When news came in recently about nature’s work severely disrupting man’s in the human settlement of Joshimath, my thoughts rolled 50 years back to the expedition I was invited to lead by the Wadia Institute of Himalayan Geology. I was then teaching at the University of Roorkee, or rather learning how to evoke in young minds the yet dimly understood processes whereby the earth occasionally convulses to relieve its pent-up stresses.
The expedition was aimed at studying some of the iconic landforms and rock formations of the high Himalayan terranes in Uttaranchal, which we planned to traverse along two river valleys: the Goriganga at Munsiari in eastern Kumaon and the Alaknanda near Joshimath.
Three major earthquakes had originated in the Himalaya since the end of the 19th century, exacting a high toll on life and property. Would there be some hint about the processes of their nucleation in the landscape of the region and their imagined extensions underneath? Even some insightful epiphanies, perhaps, evoked by the lived experience of local communities and their time distilled fables, that I dreamed of gleaning from fireside chats.
Arduous journey
For interrogating nature, however, I armed myself with a gravity meter capable of sensing minute variations in the earth’s gravitational pull as a measure of the density and material properties of subsurface rocks along our route and some gears to establish rock markers across major fracture systems to determine their relative slips from annual repeat measurements.
To keep the expedition short enough not to unduly interfere with the academic schedule, we would motor to Munsiari—the gateway to the high Himalaya along the Goriganga in Pithoragarh, before trekking up to our destination in Sangcha Malla, an outlying border settlement about 80 kilometres northeast of Joshimath—the other gateway to the Great Himalaya through which we would finally return.
Shortly after we had started, however, torrential rains demolished most of the mountain roads, virtually doubling the length of our planned trek of about 90 km. It was a fortuitous intervention.
I walked as one possessed through the enchanting domains of the Lesser and Great Himalaya, conscious only of the ineffable tapestry of gambolling waters, terraced farms and forest canopies occasionally broken by groves of rhododendron. The rain-impaired roads would mean shortage of some materials in people’s lives but there would be no great suffering because their world was fashioned largely by the intuitive understanding of long-tested experiential knowledge and made resilient by their gift of high adaptability.
I returned from the expedition with a chaotic ensemble of sensibilities, of the unworldly beauty of mountain fastnesses and its living world, and not least of the lyrical lives of its people. A constant refrain, however, was the wonder about the nature of those inscrutable forces that built the Himalaya and held up its majesty. Are they still at work and if so, how uniformly and at what pace? Do they vary in some ways along the arc, as some specific differences in the regional structures of the Himalaya seem to suggest despite their seeming uniformity? Tantalising questions such as these would now join my viewing of the sun-hued Himalaya from the bench in front of my house in a corner of the university campus.
Rescue operations under way at the Tapovan Tunnel after a glacier broke off in Joshimath, causing a massive flood in the Dhauliganga river, in February 2021. | Photo Credit: PTI
Sometimes I wonder if the beauty of the spectacle in some way helped resolve the wondering. I found myself writing a research proposal for a grant to buy about half a dozen portable seismographs to record ground vibrations in the Himalaya and try to decode any whisperings that they may hold of its deeper workings underneath.
Geological perspective
A pair of Swiss geologists, Arnold Heim and Augusto Gansser, who had preceded our expedition by three and a half decades, had provided a first order geological perspective of the region. In particular, they identified three major fracture zones sloping northward towards Tibet. Thick sheets of rocks had been pushed up and southward along these fracture zones, delineating three parallel longitudinal ranges, which suggested the work of some agency tending to shorten the distance between India and Tibet.
They also found that rocks of the northernmost range called the Tethys Himalaya lying at altitudes of over 5,000 metres were clearly of oceanic origin. The forces that were pushing India and Tibet towards each other had obviously squeezed up the once intervening ocean that lay between them.
Heim and Gansser’s southernmost range is the Lesser Himalaya of wide valleys and gentle topography overriding the Indian plains along a fracture zone called the Main Himalayan Thrust (MHT). It is now well established that the Indian continent has pushed into Tibet for the past 50 million years, its leading edge being episodically shaved off, thrust back on itself and stacked to form the Himalayan wedge south of the bulldozing face of Tibet.
