The Role of Climatic Change in Alluvial Fan Development

Alluvial fans develop at the base of drainages where feeder channels release their solid load (Blair and McPherson, 2009; Leeder et al., 1998; Harvey et al., 2005). A classic fan-shape forms where there is a well-defined topographic apex. Multiple feeder channels, however, often blur the fan-shape resulting in a merged bajada. Alluvial fans can be found in almost all terrestrial settings. These include alpine (Beaudoin and King, 1994), humid tropical (Iriondo, 1994; Thomas, 2003), humid mid-latitude (Bettis, 2003; Mills, 2005), Mediterranean (Robustelli et al., 2005; Thorndrycraft and Benito, 2006), periglacial (Lehmkuhl and Haselein, 2000), and different paraglacial settings (Ballantyne, 2002). The geographical focus of this chapter, however, rests on alluvial fans in regions that are currently deserts or that experienced episodes of aridity in the Quaternary. The research literature contains a host of different ways of thinking about and conducting research on desert alluvial fans (Table 24.1). Despite the wealth of research hypotheses and perspectives, many researchers keep returning to climate change as a vital forcing factor on desert fan evolution. Although some reject climatic change as important (De Chant et al., 1999; Webb and Fielding, 1999; Rubustelli et al., 2005), the following sorts of judgments commonly pepper the literature on fans found in arid and semi-arid regions: