Landform Classification: A Comprehensive Guide to Terrain
1. Landscape and Relief
The appearance of the Earth’s surface, excluding biotic elements, is represented in topographic maps.
1.1. Descriptive Landform Classification
Landforms are classified based on their appearance:
- Mountain: An isolated relief with a significant gap between its base and peak.
- Hill: An isolated relief with slight unevenness.
- Gorge/Throat: A narrow valley with steep walls.
- Plateau: An isolated, flat-topped topography.
- Terrace: A step-like relief.
1.2. Landform Classification by Formation Process
Landforms are classified by their formation process:
- Mountain: A prominent relief formed by folding or volcanic activity. A ridge is a line of mountains.
- Cerro Witness: An isolated peak representing a former higher elevation.
- Terrace: A fragmented, tiered area formed by successive river interlocks.
- Anthropogenic Landform: Created by human activity (e.g., embankments, plains).
2. Main Terrain Types
Oceanic Crust: Composed of basalt, forming ocean basins and covered by water.
- Abyssal Plains: Vast submarine plains.
- Mid-Ocean Ridges: Alignments of volcanoes with intense volcanic fissures.
- Isolated Volcanic Reliefs/Volcanoes: Isolated points of volcanic activity; above water, they form volcanic islands.
- Island Arcs: Volcanic ridges emerging from the sea, forming islands.
Continental Crust: Composed of granite and metamorphic rocks; thicker, less dense, and forms most continents.
- Peneplains: Vast plains formed by erosion, sloping towards the sea.
- Cordilleras: Mountain ranges formed by folding or volcanic activity.
- Rifts: Elongated depressions formed by the breaking, stretching, and subsidence of the continental crust.
- Continental Shelf: Part of the continental crust covered by the sea; epicontinental seas can be found here.
- Slopes: The edges of continents, between the continental shelf and oceanic crust.
3. External Geological Processes: Weathering and Erosion
Weathering: The disintegration of rocks by geological agents, altering their fractures and minerals.
Erosion: The removal of material by geological agents; it erodes reliefs and shapes landscapes.
Transport: The movement of materials by geological agents.
Sedimentation: The accumulation of materials in sedimentary basins.
3.1. Weathering
Mechanical Weathering:
The breaking of rocks due to various processes:
- Gelifraction: Water freezing in rocks, expanding and breaking them.
- Termoclastia: Breaking due to high temperatures.
- Decompression: Expansion and cracking due to pressure differences.
Chemical Weathering:
The disintegration of rocks by chemical alteration of minerals:
- Oxidation: Reaction of oxygen with minerals.
- Dissolution: Minerals dissolving in water.
- Carbonation: Reaction of minerals with water and CO2.
- Hydrolysis: Reaction of minerals with water ions.
Biological Weathering:
The breaking or chemical alteration of rocks by living beings.
3.2. Erosion
Geological agents eroding relief produce:
- Removal of debris (rock fragments).
- Characteristic land surface modeling.
- Peneplain formation.
- Continental mass redistribution (weight loss in mountains, increase in lower areas).
4. External Geological Processes: Transport and Sedimentation
4.1. Transport Parameters
- Energy: An agent’s ability to move geological sediments.
- Clast Selection: High-energy agents don’t select clasts by size.
- Sediment Maturation: Changes in sediment composition, shape, and size during transport.
4.2. Transport Forms
- Contact with the bottom: When a river cannot keep sediments suspended (rolling, saltation, dragging).
- Without touching the bottom: Fine materials are suspended, floating, or in solution.
4.3. Sedimentation
Whether sediments are transported or accumulated depends on the site:
- Lifting Process: Subjected to erosion, may be transported again.
- Collapse/Subsidence Process: Eventually transformed into sedimentary rocks.
4.4. Sediment Accumulation
Sediment accumulation can result from:
- Decanting: Clasts fall to the bottom when the current stops.
- Kinetic Accretion: Clasts encounter an obstacle and accumulate.
4.5. Clast Management; Sedimentary Structures
Sedimentary structures include:
- Stratification: Layering.
- Lamination: Layering of a few millimeters.
- Settling: Sorting of clasts by size.
- Cross-Lamination: Intersecting layers.
5. Watersheds and Sedimentary Environments
Sedimentary basins are large areas of land subsidence.
5.1. Sedimentary Environments
Continental Sedimentary Environments:
(Based on geological agent)
- River: Related to rivers.
- Torrential: Related to fast-flowing waters and streams.
- Glacial: Related to glaciers.
- Wind: Deposition by wind.
- Karst: Produced by water dissolving certain rocks.
Marine Sedimentary Environments:
(Based on geographical position and characteristics)
- Coastline: Dominated by wave action.
- Reef: Formed by corals, sponges, etc., at shallow depths.
- Continental Platform: Wide areas with various sedimentary environments.
- Continental Slope: Fine materials accumulate, brought by turbidite flows to the abyssal plain.
Transitional Sedimentary Environments:
(Between sea and land)
- Beaches: Areas with waves and currents, accumulating sand and gravel.
- Deltas: River sediment influenced by waves.
- Estuaries: Rivers with strong tidal influence.