ENVIRONMENTAL HAZARDS IN THE HIMALAYAS
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INTRODUCTION: Himalayas—the youngest mountain chain in the world is of immense importance to the nation. Of late the hazardous environment of the Himalayas is posing serious problems to the common people, to the environmentalists and the country as a whole. DEVELOPMENT OF THOUGHT: The ecologically fragile environment of the Himalayas is under grave threat from big dams, deforestation, and mining activities. All these have led to increased landslides, flash floods etc. The safety of dams such as Tehri in the seismically sensitive Himalayan ranges is debatable. An earthquake could lead to disastrous floods In downstream areas and hence dams need to be assessed in terms of environment changes too. Similarly, environmental awareness is yet to establish itself in the form of afforestation and reclamation of mined land in the area. While some- planning and implementation of remedial policies such as afforestation and hazard zone mapping having been carried out; nonetheless, it is inadequate and greater sensitivity is imperative. CONCLUSION: Unless and until we create consciousness in the minds of the people towards this pertinent issue, we will fail in our efforts to save the Himalayas from ecological disaster. |
The Himalayas the youngest mountain chain in the world, gained its present form after three orogenic upheavals, the last one occurring around 30 million years ago. In spite of this time gap, it is still tectonically active and is constantly rising.
The Himalayas extends from the end of the Indus river in the North West to the Brahmaputra in Assam in the East, covering a length of about 2500 km. Transversely Himalaya has been classified into four major mountain ranges—Shivalik or Outer Himalaya, the lesser Himalaya, the Great Himalaya and Trans Himalaya. These subdivisions are separated by major geologic faults and thrusts. They are thus dynamically, very sensitive and the ecosystems they support are in a fragile condition.
The major rivers of the Indian sub-continent such as Ganges, Indus, Sutlej, Brahmaputra and Kosi originate in the Himalayas. Thus the Himalayas is the primary source of water in India. These rivers emerge into the plains through the valleys controlled by faults which are seismically active. This high seismicity of the region and the presence of faults, folds and thrusts besides the network of numerous rivers and springs renders the Himalayan ecology fragile.
The Himalayas has been ruthlessly and indiscriminately stripped of its forest cover and deforestation continues. This results in devastating landslides due to exceptionally heavy rainfall. Besides large scale construction of dams, roads, tunnels, buildings and other public utilities combined with indiscriminate mining and quarrying has also contributed to the fragility of the Himalayan ecology, creating an ecological imbalance in the region. This imbalance is the progeny of various important, carcinogenic factors, both natural as well as man-made. However, a few of them shall be slightly touched in this essay.
The distribution of epicentres in the Himalayan region generally follows the trend of the mountain arc. The region has been rocked by several earthquakes including major earthquakes of magnitude 8 on Richter scale. There are many areas of high seismicities, such as Srinagar in Kashmir, Spiti valley in Himachal Pradesh, Dharchula-Bajang in the Indo-Nepal border, Arun valley along the Nepal-Darjeeling border etc. The Indo-Nepal border registers the largest number of earthquakes per year. There are small pockets of higher micro-seismicity in the Uttarkashi area (about 40 km NW of the Tehri dam site.).
 The Himalayan earthquakes have originated as a result of movements along fault planes. Geomorphic features reveal uplift of the Siwalik resulting from vertical movements of the order of 30 to 80 m near Nainital in Kumaun and in Lansdowne, Garhwal. The larger earthquakes have caused considerable damage to the life and the land through destructive landslides over extensive areas, the most devastating ones being the Assam earthquake of 1897 and the Kangra earthquake of 1905.
 Besides, analysis of seismic data from a number of reservoir sites all over the world has established, beyond doubt, that seismicity is induced by and increases soon after the impounding of water in reservoirs behind large dams. The occurrence of reservoir-induced seismicity is critically related to the height of the water column rather than to the volume of the impounded water. Reservoir-induced seismicity occurs only in tectonically unstable areas. The impounded water finds its way by infiltration through fissures, shear zones cavities and joints into the fault zones and reduces the shear strength of the subsurface rocks initiating the failure of the otherwise unfailing rocks. So the presence of high stresses and that of fault zones are responsible for reservoir-induced seismicity.
