A disaster may be caused by nature or by humans and is considered to be any that injures or kills many people at one time.

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. Among the natural hazards and possible disasters to be considered are:

Earthquakes

Volcanic Eruptions

Tsunami

Landslides

Subsidence

Floods

Droughts

Hurricanes

Tornadoes

Asteroid Impacts

All of these processes have been operating throughout Earth history, but the processes have become hazardous only because they negatively affect us as human beings. Important Point - There would be no natural disasters if it were not for humans. Without humans these are only natural events.

Risk is characteristic of the relationship between humans and geologic processes. We all take risks everyday. The risk from natural hazards, while it cannot be eliminated, can, in some cases be understood in a such a way that we can minimize the hazard to humans, and thus minimize the risk. To do this, we need to understand something about the processes that operate, and understand the energy required for the process. Then, we can develop an action to take to minimize the risk. Such minimization of risk is called hazard mitigation.

Although humans can sometimes influence natural disasters (for example when poor levee design results in a flood), other disasters that are directly generated by humans, such as oil and toxic material spills, pollution, massive automobile or train wrecks, airplane crashes, and human induced explosions, are considered technological disasters, and will not be considered in this course, except when they occur as a secondary result of a natural disaster.

the ileocecal valve (also called bauhin valve), which limits the rate of food passage into the cecum and may prevent material from returning to the small intestine.