Interpreting slope failure in the early Holocene has traditionally focused on climatic change. Little research considers the role of soil-profile characteristics, in particular the effect of fragipan occurrence. Fragipan formation has been associated with periglacial processes in northwest Europe, but recent evidence suggests that fully developed fragipans did not exist until 2000-3000 years after the close of the Lateglacial. Fragipans have been widely reported as having reduced permeability and altered soil moisture retention curves. The implications of such hydrological properties for slope stability is considered in this paper, by comparing stability of a soil profile containing a fragipan with one that is freely draining using a physically based soil hydrology-slope stability model. The results suggest differences in angles of limiting stability of 15° between the two soil profiles, while differences resulting from likely climatic variation are only 3-4°. Modelling results of maximum stable slope angles for fragipans are consistent with those reported in the landscape, placing confidence in model outputs. This is used as a basis for suggesting that pedologic factors might be more significant than climatic factors when interpreting early Holocene slope instability. The potential utility of physically based modelling is explored more generally, and suggestions are made for future research to elucidate more fully the role of fragipans in slope stability.
Anderson, M.G. and Howes, S.1985: Development and application of a combined soil water-slope stability model. Quaternary Journal of Geology18, 225-36.
2.
Anderson, M.G. and Shen, J.M.1987: Modelling the effectiveness of a soil-cement protective cover for slopes. In Anderson, M.G. and Richards, K.S. (editors) Slope Stability: geotechnical engineering and geomorphology, Chichester: John Wiley and Sons.
3.
Anderson, M.G. and Lloyd, D.M.1991: Using a combined slope hydrology-stability model to develop cut slope design charts. Proceedings of the Institute of Civil Engineers 2, 705-18.
4.
Brazier, V. and Ballantyne, C.K.1989: Late Holocene debris cone evolution in Glen Feshie, western Cairngorm mountains, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences80, 17-24.
5.
Brooks, S.M., Richards, K.S. and Anderson, M.G.1993: Shallow failure mechanisms during the Holocene: utilisation of a coupled slope hydrology-slope stability model. In Thomas, D.S.G. and Allison, R.J. (editors), Landscape Sensitivity, Chichester: John Wiley and Sons.
6.
Butler, B.E.1959: Periodic phenomena in landscapes as a basis for soil studies . CSIRO Australian Soil Publication 14.
7.
Campbell, R.H.1975: Soil slips, debris flows and rainstorms in the Santa Monica Mountains and vicinity, Southern California. United States Geological Survey, Professional Paper 851.
8.
Crampton, C.B.1965: An indurated horizon in the soils of South Wales . Journal of Soil Science16, 230-42.
9.
Daniels, R.B., Nettleton, W.D., McCracken, RJ and Gamble, E.E.1966: Morphology of soils with fragipans in parts of Wilson Country, North Carolina. Soil Science Society of America Journal30, 376-80.
10.
Dietrich, W.E., Wilson, C.J. and Reneau, S.L.1986: Hollows, colluvium and landslides in soil-mantled landscapes . In Abrahams, A.D. (editor), Hillslope Processes, Binghamton Symposia in Geomorphology: International Series, No.16.
11.
Fitzpatrick, E.A.1956: An indurated soil horizon formed by permafrost . Journal of Soil Science7, 248-57.
12.
— 1969: Some aspects of soil evolution in north-east Scotland . Soil Science107, 403-408.
13.
Habecker, M.A., McSweeney, K. and Madison, F.W.1990: Identification and genesis of fragipans in Ochrepts in North Central Wisconsin. Soil Science Society of America Journal54, 139-46.
14.
Hallmark, C.T. and Smeck, N.E.1979: A rupture technique to determine fragipan strength . Soil Science Society of America Journal43,198-200.
15.
Harvey, A.M., Oldfield, F., Baron, A.F. and Pearson, G.W.1981: Dating of postglacial landforms in the central Howgills . Earth Surface Processes and Landforms6, 401-12.
16.
Innes, J.L.1983: Lichenometric dating of debris flow deposits in the Scottish Highlands. Earth Surface Processes and Landforms8, 579-88.
