Natural Risks and their Prevention: A Comprehensive Guide
Natural Risks: Definition and Evaluation
Natural risk is the likelihood of a population in a given area suffering injury or catastrophe due to a natural event. According to UNESCO, it’s the probability of loss of human lives, productive capacity, property, or resources due to natural phenomena. Natural risks stem from physical phenomena of geological origin (internal or external dynamics). When an event occurs, it can result in minor changes or a catastrophe.
Evaluation of Natural Risks
- Hazard: Emphasizes potential risk factors and is defined by:
- Location of the area under study
- Magnitude or intensity of the event
- Return time or interval
- Exposure: Number of people or properties potentially affected by the risk.
- Vulnerability: Percentage of people or assets affected out of the total exposure.
Based on risk assessment, risk zones are established:
- Risk-free zone
- Very low-risk area (manageable)
- Low-risk area (assimilable)
- Medium-risk area
- High-risk area
- Very high-risk area
Prediction, Forecasting, and Prevention of Natural Disasters
Predicting, forecasting, and preventing natural disasters involves identifying processes and risk factors that may pose a risk to a population.
- Prediction: Aims to determine and announce, before the occurrence of a phenomenon, where and when it will occur, its development, and strength.
- Mitigation: Implementing protective measures before a disaster to reduce its effects.
- Forecast: Deepens the study of risk by identifying the probability of occurrence of a phenomenon and its intensity and frequency.
- Prevention: Measures and activities based on prediction and forecasting, implemented to avoid the adverse impact of potentially dangerous phenomena.
Land Management
Land management involves designating land for its most suitable use. It’s mainly used in environmental management to prevent environmental impacts and risks.
Seismic Risk
Areas with higher tectonic activity experience the greatest seismic activity. The main effects of large earthquakes include:
- Ground shaking and building collapse: The majority of deaths occur due to building collapse.
- Ground surface displacement: Occurs along fault lines.
- Landslides: A violent earthquake can trigger thousands of landslides.
- Tsunamis: Series of high-speed waves caused by the displacement of ocean water due to vertical movement of the seafloor.
Earthquake Prediction
Earthquakes are often preceded by tremors, ground deformation, changes in water levels, etc. These phenomena are used to predict earthquakes. However, these indicators are not always reliable.
Seismic Risk Prevention
To prevent seismic risks:
- Create and establish areas with construction restrictions near known faults.
- Restrict land use in areas prone to landslides.
- Strengthen existing building structures and design new ones to withstand ground shaking.
- Follow construction regulations.
- Encourage insurance to mitigate economic losses.
Factors Increasing Earthquake Risk
- Large human concentrations in areas with fractures or poorly consolidated soils.
- Overpopulated areas in cities of developing countries with low-quality constructions.
- In developed countries: aging population, value of assets, and reliance on technology that becomes useless after an earthquake.
Volcanic Hazards
Volcanic hazards are less perceived than earthquake risks because volcanoes can be inactive for long periods. However, volcanic eruptions are dangerous and can lead to major catastrophes. The energy released in an eruption is equivalent to an earthquake of magnitude 6 to 8.5.
Prevention of Volcanic Hazards
The only way to prevent the effects of a volcanic eruption is to know when it will happen. This requires careful and constant study of the volcano to detect signs of an impending eruption. Only 1% of volcanoes are considered active and monitored with adequate instruments.
Detecting Volcanic Eruption Risk
Methods used to detect eruption risk:
- Monitoring seismic movements near the volcano.
- Detecting ground elevation associated with rising magma.
- Observing changes in magnetic and electric fields, as well as heat flow variations.
- Analyzing gravity anomalies that occur when magma rises.
- Monitoring thermal vents for chemical changes related to magma ascent.
Volcanic Hazards in Spain
Volcanic areas in mainland Spain have no historical volcanism and are considered extinct. The Canary Islands have experienced 17 eruptions in historical times, the most significant being the Timafaya eruption in Lanzarote (1730). The last eruption was Teneguía in La Palma (1971).
The Danger of Volcanoes
The danger of a volcano is related to:
- Explosiveness of eruptions: Greater viscosity and gas content in magma lead to more violent explosions.
- Type of ejected materials: Pyroclastic materials projected into the air during explosive eruptions. Large fragments can cause damage, while finer ash can affect visibility, engine operation, and bury crops. Some volcanoes emit poisonous gases.
- Lahars: Mudflows and debris avalanches formed by melting snow or ice due to an eruption or heavy rains. They can cause mass destruction.
- Lava flows: Fluid magma with low gas content forms lava flows. They can cause extensive material damage and cover the ground.