The pushing continues apace at the rate of about two metres a century as proved by GPS-derived shortening over the past 20 years. The Indian continental plate, being relatively more stolid, has already penetrated deep into Tibet, and currently lies at a depth of about 80 km beneath Lhasa.
It took me three years or perhaps four to finally persuade one of the more empathetic of DST [Department of Science and Technology] functionaries to consider the proposal seriously. It had the fatal flaw of not having a precedent in India and its proposer not having any experience in the field, save untested imagination.
About six years after my return from the expedition, I finally had six moderate-sensitivity earthquake recorders ticking along the second fracture zone of Heim & Gansser, the Main Central Thrust in Kumaon along which the Higher Himalaya of crystalline rocks is thrust over the Lesser Himalaya.
Fig. 1: A satellite image of the Great Himalaya of steep valleys, created by the National Remote Sensing Agency. The Joshimath human settlement is delineated by a yellow contour. | Photo Credit: By Special Arrangement
I shall never forget the ineffable joy I experienced on my first glimpse of this fracture zone on crossing the ridge that bordered Munsiari town and, a little further, of the magical Panchachuli peaks of the Great Himalaya shot by the setting sun. A few weeks later and about 90 km to the northwest, the same fracture zone would be seen majestically sitting atop the Helang peak a few kilometres downstream of Joshimath.
High stress belt
It took a few more years to painstakingly clean up the ground motion records and discover the existence of a high stress belt about 10 km wide. The belt revealed itself by a cluster of small earthquakes that had been recorded by our seismic network, albeit they were too feeble to be felt at the surface.
Fractures have been known to result from the sudden release of progressively accumulating stresses in a system when they exceed the system’s bearing capacity, much like a nervous breakdown in humans. Like human illness, fractures in the earth are also believed to be preceded by small, early warning slips as growing stresses approach breaking point.
The belt of small earthquakes thus discovered had one clear message: that the region was being steadily stressed and would, someday, surely suffer a fracture; but we had no theory at the time to estimate where and when in the future that may actually happen.
As already explained, the steady convergence between India and Tibet is mediated by India slipping and marching northward under Tibet and its adjoining Himalayan wedge. However, since the frictional resistance at the slipping interface decreases with rising temperature, only the part of the plate that lies deeper than about 12 km slips steadily beneath the overlying mountains.
Its colder, shallower southern part, about 100 km wide, remains stuck to the southern Himalaya which, in consequence, is dragged northward along with the descending Indian plate, in opposition to the rest of the overlying Himalaya-Tibet mass advancing southwards.
A segment of the interface between its freely slipping part and that locked by friction thus keeps accumulating stress in the form of a compressed zone like a stressed spring (Fig. 2). With annually rising accumulated stresses, this locked interface would someday be breached and the locked Himalayan wedge would slip southward by a few metres, creating a big rupture and a major earthquake. The cycle goes on.
The belt of small earthquakes beneath the surface trace of the MCT, signalling the presence of a high stress zone underneath, has since been found to exist along most of the length of the MCT. It is now identified with the inter-seismic zone produced by the transitional behaviour of the MHT, also known as the Himalayan decollement, that marks the upper surface of the buried Indian plate slipping northward.
We now have well constrained rates (14-18 millimetres a year) at which the Indian plate slips under Tibet or equivalently, the rate at which Tibet slides southward over India compressing the inter-seismic interface. This figure can be translated into yearly addition of stress to the inter-seismic stress reservoir. We also have a fair estimate of the strain bearing capacity of rocks: about 10-4 or the strain suffered by a 100-metre-long steel bar when compressed by 1 centimetre.
