Landscape Evolution: Relief, Weathering, and Erosion
7A Landscape and Relief Evolution
Relief is the aspect of the land surface shaped by biotic factors. Relief maps, or topográficos, represent this aspect. Classification uses descriptive and interpretive criteria.
Descriptive Classification
Relief forms are classified by their appearance.
Interpretive Classification
Based on the processes leading to relief forms.
Weathering and Erosion
Weathering: The breakdown of rocks due to environmental agents, fracturing and changing their minerals.
Erosion: The evacuation of material by geological agents, resulting in relief erosion and landscape modeling.
Transport: The movement of materials by geological agents, continuing fragmentation and alteration.
Sedimentation: The accumulation of materials in depressed areas of the Earth’s surface, such as sedimentary basins.
Weathering
Can be:
Mechanical Weathering
Breakdown of rocks due to tensions:
- Xelifraction: Water freezing and expanding in rock crevices.
- Thermoclasty: Breaking of rocks exposed to intense sunlight.
- Decompression: Expansion and cracking in rocks formed at great depth.
Chemical Weathering
Disintegration of rocks due to chemical alteration of minerals:
- Oxidation: Oxygen reacts with minerals like mica.
- Dissolution: Minerals dissolve in water, such as carbonates, sulfates, and chlorides.
- Carbonation: Reaction of minerals with water containing CO2.
- Hydrolysis: Alteration of minerals by reacting with water ions.
Biological Weathering
Breakage or chemical change by living beings.
Erosion
Geological agents erode relief and produce various effects:
- Removal of debris: Rock fragments produced by weathering.
- Modeling features on Earth’s surface: Geological agents move clasts, creating recognizable relief forms.
- Peneplain formation: Large, flat areas resulting from long-term erosion.
- Redistribution of continental mass: Erosion reduces weight in mountainous areas and increases it in lower parts.
Transport and Sedimentation
Transport Parameters
- Energy: The ability of a geological agent to mobilize sediments.
- Clast Selection: High-energy agents carry unselected clasts of various sizes.
- Sediment Maturation: Changes in composition, shape, and size during transport.
Means of Transport
- Contact with the bottom: Clasts move by attrition or saltation.
- Without touching the bottom: Fine clasts transported in suspension or solution.
Fluvial Modeling by Rivers
Rivers originate from three basic relief forms:
- U-shaped valleys: Formed when a river has high erosive capacity and cuts deep into the ground.
- Flat-bottomed valleys: As a river loses speed, it forms meanders, creating broader, flat-bottomed valleys.
- Peneplains: Formed when rivers expand their valleys and join, redistributing mass.
Erosion can create:
- Witness hills: Isolated residual reliefs with flat tops.
- Terraces: Represent successive enlargements of valleys in rising areas with fluvial erosion networks.