In a large part of the fault-riven Lesser Himalaya and Kumaun and Darjeeling regions, high stresses prevail. The impoundment of large volumes of water to heights greater than 100 m would in all likelihood increase the seismicity of the region. In this context, large dams like the Tehri on the Bhagirathi river should be reviewed scientifically. Even though the Tehri Dam site is free from the release of internal stresses through earthquakes, the area 20 km north-west is registering appreciable seismicity. Since earthquakes of magnitude 8 do not release strain substantially, the probability of occurrence of a -major earthquake in the region cannot be ruled out. Any earthquake occurring in the Himalayas can be devastating as such and if it occurs close to a reservoir the damage is multiplied many folds. By virtue of the tremendous amount of water stored in the reservoirs, in the event of an earthquake, a large number of downstream towns could be flooded completely.
Dams are, therefore, not to be viewed within the framework of technical feasibility and economic gains but are also to be assessed in terms of the environmental changes they produce and the socio-cultural impacts they would have on the communities affected.
The interaction of processes of mineral exploitation with the environment, cause ecological imbalance. Unsystematic and indiscriminate mineral extraction leads to environmental degradation in the form of land misuse and pollution of air and water. The Himalayas, rich in deposits is no exception to this imminent problem. Mining activity including large scale excavation, land subsidence, solid waste disposal, water/ air/noise pollution, occupational health and safety hazards are several factors of paramount importance responsible for environmental degradation.
 In the Mussoorie hills on an average three blasts per day per quarry have weakened the jointed and brecciated rocks resulting in acceleration of incidence of mass movements and drying up of springs feeding streams. The discharge of many springs in more than a dozen valleys has diminished and many streams are now quite dry.
Ugly scarification and drastic reshaping of the landscape and destruction of forests have occurred here as a result of the mining of limestone and dolomite over a stretch of 40 km. When saturated with rainwater, the loose material becomes debris flow which descends into the valleys, clogging the channels and spreading over fields. Indiscriminate mining induces landslides and aggravates erosion as witnessed on the Mussoorie Hills, as well in Sikkim where foliated and jointed phyllite are being mined for uraniferous polymetallic sulphides.
About 14 hectares of forested hillslopes in Kosi valley, Almora district, and several hundred hectares of the Hiunpani forest ‘in the Chandak area elsewhere in Pithoragarh district in Kumaun are being crudely mined for soapstone and magnesite. More than 4820 ha of land in Kumaun Himalaya, 11471 ha in the Darjeeling Hills, 438ha in Himachal Pradesh and 886 ha in J&K have been very seriously affected by mining.
Deeper excavation causes the water table to sink locally, resulting in the drying up of wells and springs of the neighbourhood area in Mussoorie hills, the discharge of the Sahasradhara seepage has gone down due to mining in the area.
Exposure of fresh rocks due to mining initiates weathering with the inevitable generation of substances which cause water pollution. Among the minerals involved is pyrite, marcasite, siderite, ankerite which produce sulphuric acids and other soluble salts. All these substances adversely affect flora and fauna.
Phosphorite deposits in Doon Valley are being actively mined. The presence of permeable horizons in the mining area initiate the interaction of mine water with subsurface and open natured drainage water. This introduces phosphoric content in the subsurface and if such mixing is allowed to increase to the level of toxicity, it could become hazardous and unpotable for human consumption. Environmental awareness is yet to establish itself in the form of afforestation and reclamation of mined land in the area.
There is probably no other area of India’s environment that has been more viciously attacked and destroyed in the last century than the country’s forests. The current rate of deforestation is placed well over one million hectares every year. The rate of depletion of forests in the Himalayan ranges, which represent a quarter of India’s forest reserves is so immense that this mighty mountain chain could become bare by the first half of the next century.