17.
Lamb, H.H.1982Climate, history and the modern world. London: Methuen.
18.
Lindbo, D.L. and Veneman, P.L.M.1993: Morphological and physical properties of selected fragipan soils in Massachusetts. Soil Science Society of America Journal57, 429-36.
19.
Marsam, F.A. and Torrent, S.1989: Fragipan bonding by silica and iron oxides in a soil from NW Ibly. Soil Science Society of America Journal53, 1140-45.
20.
Meyerhoff, G.G.1976: Bearing capacity and settlement of pile foundations . Proceedings of the American Society of Civil Engineers102, GT3.
21.
McCormack, D.E. and Wilding, L.P.1981: Soil properties influencing penetration resistance of Canfield and Geeburg soils: Soil Science Society of America Journal45, 1148-52.
22.
Miller, F.P., Holowaychuk, N. and Wilding, L.P.1971: Canfield silt loam, a Fragiudalf: 1 Macromorphological, physical and chemical properties. Soil Science Society of America Journal35, 319-24.
23.
Parlange, M.B., Steenhuis, T.S., Timlin, DJStagnitti, F. and Bryant, R.B.1989: Subsurface flow above a fragipan horizon. Soil Science148, 77-86.
24.
Payton, R.W.1988: The characteristics and genesis of fragipans in British soils. PhD thesis, University of Newcastle upon Tyne.
25.
— 1993a: Fragipan formation in argillic brown earths (Fragiudalfs) of the Millfield Plain, northeast England. I Evidence for a periglacial stage of development. Journal of Soil Science43, 621-44.
26.
— 1993b: Fragipan formation in argillic brown earths (Fragiudalfs) of the Millfield Plain, northeast England. II Post Devensian developmental processes and the origin of fragipan consistence. Journal of Soil Science44, 703-23.
27.
Peck, R.B., Hanson, W.E. and Thombum, T.H.1974: Foundation engineering. New York: John Wiley and Sons,
28.
Petersen, G.W., Ranney, R.L., Cunningham, R.L. and Matelski, R.P.1970: Fragipans in Pennsylvania soils: a statistical study of laboratory data. Soil Science Society of America Journal34, 719-22.
29.
Pickering, E.W. and Veneman, P.L.M.1984: Strength characteristics of three indurated horizons in Massachusetts. Soil Science Society of America Journal48, 133-37.
30.
Prasad, K.G. and Perkins, H.F.1978: In situ hydraulic conductivity of a fragipan soil in the southern coastal plains. Soil Science126, 263-68.
31.
Scotter, D.R., Clothier, B.E. and Corker, R.B.1979: Soil water in a fragiaqualf. Australian Journal of Soil Research17, 443-53.
32.
Selby, MJ1976: Slope erosion due to extreme rainfall: a case study from New Zealand. Geografiska Annaler58A, 131-38.
33.
Soil Survey Staff 1975: Soil Taxonomy, USDA Handbook No. 436. Washington DC: United States Government Printing Office.
34.
Starkle, L.1966: Postglacial climate and the moulding of European relief . Proceedings of the International Symposium of World climate 8000 to O BC, Royal Meteorological Society of London, 15-32.
35.
Van Vliet, B. and Langhor, R.1981: Correlation between fragipans and permafrost with special reference to Weichsel silty deposits in Belgium and Northern France . Catena8, 137-54.
36.
Veneman, P.L.M. and Bodine, S.M.1982: Chemical and morphological soil characteristics in a New England drainage toposequence. Soil Science Society of America Journal46, 359-63.
37.
Walker, P.H., Hall, G.F. and Protz, R.1968: Soil trends and variability across selected landscapes in Iowa. Soil Science Society of America Journal32, 97-101.
38.
Wang, C., Nowland, J.L. and Kodama, H.1974: Properties of two fragipan soils in Nova Scotia including scanning electron micrographs. CanadianJournal of Soil Science54, 159-70.
39.
Yassaglou, NJ and Whiteside, E.P.1960: Morphology and genesis of some soils containing fragipans in northern Michigan. Soil Science Society of America Proceedings24, 396-407.
