events which directly threaten human life and property by means of acute physical or chemical trauma. Any manageable definition of environmental hazards will be both arbitrary and contentious. But, despite their diverse sources, most disasters have a number of common features: (1) The origin of the damaging process or event is clear and produces characteristic threats to human life or well-being, e.g. a flood causes death by drowning. (2) The warning time is normally short, i.e. the hazards are often known as rapid-onset events. This means that they can be unexpected even though they occur within a known hazard zone, such as the floodplain of a small river basin. (3) Most of the direct losses, whether to life or property, are suffered fairly shortly after the event, i.e., within days or weeks. (4) The exposure to hazard, or assumed risk, is largely involuntary, normally due to the location of people in a hazardous area, e.g. the unplanned expansion of some Third World cities onto unstable hillslopes. (5) The resulting disaster occurs with an intensity that justifies an emergency response, i.e. the provision of specialist aid to the victims. The scale of response can vary from local to international (Smith 1996, 15-16).