The definition of natural disasters is any catastrophic event that is caused by nature or the natural processes of the earth. The severity of a disaster is measured in lives lost, economic loss, and the ability of the population to rebuild. Events that occur in unpopulated areas are not considered disasters. So a flood on an uninhabited island would not count as a disaster, but a flood in a populated area is called a natural disaster.
All natural disasters cause loss in some way. Depending on the severity, lives can be lost in any number of disasters. Falling buildings or trees, freezing to death, being washed away, or heat stroke are just some of the deadly effects. Some disasters cause more loss of life than others, and population density affects the death count as well.