms and 22

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threat in the region, and there is a pressing need to provide scientific means for the mitigation of the desertification hazard in the area. The Turtuk area sets the ideal context for understanding and investigating environmental hazards and their effects on the mountain communities in the Shyok-Nubra Valley. Being nestled within high altitude mountains and glacial melt rivers, flooding and rock fall frequently hit Turtuk. The region is also vulnerable to earthquakes [39] and was severely damaged during the 2010 and 2015 flash floods. In Turtuk, the geological processes, coupled with anthropogenic activities and climate change have given rise to and exacerbated numerous hazards viz. earthquakes, down-slope movements and debris flows, and floods. In order to minimize the risk of future disasters, it is necessary to monitor imminent hazards and construct safety models [50].

• •

4.2. Conclusions

Acknowledgements

In the Shyok-Nubra Valley dynamic geological processes, intense and abrupt climatic fluctuations, fragile hill slopes, coupled with heterogeneous sediment accumulations has exacerbated erosion and transportation, mass wasting, land instabilities, melting of glaciers and floods. This paper provides a preliminary documentation and understanding of the drivers of natural hazards (viz. earthquakes, mass movements, fan-hazards, floods, glacial lake outburst floods (GLOFs), cloudburst, snow-avalanches and desertification) in this region and the following conclusions are drawn:

This paper is the outcome of the collaborative research between Institute for Risk and Disaster Reduction (IRDR), University College London, U.K. and the Institute of Energy Research and Training (IERT), University of Jammu, India. This research was funded by the National Environment Research Council - Global Challenges Research Fund (NERC-GCRF) grant, reference: NE/P016138/1.1. Appendix A. Supplementary data

• The geological conditions and intense deformation coupled with • •

•

•

• • • •

and debris flows) sets the ideal context for understanding and investigating environmental hazards and their effects on the mountain communities in this region. This work provides a suitable context for the future disaster management and risk reduction policy framing and in resolving problems related to natural hazards susceptibility and developmental works in the Shyok-Nubra Valley. Advanced and extensive investigations involving field based studies, large-scale hazard mapping, geology, remote sensing and Geographic Information System (GIS), computer modelling, geochronology, and real-time monitoring of the natural processes will shed new light on the evolution and understanding of the geomorphic hazards in this part of the Hindu Kush-KarakoramHimalaya.

Supplementary data to this article can be found online at https:// doi.org/10.1016/j.ijdrr.2019.101094.

extreme climatic events have given rise to intense erosion, sedimentation, debris flows, floods and numerous other hazards in this region. Earthquake hazard in this region is primarily associated with community location, man-made structures, construction standards and rock fall and debris flows. Here, most of the building structures are of Type-I and Type-II which are susceptible to damage and collapse by ∼ Mw 5 to 5.9 (and greater) earthquakes. In the entire region, the ridges, slopes and valleys are covered with massive accumulation of unconsolidated sediment/debris that is susceptible to mass movements. The frequent occurrences of cloudbursts and rain-storms in the region have resulted in severe debris flows, Diskit and Turtuk are particularly vulnerable to such hazards. Floods and GLOFs are very powerful and severe in this region as evidenced by the recent and historical events. OSL dating of the ponded sediments shows the existence of two palaeo-lakes (close to Turtuk), and two flooding events that can be bracketed between 8.5 ± 0.4 and 7.5 ± 0.4 ka. The dates also show the increase in sedimentation rate from 1.2 mm/year to 4.2 mm/year over a time span of c. 4 ka. The fans in the region are attractive sites to settle, but at the same time are highly vulnerable because of being very active and highly susceptible to debris flows. The fan hazard assessment in Diskit revealed four zones of very high risk, safe zones were also identified. Similar assessment needs to be extended to all the inhabited fans in the region. Cloudbursts and rain-storms are of frequent occurrence in the region, and here, it is important to understand the regional climate variability. Large area of this region is glacier bound, high relief, steep slopes and high passes are susceptible to snow avalanches. Largely, the settlements are in the low susceptibility zone, except for the inhabited areas in the proximity of the steep slopes, e.g. Turtuk. The region is desertification prone owing to intense aeolian geomorphic processes, most of these aeolian deposits are increasing in extent, thus posing a threat to agricultural land. Among all the localities, Turtuk (nestled within high altitude mountains and glacial melt rivers, and prone to flooding, rock fall

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