Spanish Plateau: Relief and Geological Features

The Spanish Plateau: Inner Mountain Ranges and Ridges

The Plateau, a dominant feature of the Spanish landscape, occupies the center of the Iberian Peninsula and accounts for 45% of Spain. During the Alpine movements, the plateau's block fractured into two parts:

The Northern Sub-Plateau

With an average altitude of 800-850m, the northern sub-plateau extends from east to west and is drained by the Duero River network. Rivers on this plateau have carved their way through the landscape, creating a varied topography. The presence of hard Hercynian materials has led to the formation of pits and gorges.

The Southern Sub-Plateau

Averaging 500-700m in altitude, the southern sub-plateau is divided into two parts by the Toledo Mountains. It is characterized by the Tagus and Guadiana river basins. This sub-plateau is slightly inclined towards the Atlantic, where its rivers eventually flow. The vast expanse of La Mancha, a significant plain in Spain, extends across this region.

Units Related to the Plateau

Several distinct units can be identified within the plateau:

• The Old Paleozoic Socket: Outcrops on the western side of the plateau, forming a narrow strip of peneplain from Zamora and Salamanca to the Portuguese coast. This peneplain contains remnants of ancient materials like granite, slate, and quartzite, which stand out due to their toughness.
• The Sedimentary Basins: On the eastern side of the plateau, the old socket is buried under enormous deposits of materials that form sedimentary basins. These materials include sand, clay, chalk, and marl in the lower strata, while the upper strata are composed of limestone formed by the accumulation of organic remains. These materials have given rise to a landscape of moors, fields, and hills.
• The Inland Mountain Ranges of the Plateau: Formed during the Tertiary Alpine movements, these mountain ranges resulted from the fracturing and displacement of the old socket blocks.
• The Mountain Ridges of the Plateau: These ridges formed during the Alpine movements when pressure on the Earth's crust caused the edges of the old socket to fracture. The materials deposited along these edges were bent and folded, creating the mountain ranges that surround the plateau.

Interior Mountains and Plateaus

The Central System and the Toledo Mountains, running from east to west, are part of the former base. They are composed of granite, slate, and gneiss. These mountains present smooth, rounded shapes, with quartzite ridges standing out due to their resistance to erosion.

The Central System

The Central System divides the plateau into two halves and is formed by a series of mountain ranges with considerable altitude: Somosierra, Guadarrama, Gredos, Gata, and the Serra da Estrela in Portugal. The highest peak is Mansur (2592m) in the Sierra de Gredos. Between the mountain ranges of the Central System are sunken blocks that form open valleys and passes, facilitating communication even in winter (e.g., Somosierra).

The Montes de Toledo

The Montes de Toledo divide the southern sub-plateau into two parts, acting as a watershed between the Tagus and Guadiana basins. These mountains reach altitudes of up to 1400m and include the Montes de Toledo, Sierra de Guadalupe, and San Pedro Montanez. Transverse corridors facilitate communication across these ranges.

Mountainous Borders of the Plateau

The main mountain ranges surrounding the plateau are the Galician-Leonese Massif, part of the Cantabrian Mountains, and a large part of the Sierra Morena. These ranges form a complex system of blocks.

Galician-Leonese Massif

Part of the northwestern peninsular relief, the Galician-Leonese Massif is a mountainous area of approximately 200km per side. It includes Galicia, the western mountains of Asturias, the mountains of Leon, and the Sierra da Cabrera. Its peaks generally do not exceed 500m, except for Teleno and Trevinca, which reach 2000m. This massif is a fragment of the oldest relief on the peninsula. Subsequent movements of the Earth's crust formed a series of elevated and sunken blocks, creating a staircase-like landscape where rivers have carved deep valleys.

The Cantabrian Mountain Range

The Cantabrian Mountain Range forms an energetic line with significant elevation changes, particularly accentuated on its northern, Cantabrian facade. It is characterized by asymmetry between its western and eastern parts.

• Western Part: The Asturian Massif is a series of dislocated Paleozoic blocks. This area contains Spain's largest coal deposits, along with various metals such as iron.
• Eastern Part: The mountains in the eastern part are lower in altitude. The relief is dominated by folded sedimentary materials, including abundant sandstone and limestone.