Geomorphology 102 (2008) 205–206
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Geomorphology j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / g e o m o r p h
Dryland geomorphology and interacting processes
The geomorphology of arid lands is often seen as a distinct branch of the subject, spawning its own literature and its own range of textbooks (e.g. Cooke et al., 1993; Abrahams and Parsons, 1994; Thomas, 1997). However, although aeolian processes are often seen as the most characteristic, a wide range of geomorphic processes operate in most drylands, albeit conditioned by the climatic aridity. Sustained and marked moisture deﬁcits dominate such climates, and condition the geochemical environment, weathering regimes, soil formation, plant cover and inﬁltration behaviour. Rainfall is unreliable and tends to occur in rare, but sometimes extreme events (Baker, 1977). Together these characteristics inﬂuence the style of geomorphic processes. Given the availability of material, aeolian activity tends to be high. Hillslope processes tend to be dominated by overland ﬂow rather than by surﬁcial mass movement processes. Fluvial processes tend to be ﬂood dominated. There is little evidence of a sensitive adjustment of landforms to “dominant processes” as may characterise more humid environments (Wolman and Miller, 1960). Individual processes tend to operate over different timescales, and have variable spatial expression, such that the landscape as a whole exhibits spatial and temporal discontinuities. Interactions between different processes and the coupling between different parts of the geomorphic system (Harvey, 2002), therefore, are also spatially and temporally variable. Their expression in landform and sediment relationships can reﬂect three aspects of arid-zone geomorphology. First, it gives evidence of the relative dominance of individual processes. Second, it can provide evidence for short-term event sequences. Third, and perhaps most importantly (especially on the margins of the arid zone), older deposits and landforms may preserve a signal related to past process interactions and may therefore yield information relating to climatic change (e.g. Nanson et al., 1995; Enzel et al., 2003; Al Farraj and Harvey, 2004). With these points in mind the seven papers included in this Special Issue of Geomorphology have been selected from the 24 papers presented in the Arid Geomorphology (S2) and Interactions between Fluvial, Aeolian and Lacustrine Processes (WG5) at the 6th International Conference on Geomorphology, of the International Association of Geomorphologists, held in Zaragoza, Spain, in September 2005. For abstracts of all the papers see Gutierrez et al. (2005). The manuscripts included in this Special Issue are related to geomorphologic processes acting in different environmental settings from drylands, and several of them report the connection of these features with past climatic changes. Two of the papers deal with aeolian processes and related climatic changes since the Late Pleistocene in different settings. Bernat Rebollal and Pérez González apply the morphological and textural analyses of aeolian bodies in Central Spain, assisted by luminescence dating, to correlate these aeolian bodies with the environmental changes recorded in the 0169-555X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2008.05.001
northern hemisphere since the Last Glacial Maximum. Bubenzer and Bolten, analyze two different Sand Seas in Africa (Egypt and Namibia) by means of new digital elevation data, resulting in high-resolution elevation models considered as an important tool for reconstructing recent palaeoclimatic changes. Three papers deal with the role of vegetation in the activity of different geomorphic processes in different environmental settings. Dunkerley deals with the role of vegetation in the stability of distinctive channel features in ephemeral streams from Australia. Lázaro et al., analyze the role of lichen crusts in the evolution of badlands in SE Spain, based on a 13 year photomonitoring recording the cover and pattern of bare soil and biological soil crusts (brown crust and white crust). Sauer and Ries study the role of vegetation in abandoned ﬁelds (Ebro Basin) showing a complex relationship between vegetation cover and geomorphodynamics, and applying a methodology based on the development of change maps (vegetation cover, geomorphic processes). Godfrey et al., use a 40 years erosion-pin study in badlands from Utah, in describing the differential geomorphic activity of the different landscape units. Results show the important inﬂuence of seasonality for each landscape unit and diverse connectivity between them. The ﬁnal paper, by Yang et al., although dealing primarily with the dating and provenance of aeolian sediments in western China, has implications for reconstructing changes in wind circulation during the Late Quaternary. Two themes therefore run through this short selection of papers. The ﬁrst relates to process interactions, including coupling within geomorphic systems and the relationships between vegetation and geomorphic processes. The second relates to reconstruction of past environments. Both of these themes are central to modern research in arid geomorphology. Acknowledgments We acknowledge the help provided by the following referees in reviewing the submitted papers: Roy Alexander, Helga Besler, Jo Bullard, Adolfo Calvo, Gloria Desir, Bernard Eitel, Hazel Faulkner, Eduardo Garcia Melendez, Andrew Goudie, Mateo Gutierrez, Nick Lancaster, R.G. Millar, Stephen Mischke, José Manuel Nicolau, Salvador Ordoñez, Ameur Oueslati, Ana Pintado, Juergen Runge, Stephen Tooth, Xiaoping Yang. Note (1): We were saddened to hear of the sudden and unexpected death of Andrew Godfrey during the preparation of this Special Issue. We send our condolences to his widow, Marie Godfrey. References Al Farraj, A., Harvey, A.M., 2004. Late Quaternary interactions between aeolian and ﬂuvial processes: a case study in the northern UAE. Journal of Arid Environments 56, 235–248.
Abrahams, A.D., Parsons, A.J. (Eds.), 1994. Geomorphology of Desert Environments. Chapman and Hall, London. 64pp. Baker, V.R., 1977. Stream channel response to ﬂoods, with examples from central Texas. Geological Society of America Bulletin 88, 1057–1071. Cooke, R.U., Warren, A., Goudie, A.S., 1993. Desert Geomorphology. UCL Press, London. 526pp. Enzel, Y., Wells, S.G., Lancaster, N. (Eds.), 2003. Paleoenvironments and Paleohydrology of the Mojave and Southern Great Basin Deserts. Geological Society of America, Special Paper, vol. 368. 249pp. Gutierrez, F., Gutierrez, M., Desir, G., Guerro, J., Lucha, P., Marin, C., Garcia-Ruiz, J.-M. (Eds.), 2005. Sixth International Conference on Geomorphology, Abstracts Volume, University of Zaragoza, Spain. 511 pp. Harvey, A.M., 2002. Effective timescales of coupling within ﬂuvial systems. Geomorphology 44, 175–201. Nanson, G.C., Chen, X.Y., Price, D.M., 1995. Aeolian and ﬂuvial evidence of changing climate and wind patterns during the past 100 ka in the western Simpson Desert, Australia. Palaeogeography, Palaeoclimatology, Palaeoecology 113, 87–102. Thomas, D.S.G. (Ed.), 1997. Arid Zone Geomorphology; Process Form and Change in Drylands, 2nd Ed. Wiley, Chichester. 713pp.
Wolman, M.G., Miller, J.P., 1960. Magnitude and frequency of forces in geomorphic processes. Journal of Geology 68, 54–74.
Teresa Bardají Department of Geology, Universidad de Alcalá, 28871 Alcalá de Henares, Spain E-mail address: [email protected]
Corresponding author. Adrian Harvey Department of Geography, University of Liverpool, PO Box 147, Liverpool L69 3BX, UK E-mail address: [email protected]