Nainital : A Landslide Town

Nainital: A Landslide Town

Nainital township (29° 24' N, 79° 28' E), a popular hill resort of Kumaun Himalaya, is developed around a 1.4 km long and 0.45 to 0.25 km wide lake extending in NW-SE direction and having a maximum depth of about 27m. The lake is situated at an elevation of 1935 m at the prominent Nainia Peak towards north of the lake. The annual rainfall in Nainital varies from 2600 mm to 2900 mm of which 2400 mm is precipitated during monsoon. Nainital has temperate summers (maximum temperature 27°C, or 80°F; minimum temperature 10°C, or 50°F) during which its population increases more than fivefold with an annual influx of tourists predominantly from the plains of Northern India. In the winter, Nainital receives snowfall between December and February with the temperatures varying between a maximum of 15°C (59°F) and a minimum of -3°C (26°F). As of 2001 Census of India, Nainital had a population of 38,559. Males constitute 54% of the population and females 46%. Nainital has an average literacy rate of 81%, higher than the national average of 59.5%: male literacy is 86%, and female literacy is 76%. In Nainital, 9% of the population is under 6 years of age.

The Kumaun Hills came under British rule after the Anglo-Nepalese War (1814-16), but the hill station town of Naini Tal was founded only in 1841, with the construction of the first European house (Pilgrim Lodge) by P. Barron. In his memoir, he wrote: "It is by far the best site I have witnessed in the course of a 1,500 miles trek in the Himalayas." In 1846, when a Captain Madden of the Bengal Artillery visited Naini Tal, he recorded that "houses were rapidly springing up in most parts of the settlement: some towards the crest of the limitary ranges were nearly 7,500 feet above sea level: the rugged and woody Ayarpatta was being gradually planted and that the favourite sites were on the undulating tract of forest land which stretched back from the head of the lake to the base of China and Deopatta (Camel's Hump). The Church, St. John in the Wilderness, had been built ...” Soon, the town became a health resort favored both by British soldiers and by colonial officials and their families trying to escape the heat of the plains. Later, the town also became the summer residence of the Governor of the United Provinces.

In view of the importance of the town as a popular hill resort, several earth scientists have studied the landslide problem of the town time and again. R.D.Oldham (1880) was the first to investigate into the causes of failure of the slopes in the Nainital valley. Subsequently, the hill slopes instability was studied by Middlemiss (1890), Greisback (1895), Holland (1897), Coulson (1928), Auden (1942) and Nautiyal (1949). Hukku and Jaitle (1966) and Hukku et.al. (1966-67) carried-out geological mapping of Nainital area on 6”=1mile scale. Subsequently, Srivastava (1967-68), Ashraf (1978), Jaitley (1979-80) studied the problem of slope instability around the township. Layer Pant and Kandpal (1988-89) studied the instability of the adjoining Balia nala which drains the lake area.

The Nainital area forms a prominent physiographic unit of Kumaun Himalaya situated in a synclinal basin (Auden, 1942). Middlemiss (1890) was the first to study the geology of Nainital area and the carbonate rocks in and around Nainital area were identified as Krol by him. Holland (1897) gave a more detailed account of the area. Subsequently, Auden (1942), Nautiyal (1949),Hukku and Jaitley (1964) and many other workers have contributed towards understanding the stratigraphy and structure of the area. The area around lake is occupied by the rocks of Krol formation. The Lower Krol formation is represented by thinly bedded, sheared, variegated slates/shales, marls with subordinate bands and lenses of limestone which are mainly exposed in the eastern and northeastern parts of the lake basin. The western, southwestern and southern portions of the area are occupied by limestone/dolomite and red shales of Middle Krol and Upper Krol members and slates and phyllite of Tal formation. The prominent faults in the lake area are; Lake fault (NW-SE) and Sherwood fault (WNW-ESE). A number of other faults and fractures trending NE-SW, NNE-SSW, E-W, WNE-WNW have been demarcated in the area on the basis of break in slopes, topographic scarpments and swing in the strike directions.

The in-situ strength determined with the help of Schmidt Hammer indicates that the values of in-situ atrength of Upper Krol, Middle Krol, Lower Krol, Infra Krol and Tal formations are of the order of 300 kg/cm² (very good to excellent rock quality designation), 120-150 kg/cm² (poor rock quality designation), 120-130 kg/cm²(poor to very poor rock quality designation), 100-120 kg.cm²(poor to very poor rock quality designation)  and 100-120kg/cm²  (poor to very poor rock quality designation) respectively. A large part of the Nainital area is occupied by the debris/overburden material of recent to sub-recent age. The debris is derived mainly due to recurring landslides and slope wash all along the hill slopes. Number of landslides scars (palaeo scarps and active scarps) is found in the area. The landslide debris generally comprises clay and silt mixed with slate fragments, boulders/blocks of limestone/dolomite besides masses of Upper Krol dolomite. The physical character of debris material with varied assortment in the area that has been classified into three broad categories (1) mainly scree of shale/slate in a matrix of sil-clay with variable proportions (2) shale/slate debris mixed with limestone/dolomite boulders and (3) dislodged blocks of limestone/dolomite. Lacustrine sediments occur all along the rim area of the lake, associated with the landslide debris of the surrounding hill slopes.

