Geological Hazards: Causes and Risk Factors
Expansive Soils
Expansive soils are soils that increase in volume in the presence of water. They can exert pressure as strong as a floor, for example. This type of expansive soil is formed by clays, plasters, and anhydrite.
Radon
Radon is the main cause of radiation risk as a natural contaminant worldwide. It lodges in the lungs and can cause lung cancer. The toxic effects are seen with the passage of time.
Instability of Slopes
Human Causes
Human causes are diverse. They can be caused by the rejection of rocks that accumulate and are dangerous to the landfill because the garbage can cause an avalanche, by excavations at the foot of a slope, by overload on the upper side, or by the alteration of natural drainage diversion caused by infiltration by a river and the immediate saturation of the terrain, for example.
Risk Management
Risk map: Aims for land management that avoids construction in unsafe areas.
Corrective measures: Measures to reduce instabilities, such as anchors, nets, or metal gutters on roads.
Risk Factors of Snow Avalanches
- Slope gradient of 35 to 40 degrees tilt (if the slope is less than 25 degrees, there is almost no risk).
- The amount of snow (if the snowpack is high, there may be significant accumulations of newly fallen snow, increasing the risk of an avalanche).
- Increasing temperature (if the temperature is high, the snow becomes dangerously soft, possibly resulting in an avalanche).
- Slopes with a convex profile (this profile favors the flood since it emits a traction force).
- Orientation to the sun (slopes where the sun shines are more likely to have landslides).
Geological Hazards Caused by External Factors
Main Indicators of Natural Instability
- Soil type (with water saturation, there is a higher probability of landslides).
- Orientation of structural plans (slides occur when stratification, schistosity, or fracture plans are in the same direction as the topographic slope).
- Excavations at the foot of the slope (this is when water erodes the cliff and leaves very unstable cornices).
- Earthquakes (vibrations caused by earthquakes).
- Heavy rainfall (water acts as a lubricant, causing landslides, and is their main trigger).
- Form and slope gradient (stability is higher with a concave shape, and convex slopes pose a higher risk; i.e., the steeper the slope, the greater the risk).
Subsidence and Landslides
Subsidence is the gradual collapse of the local terrain surface.
Landslides: This term is reserved for situations where the process occurs suddenly.
Causes of Collapse
Human Causes
Human causes include practices such as mining, fluid extraction, or anthropic filling. The latter is caused by the edges of rubble heaps on slopes.
Natural Causes
Possible explanations include tectonic processes, karstification (as it is present in many landslides), and compression of calcareous soils and weak rocks. When the packing of particles is less dense, soil resistance is weaker, and therefore there is a higher risk.