The village of Garbyang that is witnessing the problem of ground subsidence for a long time is situated on the Indo-Nepal border at a distance of 25 km from the road head at Dharchula on the right bank of river Kali in Pithoragarh district of Uttarakhand and has a population of 210 (119 males and 91 females Census of India, 2001). The village once occupied vast expanse of flat ground overlooking the river. The lacustrine deposits forming a flat ground at Garbyang provided a vintage point to the people whose economic activity thrived on flourishing trade with Tibet supported by a strong backing of livestock. Atkinson (1882) provides vivid account of the multistoried buildings at Garbyang. This region was at that time one of the most prosperous tracts of entire Kumaun region and the economy of the region was intricately interwoven with the migratory traders of the region. Importance of trade with Tibet can well be assessed from the fact that Khasdeshadhipati (king of Khasdesh the land of Khasas - the local inhabitants of the region) Baz bahadur Chand (1638-78) personally supervised the construction of the trade route (Atkinson, 1882).

The ground surface around Garbyang is presently broken into undulating terraces. Once prosperous village having multistoried houses with ornate woodwork now lies in a dilapidated state. The yielding ground has taken toll of the houses and many have been consumed by sinking ground and hitherto adjacent ones appear at different levels. Villagers have moved out to nearby safe grounds and most of the exquisitely carved wooden panels have found their way across the Kali in the Napalese territory. The administration has done little to restore the village and has devised an easy alternative of relocating the people in far off plains that amounts to the alienation of a culture. This approach is not new these people, basically traders, were previously granted tribal status on the disruption of Tibetan trade following the Sino-Indian border dispute as a poor substitute for their economic loss. It is informed that the ground sinking was out vocally observed sometime after the disruption of the Tibetan trade.

Geomorphology and Geology of the Garbyang basin: Garbyang basin is a NE-SW trending valley with flight of terraces cut on lacustrine sediments. The village is located towards the northern flank of the basin and river Kali drains parallel to the southern flank of the mountain. The steep mountain running parallel to the village in the north acts as eyebrow and protects the village from natural hazards. Being a north facing slope, high rates of evpotranspiration result in little vegetal growth.

Chialekh (lekh = pass in local parlance) is the highest elevation (~ 3500 m) towards the west and acts as a major divide separating the lower Kali basin in the west from the higher basin towards the east. The lake sediments (varves) start appearing just below the Chialekh and continue E-NE till Gunji for a distance of 11 kilometers. The relict varve deposits are presently terraced and these run parallel to the valley. The morphology of the terraces suggests these to be tectonogenic with sharp vertical breaks. The degree of preservation is good towards the west while towards the central part and in the east these merge together. The central part of the terraces is undergoing extensive slumping. The axes of slumping coincides with the concavity of the Kali meander that has been pushed towards the north by colluvial debris descending from the southern mountain range along an avalanche chute. River Kali after meeting the Tinkar flows westward on a nearly flat surface which after draining through the basin makes its exit through a narrow outlet just below the Chialekh.

Unlike most Himalayan rivers which normally follow the strike of the country rocks, Kali cuts across the strike like an antecedent river system. Lithological control on the drainage pattern does not appear to be very striking, on the contrary the structural configuration seems to dominate the drainage basin.

Tethyan Fault, along which the high grade Central Crystalline rocks are juxtaposed against the Tethyan sedimentaries to the north, expresses itself geomorphologically by prominent ridges. Chialekh ridge in the Kali valley is the surface expressions of this tectonic plane. This ridge defined the distal end of the palaeolake at Garbyang in which was laid down a continuous sedimentary record.

Deformational features around Garbyang: Four distinct episodes of tectonic disturbances are observed in the varve succession at Garbyang and these are attributed to past seismicity in the region. The fault planes in all the four deformational events show similar spatial orientations which is suggestive of their similar causative force, though separated by considerable time gap. The fault planes dip towards north and south at moderate to high angles. The sediment mass in the proglacial lake has thus witnessed gravity induced faulting in response to the tectonic disturbances in the vicinity as many as four times. Proximity to the Tethyan tectonic boundary is suggestive of the seismic activity being related to the movement along this plane.

Deformation in the slided down mass is observed at the right bank of Kali to the south of the insitu section. The slided down mass has formed folds that are owed to gravity gliding.

These deformations are the product of gravity gliding alone the mass has slided down from N-NE along the weak plane paralleling the valley walls. Such weak planes are also observed in the Garbyang village, where along a E-W oriented fault plane the sediments have gone down as much as 4 meters at the eastern end. The displacement at the western end is however of the order of 20 meters. This plane is observed for 150 meters and is associated to the Dharchula earthquake of 1980. Erosive forces have not yet concealed the scrap and the surface is still fresh. No shattering of boulders was however observed along this scrap. Houses that were once at one level are now observed at different levels across this fault line.

Discussion: The faulting observed in the insitu varve deposits at Garbyang is the manifestation of the palaeoseismicity in the region related with the movement along the Tethyan Fault that forms the distal boundary of the proglacial lake. The absence of liquefaction features that are commonly cited as evidences of past earthquakes is attributed to the absence of sandy horizons in the varve succession, as it is the increased pore water pressure associated with the liquefaction of sand rich layers that causes these features (Obermeier 1996). The region is tectonically active and has experienced many earthquakes in the past (Paul 1986, Srivastava et al. 1986). These disturbances are observed to be confined to the lower part of the profile followed by a long phase of quiescence.

The subsidence of the ground surface at Garbyang is caused by the toe erosion by Kali river and consequent down slope movement. The mass is moving under gravity along the preexisting tectonogenic weak planes. The toe erosion by Kali is accelerating the pace of movement and ground subsidence.

The central part of the Garbyang basin that houses the Garbyang village is undergoing severe land subsidence. Currently, the village is undergoing serious land degradation amounting to total and near partial damage of the houses. According to the villagers there were four streets in the village (situated at Terrace – 1) that were parallel to the terrace i.e. E-W trending. Today there exist virtually no streets and there are only a few house left on Terrace - 1. All the streets have merged together constituting the shamble of house put together in basket. Except for the few house on Terrace - 1 which is very close to the mountain and is protected from the north by the calc-silicate ridge, all other terraces in the central part have been merged together due to the continuous land movement, though the downward movement accompanied by vertical subsidence varies from locality to locality in the village. A maximum of around 20 meters of displacement is deciphered in houses where the old reference surfaces are available. The development of fissures, cracks, distortion and buckling in the houses is the adjustment of the near rigid structure of the buildings due to the stresses developed due to the yielding earth beneath them.

The Kali river which flows E-W is constantly eroding the varve deposits from the base and thus the mass from the north is moving down along preexisting seismogenic weak planes. This movement expresses itself in the folding of the sediments and is threatening the very existence of Garbyang village.