Landforms: Classification and Characteristics
Relief is the aspect of the land surface, influenced by the biota.
Descriptive Classification of Landforms
Landforms are classified by their appearance. This classification uses terms such as:
- Mountain: Isolated relief that has a large gap between its base and the surrounding region.
- Hill: Isolated relief with little difference in elevation.
- Valley: A generally low-lying area that has narrow, steep walls on either side.
- Plateau: Isolated, elevated, flat relief.
- Terraces: Graduated relief.
Major Landforms
The land area could be differentiated into two zones:
- The oceanic crust: Composed of basalt, it forms the ocean basins and is covered by water.
- Continental crust: Made of granite and metamorphic rocks, it is thicker and less dense than the oceanic crust.
Characteristic Reliefs of the Oceanic Crust
- Abyssal plains: Extremely extensive submarine plains with an average depth of 4500 m.
- Mid-ocean ridges: Alignments of volcanoes with intense fissural volcanic activity.
- Isolated volcanic reliefs: Result from concrete volcanic activity.
- Trenches: Extended furrows where very large depths are reached; these are areas of intense seismic activity.
- Volcanic island arcs: Mountain ranges that emerge from the sea and form islands; the volcanic activity is related to the sinking of the crust that is produced in the trenches.
Characteristic Reliefs of the Continental Crust
- Peneplains: Lowlands resulting from erosion produced by geological agents.
- Mountain ranges: Alignments of mountains formed by the folding of materials.
- Rift: Elongated depressions formed by the breaking, distension, and depression of the continental crust along large fractures.
- Continental shelf: Part of the continental crust covered by sea.
- Slopes: They represent the edges of continents and cover the areas of hillside located between the continental shelf and oceanic crust.
Weathering
Weathering is the breakdown of rocks and is produced in several ways:
Mechanical Weathering
It consists of a breakdown of rocks due to tensions that can originate by different processes:
- Gelifraction: The wedging action that occurs when water freezes and swells within the crevices of rocks.
- Thermoclasty: The breakdown of rocks exposed to intense sunlight because the outside heats and expands more than the inside.
- Decompression: The expansion and cracking that is produced in rocks formed at great depth, such as granite.
Chemical Weathering
Chemical Weathering is the breakdown of rocks due to the chemical alteration of minerals. It can occur by:
- Oxidation: Oxygen from the air, or that is dissolved in water, reacts with some minerals such as mica.
- Dissolution: Affects minerals that dissolve in water, such as carbonates and chlorides.
- Carbonation: The reaction that occurs in some minerals, such as calcite, in contact with water that has CO2 in solution.
- Hydrolysis: The alteration of minerals to react with the ions.
Biological Weathering
Biological Weathering is the breakage or chemical alteration of rocks due to the action of living beings.
Erosion
The geological agents of erosion and relief produce various effects on the surface:
- Drainage from waste: Rock fragments or clasts produced by weathering and accumulated at the foot of the escarpment.
- Modeling the Earth’s surface features: During the erosion, geological agents may also start clasts of rocks producing a form of relief.
- Formation of peneplains: Large flat surfaces, a result of erosion produced by geological agents.
- Redistribution of the mass of the continents: Erosion, along with the transport of sediment and subsequent deposition in sedimentary basins.