Iberian Peninsula: Geological Formation & Relief

Geological Origin: Plate Movement

The relief units in the Iberian Peninsula are composed of layers of rock that have been folded or fractured. All these changes are caused by plate tectonics. The geological history of Spain is conditioned by the interaction of two plates: the Eurasian and African plates.

• Precambrian or Archaic Era

  (Started ~4 billion years ago) A set of lands emerged from the sea, with outcrops consisting of gneiss and slates in what are now the Central System and the Montes de Toledo. These were later eroded and covered by the sea. The Iberian Peninsula formed a vast geosyncline where materials were deposited.

• Primary or Paleozoic Era

  (Started ~600 million years ago) The first major orogeny occurred: the Hercynian orogeny. After this folding, the Hercynian landscape of Spain included:

  • Hesperian Massif

    Origin of the Meseta Central, Galician Massif, Sierra Morena, and parts of the Cantabrian Mountains (western peninsula).

  • Aquitaine Massif

    Origin of the Central Pyrenees.

  • Betic-Rif Massif

    Origin of the Sierra Nevada.

  • Ebro Massif

    Origin of the Ebro Depression.

  These massifs, composed of granite, slate, and quartzite, were separated by arms of the sea. Also, they were eroded, forming a plateau sloping towards the Mediterranean Sea.

• Secondary or Mesozoic Era

  (Started ~225 million years ago) A period of orogenic calm dominated, characterized by erosion and sedimentation. The sea acted as the main erosive agent through changes in sea level (transgressions and regressions).

• Tertiary or Cenozoic Era

  (Started ~68 million years ago) The Alpine orogeny occurred due to pressure between the African and Eurasian plates and the sinking of the Tethys Sea, transforming the landscape almost to its present state. It began in the northwest, expanded southwards, and caused Spain's major relief units to emerge. The Meseta Central began to tilt towards the West. Towards the end of this era, volcanic activity occurred in areas like Olot, Cabo de Gata, Campo de Calatrava, and Cabo de Palos.

  Depending on the rock materials involved, two main types of relief formed:

  • Jurassic Relief

    Occurs when folding acts on pliable materials, creating relief primarily formed by folds. E.g., Betic System, Catalan Coastal Range.

  • Germanic Relief

    Occurs when folding acts on hard, brittle materials, causing them to break and form relief characterized by faults, creating horst (uplifted blocks) and graben (downthrown blocks) structures. E.g., Central System.

  The Balearic Islands also arose during the Alpine orogeny, linked to the formation of the Betic System and Catalan Coastal Range.

• Quaternary Era

  (Started ~1-2 million years ago to present) Although no major orogeny occurred, existing reliefs were modified by glacial and fluvial erosion, leading to features like river terraces and floodplains. Coastlines were shaped, forming features like the Mar Menor and the Albufera of Valencia. The final tilting of the peninsula towards the Atlantic Ocean formed the Galician rias.