Spain’s Diverse Landscapes: Siliceous, Limestone, Clay
Siliceous Spain
Silicea consists of ancient rocks from the Precambrian and Primary eras. Therefore, they are in the western mainland and have branches to the western part of the Cantabrian Mountains, the Central System, the Montes de Toledo, and Sierra Morena. There are outcrops in the axial zone of the Pyrenees, the Sistema Ibérico-Catalan coastal mountain range, and the Penibaetic System. In this area, the rock is predominantly granite. The modeling is determined by the characteristics of this crystalline and rigid rock, sensitive to different forms of change. In high mountain areas, the rocks are broken by water seeping through the fractures and then freezing, so ice presses in rock fissures and ruptures them. They form sharp ridges, steep and jagged, and rocky accumulations of rock fragments at the foot of the lower tiers. Rounded mountains appear. Other typical forms are scree.
Limestone Spain
It is formed by sediments from the Secondary era, folded during the Tertiary. The limestone soils form an inverted “Z” spanning the Pre-Pyrenees, the Basque mountains, the eastern sector of the Cantabrian Mountains, the Iberian System, part of the Catalan Coastal Range, and the Subbaetic Range. The prevailing rock is limestone, a hard rock that fractures, forming striking cracks or joints, but it is easily dissolved in rainwater. This also forms a karst relief:
- Gorges, pockets, or sickles: Narrow, deep valleys, surrounded by steep slopes, caused by rivers.
- Caves: Created by water seeping through the fissures of limestone. They usually form stalactites and stalagmites.
- Sinkholes or dolines: Cavities that originate in areas where water stagnates.
- Chasms: Narrow openings that communicate the interior of caves with the surface.
- Polje: Horizontal bottom depressions. They are wholly or partly toured by water currents. They can be temporarily or permanently flooded, transforming into lakes.
Clay Area of Spain
It is constituted by little-resistant sedimentary materials (clays, marls, and gypsum) deposited during the Quaternary and after the Alpine orogeny. It includes much of the depressions of the Ebro and Guadalquivir and the Mediterranean coastal plains. The clay relief is horizontal due to rapid erosion. The rivers open valleys that separate horizontal structures that lead to rolling relief. In areas where long dry periods alternate between hot and heavy, short, and intense rains, and there is no plant protection, water erodes the sides of streams, creating gullies or narrow and deep grooves separated by ridges. Its large development on a site area gives the landscape the name of badlands.
Relief Caused by Differential Erosion
When the strata are horizontal, platforms, tables, or moors are formed. The sides are eroded more quickly, so the tables are reduced and eventually become hills. When the strata are gently inclined, alternating hard and soft materials form cuestas. When the strata are folded, Appalachian reliefs result. Differential erosion exposes the hard layers, which form ridges separated by depressions in the soft layers. Examples of this relief can be found in the Montes de Toledo and Sierra Morena.