Landforms: Classification, Relief Types, and Geological Processes

Posted on Jan 7, 2025 in Geology

Landform Classification and Interpretation

1 – When we observe a landscape, we perceive different elements simultaneously. The relief is the aspect of the Earth’s surface, regardless of biotic elements.

Descriptive Classification of Landforms

Landforms are classified by their appearance:

  • Mountain: Isolated relief with a large gap between its base and top.
  • Cerro: Isolated relief with little unevenness.
  • Gorge or Throat: Narrow valley bottom featuring steep walls on either side.
  • Plateau: Isolated, flat-topped topography.
  • Terraces: Stepped relief.

Classification by Formation Process

This classification is based on the process that has led to the formation of the relief:

  • Mountain: Relief that stands out from the surrounding areas, formed by the folding of materials or by volcanic activity.
  • Cerro Witness: Isolated relief whose summit is at the height of the surrounding area in the past.
  • Terraces: Fragmented and tiered zone, consisting of successive river engagements.
  • Anthropic Modeling: Relief produced by human activity, such as an embankment, a plain, or terracing.

Main Land Reliefs

2 –

Oceanic Crust (OC)

Composed primarily of basalt, it covers ocean basins and is almost entirely covered with water.

Continental Crust (CC)

Formed mainly by granite and metamorphic rocks, it is thicker and less dense than the oceanic crust, forming the continents.

Reliefs Characteristic of the Abyssal Plains (OC)

  • Submarine Plains: Very extensive plains with an average depth of about 4500m.
  • Oceanic Ridges: Alignments of volcanoes with intense volcanic fissures.
  • Isolated Volcanic Reliefs: Isolated volcanoes resulting from volcanic activity over time.
  • Oceanic Trenches: Elongated grooves reaching vast depths, with significant seismic activity.
  • Volcanic Island Arcs: Cordilleras emerging from the sea, forming islands, with volcanic activity related to the collapse of the cortex in the trenches.

Reliefs Characteristic of the Continental Crust (CC)

  • Peneplains: Vast plains resulting from erosion caused by geological agents.
  • Cordilleras: Aligned mountains.
  • Rifts: Elongated depressions formed by the rupture, strain, and subsidence of the crust along large fractures.
  • Platforms: Part of the continental crust covered by the sea; epicontinental seas can be found here.
  • Continental Slopes: Represent the edges of continents, covering sloping areas between the continental shelf and the oceanic crust.

External Geological Processes

3 –

Weathering

Disintegration of rocks due to the effect of environmental agents that alter and fracture their minerals.

Various Forms of Weathering:

Mechanical Weathering

Breaks rocks due to tensions arising from different processes:

  • Gelifraction: Action of a wedge where water freezes and increases in volume within rock crevices.
  • Thermoclasty: Rupture of rocks exposed to intense heat.
  • Decompression: Expansion and cracking that occurs in rocks formed at great depths.
Chemical Weathering

Fragmentation of rocks due to chemical alteration of their minerals:

  • Oxidation: Oxygen reacts with some minerals, causing oxidation.
  • Dissolution: Minerals dissolve in water.
  • Carbonation: Reaction that occurs in several minerals upon contact with water that has dissolved CO2.
  • Hydrolysis: Alteration of minerals by reacting with H+ and OH- of water.
Biological Weathering

Rupture or chemical alteration of rocks by the action of living beings.

Erosion

Removal of materials by geological agents.

Transport

Transportation of materials by geological agents.

Forms of Transport:

  • In contact with the bottom: By rolling or saltation entrainment.
  • Without touching the bottom: Suspension, flotation, or in solution.

Sedimentation

Accumulation of material on the Earth’s surface: sedimentary basins.

Sediment Accumulation:

  • Decanting: Fall or precipitation of clasts at the bottom of the medium in which they were.
  • Kinetic Accretion: Occurs when clasts being transported face an obstacle and stop, accumulating on one another.

Sediment Arrangement:

  • Stratification: Provision of sediments in layers several meters thick.
  • Lamination: Provision in thin layers.
  • Grading: Management by size of the clasts.
  • Cross-Lamination: Disposition in sheets.