Alluvial fans: geomorphology, sedimentology, dynamics - introduction. A review of alluvial-fan research

This volume presents a series of papers on the geomorphology, sedimentology and dynamics of alluvial fans, selected from those presented at the 'Alluvial Fans' Conference held in Sorbas, SE Spain in June 2003. The conference was sponsored primarily by the British Geomorphological Research Group and the British Sedimentological Research Group, both organizations affiliated to the Geological Society of London. It is some time since an international conference has been held that was exclusively devoted to the geomorphology and sedimentology of alluvial fans. The previous such conference was that organized by Terry Blair and John McPherson in 1995, and held in Death Valley, a classic setting for alluvial fans (Denny 1965; Blair & McPherson 1994a). Although many of the papers presented there have since been published, no dedicated volume on alluvial fans as a whole resulted from that meeting, so even longer has elapsed since there has been a specific publication devoted wholly to a series of papers on the geomorphology and sedimentology of alluvial fans (Rachocki & Church 1990). South-east Spain was chosen as the venue for this conference, partly for logistic reasons and partly because it is a tectonically active dry region within which there is a wide range of Quaternary alluvial fans. These fans exhibit differing relationships between tectonic, climatic and base-level controls (Harvey 1990, 2002a, 2003; Mather & Stokes 2003; Mather et al. 2003), core themes in consideration of the dynamics of alluvial fans. An emphasis within the previous alluvial fan literature has been on fans within the deserts of the American South-west (Bull 1977), with a focus especially on the alluvial fans of Death Valley (Denny 1965; Blair & McPherson 1994a). However, alluvial fans are not exclusive to drylands, nor to the particular combination of processes and morphology that characterize the Death Valley fans. Depositional processes may range from debris flows to sheet and channelized fluvial processes. Scales may range from small debris cones (<50 m in length: e.g. Wells & Harvey 1987; Brazier et al. 1988; Harvey & Wells 2003) to fluvially dominated megafans (up to 60 km in length: Gohain & Parkash 1990). Alluvial fans, although common in desert mountain regions (Harvey 1997), may occur in any climatic environment, in arctic (e.g. Boothroyd & Nummendal 1978), alpine (e.g. Kostaschuk et al. 1986), humid temperate (e.g. Kochel 1990) and even humid tropical environments (e.g. Kesel & Spicer 1985). In all climatic environments alluvial fans may play an important buffering role in mountain geomorphic or sediment systems (Harvey 1996, 1997, 2002b). They trap the bulk of the coarse sediment delivered from the mountain catchment, and therefore affect the sediment dynamics downstream, either in relation to distal fluvial systems or to sedimentary basin environments. In doing so, fans preserve a sensitive sedimentary record of environmental change within the mountain sediment-source area, rather than a broad regional record as would, for example, pluvial lake sediments (Harvey et al. 1999b). One of the aims of the 2003 conference was to bring together current research on the geomorphology, sedimentology and dynamics of alluvial fans, ranging from studies of modern processes through to studies of Quaternary fans and to those of ancient fan sequences within the geological record. We sought papers relating to a range of scales and of climatic and tectonic contexts. Some of the papers presented at the conference were 'in press' in other publications at the time (e.g. Harvey & Wells 2003) or are being published elsewhere (Garcia & Stokes in press; Saito & Oguchi 2005; Stokes et al. in press). In this volume we present a selection of the papers presented at the Sorbas meeting that spans a wide range of alluvial fan research. We group them into three main themes: those dealing with processes on fans; those dealing with the dynamics and morphology of Quaternary alluvial fans; and those dealing with the interpretation of