Natural disasters and hazards

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A natural disaster is a natural event, such as an earthquake, flood, or hurricane, which negatively affects society, either through damage to property or through loss of life. A natural hazard is a disaster that has not yet occurred. Natural events are often referred to as natural hazards when referring to the general phenomenon, but they are called natural disasters when referring to a specific event, such as the 2004 Indian Ocean earthquake and tsunami or Hurricane Katrina. If a natural event does not pose any risk to human property or lives, it is simply a natural event; hazards and disasters only occur in conjunction with human society. [1][2]

Types of natural hazards

Hurricane Isabel as seen from Earth orbit

Natural hazards fall into four main categories depending upon the driving forces of the event: geological hazards, atmospheric hazards, hydrological hazards, and biological hazards.

  • Geological hazards occur because of geological processes such as movement in the tectonic plates and volcanic activity. These events include earthquakes, volcanic eruptions, and landslides.
  • Meteorological hazards occur as a result of processes in the atmosphere. Meteorological hazards include extreme temperatures, hurricanes, tornadoes, droughts, and severe storms.
  • Hydrological hazards are hazards involving water processes. Examples include floods, droughts, and tsunamis.
  • Biological hazards occur due to the biological processes of the earth and primarily involve the spread of diseases and pests. Epidemics, pandemics, and insect swarms all fall into the biological hazards category.

Sometimes, natural hazards can fit into more than one category. For example, an earthquake in the middle of the ocean can also cause a tsunami; this would be a geological and a hydrological disaster because the earthquake (a geological event) caused the tsunami (a hydrological event). Another example is when a volcanic eruption (a geological event) spews ash and dust into the atmosphere to cause lower temperatures (a meteorological event). [3][4] Natural hazards also fit into three categories that describe the speed and extent of a hazard: catastrophic hazards, rapid onset hazards, and slow onset hazards.

  • Catastrophic hazards are large-scale that effect large numbers of people or have worldwide effects. Pandemics, large volcanic eruptions, and worldwide droughts are all examples of catastrophic natural hazards.
  • Rapid onset hazards occur quickly and with little warning. Volcanic eruptions, earthquakes, flash floods, and landslides are examples of rapid onset hazards.
  • Slow onset hazards occur slowly and may take years to develop. Epidemics, insect infestations, and droughts are all slow onset hazards. [5]

Effects of natural disasters

A large volcanic eruption can disrupt plant growth by spewing enough ash into the air to restrict sunlight and cool temperatures. This would be considered a tertiary effect of the disaster

The effects of natural disasters are many and varied. Some are short term effects that can be fixed with relative ease while others last for years. Natural disasters have three general types of effects: primary effects, secondary effects, and tertiary effects. [6]

  • Primary effects are the direct result of the natural disaster, such as collapsed buildings and water damage.
  • Secondary effects are the result of primary effects. Examples of secondary effects include power outages due to fallen trees or damaged building and fires from broken gas lines. In these examples, the fallen trees and the damaged building would be primary effects that caused the power outages and fires (secondary effects).
  • Tertiary effects are the long term effects of natural disasters. These include changes in the landscape and natural features, loss of habitat, and crop failure or reduction due to cooler temperatures or other interference. [7]

Human responses to natural hazards

Humans have always had to deal with natural hazards; whether through preparing for them or responding when a disaster occurs. One of the most important ways humans respond to natural hazards is by preparing for their occurrence. As technology has improved, so has the ability to prepare, predict, and forecast future natural disasters.

  • Hazard assessment is when scientists study natural hazards to determine characteristics of various hazards. A hazard assessment differs from a risk assessment primarily because and hazard assessment focuses mainly on the natural processes of a possible event while a risk assessment includes a hazard’s possible effects on a society. Hazard assessment generally determines the location and timing of past hazardous processes, the severity and frequency of past hazardous processes, probable effects of different processes depending upon the magnitude (severity) of a possible event, and organizing the information into a usable form for officials and policy makers.
  • Risk assessment incorporates the information from a hazard assessment, but also includes possible socio-economic effects. A risk assessment includes locations of buildings and infrastructure in hazardous areas, the potential for exposure due to the physical effects of a hazard, community vulnerability in the event a hazard becomes a disaster, and a hazard assessment.
  • A prediction is a statement of probability that an event will occur. In terms of natural hazards, predictions are made through various scientific observations. A common observation that could lead to a prediction is the identification of a precursor event. A precursor event is a smaller event that usually precedes a larger event, such as tropical depression leading to a tropical storm before becoming a hurricane or numerous small earthquakes around a volcano indicating an imminent eruption.
  • Forecasting is similar to a prediction and is often used synonymously; however, in certain instances a forecast can be slightly different from a prediction. The term forecast is usually used as a short-term prediction of the severity, location, and timing of weather related events. It can also be used for long-term probabilities of an event occurring within a certain time frame. This long term forecasting is not as precise as a weather forecast. [8]

See also


  1. - introduction.pdf. (n.d.). Retrieved from
  2. What is a Natural Hazard? | GEOG 030: Geographic Perspectives on Sustainability and Human-Environment Systems, 2011. (n.d.). Retrieved August 6, 2015, from
  3. - introduction.pdf. (n.d.). Retrieved from
  4. What is a Natural Hazard? | GEOG 030: Geographic Perspectives on Sustainability and Human-Environment Systems, 2011. (n.d.). Retrieved August 6, 2015, from
  5. - introduction.pdf. (n.d.). Retrieved from
  6. - introduction.pdf. (n.d.). Retrieved from
  7. - introduction.pdf. (n.d.). Retrieved from
  8. - introduction.pdf. (n.d.). Retrieved from

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