In the middle Himalayan belt, which rises to an average height of 3000m, the forest area, originally estimated as being a third of the total area, has been reduced to a mere six to eight per cent. The forests are not regenerating, therefore growing stocks have dwindled and most forests have been totally encroached upon and destroyed. Sunderlal Bahuguna, the champion in the cause of environmental preservation rated the commercial exploitation of forests as the most powerful one. Another factor is the construction of roads without adequate soil conservation measures. Trees are felled and damaged and landslides caused by careless construction have eroded the land so permanently that trees cannot grow there any longer. As a result, many roads have become unstable; the Daksum Chingaon road, for instance, which goes through 70 km of uninhabited area, remains open only for three months in a year. The rest of the time it is blocked either by snow or by landslides.
The northeast of India has one of the largest reserves of subtropical forests in India. The north-east represents 1/7 of the total area under forests in India. Today many tribes still follow the age-old method of cultivation called jhum (shifting cultivation). The forest areas are decreasing, human habitations are increasing and, the fertility of the soil is diminishing turning the land barren.
With the control of malaria, the forests in the foothills of UP were totally decimated during the 1950s. They have since made way for rich croplands and today this erstwhile forest region constitutes the most prosperous agricultural area in the state. Forests in UP are now mainly concentrated in the 8 northern mountainous districts together called Uttarakhand. Although about 30% of it is under forest cover, about 1/2 of this forest area is degraded with poor tree
density. The optimum density necessary for effective soil and water conservation is now found only in remote valleys of the region. 8% of the total area is facing severe soil erosion and needs to be tackled on a priority basis. The region gives rise to the mighty tributaries of Ganga—Bhagirathi and Alaknanda. Much of the region is prone to landslides and soil erosion.
Stripped of the protective vegetative cover, the Himalayan soils are fast losing their capacity of absorbing rainwater, which largely runs off on the surface, bringing about recurrent damaging floods on the plains. Since little water percolates into the ground, the hill springs are drying up. Over one million hectares of forests are cut every year. Some 0.15 million hectares of forests are lost to the development of projects annually.
Landslides and other mass movements are severe environmental hazards in the Himalayas. Individual landslides are generally not so spectacular or costly as earthquakes, major floods, volcanoes etc., yet they are more widespread, and over the years may cause more loss than any other geological hazard.
 The occurrence of landslides is very common in geodynamically sensitive belts in zones and areas repeatedly rocked by earthquakes and affected by other neotectonic activities. The Darjeeling Himalayas, for example, recorded more. than 20,000 landslides in a day.
The principal factors that trigger mass-movements are — Heavy and prolonged rainfall, cutting and deep excavations on slopes, and earthquake shocks.
All these factors operate in the Himalayan region.
Extensive landslides caused by the 1950 earthquake in eastern Arunachal Pradesh and by the 1934 North Bihar earthquake bear testimony to this fact. The vibrations generated by the passages of heavy vehicles create oscillations of different frequency in the rocks and thus change the stress pattern, reducing shear strength and inducing mass movements.
Most hazards are associated with high-speed mudflows and avalanches which acquire speeds as high as 3 to 50m/s. One great example is the devastating debris flow in the year 1880 on the slopes of Sher-ka-Danda hill in Nainital which travelled 1 km in 30 sec., killed 150 people and swept away ‘Victoria Hotel’, Naina Temple’ and other building and filled a part of the lake.
 The available case records suggest that reactivation of old Himalayan landslides invariably takes place following heavy or prolonged rains. Rainfall in the Himalayas is often punctuated by flashes of cloudbursts. A cloudburst lasts for a few minutes to as long as three hours at a time and results in a hazard worse than the combined effect of rainfall for rest of the season. It has been seen that cloudbursts of intensities exceeding 1,000mm in 24 hrs. trigger mass movements in any circumstances. A striking example of devastating landslides in the eastern Himalayas is provided by Darjeeling floods of 1968. Towards the end of monsoon, vast areas of Sikkim and West Bengal were destroyed by some 20,000 landslides killing 33,000 people.
