Geological Evolution and Relief of the Iberian Peninsula

1. Characteristics of the Iberian Peninsula Relief

Solid Form

The Iberian Peninsula’s solid form is characterized by its significant width from west to east coasts and relatively straight coastlines.

High Average Elevation

The high average elevation results from the presence of high mountains and an extensive central plateau (Meseta Central).

Peripheral Mountainous Provision

The plateau’s inland location, away from the sea’s influence, creates a stark contrast between the coastal and inland areas.

2. Morphostructural Units

Sockets

Sockets are plains or plateaus formed during the Paleozoic Era, either primarily or as a result of erosion of older mountain ranges.

Ancient Massifs

These mountains were formed in the Tertiary Period by the uplift of basement blocks due to the pressures of the Alpine Orogeny.

Fold Mountains

Large mountain ranges formed during the Alpine Orogeny in the Tertiary Period by the folding of sedimentary materials deposited in the seas during the Mesozoic Era.

Sedimentary Basins

Sunken areas or depressions formed in the Tertiary Period and filled with sediments, primarily clay and limestone.

3. Geological Evolution of the Iberian Peninsula

Archean and Precambrian Eras (4000-600 Million Years Ago)

A band of arcuate mountains, composed of shale and gneiss, emerged from the sea. These mountains encompassed most of Galicia, with isolated elevations appearing in the central system and the Montes de Toledo.

Paleozoic Era (600-225 Million Years Ago)

The Hercynian Orogeny occurred during this era. Hercynian mountain ranges, composed of siliceous materials, emerged from the seas that covered much of the peninsula. The Hesperian Massif rose to the west, undergoing erosion and becoming a primary peneplain or plateau sloping towards the Mediterranean. Other massifs, such as the Aquitaine, Ebro, and Betica-Rif, also appeared.

Mesozoic Era (225-68 Million Years Ago)

A period of calm prevailed, characterized by erosion and sedimentation. The Hercynian reliefs continued to erode. Sedimentation, primarily limestone, occurred in two sea-covered areas. A thin layer of sediment was deposited on the eastern edge of the plateau.

Tertiary Period (68-1.7 Million Years Ago)

The Alpine Orogeny caused significant changes to the Iberian relief:

  • Alpine ranges formed due to the folding of materials deposited in basins between the ancient massifs.
  • Pre-alpine depressions, such as the Ebro and Guadalquivir basins, formed parallel to the new ranges.
  • The plateau was affected by folding, forming mountain ridges on its eastern and southern edges. The plateau’s base experienced fracturing and faulting.

Quaternary Period (1.7 Million Years Ago to Present)

Glaciation and the formation of river terraces were the most significant events. Glacial cirques formed at the heads of valleys. Valley glaciers, or rivers of ice, formed when the ice in the cirques became thick enough. River terraces, flat raised bands along river margins, formed due to Quaternary climatic alternations.

4. Rock Types and Relief

4.1 Silica Area

Composed of ancient rocks from the Precambrian and Paleozoic eras, located in western Iberia, with ramifications extending to the Cantabrian Mountains, Central System, Montes de Toledo, and Sierra Morena. Granite is the predominant rock, creating various relief forms through weathering.

4.2 Limestone Area

Composed of Mesozoic-era rocks, extending through the Pre-Pyrenees, Basque Mountains, eastern Cantabrian Mountains, Iberian System, Catalan Coastal Range, and Subbaetic Range. Limestone is the predominant rock, featuring:

  • Lenar: Sinkholes or grooves separated by sharp partitions, formed by runoff.
  • Gorges: Narrow, deep valleys with steep slopes, carved by rivers.
  • Poljés: Elongated depressions with horizontal bottoms and steep sides.
  • Sinkholes (Torcas): Large cavities formed where water stagnates.