When is natural disasters mostly occur such as volcanoes?

Answer 1

A natural hazard is a threat of a naturally occurring event will have a negative effect on humans. This negative effect is what we call a natural disaster. In other words when the hazardous threat actually happens and harms humans, we call the event a natural disaster. Natural Hazards (and the resulting disasters) are the result of naturally occurring processes that have operated throughout Earth's history. Most hazardous process are also Geologic Processes. Geologic processes effect every human on the Earth all of the time, but are most noticeable when they cause loss of life or property. If the process that poses the hazard occurs and destroys human life or property, then a natural disaster has occurred.