Geological Processes and Landform Evolution

Posted on Mar 29, 2025 in Geology

Geological Processes

External Geological Processes

Weathering

Weathering is the disintegration of rocks due to external agents. It alters geological fractures and minerals. There are two main types:

  • Gelifraction (Frost Wedging): Water expands upon freezing, widening cracks within rocks.
  • Thermoclastia: Rock rupture due to intense sunlight exposure.
  • Decompression: Expansion and fracturing of rocks formed at great depth.

Chemical Weathering

Chemical weathering is the disintegration of rocks due to chemical alteration of their minerals.

  • Oxidation: Oxygen from the air or dissolved in water reacts with certain minerals, forming oxides.
  • Dissolution: Affects minerals soluble in water (carbonates, sulfates, and chlorides).
  • Hydrolysis: Alteration of minerals reacting with H+ and OH- ions from water.

Erosion

Geological agents erode the Earth’s surface, causing various effects:

  • Debris Evacuation: Removal of clasts (rock fragments) produced by weathering.
  • Land Surface Modeling: Shaping of landforms.
  • Peneplane Formation: Creation of extensive, virtually flat surfaces due to continuous erosion over millions of years.
  • Redistribution of Continental Mass: Movement of weathered material across continents.

Transport and Sedimentation

Transport: Characterized by three parameters:

  • Energy: The capacity of a geological agent to move sediments.
  • Clast Selection: Related to the energy of the transporting agent.
  • Sediment Maturation: Changes in sediment composition and form during transport.

Modes of Transport:

  • Contact with the Bottom (Clasts): Rolling, dragging, or saltation.
  • Without Touching the Bottom (Clasts): Suspension, flotation, or dissolved transport.

Sedimentation: The accumulation of transported materials.

  • Sedimentary basins are areas where sinking or subsidence leads to sediment accumulation.

Fluvial Modeling (River Modeling)

Creates V-shaped valleys, flat-bottomed valleys (meandering), and peneplanes.

  • Hills: Isolated residual reliefs.
  • Terraces: Stepped landforms representing successive valley deepening and widening.

Fluvial Sediment Transport

Rivers cause intense sediment maturation, reducing clast size, rounding them, and removing unstable minerals.

Torrential Modeling

  • Xaragalls (Gullies): Deep, narrow channels in the ground.
  • Ravines: Deep, V-shaped valleys formed by intense erosion in steep areas.
  • Ramblas (Dry Riverbeds): Wide channels that can remain dry for years.

Sedimentary Structures

  • Dejection Cones: Small accumulations on steep slopes formed by small streams.
  • Alluvial Fans: Very large accumulations of sediment.
  • Pediments: Result from the merging of several alluvial fans.

Wind Modeling

  • Dunes: Accumulations of sand that can be crescent-shaped, straight, or ridged, often found in deserts (ergs).

Coastal Modeling

Stronger waves cause more intense abrasion by sand and gravel. Two main erosive processes:

  • Cliff Retreat: Waves undermine cliffs, causing blocks to fall, creating an abrasion platform.
  • Crushing and Washing of Materials: Fragmentation of rocks.

Coastal Sediment Transport

  • Forms beaches, spits, bars, and littoral barriers (creating lagoons and coastal marshes).

Karst Modeling

Dissolution of rocks, both on the surface and underground.

Determinants of Landscape Modeling

Landscape modeling is influenced by:

  • Climate: Arid, temperate, polar, or high-mountain climates.
  • Tectonics: Faults and fractures.
  • Land Uplift: Vertical movement of the Earth’s surface.
  • Lithology: Rock type influences residual reliefs.
  • Anthropogenic Factors: Human activities.