Fig. 2: The persistent source of Himalayan hazards comes from the underthrusting of the Indian continental plate beneath Tibet, powered by an expanding Indian Ocean. | Photo Credit: By Special Arrangement
Estimating ruptures
From a knowledge of the time elapsed since the last major rupture (earthquake) in a region, one can thus calculate how close a region may be to the next major rupture. Such an estimate which is quantitatively credible and based on experimental data provides reliable warning for ensuring that the siting and design of new buildings incorporate safety figures that would enable them to withstand the estimated hazard, and that appropriate action is taken to identify and retrofit vulnerable buildings.
Believing that development and environmental safety are not mutually exclusive, I have always stressed the imperatives of marrying new technological interventions with equally challenging safety measure technologies. The latter invariably call for a rigorous analysis of attendant risks and their quantification, based on incisive analytical tools and field experiments predicated by their methodology.
This part of resilient development is, in most cases, more challenging because, unlike the standard nature of the machinery and tools involved in most development projects, resilience-design is quite exacting. A necessary condition to ensure the integrity of resilience-building measures is the availability of transparent details and testing protocols in the public domain.
Apparently, this runs counter to the prevailing culture of secrecy that claims to be fuelled by concerns of national security, but in most cases is rooted in the fear of being found wanting. As a result, the execution of safety measures in a very large number of projects in our country has tended to be less than satisfactory.
Let me cite an example. In the early 1980s, I was asked by the Ministry of Environment to critique the design safety figure of Tehri dam, which had been recommended by Roorkee University earthquake engineers. With little rigorous data about the deep structure of the region other than the well-established existence of the aforementioned high stress zone, I interpreted it in the light of the recently established theory of “plate tectonics”.
Its implications suggested that the design safety figure of 0.25 g (a quarter as strong as the force of gravity) adopted by them was a gross underestimate. My report presenting these findings required a three- to four-fold higher safety factor. This was viciously attacked by the Roorkee University earthquake engineers, the paid consultants of the project, who declared that they did not believe in “plate tectonics”.
Several years and several committees later, as the government desperately sought a credible answer and the required figures suggested by me were largely accepted, the consultants at Roorkee claimed that they had revised the design to meet the implications of ground acceleration, as calculated by me.
However, the doable three-dimensional test of the design endorsed by all but one member of the committee as a prerequisite for government approval was trashed by the final one-member committee, who was a part of the said consultants.
Hopefully, the Tehri dam has sufficient in-built strength to withstand the impact that a future earthquake might produce, given the resistance to assure the nation that this would indeed be so, using rigorous scientific analysis globally available at that time.
Lack of transparency
The reluctance to have designs transparently tested is widespread in our country and lies at the root of avoidable failures of designed systems.
Engineering technology available today has the analytical tools to construct a fail-safe structure according to the level of stresses that it may face in its lifetime. It is the laxity in heeding the requirements of resilient design while planning development projects that turns natural and man-made hazards into disasters.
The recent Joshimath disaster, to my mind, is of a piece with the prevailing resilience-indifferent culture of planning and development in the country.
The Joshimath Himalaya constitutes the base of a 12 to 15 km thick slab of crystalline material that was pushed over the Lesser Himalaya by Heim and Gansser’s second fracture system, the MCT. This fracture system is dramatically exposed, marking the top of Helang peak just south of Joshimath. It lies directly above the high-stress inter-seismic belt that marks the northern edge of the friction-locked decollement (Fig. 2), and by implication, that of future ruptures and associated earthquakes, as demonstrated by the 2015 Nepal earthquake.
Close to breaking point
The several moderate earthquakes in Uttarkashi and Chamoli in recent decades strongly suggest that the region is already stressed close to the breaking point.
According to the 19th century Himalayan Gazetteer (Atkinson), human settlement at Joshimath at the close of that century was located on the left bank of the river Alaknanda in a hollow recess and on a declivity descending from Trisol peak.
In 1881, it housed about 572 individuals, largely related to priestly and religious functions. The site was situated on an older debris flow, which must have made for a relatively gentler landscape amidst the otherwise steep valleys of crystalline Himalaya, gradually attracting even farming communities and swelling the population, which today is close to 20,000.
There is no available report to show whether they witnessed such disasters in the past, but even if they did, they would have quickly bounced back on the strength of locally available resources and skills.
