Why do hazards occur

Hydrometeorological hazards are of atmospheric, hydrological or oceanographic origin. Examples are tropical cyclones also known as typhoons and hurricanes ; floods, including flash floods; drought; heatwaves and cold spells; and coastal storm surges. Hydrometeorological conditions may also be a factor in other hazards such as landslides, wildland fires, locust plagues, epidemics and in the transport and dispersal of toxic substances and volcanic eruption material.

Technological hazards originate from technological or industrial conditions, dangerous procedures, infrastructure failures or specific human activities. Examples include industrial pollution, nuclear radiation, toxic wastes, dam failures, transport accidents, factory explosions, fires and chemical spills.

Technological hazards also may arise directly as a result of the impacts of a natural hazard event. Home Terminology Hazard Hazard. A physical event , such as a volcanic eruption, that does not affect human beings is a natural phenomenon but not a natural hazard.

A natural phenomenon that occurs in a populated area is a hazardous event. In areas where there are no human interests, natural phenomena do not constitute hazards nor do they result in disasters.

This definition is thus at odds with the perception of natural hazards as unavoidable havoc wreaked by the unrestrained forces of nature.

It shifts the burden of cause from purely natural processes to the concurrent presence of human activities and natural events. Although humans can do little or nothing to change the incidence or intensity of most natural phenomena, they have an important role to play in ensuring that natural events are not converted into disasters by their own actions.

It is important to understand that human intervention can increase the frequency and severity of natural hazards. For example, when the toe of a landslide is removed to make room for a settlement, the earth can move again and bury the settlement. Human intervention may also cause natural hazards where none existed before. Volcanoes erupt periodically, but it is not until the rich soils formed on their ejecta are occupied by farms and human settlements that they are considered hazardous.

Finally, human intervention reduces the mitigating effect of natural ecosystems. Destruction of coral reefs, which removes the shore's first line of defense against ocean currents and storm surges, is a clear example of an intervention that diminishes the ability of an ecosystem to protect itself.

An extreme case of destructive human intervention into an ecosystem is desertification, which, by its very definition, is a human-induced "natural" hazard. Earthquakes and volcanoes occur most commonly at the collision zone between tectonic plates. Earthquakes represent a particularly severe threat due to the irregular time intervals between events, lack of adequate forecasting, and the hazards associated with these: - Ground shaking is a direct hazard to any structure located near the earthquake's center.

Structural failure takes many human lives in densely populated areas. Flows and lateral spreads liquefaction phenomena are among the most destructive geologic hazards.

Subsidence occurs in waterlogged soils, fill, alluvium, and other materials that are prone to settle. Volcanoes Volcanoes are perforations in the earth's crust through which molten rock and gases escape to the surface.

Volcanic hazards stem from two classes of eruptions: - Explosive eruptions which originate in the rapid dissolution and expansion of gas from the molten rock as it nears the earth's surface.

Explosions pose a risk by scattering rock blocks, fragments, and lava at varying distances from the source. Flows vary in nature mud, ash, lava and quantity and may originate from multiple sources. Flows are governed by gravity, surrounding topography, and material viscosity. Hazards associated with volcanic eruptions include lava flows, falling ash and projectiles, mudflows, and toxic gases.

Volcanic activity may also trigger other natural hazardous events including local tsunamis, deformation of the landscape, floods when lakes are breached or when streams and rivers are dammed, and tremor-provoked landslides. Landslides The term landslide includes slides, falls, and flows of unconsolidated materials. Landslides can be triggered by earthquakes, volcanic eruptions, soil saturated by heavy rains or groundwater rise, and river undercutting.

Earthquake shaking of saturated soils creates particularly dangerous conditions. Hazard Assessment and Risk Assessment are2 different concepts! Risk assessment aids decision makers and scientists to compare and evaluate potential hazards, set priorities on what kinds of mitigation are possible, and set priorities on where to focus resources and further study. Risk and vulnerability can sometimes be reduced if there is an adequate means of predicting a hazardous event. Sometimes the word "forecast" is used synonymously with prediction and other times it is not.

