Introduction

Like many geomorphological processes, weathering can pose a hazard if it affects humans, their property and livelihoods. Unlike many geomorphological processes that are known to cause a hazard, such as landslides, avalanches and coastal erosion, weathering is generally slow and small scale, though once thresholds have been breached or humans have accelerated the processes involved, weathering can have dramatic results (such as the rapid, catastrophic weathering of limestone facades recognised by Smith and Viles,2006). The slow rate and small-scale nature of weathering means that it is often overlooked in hazard research, but it can have serious economic effects as well as being capable of irreparably damaging items of our cultural heritage. For example, relatively minor (in geomorphological terms) rates of weathering can disfigure valuable carving and statuary or induce fragments of stonework to fall from a facade, which are capable of causing injury or death. It can also contribute to more catastrophic events such as rockfalls (Figure 12.1) and rockslides (Matsuoka and Sakai, 1999; Jaboyedoff et al., 2004; Borrelli et al., 2007) and promote landslides in deeply weathered materials (Durgin, 1977) and in clays (Gullà et al., 2006). Chemical weathering may also pose hazards to human health by liberating toxic chemicals (e.g. excessive amounts of arsenic, fluoride, heavy metals etc. from bedrock and mine waste) (Islam et al., 2000; Saxena and Ahmed, 2001; Dang et al., 2002).