Natural hazards are physical phenomena caused by atmospheric, water or tectonic processes that threaten people, property or the environment. They can occur within a short or long period of time.
What is the difference between natural hazards and natural disasters?
The term natural hazard should not be confused with a natural disaster. Natural hazards can subsequently lead to natural disasters. A natural hazard is considered a natural disaster when it has exceeded a certain threshold, i.e. when it has caused significant damage to society or a community and the community can no longer cope with its resources. It includes adverse effects of a human, material or environmental nature, such as loss of life, injury and damage to infrastructure. A threshold may be a certain number of deaths or a certain number of economic losses.
What are the different types of natural hazards?
The different types of natural hazards include:
- Geophysical hazards (e.g., earthquakes, volcanic eruptions, and tsunamis).
- Hydrological hazards (e.g., floods).
- Meteorological hazards (e.g., cyclones and storms).
- Climatological hazards (e.g., droughts and wildfires).
- Biological hazards (e.g., pandemics and epidemics).
What are the causes of natural hazards?
The causes of natural hazards depend on the type of natural hazard.
Geophysical hazards
Tectonic processes cause geophysical hazards.
Hydrological hazards
Hydrological hazards result from heavy rainfall, melting of ice and snow, and storm surges. Deforestation and the breaching of dams and channels with steep banks exacerbate these hazards.
Meteorological hazards
Extreme weather conditions, such as rain, wind, hail and snow, cause meteorological hazards. Climate change has exacerbated meteorological hazards.
Climatological hazards
Long periods of heat or cold cause climatological hazards. Climate change exacerbates them as global surface temperatures rise.
Biological hazards
Bacteria, viruses, parasites, moulds, or fungi that can affect human health through disease are biological hazards. Many arise from new pathogens transmitted from animals to humans. An obvious example is the current Covid-19 pandemic.
Impacts of natural hazards
Hazards can have social, economic, and environmental impacts on the affected country or community. Possible consequences include loss of life, injuries, damage to infrastructure, businesses and ecosystems. Natural hazards can also cause secondary hazards. For instance, flooding can induce landslides, which can then cause further damage.
Comparing natural hazards
Comparing hazards involves using appropriate scales for the hazard in question to quantify its magnitude and impact and understand it compared to others. By comparing the different potential hazards in a location, we can prioritise which to focus on and develop an appropriate mitigation plan.
The measurements used to compare the intensity of tectonic hazards are the Moment Magnitude Scale (MMS), Mercalli and the Volcanic Explosivity Index (VEI).
Earthquake magnitude
Earthquake magnitude is measured based on the Moment Magnitude Scale (MMS), which quantifies the total seismic moment released by an earthquake. The scale ranges from 1 Mw to 10 Mw. We calculate it in terms of the distance the ground has moved along the slip and the force required to do so. The Moment Magnitude Scale is logarithmic, meaning that from one integer to the next, the amplitude of the ground motion is ten times greater, and the amount of energy released is 30 times greater. We record the moment magnitude with a seismograph.
Earthquake damage
We measure the visible damage that earthquakes cause using the Mercalli scale. It focuses on specific locations and can be subjective. You can see the different levels of the Mercalli scale below.
Mercalli scale, usgs.gov
Volcano magnitude
We measure the magnitude of volcanic eruptions using the Volcanic Explosivity Index (VEI). It is based on the volume of pyroclastic material, column height, and eruption duration. Like the Moment Magnitude Scale, the Volcanic Explosivity Index is logarithmic.
The nature of the magma and the plate margins determine the explosivity. Low VEI, between 0 and 3, tend to occur at divergent plate margins. Basalt lava has a high viscosity and low gas content. However, high VEI, between 4 and 7, often happen at convergent margins.
Magma from the subduction process has a high gas and silica content and tends to erupt frequently and with great force.
How are characteristics of hazards compared using hazard profiles?
Hazard profiles help understand the different hazard impacts, vulnerability, and resilience and serve as a mitigation plan. It is completed for each type of natural hazard and considers the physical processes, including magnitude, speed of onset and areal extent, duration, frequency and spatial predictability. Hazard profiles allow you to rank the different hazards and identify which ones to focus on and invest in to reduce the potential impact.
California Natural Hazards Profile, cahazardprofilemitigationplan.com
Difficulties in comparing hazards
Some limitations exist because of the difficulty of comparing different types of hazards. For instance, the challenge in comparing hazards in different countries lies in the different socio-economic situations. The total economic loss in developed countries may be much higher than in developing countries, but the ratio to GDP is lower. However, it is easier to compare the potential of earthquakes in two different places than the potential of tsunamis and volcanic eruptions in one place. The reason is that the scales used for tsunamis and volcanic eruptions are different.
Natural Hazards - Key takeaways
- Natural hazards are physical phenomena caused by atmospheric, water or tectonic processes that threaten people, property or the environment.
- The different types of natural hazards include:
- Geophysical hazards.
- Hydrological hazards.
- Meteorological hazards.
- Climatological hazards.
- Biological hazards.
- A natural hazard is considered a natural disaster when it has exceeded a certain threshold, i.e. when it has caused significant damage to society or a community and the community can no longer cope with its resources.
- Hazards can have social, economic, and environmental impacts on the affected country or community. Possible consequences include loss of life, injuries, damage to infrastructure, businesses and ecosystems.
- We use suitable scales to compare natural hazards against each other and to quantify their magnitude and/or impact. Examples of scales include the Moment Magnitude Scale (MMS) for earthquake magnitude and the Volcanic Explosivity Index (VEI) for volcanic eruptions.
- Hazard profiles help understand the different hazard impacts, vulnerability, and resilience and serve as a mitigation plan. It is completed for each type of natural hazard and considers the physical processes.
- The difficulties in comparing hazards in different countries lie in the different socio-economic situations. It is also difficult to compare different types of natural hazards against each other.
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