A warning is a statement that a high probability of a hazardous event will occur, based on a prediction or forecast. If a warning is issued, it should be taken as a statement that "normal routines of life should be altered to deal with the danger imposed by the imminent event". The effectiveness of a warning depends on: The timeliness of the warning Effective communications and public information systems to inform the public of the imminent danger.

The credibility of the sources from which the warning came. If warnings are issued too late, or if there is no means of disseminating the information, then there will not be time enough or responsiveness to the warning.

If warnings are issued irresponsibly without credible data or sources, then they will likely be ignored. Thus, the people responsible for taking action in the event of a potential disaster will not respond. Frequency of Natural Disasters. Again, it is important to understand that natural disasters result from natural processes that affect humans adversely.

So, what we have to worry about is large events that strike areas where humans live. Thus, in natural hazards studies, it is important to understand the relationship between frequency of an event and the size of the event. Size is often referred to a magnitude. For just about any event, statistical analysis will reveal that larger events occur less frequently than small events. Statistical analysis of some types of events for specific locations allow one to determine the return period or recurrence interval.

Although we as humans have not had the opportunity fortunately of observing large asteroid or meteorite impacts, the data suggest that impacts of large asteroids 1 km or larger occurs only once every 10 million years.

Those with magnitudes greater than 8. Are natural disasters becoming more frequent as it seems from news reports of recent activity? But, this suggests some other important questions before we start making conclusions about the end of the world:.

First, Is the frequency of hazardous events increasing? This is much more difficult to answer since natural events responsible for natural disasters have been occurring throughout the 4. Nevertheless, there is no evidence to suggest that hazardous events are occurring more frequently.

What about global warming? There is evidence to suggest that weather related disasters are becoming more frequent, compared to other disasters like earthquakes. For example, the frequency of disasters from tropical cyclones and floods has been increasing, the frequency of earthquakes has changed little.

Although this is what we expect from global warming, there is not yet enough statistical data to prove this right now. Second, is there another explanation for the the frequency of natural disasters increasing? First consider the following facts:. Human population has been increasing at an exponential rate. With more people, vulnerability increases because there are more people to be affected by otherwise natural events.

These are areas most vulnerable to natural hazards such as tropical cyclones, tsunami, and, to some extent, earthquakes. Our ability to communicate news of natural disasters has been increasing, especially since the invention of the internet. Earlier in human history there may have been just as many disasters, but there were few ways the news of such disasters could be communicated throughout the world. The location of natural hazards primarily depends on natural processes, including the movement of tectonic plates, the influence of weather systems, and the existence of waterways and slopes e.

But processes such as urbanization, environmental degradation and climate change can also influence the location, occurrence frequency and intensity of natural hazards. These processes are known as risk drivers. The classification schemes for hazards vary across different research institutions and governments, but these can be divided into :. Each hazard often triggers a sub-set of hazards, for instance tropical cyclones known as hurricanes in the Atlantic Ocean, cyclones in the Indian Ocean and typhoons in the Northern Pacific Ocean can bring intense winds, storm surge and heavy rainfall, as well as trigger secondary hazards, for instance landslides.

A series of triggering relationships can cause a domino or cascading effect, for instance in the case of the tsunami-earthquake-nuclear crisis in Japan, Natural hazard events can be characterized by their magnitude or intensity, speed of onset, duration, and the area they cover.

Hazards occur at different intensities or magnitudes over different time scales sometimes known as temporal scales. Scientists talk about the occurrence of hazards of different intensities in terms of probabilties or return periods also known as recurrence intervals , within the context of uncertainty. In general, the longer the return period the less frequent the hazard the greater the intensity of the hazard.

Because of these long return periods, some communities may have no memory of the potential threat of a high intensity hazard. This was the situation in the eruption of Mt Pinatubo in the second largest volcanic eruption of the 20th century , which displaced 20, indigenous peoples living in its foothills and triggered large mudslides known as 'lahars' which affected people for several years after the eruption.

Hazards also occur at different geographical spatial scales. For instance, the occurrence and impact of tornadoes tends to be quite localised, whereas droughts can occur over several tens of thousands of kilometres. See here differences between intensive and extensive risk. Many countries are exposed to multiple hazards.