Volcanic and Landslide Hazards: Prediction, Prevention, and Mitigation
Volcanic Hazards
Risk Factors
Volcanoes offer benefits like fertile land, mineral resources, and geothermal energy. However, human settlement in volcanic areas transforms these natural processes into significant risks.
- Population increase in these areas elevates the exposure factor.
- Eruption type influences the hazard level. Intensity depends on factors such as the number of volcanoes, frequency of explosive eruptions, lava viscosity, and presence of gases.
Main Volcanic Hazards
- Lava flows: Can cover extensive areas.
- Pyroclastic flows: Pose deadly threats due to impact, building collapse, and crop destruction.
- Boiling eruptions and fiery clouds: Among the most dangerous volcanic manifestations.
Other Volcanic Risks
- Phreato-magmatic eruptions: Occur when rising magma interacts with water, leading to violent explosions due to superheated steam.
- Lahars (mudflows): Caused by melting ice or snow, resulting in devastating consequences.
- Tsunamis: Triggered by submarine caldera collapses, potentially causing more damage than the eruption itself.
- Landslides and debris flows: Can block valleys and cause widespread destruction.
- Toxic gas emissions: For example, sulfurous gases from the 1902 Mount Pelée eruption caused widespread fatalities and respiratory problems.
Predicting Volcanic Activity
Predicting volcanic effects requires understanding each volcano’s history, eruption frequency (return period), and intensity. Common mitigation strategies include diverting lava flows to uninhabited areas when feasible. Preventive measures vary depending on the type of volcanism:
- Effusive eruptions: Evacuation and insurance coverage for property loss are common.
- Explosive eruptions: Risk maps help predict damage, facilitate evacuations, and guide construction restrictions in high-risk zones.
- Interim eruptions: Evacuation and alarm systems are frequently employed.
Landslide Hazards
Definition
Landslides are the gravity-driven movement of materials down a slope, affecting the entire surface layer of loose material.
Factors Influencing Landslides
Conditioning Factors
- Lithological: Presence of weathered materials on the surface.
- Structural: Rock bedding orientation, fractures, and faults.
- Climate: Cycles of rain, drought, and freeze-thaw.
- Hydrological: Increased surface runoff and water stagnation.
- Topographic: Slopes steeper than 15% are at risk.
- Vegetation: Absence or scarcity of deep-rooted vegetation increases risk.
Triggering Factors
- Natural: Heavy rain, floods, volcanic eruptions, earthquakes, and volume changes due to freeze-thaw cycles.
- Human-induced: Increased weight at the top of the slope (e.g., debris, buildings), excavation at the slope’s base.
Types of Landslides
- Creep: Slow, discontinuous movement of the superficial layer.
- Mudflows: Viscous flow of clay or mud saturated with water.
- Solifluction: Combination of flow and creep, common in periglacial environments.
- Landslides: Downward movement of rock or soil.
- Rockfalls: Abrupt detachment of rock blocks or fragments.
- Avalanches: Rapid flow of large rock boulders and snow.
Predicting, Preventing, and Correcting Landslides
Landslides are relatively easy to predict spatially through risk mapping, but temporal prediction is more challenging. Assessing landslide risk involves considering:
- Instability detection: Systematic observation and analysis of erosion patterns.
- Potential of the phenomenon: Influenced by weather, topography, morphology, and geological structure.
- Potential behavior: Determines the mode of action and danger level.
Hazard maps can be created by analyzing individual factors or by combining multiple factors.