Previous chapters have outlined how human activity in the British Isles is influenced by the region’s geology, the result of Earth processes over hundreds of millions of years. These processes are continuing, some imperceptibly slowly, some rapidly enough to affect and threaten life. Landslides, subsidence, earthquakes, coastal erosion-these are some geological hazards. Together with biological, meteorological and hydrological hazards, they form a spectrum of natural threats (Fig. 4.1). This chapter will describe hazards involving the solid Earth, but including related hydrological processes such as floods and coastal erosion. It will concentrate, though not exclusively, on hazards relevant to the British Isles.