Understanding Natural Disaster Risks: Earthquakes, Volcanoes, and More
Understanding Natural Disaster Risks
Risk Assessment: Risk level depends on several factors:
- Hazard (Peligrosidad): Probability of an event occurring.
- Exposure (Area Afectada): The value and number of people or assets in the affected area (ecological, economic, and cultural zones).
- Vulnerability: Percentage of susceptibility to damage and potential for victimization.
The risk can be calculated as: RISK = Hazard * Exposure * Vulnerability
Types of Natural Disasters
Geological (Endogenous and Exogenous)
- Endogenous (Internal Dynamics): Volcanoes, earthquakes, tsunamis.
- Exogenous (External Dynamics): Landslides, mudslides.
Meteorological
- Caused by atmospheric conditions: Storms, floods, hurricanes.
Biological
- Organisms (pests, diseases).
Cosmic
- Meteorites, solar flares, fires.
- Physical and natural radioactivity.
Volcanoes
Volcanoes are manifestations of energy released from the movement of lithospheric plates. Their distribution aligns with plate boundaries. Catastrophic events originate not only from eruptions but also from variations in air transparency and reductions in solar radiation. Large eruptions are infrequent. Studies following the Krakatoa eruption (Indonesia, 1883) demonstrated reduced solar radiation (20% less for a week, 10% less for months). The eruption killed approximately 40,000 people, and the explosions were heard 500 km away. Mount St. Helens in the U.S. erupted in 1980.
Earthquakes
Earthquakes are vibrations of the Earth’s surface due to the release of internal energy from plate movement or other shocks. Friction between plates generates deformation, eventually leading to a rupture at the weakest point (hypocenter). Seismic waves radiate from this point. The point on the Earth’s surface directly above the hypocenter is the epicenter. Seismographs measure seismic waves using scales like the Richter and Mercalli scales. Countries with high seismic risk include: Germany, Italy, China, Asia Minor, Japan, Mexico, and the Balkans. A devastating earthquake occurred in the Middle East in 1210.
Tsunamis
Tsunamis are caused by movements on the ocean floor, often triggered by earthquakes.
Landslides and Avalanches
Landslides are displacements of soil or rock, often facilitated by fracturing of the supporting surface. Factors increasing landslide risk include slope steepness and water saturation (increasing weight and reducing friction). To mitigate landslide risk, avoid construction in unstable areas. If settlements already exist, stabilize the terrain. Avalanches are rapid movements of snow and ice, often occurring in winter and spring due to temperature increases.
Storms
Storms are characterized by atmospheric phenomena, including the coexistence of air masses with different temperatures. This temperature difference, along with moisture, electrical charge differences, and ionization levels, results in heavy rain and electrical activity. Storms are among the most damaging natural disasters.
Floods
Floods result from the overflow of riverbeds or other natural waterways due to heavy rainfall, rising sea levels, or snowmelt. They are frequent and cause a large number of casualties. Countries with high flood vulnerability include India, Pakistan, Bangladesh, and China. Actions that exacerbate flood effects include:
- Paving: Prevents water absorption into the ground.
- Deforestation: Roots hold the ground; lack of vegetation cover leads to erosion.
- Uncontrolled Urbanization.
Cold Fronts (Gota Fria)
Cold fronts are atmospheric disturbances that bring heavy rain and strong winds for hours or days. They form when conditions include warm sea temperatures, an unstable atmosphere at the surface, and cold air at higher altitudes.