<P> An adverse event will not rise to the level of a disaster if it occurs in an area without vulnerable population . In a vulnerable area, however, such as Nepal during the 2015 earthquake, an earthquake can have disastrous consequences and leave lasting damage, which can require years to repair . </P> <P> A landslide is described as an outward and downward slope movement of an abundance of slope - forming materials including rock, soil, artificial, or even a combination of these things . </P> <P> During World War I, an estimated 40,000 to 80,000 soldiers died as a result of avalanches during the mountain campaign in the Alps at the Austrian - Italian front . Many of the avalanches were caused by artillery fire . </P> <P> An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves . At the Earth's surface, earthquakes manifest themselves by vibration, shaking, and sometimes displacement of the ground . Earthquakes are caused by slippage within geological faults . The underground point of origin of the earthquake is called the seismic focus . The point directly above the focus on the surface is called the epicenter . Earthquakes by themselves rarely kill people or wildlife . It is usually the secondary events that they trigger such as building collapse, fires, tsunamis (seismic sea waves) and volcanoes . Many of these could possibly be avoided by better construction, safety systems, early warning and planning . </P>

When does disaster occur and what are its causes and effects