The devastating effect of flowing water coupled with flash floods is dreadful. River slopes are stripped naked, huge landmasses roll down into rivers damming them, and avalanches of mud and water uproot trees on slopes carrying them kilometres away. In Himalayan rivers, broad bed widths alternate with narrow constructed gorges. The occurrence of flash floods, particularly in a narrow river gorge, seems to be one of the much-feared causes of some of the major Himalayan landslides.
 Accumulation of slipped masses, a charge of river silt, massive rocks throttle the narrow river passage building up a reservoir of water that ultimately flushes the obstacles. The resulting drawdown effect triggers slide in the toe region, eventually jeopardising the stability of the hill as a whole. Blockade of river Teesta by massive rocks transported by river current is common.
The narrow construction of Patal Ganga was choked in July 1970 due to a cloudburst resulting in building up of 60m high reservoir, the bursting of which resulted in floods in Alaknanda and consequently triggering a number of landslides in the immediate vicinity of the river. The flood affected a 400 km stretch and washed away several bridges. The silt carried by the flood water was so enormous that a 100km stretch of the Upper Ganges canal, some 350 km away from the upper reaches of Alaknanda was blocked. Subsequent desilting operations took a very long time. During 1978, the region witnessed massive floods again.
A number of similar examples of blockages of several Himalayan rivers in Middle Himalayas of UP, Nepal and Arunachal Pradesh have been reported. Landslide dams are made by nature and they usually bring about world’s largest catastrophic failures, rarely to be seen in the man-made dams.
In the next 15 years, an area almost equal to the entire cultivated area of India will be lost to the world if soil erosion continues unabated. Nearly 5-7 million hectares of good agricultural land is being eroded every year all over the world. As with other countries, the future of India, or at least of its ability to feed its people, will depend on the health of its soils. By the turn of this century, the Indian population is expected to cross a billion. Now the pertinent question that looms large is — can we feed such a large population without permanently destroying our lands?
Huge sediment loads are removed from the watersheds as a result of flashy streams emanating from the Himalayan ranges having steep slopes. These sediments ‘are the result of weathering of rocks and are transported by streams, glacier and wind. When there is reduction either in discharge or in slope or in the rate of sediment supply in excess of the sediment transport, the capacity of the stream is unable to transport the material supplied to it and sheds the excess load to exhibit deposition or sedimentation.
The eroding capacity of water varies in proportion to the square of the velocity and the ability to transport sediment varies in proportion to the sixth power of its velocity. The extent of erosion and sediment load movement in Bhagirathi, as in other Himalayan rivers is high.
The most glaring example of lake sedimentation today is in the Siwaliks in the Sukhna Lake which was created in 1958 at Chandigarh across Sukhna ‘Choc’ downstream of the confluence of Kansas and Sukhetri ‘Chocs’.
Annual soil loss from erosion results in increasingly devastating floods and heavy situation of the enormously expensive dams. The large quantity of soil washed away gets lodged in tanks, reservoirs, streams and river beds reduce their capacity to hold or convey water and results in heavy, disastrous floods. It is estimated that the bed of Ganga has risen by 1/2 metre in the past few years. However, the long term effect of soil erosion — a general undermining of the ecological firmament that supports our existence is even more sinister.
A survey of some reservoirs revealed that nearly thrice more sediment was flowing into these reservoirs than was estimated at the time when they were built. reducing their life on an average to a third. Reduction in a reservoir capacity to hold back heavy flood water reduces the amount of laid it can irrigate.
Strategic planning and implementation of remedial policies is the only answer to reverse the deteriorating trend of Himalayan ecology. As stated earlier, the geologically sensitive areas are vulnerable to landslides and soil erosion. Due to the fragile ecosystem, even thus slightest disturbance could be hazardous. Landslides and other related movements are natural phenomena, therefore, cannot be bridled entirely, nonetheless, their frequency and severity can be certainly minimised through appropriate engineering measures.
Some of the vital steps required are afforestation, hazard zone mapping, abandonment of development projects in hazardous areas, restraining of indiscriminate mining and remedial measures for control of landslides.
Veteran environmentalists have been partially successful in creating general awareness among the populace towards the precarious ecology of the Himalayas, nonetheless, it is inadequate and greater sensitivity is imperative.
