Natural Disaster Risk Factors and Mitigation Techniques

Defining Natural Hazard Risk

Natural hazard risk is the probability of damage or catastrophe occurring to the population of an area or to their property. The value of a risk depends on three primary factors:

• Magnitude (or Danger): The size or intensity of a potentially catastrophic event, and the frequency with which it occurs.
• Exposure: The volume of population and assets that may be affected.
• Vulnerability: The susceptibility of a community to damage.

Reducing the Effects of Natural Events

To reduce the effects of a natural event, two main strategies are utilized:

• Prediction: Based on statistical data that indicate whether a particular phenomenon occurs frequently in a zone.
• Prevention: Proposes the adoption of necessary measures for the event to have minimal effects.

Earthquakes and Seismic Risk

Earthquakes, tremors, or quakes are ground vibrations caused by the sudden release of stored energy in rocks subjected to stress. The place where an earthquake originates is the hypocenter (seismic focus). From the hypocenter, seismic waves are transmitted in all directions. The surface point closest to the hypocenter is the epicenter.

Where Earthquakes Occur

Earthquakes are primarily located within the boundaries of lithospheric plates. The movement of plates relative to one another generates seismic activity at different types of boundaries (e.g., convergent, transform/sliding sideways).

Earthquake Prevention Strategies

• Develop seismic hazard maps that allow preventive rules to be adjusted for specific circumstances.
• Establish standards for earthquake-resistant construction (e.g., limiting height, proper building techniques, using steel structures).

Tsunamis: Characteristics and Danger

A tsunami denotes a set of huge waves caused by the sudden displacement of a large mass of deep-sea water.

Why Tsunamis Are Dangerous

• Massive Water Displacement: The tsunami moves water from the surface to the bottom, involving a huge volume.
• Propagation: It propagates with little loss of intensity, allowing it to reach remote areas.
• Warning Sign: A retreat of the sea often occurs minutes before the arrival of the large waves.

Volcanic Eruptions and Associated Hazards

Types of Eruptive Activity

• Effusive Activity: Characterized by low-viscosity lava that flows smoothly from the crater. Gases escape easily, resulting in few explosions and minimal pyroclastics.
• Explosive Activity: Characterized by highly viscous lava. Gases accumulate and cause strong explosions, projecting large amounts of pyroclastics.

Volcanic Dangers

The danger of a volcano can be attributed to several factors:

• Emission of toxic gases.
• Formation of burning clouds (pyroclastic flows).
• Explosions.
• Lava mudflows (lahars).
• Lava flows.

Flooding and Watersheds

Flooding is the occupation of areas that are usually free of water. It is noted as the most important natural risk in Spain.

Defining a Watershed

A watershed is the area that includes the entire territory that drains into the same river system.