The Landslide of 1880

In September 1880 a landslide occurred at the north end of the town, burying 151 people . The first known landslide had occurred in 1866, and in 1879 there was a larger one at the same spot, Alma Hill, but "the great slip occurred in the following year, on Saturday 18 September 1880." "Two days preceding the slip there was heavy rain, ... 20 to 25 inches fell during the 40 hours ending on Saturday morning, and the downpour still lasted and continued for hours after the slip. This heavy fall naturally brought down streams of water from the hill side, some endangering the Victoria Hotel, ... (which) was not the only building threatened ... Bell's shop, the Volunteer Orderly Room and the Hindu (Naina Devi) temple were scenes of labour with a view to diverting streams. At a quarter to two the landslip occurred burying those in and around the buildings mentioned above." The total number of dead and missing were 108 Indian and 43 British nationals. The Assembly Rooms and the Naina Devi Temple were both destroyed in the disaster. A recreation area known as 'The Flats' was later built on the site and a new temple was also erected. To prevent further disasters, storm water drains were constructed and building byelaws were made stricter.

 In Nainital area incidences of landslides, old landslide scars, signs of instability in the form of creep  and tilting of trees, development of cracks and de-stressing in buildings have been observed . The slides in Upper Krol dolomites are in the form of dislodging of blocks along adversely disposed joints/fractures. In general, the area occupied by dolomites and limestones of Upper Krols (Ayarpatha slopes) are under relatively low landslide prone zone. Along the cliff face of Naina peak area, rock falls and debris flow in the stream draining the hill slopes are prevalent. The area has some important known slides of years 1888 and 1962 besides numerous other incidences that occur almost every year. In 1939, a section between east Laggan road and Middle Ayarpata road a landslide containing sandstone and dolomite along the axial plane of the syncline occurred. This slide was reactivated in 1942. The gentler debris fan below has developes due to many debris slides of the past. The rock falls are governed by the set of discontinuities and vertical joints and the poor in-situ strength of rock mass. The landslides of the year 1867 and 1880 in Sher-ks-danda slope (Lower Krol slates and shales with thin limestone bands besides overburden material) indicate that these slope failure had been caused by rapid scouring coupled with consequent movement of debris (Hukku and Jaitley, 1965-66). The presence of main Sher-ka-danda fissure (Hukku and Jaitley, 1965-66) along the top of the ridge was considered to be an important features controlling the instability of the slope. Similarly, Kailakhan spur experienced a severe landslide in the proximity of famous lake fault in 1898. 1987 witnessed rock fall in Naina peak for about fifteen days. Even at present, the hill slopes, around the lake, have developed clear cut indications of strain caused by illconcieved urban growth.  In total 25 slope instability incidences, in approximately 10 sq km of area, have been registerd in the town area.

Hill slopes around Nainital lake basin have undergone the process of mass-wasting from time immemorial. The area also falls within the zone IV (High damage risk zone) of the Seismic Zoning Map of India prepared by Bureau of Indian Standard, New Delhi. Very large landslides have taken place in and around Nainital especially during the years 1867, 1880 and 1924. The landslide of 17 August 1898 (Middlemiss, 1898) occurred following 102 cm rainfall for 8 days bringing down the upper part of Kailakhan spur where Infra Krol slates are exposed. It has been reported that the debris avalanche that surged across the valley buried the Birbhatti area and wiped out old cart road. Naina Peak area and Snow view-Fairy Hall area on Sher-ka-danda slope have been continuously ravaged by the landslides of varying proportions. The extent of landslide hazards is thus expanding progressively. Old landslide scarps could be observed on the higher slopes all around the area. All these evidences of slope instability seem to be the results of mismanaged construction activities which have crossed the ultimate limit of carrying capacity of the town ecosystem. Construction activity in hill areas involves a lot of surface cutting , which disturbs the angle of repose of an old unstable surface which again reactivates.  Further, removal of the cut soil from the site to certain approved dumping ground involves high transportation costs. But over the recent years people have found an easy solution to this problem through their ingenuity. They even do not bother to remove the cut soil to the approved places and, instead of it, just spread it over hillsides. There are few persons who dump the cut soil in nearby streams. Theses streams carry the cut soil to the lake.
Different types of slope movement threaten the urban development in different areas. ‘Safe’ and ‘dangerous’ areas for the construction of buildings were demarcated by Nautiyal (1949). Subsequent work by Hukku and Jaitely (1965-66), Srivastava (1967-68), Ashraf (1978), Jaitley (1979-80). Pant and Kandpal (1988-89) evaluated the stability conditions around the lake.

RAVINDRA K PANDE
Dept of Geography,
Kumaun University,
Nainital

Comment by Praful Rao
I had the pleasure of meeting Prof RK Pande, recently during the Landslide Conference held at Nainital. I do hope that we can learn from his tremendous experience both as a geographer and an expert on disaster management in the future.
My thanks to him for this article.
Photo Credit : SaveTheHills