Understanding Natural Hazards and Seismic Risks
3. Classification of Risk Types: Natural, Social, and Technological Hazards. Natural hazards and risks are classified according to the type of agent that produces them: biological (pests and diseases), physical, and geological. Geological hazards include volcanic and seismic events, weather phenomena, etc. Geohazards encompass internal and external geological risks, such as seismic activity, tsunamis, volcanoes, deformation, subsidence, collapses, erosion, gravitational events, glaciers, rivers, coastlines, and atmospheric events.
5.A Causes of Seismic Movements. Areas of greatest tectonic activity experience increased seismic activity. Causes include volcanic activity, landslides, explosions, extraction and injection of fluids in the ground, reservoirs, and mining activities. Large earthquakes cause huge disasters. 5.B Effects of Earthquakes. The ground shakes, and buildings collapse. Surface soil displacement occurs along fault lines. Tsunamis or tidal waves are waves moving at high speed, driven from the seabed by a force that violently displaces water vertically. They are measured by the height of the waves, which can reach tens of meters. Avalanches, volcanic eruptions, and underwater explosions can cause tsunamis, but the waves may dissipate quickly. 5.C Factors That Increase Seismic Risk. Human concentrations in fracture zones, poorly consolidated soils exposed to earthquakes, and populous, poor neighborhoods with low-quality buildings are risk factors. In rich countries, risk factors include an aging population, the value of natural resources, and dependence on technology.
8.A Characteristics of Volcanic Hazards. These hazards are less noticeable because volcanoes can be inactive for long periods, providing a false sense of security. They can cause great catastrophes. A great deal of energy is released, but the release is not instantaneous; it is gradual. 8.B Risk Factors Induced by Volcanic Activity. Volcanic hazards in Spain: Many people around the world live in potentially dangerous volcanic regions, attracted by the fertility of their soils. In the peninsular volcanic areas, no historical volcanism has been recorded, and the volcanoes are considered extinct. In the Canary Islands, 17 eruptions have occurred in historical times, the most important being Timanfaya (Lanzarote). It remains active and poses a real risk. Increasing population density in the archipelago increases the risk, as does the value and vulnerability of many areas.
8.C Prevention of Volcanic Risk. Knowing when an eruption will occur requires careful and constant study of the volcano to detect phenomena that indicate an impending eruption. Precursor phenomena of volcanic eruptions are the same as those of magma intrusion in the fractures near the surface. Only 1% of volcanoes are considered active-controlled detectors and adequate measurement instruments (network monitoring).
15.A Causes of Floods Related to Weather Phenomena. The weather: heavy rainfall concentrated in a few areas (rain or cold drop). Melting ice: rapid fusion of ice and snow due to a sudden rise in temperature in spring or volcanic activity. The activity increases risk when heavy rains coincide. 15.B Natural Causes Unrelated to Flooding and Climatic Factors. Coastal flooding: sea level rise and abrupt tsunamis. Rupture of natural dikes (moraines). Anthropogenic causes: poorly constructed dam breaks, waterproofing of land, deforestation, and occupation of flood channels or plains. 15.C Induced Human Causes of Flood Risk.
15.D Main Catastrophic Effects of Floods. The loss of human lives in the settled population and crop margins. Economic losses: livestock, industry, and commerce. Deterioration of infrastructure.