Understanding Natural Disaster Risks: Earthquakes, Tsunamis, Volcanoes, and Floods
Understanding Hazard Risk
Hazard risk is not equal to the value that achieves a risk. It depends on three factors:
- A hazard’s potential to be catastrophic, often occurring with quick escalation.
- Overexposure or the volume of population and property that may be affected.
- Vulnerabilities of a community to be damaged.
Prediction is based on statistical data that indicate whether a particular phenomenon is common in the area.
Prevention proposes the adoption of measures necessary for the event to have minimal effects on the population or property.
Earthquake Risk
Earthquakes are ground vibrations caused by the sudden release of energy accumulated in rocks under stress.
The place of origin is the hypocenter. Vibrations occur everywhere.
Measuring Earthquakes
To record earthquakes and measure their magnitude, instruments called seismographs are used, which draw seismograms.
The magnitude of an earthquake is the amount of energy that is released, measured by the Richter scale.
Earthquake Locations
Places with high seismicity are those in the greatest fault zones that coincide with the boundaries between lithospheric plates. These plates move relative to each other, generating earthquakes.
Earthquake Prediction
Currently, there is no reliable system to predict the occurrence of an earthquake. Research is being conducted on precursors to map seismic risk. Factors to consider include:
- Location or area in a plate boundary.
- Local geological characteristics, such as existing materials and especially the presence and length of active faults.
- Seismic history of the area.
Earthquake Prevention
Preventive measures include seismic risk mapping and setting standards for earthquake-resistant construction.
Tsunamis
A tsunami is a set of huge waves caused by a sudden rise in volume of a large body of water at the bottom of the sea.
Catastrophic Tsunami Effects
- Moves a large volume of water.
- Propagates with little loss of intensity.
- Is usually preceded by a retreat of the sea.
Volcanic Eruptions
What Makes an Eruption Dangerous?
There are two types of volcanic activity:
- Effusive activity: The lava is less viscous and flows out of the crater smoothly. Gases escape easily, and there are few pyroclastic explosions.
- Explosive activity: The lava is very viscous, solidifies, and clogs the exit pipes. Gases accumulate and cause large explosions, projecting large amounts of pyroclastics into the air.
Volcanic hazards can be due to:
- The emission of toxic gases.
- Formation of burning clouds of pyroclastic flow.
- Explosions.
- Mudflows or lahars.
- Lava flows (generate few victims).
Floods
Floods are the occupation by water of areas normally free of it.
Human Influence on Flooding
Flooding is a risk induced by human activities such as:
- Occupation of flood plains.
- Deforestation.
- Land cover with impermeable materials.
- Infrastructure that interferes with the channel.