Understanding River Modeling and Geological Risks

Posted on May 15, 2024 in Geology

River Modeling

Morphoclimatic-Wet Systems

Rivers, as typical morphoclimatic-wet systems, are the primary carriers of mineral matter from continents to oceans. They possess significant energy, utilized in erosion, material transport, and channel deepening, resulting in a characteristic “V” shape.

Channel Geometry

While watercourses exhibit varying geometry along their paths, they can be categorized into three groups:

  • Straight: The channel’s sinuosity is negligible.
  • Branched: A series of divisions form multiple channels.
  • Meandering: The channel features curves throughout its trajectory.

Fluvial Erosion

River erosion is influenced by flow, the slope of the current-carrying products, and the bed’s constituent materials. Fluvial abrasion, a mechanical wear process, occurs when current-borne particles strike the channel walls, dislodging fragments that roll along the riverbed, breaking into smaller grains of varying sizes. This process creates holes and waterfalls.

Sedimentation

Streams with seasonal flow and fixed beds erode the channel bottom in the reception basin, transporting materials through the drainage channel until they settle in the alluvial fan, forming piedmont deposits. Sedimentation occurs when flow rate decreases, typically due to reduced slope. Rivers effectively classify geological deposits; as flow velocity decreases, thicker materials deposit first, while finer ones travel further before settling.

River Terraces

River terraces represent ancient alluvial deposits that have been sculpted around the river, eroding its floodplain. They are traditionally linked to Quaternary glaciations, during which the river’s erosive power could be reactivated by glacial pulses.

Karstic Processes

Carbonate Rock Dissolution

Karstic processes occur in carbonate rocks, impacting casting. These rocks are impermeable but allow water to permeate through fissures. Rainwater, containing dissolved carbon dioxide, reacts with the rock, forming carbonic acid, which dissolves calcium carbonate as follows:

H2O + CO2 <—> H2CO3

H2CO3 + CaCO3 (insoluble) <—> Ca(HCO3)2 (soluble)

This solvent action gradually widens cracks, facilitating groundwater flow and filling cavities. On the limestone massif’s surface, grooves appear, forming lapiaz or lenar. Within, caves originate at various levels, interconnected by galleries that reach deep, basic levels.

Cave Formation

Lowering water levels in upper cavities leads to decompression and roof subsidence. Simultaneously, water saturated with Ca(HCO3)2 drips from the ceiling, releasing dissolved CO2 and precipitating CaCO3. This forms stalactites on the ceiling and stalagmites on the floor, which may eventually unite to create columns. The collapse of these galleries and internal cavities results in depressed areas known as torques or sinkholes.

Geological Risks

Seismic Risk

Earthquakes occur when accumulated tension along a fault line surpasses the friction within the plane. This releases immense energy, propagating through Earth’s interior as P (primary) and S (secondary) seismic waves, causing elastic deformation. Upon reaching the surface, these waves generate L surface waves, responsible for destructive geological phenomena.

Increased Risk

High-risk situations have escalated due to increased exposure. Many cities exhibit high vulnerability, as their buildings lack adequate occupant protection. These factors amplify earthquake danger, necessitating understanding population distribution, structural earthquake resistance, and earthquake distribution in time and space.

Assessment Scales

Different scales assess these phenomena: the Mercalli scale measures intensity, while others, like the Richter scale, quantify magnitude.

Intensity

Intensity degrees are defined by an earthquake’s effects. The EMS-98 scale, proportional and represented by Roman numerals, establishes 12 intensity degrees, ranging from I (imperceptible) to XII (total devastation).

Intensity Levels

Grade II earthquakes are perceptible to individuals at rest. Grade III causes indoor vibrations. Grade IV vibrates windows and doors. Grade V may slightly affect infrastructure. Grade VI causes small objects to fall and furniture to move. Grade VII witnesses falling cornices (ceilings). Grades VIII and IX can cause loss of balance, furniture overturning, and significant infrastructure and building damage. Grades X and XI affect all building types, bridges, and dams.

Magnitude

Magnitude represents the elastic energy released by an earthquake, measured using the Richter scale. Intensity scales are heavily influenced by population density and building vulnerability.

Associated Phenomena

Several phenomena associated with earthquakes can heighten their danger:

  • Soil Effect: Variation between nearby points due to geological and geometric configuration, dynamic properties of surface formations, or topography.
  • Landslides and Avalanches: Seismic instability causing land and snow or rock avalanches.
  • Tsunamis: Waves or wave series generated by a body of water being violently pushed by a vertical force, potentially exceeding 30 meters in height.
  • Liquefaction: Earthquakes cause poorly consolidated soft soils like sand or clay saturated with water to lose resistance and flow.
  • Floods: Dam ruptures caused by earthquakes.
  • Fires: Ruptured pipelines igniting fires.
  • Epidemics: Resulting from corpse decomposition and broken water pipes.
  • Infrastructure Damage: Affecting telecommunications, highways, etc.

