Interaction between hazards . Most of the times, natural disasters are interconnected, i.e. one disaster may be accompanied by another. For example, a volcanic explosion may produce a significant earthquake or even a tsunami, which in turn may produce other disasters such as fire, flooding or slope failure. Scientists try to decipher these interactions and find ways to mitigate the effect of combined hazards.

Natural hazards rarely happen alone. It is very usual that certain hazards cause or activate other hazards to occur. It is very important to note that almost any combination of hazards is possible, and the following examples are only indicative ones.

Earthquake hazards
When an earthquake happens, it involves first-order factors, such sudden shaking of the ground surface, as well as surface faulting. Shaking of the ground causes damages to houses and infrastructures, sometimes causing collapsing of buildings and casualties.

Surface faulting causes extreme damage on buildings that are situated directly above the fault, but it generally does not cause widespread damage.

Due to the above-mentioned effects, several other second-order natural disasters may happen, such as liquefaction of soil, landslides and rockfalls, tsunamis, etc.), which in turn may cause even more damages.

Third-order hazards may include either natural (floods, fires, aquifer alteration, etc.) or technological (fires, gas leakage, industrial accidents, etc.) ones, depending on each case.

Atmospheric hazards
Atmospheric phenomena can have very broad and varied effects. The following scheme explains the interaction between some of them in both the broader and strict sense:

One of the most common examples in this scheme is the widespread problem of deforestation. It happens throughout Europe, especially in western and southern regions, and it is caused by the ongoing urbanization. Forests provide a natural means for restraining the surface flow of water, enriching therefore subterranean aquifers and obstructing wash of surface soil. When an area becomes deforested, either by human or natural (e.g. fires, diseases) causes, the soil cannot be held any more in place, leading to desertification; furthermore surface runoff cannot be avoided, resulting in uncontrolled water flow, leading to floods and possibly landslides.

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