Connectivity in the Himalaya is mostly facilitated by tracks and roads constructed along valley slopes, especially in the high crystalline Himalaya, where narrow and steep valley slopes make the task even more challenging. Reliable connectivity in the Himalaya is a national imperative today for safeguarding the frontiers.
Higher gradients also mean higher available potential energy from rivers, which can be transformed into electrical energy with much higher efficiency than thermal power and which does not use fossil fuels. Both these programmes necessarily require extensive earth works in turbulent topography and steep slopes which, in turn, will exact environmental costs. I believe a visionary approach would be to desist from posing the problem as an either/or one and seek acceptable trade-offs instead.
Managing the triad
We have unprecedented knowledge available today, as robust models on the one hand and incisive sensing systems and computational tools on the other. These can quantify slope stability; evaluate subsurface distribution of material properties; test and model soil strengths under varying saturations and the probabilistic intensity of natural hazards; audit the vulnerabilities of structures and thus the probabilistic risk posed by anticipated hazards; and, of course, thereby design fail-safe structures.
Accordingly, one anticipates that with imagination and diligent engagement with knowledge, buttressed by experimental data, there is a high probability of managing the triad: the national imperative, the planetary imperative, and the imperative of safeguarding lives and works in a symbiotically organised ecosystem.
To apply this idea to the Joshimath happenings, one may begin with the recognition that the ground under the existing settlement started creeping over a year ago and has since accelerated as demonstrated by the progressive widening of the chasms.
Experimental determination to characterise the space-time behaviour of the creeping process is expected to provide helpful clues as to whether the affected area can be relied upon to have stabilised under the prevailing stresses, and to what extent.
“Ecological integrity must be followed by limiting tourist arrivals.”
As this investigation is likely to require at least a year of monitoring, possibly longer, alternative sites for rehabilitation could be selected nearby after rigorous geotechnical characterisation of the subsurface and, wherever necessary, by stabilising it using appropriate geotechnical solutions.
Concurrently, an exercise should be launched to a) calculate the maximal intensity of potential hazards at the site that may be posed by landslides, floods and earthquakes, and b) ensure that all new structures are designed with safety factors predicated for the calculated hazard intensity.
Meanwhile, the present destabilised terrain could be turned into a profitable space with livelihood opportunities, such as orchards and food-processing units. Finally, the principles of balanced growth and ecological integrity must be followed by limiting tourist arrivals.
In conclusion, it may be stressed that the surest way to safeguard the lives and work of mountain communities in the wake of a host of potentially deleterious socioeconomic activities is to enhance their resilience to hazards, which are often hastened or aggravated by such activities.
It is important that we ask scientists for a) quantitative figures that calculate risks and vulnerabilities and guide resilience measures and b) easy designs to retrofit vulnerable habitats and structures.
The mountain States today are teeming with private engineering institutions. It would be productive to involve their students in the generation of knowledge products and technologies that enhance community resilience and bridge the yawning gap between knowledge and its application. Only this can improve the quality of life in one of the most richly endowed and beautiful parts of earth, one that is also highly vulnerable to exploitation because of those very attributes.
Vinod Kumar Gaur, currently an Emeritus scientist at the CSIR 4th Paradigm Institute, works on Earth System problems. He was formerly Director of the National Geophysical Research Institute and Secretary to the Government of India.
The Crux
- Three major earthquakes originated in the Himalaya since the end of the 19th century.
- Swiss geologists Arnold Heim and Augusto Gansser provided a first order geological perspective of the region.
- They identified three major fracture zones sloping northward towards Tibet.
- Fractures in the earth are preceded by small, early warning slips.
- Development and environmental safety are not mutually exclusive.
- Availability of transparent details and testing protocols is key to ensure integrity of resilience-building measures.
- Joshimath disaster is a result of resilience-indifferent culture of planning and development.
- The region is already stressed close to the breaking point.
- All new structures must be designed with safety factors predicated for the calculated hazard intensity.
- Balanced growth and ecological integrity must be followed by limiting tourist arrivals.
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