Volcanic Risk

High temperatures and pressures at great depths melt rocks, forming magma. This releases gases that expand, pushing material through cracks or vulnerable areas in Earth’s crust, ultimately reaching the surface.

Intensifying Factors

Factors intensifying volcanic hazard include:

  • Population Increase: Higher population density within a volcano’s sphere of influence increases exposure. Volcanoes offer fertile land, mineral resources, and geothermal energy, attracting human settlements since ancient times.
  • Danger Level: Determined by eruption type, volcano count, and eruption frequency.
  • Eruption Type: Dependent on magma’s physical and chemical characteristics.

Magma Types

Basic magmas (low in silica), being more fluid, generate calmer lava eruptions (Hawaiian type). Acidic magmas (rich in silica), being more viscous, trap gases, leading to explosive eruptions characterized by pyroclastic flows and burning clouds.

Associated Phenomena

Several phenomena associated with volcanic eruptions can significantly increase danger:

  • Lahars: Mudflows produced by the melting of snow and glacial ice.
  • Phreatic or Phreatomagmatic Eruptions: Originating from water-magma interaction.
  • Tsunamis: Occurring in areas exposed to the eruption.
  • Ground Movements: Stemming from instabilities caused by eruption-induced vibrations.

Flooding

Flooding, or the temporary inundation of dry areas, results from a sudden influx of water exceeding the usual amount. It can be caused by natural phenomena or human actions.

Natural Causes

Natural phenomena can be climatic (torrential rain, thaw, etc.) or geological, such as landslides or snowmelt.

Human-Induced Causes

Direct or induced human actions modify the natural hydrologic cycle, increasing exposure and vulnerability, primarily due to:

  • Water Infrastructure Failure: Typically dam breaches.
  • Industrial Facility Construction: Altering natural drainage patterns.
  • Aggregate Extraction: In floodplains of certain rivers.
  • Floodplain Over-Harvesting: Reducing water absorption capacity.
  • Urbanization: Significantly increasing flood risk by altering watersheds.
  • Public Works: Roads, railways, etc., disrupting natural water flow.

Gravitational Movements

Gravitational movements, also known as slope phenomena, occur when surface materials are pulled downward by gravity. These ground movements can manifest in various forms:

  • Rockfalls: Continuous falls of particles (songs and blocks) from canyon and mountain walls.
  • Landslides: Characteristic of solid mass movement along a displacement plane.
  • Mudflows: Fluid mud flows gliding through mountain canyons, common in arid areas.
  • Soil Creep: Individual particles move downslope relative to others, causing the entire surface mantle to decline. Originates from ground heating and cooling, alternating drying and wetting of the soil.

Human Exacerbation

Human actions can exacerbate the danger of these risks:

  • Valley Settlements: Increased exposure due to human settlements in narrow valleys where mudflows circulate. These fertile areas are often densely populated.
  • Deforestation: Reduced infiltration and increased runoff.
  • Artificial Embankments: Related to works like roads, altering natural slopes.
  • Material Accumulation: Debris, spills, etc., on slopes, increasing instability.
  • Over-Watering: Soil layer saturation promoting displacement.

Fossil Fuels

(coal, oil and natural gas) provide most of the energy we consume power because of its high heatIFIC, which comes from the large amount of carbon and hydrocarbons it contains. Adeams of being renewable, these fuels have one major drawback: its comubistion generates a large amount of air pollutants, primarily CO2, sulfur oxide and nitrogen, hydrocarbons, solid particles, etc.. COAL: Coal is a sedimentary organic rock that results from the transformations, by anaerobic bacteria, plant debris accumulated at the bottom of swamps, lagoons .. These microorganisms cause the decomposition of organic molecules from plants that are gradually enhanced in carbon (carbonization) and other products. To avoid this process possible, we need a rapid burial to avoid aerobic alteracoin plant debris. On occasion, the strata of coal are interspersed between layers of other kinds. Depending on the degree of carbonization is achieved puee Four types of carbons, which increases with the calorific content of coal: peat, lignite, and anthracite coals. If the carbon enrichment process continuesCan form graphite (pure carbon). OIL: Oil is a liquid water enso less dark in color and characteristic odor. This consists of a mixture of hydrocarbons found in the three states físicos.-Liquids: such as benzene, octane, form the principal.-Gas: methane and butane are stored in the basement to huge pressure and natural gas CONSTITUTE called. -solid: Asphalt and bitumen. / The oil is of orgáncico: usually formed from the massive death and marine plankton, due to sudden changes of t ª o salinity water. / Materai the transformation of the organic petóleo is an enrichment in carbon and hydrogen and a depletion in oxygen and nitrogen, which is possible in reducing environments where anaerobic bacteria can live DIXA responsible for fermentation. For this reason, deposits are petóleo impregnating pores and cracks in rock mass with high porosity and permeability of rocks called store.