Deep-seated mass rock creep along the Karakoram Highway and its geomorphological consequences in the Middle Indus Valley near Chilas, Northern Pakistan
Abstract
Unexpected sudden landslides along the Karakoram Highway (KKH) are a common and feared phenomenon, but the causes have scarcely been related to processes of persistent rock creep, which are to be presented here. Mass rock creep in motion cannot be experienced by direct observation because of being an extremely slow type of mass movement; the rate of velocity measures only - 1-10 mm/a. However, the results of these extremely slow rock movements are morphologically conspicuous and important from the point of view of engineering geology, especially along glacially eroded valley flanks as in the case of the Indus valley course in question.
Mass rock creep in the sense of deep-seated gravitational slope movement produces irregular slope profiles with trenches accompanied by opening of joints, fracturing and dilation.
As a consequence, the rock walls are progressively failing and exhibiting various phenomena of collapse structures sometimes even reaching the mountain tops and ridges, adjacent to the valley. In the course of our study on mass rock creep in the region of Chilas, ~8 km up- and downstream of this village, we can distinguish mainly two modes of slope deformation.
- Toppling movements, consisting of numerous book-like rock segments on the upper slope, rotating out of the slope, representing a primary system, resulting in convex slopes, sections through bulging.
- Sliding movements, consisting of several massive rock (slabs) slowly gliding downwards upon each other, showing secondary listric bending of shear planes in the distal part near the slope foot, representing a secondary system, resulting in concave slopes.
Geologically speaking the mountainous region of Chilas is made up of mafic-ultramafic plutonites of a former oceanic island arc, which have entered the geological literature as Chilas Complex of the Kohistan Arc in the Karakoram.
References
Bovis, M. J., 1982. Uphill-facing (antislope) scarps in the Coast Mountains, southwest British Columbia, Geological Society of America Bulletin, 93, 804-812.
Bovis, M. J., 1990. Rock slope deformation at Affliction Creek, southern Coast Mountains, British Columbia, Can. J. Earth Sci. 27, 243-254.
Bovis, M.J. & Evans, S.G., 1995. Rock slope movements along the Mount Curri “fault scarp”, southern Coast Mountains, British Columbia, Can. J. Earth Sci., 7, 2015-2020.
Bovis, M.J. & Evans, S.G., 1996. Extensive deformations of rock slopes in the southern Coast Mountains, southwest British Columbia, Canada, Engineering Geology, 44, 163-182.
Briggs, D., Smithson, P., Addison, K. & Atkinson, K., 1997. Fundamentals of the Physical Environment, London and New York, 557pp.
Chigira, M., 1992. Long-term gravitational deformation of rocks by mass rock creep, Engineering Geology, 32, 157-184.
Cruden, D.M. & Varnes, D.J., 1996. Landslide types and processes. in: Turner & Schuster, Eds., Landslides, investigation and mitigation. Spec. Rep. 247, Transp. Res. Nat. Res. Council Washington, DD., USA, 36-75.
Hanmer, S. & Passchier, C., 1991. Shear-sense indicators: a review, Geological Survey of Canada, Paper, 90-17, 3-72.
Hutchinson, J. N., 1988. General report: morphological and geotechnical parameters of landslides in relation to geological and hydrogeology. 5th International Symposium on Landslides, Lausanne, Switzerland. Proceedings, 1, 3-35.
Kazmi, A.H. & Jan, M.Q., 1997. Geology and Tectonics of Pakistan, Islamabad, Pakistan, 554 pp.
Kuhle, M., 1997. New Findings concerning the Ice Age (Last Glacial Maximum) Glacier Cover of the East-Pamir, of the Nanga Parbat up to the Central Himalaya and of Tibet, as well as the Age of the Tibetan Inland Ice; GeoJournal, 42, 87-257, The Netherlands.
Radbruch-Hall, D.H., Varnes, D.J. & Savage, W.Z., 1976. Gravitational spreading of steep-sided ridges (“Sackung”) in Western United States, Bulletin International Association of Engineering Geology, 14, 23-35.
Savage, W.Z. & Varnes, D.J., 1987. Mechanics of gravitational spreading of steep-sided ridges ("Sackung"). Bulletin of the International Association of Engineering Geology, 35, 31-36.
Searle, M.P. & Asif Khan, M., 1998. (Eds.), Geological map of North Pakistan and adjacent areas of northern Ladakh and western Tibet, Scale 1: 650000.
Selby, M.J., 1985. Earth's changing surface. Clarendon Press, Oxford, U.K., 607 pp.
Shroder, J.F. jr., Owen, L. Derbyshire, E., 1993. Quaternary glaciation of the Karakoram and Nanga Parbat Himalaya. In: Himalaya to the sea (J.F. Shroder, Jr., (eds.), 132-158.
Varnes, D. J., Racibruch-Hall, D.H. & Savage, W. Z., 1989. Topographic and structural conditions in areas of gravitational spreading of ridges in the Western United States, U.S. Geological Survey Professional Paper 1496, 1-28.
Voelk, H.R. & Schmelzer, R., in prep., Glacial and postglacial geomorphology of the middle Indus valley around Chilas, Northern Pakistan.
Voelk, H.R., 2000. The Tatopani landslide in the Kali Gandaki valley of Western Nepal. Cause and relation to deep-seated rock creep, Journal of Nepal Geological Society, Kathmandu, in press.
Zischinsky, U., 1966. On the deformation of high slopes, Intern. Soc. Rock Mechanics Congr., 1st, Lisbon, Proc. 2, 172-185.
Zischinsky, U. 1969. Uber Sackungen, Rock Mechanics, 1, 30-52.
