Some Problems on Mass Movements

Abstract

A hard and fast classification of mass movements can neither be given nor make sense, because its practical application to the actual or natural phenomena encounters great difficulties. For the time being a simplification is preferable to pining for a too detailed classification of mass movements. This paper is chiefly concerned with clay minerals in areas of mass movements of flowand slip-type in Canada, compared with those in Scandinavia and in Japan, and it stresses the important role of swelling clay minerals. Classification of mass movements The classification of types of mass movements proposed by Sharpe (1938, pp. 97, Fig. 14) is well-known, and it appears to be very comprehensive and nicely systematic. However, it has neither any standard measure nor scientific criterion; and thus conscientious researchers must have been sorely perplexed in its application to their own studies. In this connection, a much better classification of landslides has been recently presented by Varnes (1958, pp. 20-47). The writer (Yatsu 1966, pp. 102-103) has proposed a tentative classification of mass movements which emphasized only the mechanics of the phenomena and ignored shapes and so forth, since it is doubtful whether complicated classifications are of any practical use at all. The most important task at present is to clarify the mechanism of movement in individual cases which will then be assigned to one type or a transitional type of fall, creep, rupture, slip, flow, and others. Generally speaking, falls, creeps, and ruptures are observed everywhere under certain conditions irrespective of rock types, while slips and some of the flows seem to be conspicuously associated with materials of which the slopes are composed, especially with the type of clay minerals. Clay minerals in areas of slipand flow-types of mass movements Slips or landslips, presumably most closely corresponding to earthflows in Sharpe's classifica396 tion of types of mass movements, have a remarkable relationship to swelling clay minerals and occur on slopes more gentle than those of lope ruptures which occur withouttheexistence of clay minerals. The results of studies on this problem in Japan (Nakano, Yatsu and Teruta 1961, pp. 1-20; Yatsu 1964, pp. 7-30; Yatsu 1965, pp. 54-66) will now be compared with those in Canada and in Scandinavia. In eastern Canada, most mass movements of flow-type, called flowslide by civil engineers, have occurred in the valleys of the Ottawa and the St. Lawrence rivers where extrasensitive quick clays are observed. Also in British Columbia and in the Prairie Provinces, mass movements of slipor flow-type are frequently observed in glacial till deposits. The writer has observed mass movements of flow-type near Lakelse Lake, B.C. and near Pavilion, B.C.; and those of slip-type at Spences Bridge, B.C., and near Hixon Station B.C., (about 1.5 miles north of the station along the railway). Many slope ruptures are observed, of course, along the Fraser River which erodes the tips of the slopes and causes their occurrence. Concerning the clay mineralogy of Canadian soils, Forman and Brydon (1961, pp. 140-146) have reviewed and have mentionedthe existence of montmorillonites in prairie soils. Kodama and Brydon (1965, pp. 151-173) have reported interstratified montmorillonite-mica clays, and Maiklem and Campbell (1965, pp. 354-371) studied mixed layer clays of the Prairie Province. In Leda clay from eastern Canada, clay fractions have been examined and show a predominant composition of illite and chlorite with occasional traces of montmorillonite (Allen and Johns 1960, pp. 75-86; Brydon and Patry 1961, pp. 169-181). The X-ray identification of clay minerals was done on several samples collected from mass movement areas of flowor slip-type in British Columbia and around Ottawa, and also on Scandinavian quick clays. Some examples of This content downloaded from 157.55.39.175 on Sun, 02 Oct 2016 05:41:26 UTC All use subject to http://about.jstor.org/terms SOME PROBLEMS ON MASS MOVEMENTS