Natural hazards are hazards attributed to natural phenomena, which can imply a significant threat to people, infrastructure, economic assets and the environment and result in a disaster.

The magnitude of a disaster is not entirely due to natural phenomena as human activity can aggravate or mitigate risks through, for example, the level of consideration to where and how settlements are built, or how natural resources are exploited. Disasters are, therefore, complex events and the problem of disaster prevention and mitigation has many facets.

Natural hazards are usually classified based on their causes and are thus subdivided in “Geological hazards” and “Hydro-Meteorological hazards”.

Geological hazards are caused by earth processes either internal (volcanic eruptions and earthquakes) or external (landslides). Tsunamis can be included among them as they are triggered by undersea earthquakes and other geological events.

Hydro-Meteorological hazards are most often weather-related phenomena (such as floods, droughts/desertification, avalanches, hurricanes/storm surges and sea level rise).

It is important to underline that a type of natural hazard can trigger another natural hazard (e.g. a storm can trigger floods, an earthquake can trigger tsunamis and landslides, a volcanic eruption can cause wild fires) or even a technological accident (e.g a tsunami can cause a nuclear accident, a dam failure can cause floods).