Iberian Peninsula Relief Features and Geological Evolution
Item 2: Iberian Peninsula Relief Features
The Iberian Peninsula exhibits three primary features:
- Massive Form: The peninsula’s substantial width from west to east, with minimal coastal irregularities.
- High Average Altitude: An average elevation of 660 meters due to the presence of high mountains and an extensive upland core, the Plateau, with altitudes between 600 and 800 meters.
- Peripheral Mountainous Terrain: Surrounding the Plateau, curbing maritime influence and creating a stark contrast between the coast and the interior.
Geological Evolution of the Iberian Peninsula
The peninsula’s geological evolution unfolded in three stages:
Paleozoic Era (600-225 million years)
The Hercynian orogeny occurred, forming cordilleras composed of siliceous material (e.g., granite). The Hesperic Massif, Aquitaine, Catalano-Balearic, Ebro Massif, and Betic-Rif beds emerged.
Mesozoic Era (225-68 million years)
Erosion and sedimentation dominated, primarily with limestone material. The Pinera and Béticas areas arose.
Tertiary Period (68-17 million years)
The Alpine orogeny took place, resulting in:
- Alpine ranges: The Pyrenees and Andalusian ranges.
- Prealpine depressions: The Ebro and Guadalquivir depressions.
- Plateau: Shifted towards the Atlantic, forming eastern and southern mountain ridges. Fractures and faults uplifted blocks, creating the Massif Galaico, parts of the Cantabrian Mountains, the Central System, and Montes de Toledo. Sunken depressions formed interior sub-plateaus. Volcanic activity occurred (e.g., Cabo de Gata).
Quaternary Period (17 million years to present)
Glaciers and river terraces formed. Glaciers affected the highest ranges (Pyrenees, Cantabrian, Central System, Iberian System, Sierra Nevada). Two types of glaciers existed:
- Cirque glaciers: Ice accumulations at valley heads, forming small lakes upon melting.
- Valley glaciers: Ice rivers formed from substantial cirque accumulations. Only the Pyrenees were covered with thick ice.
River terraces are plain bands along river margins, notably formed by the Douro, Tagus, Guadiana, Guadalquivir, and Ebro rivers.
Rocky Areas and Relief Types
Silica Area
Composed of ancient Precambrian and Paleozoic rocks, located in the western peninsula, western Cantabrian Mountains, Central System, Montes de Toledo, and Sierra Morena. Granite is prevalent, leading to granite relief:
- High mountain areas: Water freezes in rock fractures, causing breakage and accumulation at mountain bases.
- Less exalted areas: Forms depend on fracture disposition, creating domes or balls.
Limestone Area
Composed of Mesozoic and/or Tertiary rocks, forming an inverted Z across the Pyrenees, Basque mountains, eastern Cantabrian Mountains, Iberian System, Coastal-Catalan range, and Subbética range. Limestone leads to karst relief:
- Sinkholes or Lenar: Small cavities separated by partitions, accumulating water.
- Gorges: Deep, narrow valleys formed by rivers.
- Polje: Elongated depressions with steep slopes, potentially forming lakes.
- Dolinas: Large cavities formed by water accumulation, circular or funnel-shaped, sometimes forming uvalas.
Clay Area
Composed of Tertiary and Quaternary sedimentary rocks, located in the northern and southern sub-plateau basins, Ebro and Guadalquivir depressions, and Mediterranean coastal plains. Clay generates two relief types:
- Plains: Rivers create gently rolling plains by separating horizontal structures.
- Badlands: Torrential rains erode soil in arid areas, creating gullies and rugged topography resembling small mountains.