Key Concepts in Geomorphology and Soil Formation

Posted on Dec 11, 2024 in Geology

1. Vocabulary:

  • Marine Transgression: The advance of the sea over a territory not previously occupied by it, caused by coastal subsidence or rising sea level. The transgression is accompanied by the deposition of marine sediments over that territory.
  • Evapotranspiration: The loss of moisture from the Earth’s surface due to the sun, plant transpiration, and soil evaporation.
  • Leaching: The process of rainwater carrying soluble materials from the soil’s surface horizons to deeper horizons. It is stronger with more intense rainfall.
  • Erosion: The wearing away of rock fragments, which are then transported to another location.
  • Acid Rain: Sulfur dioxide and nitrogen oxide emissions mixed with water vapor, causing alterations in water, vegetation, soil, and buildings.

2. Choose One:

a) Morphostructural Relief Units of the Iberian Peninsula:

  • A) Sockets: Plains or plateaus formed in the Paleozoic Era (Primary Era) after the razing of mountain ranges from the primary orogeny.
    • Materials: Siliceous rocks (granite, slate, quartzite, and shales).
    • They are very rigid. When facing new shifts, they do not fold but fracture or break.
    • They occupy large areas in the western half of the peninsula.
  • B) Old Beds: Mountains formed in the Tertiary Era by the rise of a new socket block due to the Alpine orogeny.
    • Materials: Paleozoic.
    • They have soft, rounded peaks, being elevated erosion surfaces.
    • Examples: Sistema Central, Montes de Toledo, Galician Massif, part of the western Cantabrian Mountains.
  • C) Fold Mountain Ranges: Large mountain ranges that emerged with the Tertiary orogeny, formed by the folding of sedimentary materials, mainly limestone, deposited in large trenches during the Secondary Era.
    • Intermediate Cordilleras: Formed by the folding of materials deposited on the edges of the bases: the Iberian and Cantabrian Cordillera Oriental Party.
    • Alpine Cordilleras: Formed by the folding of materials deposited in geosynclines or long and deep trenches: Pyrenees, Betic Cordilleras.
    • Folding ridges have steep slopes and sheer forms because, given their relative youth, they have not been smoothed by erosion.
  • D) Sedimentary Basins or Depressions: Hollow areas formed in the Tertiary Era that were filled with sediments.
    • Materials: Limestone, clay, sandstone, or marl.
    • Basin formed by the collapse of a block of a base: Tajo, Duero, Guadiana.
    • Pre-Alpine depressions: On both sides of the Alpine ranges: Depression of the Ebro, Guadalquivir Depression.
    • Formed after the Alpine orogeny or clogging of waste trenches on both sides of the new ranges.

b) Jurassic Relief:

Ridges formed in youth, composed of alternating convex folds (anticlines) and concave folds (synclines). Anticlines formed in cluses (valleys perpendicular to the top) due to water erosion and combes (anticlinal valleys parallel to the summit). The emptying of the anticlines, very fast once the erosion undermines the hard surface layer, leaves hanging synclines (old synclinal valleys) with an inversion of relief. The erosion of anticlinal valleys leaves the anticline in the lower stratum in highlight, since it is an exhumed anticline, and the erosion cycle restarts. Jurassic relief can be found in the Iberian System, the Cantabrian Mountains, the Pyrenees, and the Betic Cordilleras.

Soil Formation

Soils are heterogeneous. Horizons appear to be differentiated by color, texture, vertical management structure, etc. The set of horizons in a soil is called the soil profile.

  • Soil Profile: The vertical section of a soil, starting from the surface and reaching the bedrock at depth.
  • In a mature soil, i.e., well-formed, four horizons can be observed: A, B, C, and D.
  • Horizon A: The topsoil where cultivation occurs.
    • It is characterized by a dark color due to the large amount of organic matter it contains.
    • An A0 horizon can be identified if there is a thin layer formed by organic matter without disruption or partially altered.
    • Remnants of animals, leaves, twigs, and dung can be seen.
  • Horizon B: Lighter in color because salts carried over from the upper horizon precipitate in this stretch of soil.
  • Horizon C: Consisting of fragments of parent rock, more or less large, surrounded by fine particles that may come from the upper horizons.
  • Horizon D: Formed by unchanged bedrock.

Limestone Areas

Formed by sediments from the Secondary Era folded during the Tertiary Era. The reliefs are as follows: Pre-Pyrenees, Montes Vascos, Eastern Sector of the Cantabrian Mountains, Iberian System, part of the Cordillera Costero-Catalana, Subbética Mountains. The dominant rock is limestone. Limestone is hard and cracks or breaks, forming joints, but it dissolves with rainwater, especially when it penetrates through the joints. The dissolution of limestone by water generates a complex relief: karst relief.

Karst Relief Features:

  • Sinkholes or Lenar: Furrows or grooves opened in the rock by water, taking different forms:
    • Sinkholes of ways: Open furrows for water runoff on slopes (or on a level surface with cracks).
    • Linear sinkholes: Defined by narrow rows, separated by sharp walls.
    • Sinkholes in tables: Characterized by the existence of extensive flat surfaces between the grooves.
    • Sea of stone: Chambers separated by sharp walls, where water is retained and filtered, digging a deep hollow in the rock.
  • Gorges, canyons, or ravines: Narrow and deep valleys, surrounded by abrupt slopes, caused by rivers.
  • Polje: Closed depressions or valleys with a horizontal background. They are wholly or partly traversed by running water that suddenly disappears down a drain or ponor and continues to circulate underground. Occasionally, they flood and become a lake.
  • Sinkholes or torques: Cavities that originate in areas where water stagnates. They can take many forms (circular, funnel, well) and join with other local chambers, creating depressions called uvalas, making circulation difficult.
  • Caves: Created when water infiltrates cracks in the limestone terrain and circulates underground. They usually contain stalactites and stalagmites (formed from calcium carbonate-rich water).
  • Chasms: Narrow openings that connect the surface with underground galleries.