Understanding Risk Factors in Natural Disasters

2. Q Factors Considered in Risk Assessment

A. Dangerousness

The hazard estimates its potential to transform into the middle environment. Peligrosidad: probability of occurrence in a geographical area at a specific time. Distribución: occurrence-surface area affected, time of return or recurrence interval, hazard level, intensity, area phenomenon. Hazard maps, occurrence, occurrence + areas of its surface-recurrence-time of return; grade-intensity danger.

B. Exposure or Interference

Process naturally occurring in a particular area, and the social process. Good active preventive measures on the natural process can reduce its hazardous nature, or passive measures to avoid interference with total exposure. Number of people (social exposure) and total number of goods (economic exposure) potentially affected. Depends on population density maps.

C. Damage Planning or Vulnerability

Changes incurred or potential victims. Percentage of total economic loss exposed. Depends on prevention measures.

9. A. Factors Constraining the Danger of Volcanic Eruption

How Viscosity and Gas Content Affect Eruptions

The danger is greater the higher the viscosity and gas content in the viscous magmas. If magma is rich in volatile substances, it produces violent explosions (explosive eruptions) converting into vapor, surface water, or underground water when it comes into contact with gas clouds from magma. This results in magma fragments being ejected into the air.

B. Types of Volcanic Products

Explosive eruptions (pyroclastic) can affect large areas (up to thousands of kilometers). Depending on the altitude and direction of the wind, fragments can be projected. The finest particles remain suspended for a long time and can travel great distances. Tephra deposits (ash and lapilli) can bury supermarkets and the roofs of buildings. Ashfall can hamper the operation of motors and appliances, bury crops. Highly poisonous gases such as CO2, CO, and H2S are also released.

C. Earthquakes Associated with Volcanic Eruptions

Lahars are flows of clay and debris avalanches formed by rapidly melting snow or ice due to the heat from volcanic activity. These flows can move very quickly and cover great distances. If channeled through gullies, their speed and density increase significantly.

11. A. Factors Increasing the Risk of Erosion

The rugged slopes, low vegetation, and cohesion of materials, along with arid conditions that kill vegetation cover (due to abusive grazing, logging, mining, and urbanization) contribute to increased erosion risk.

B. Measures to Prevent Erosion Processes

Better land use in terms of sensitivity to erosion (prevent logging, establish crops, and develop on hillsides with steep slopes) and reforest or terrace slopes while maintaining vegetation cover.

C. Desertification in Spain

Slope movements are significant due to our terrain (steep slopes and inconsistent rocks) and weather conditions (frequent rains, wide variations in temperature).

13. A. Phenomena of Subsidence

Slow, sustained soil descents cause no casualties but can lead to significant economic loss. These occur at different scales and from various causes (tectonic processes, seismic tremors, mining subsidence, removal of underground fluids, etc.).

B. Damage Caused by Subsidence Phenomena

Can affect buildings and roads, lead to flooding, change slopes, and contaminate groundwater.

C. Risk Associated with Expansive Soil

Significant changes in volume can occur with water absorption, destabilizing foundations.

D. Risk Associated with Karstic Subsurface

Limestone soils can lead to subsidence or sudden collapse. In karst terrain with salts and gypsum, the risks are even greater and evolve more rapidly due to solubility.