Major Morphostructural Units and Relief Dynamics of Spain

There are three major morphostructural groups:

1. Antique Beds: Made up of mountains of medium height, flattened summits (peneplains), consisting of material folded in the Paleozoic era, deformed by Hercynian and Alpine folding.

2. The Alpine Mountains: These are very young and high; their basic material is limestone.

3. Depressions: These can be of different types:

• Some fragments are located on the old sunken Hercynian base, such as the Cuenca del Duero.
• Others occupy former inlets or bays that are silting up by sediments from the Alpine ranges, such as the depression of the Ebro and Guadalquivir.

Mainland Units and Dynamic Stresses

The fundamental unit is the Meseta peninsular relief, which is an area of highlands (600-800 m) divided into two sectors by the Central System: The Northern Plateau and Southern Plateau, the latter slightly rough in the mountains of Toledo. The plateau is surrounded by mountain ridges (Massif Galician, Cantabrian Mountains, Iberian Range, and Sierra Morena) and two outer depressions (the Ebro, or Iberian depression, and that of the Guadalquivir, or Andalusian depression) enclosed by peripheral mountain ranges (the Pyrenees, Catalan mountain ranges, and the Betic Cordilleras).

Therefore, the large peninsular units of morphostructural relief are:

1. Plateau

It is the old remains of a solid-Hesperian Massif that emerged from the Hercynian orogeny of the Primary era, which was destroyed by erosion and became a peneplain or plateau. In the Tertiary, the peneplain was deformed and largely destroyed during the Alpine orogeny, which gave rise to internal ridges, Castilian depressions, and mountain ridges.

Thus, within the Plateau, we can differentiate the following components:

• The ancient Paleozoic base: It is a flat area that only comes out today in the west, where erosion has swept the dressing of tertiary materials (peneplain Zamora-Salamanca and Extremadura).
• The mountain ranges of the Plateau: Central System and Montes de Toledo: Formed in the Tertiary where, as a result of the Alpine orogeny, the base of the Plateau experienced failures or breakages that raised a few blocks. Both are primary rocky (granite, slate, gneiss) and have soft peaks. The system is stronger, and the Central Plateau is divided roughly by half. The Montes de Toledo, of lower height, divide the South Submeseta, separating the basin of the Tajo and Guadiana.
• The interior sedimentary basins: the northern and southern sub-plateau: Also formed in the Tertiary where the Alpine orogeny caused the collapse of some blocks of the plateau, which was then filled with Tertiary sediments uprooted by erosion of the surrounding mountain ranges.

These sediments were soft at the bottom (sand, clay, gypsum, marl) and hard on top (limestone) and led to a relief of plateaus (high plains) in the limestone areas, of countryside (rolling lowlands crisscrossed by rivers) in clay and sand, and slopes between the moors and countryside.

The basin of the North Submeseta is higher (700-800 m) and uniform (all of which belong to a single river basin: the Duero). The southern sub-plateau basin is lower (600-700 m) and is uneven in its middle due to the Montes de Toledo.

2. Mountain Lips of the Plateau

Formed in the Tertiary by the rejuvenation of blocks in the Plateau or the folding of the material deposited by the sea in the Middle Ages on the edges of the plateau.

• The Galician-Leonese solid angle was not the socket of the plateau, which broke the Alpine orogeny and rejuvenated. It is, therefore, of Paleozoic materials and features rounded hills and low altitude.
• The Cantabrian Mountains: This is an area west of Paleozoic materials (Asturian Massif), which was part of the base of the plateau and rejuvenated in the Alpine Orogeny. This sector is of secondary limestone materials (mountain Santander), which were deposited by the sea on the edge of the plateau and folded in the Alpine orogeny.
• The Iberian range: Although it has a small rocky NW of Paleozoic (old rest of the Ebro Massif) with elevations above 2000 m, it is predominantly a secondary material deposited by the sea on the eastern edge of the plateau, which folded in the Alpine orogeny. Here are two sectors: the northern half of NW-SE (saws Moncayo, Picos de Urbión, Demand, and Onion) and the southern half, from Teruel, which forks into two branches: the interior or Spanish (sierra Albarracin) and external or Aragonese (Maestrazgo, Javalambre, Gúdar). Between them runs a longitudinal depression for a graben, which was filled with tertiary materials.
• Sierra Morena is not really a mountain but a sharp step that separates the Meseta from the Valle del Guadalquivir. It has been interpreted as a giant failure, but it seems that this is a great bending fractured in many places that are produced by the thrust from the south rising Betic Cordilleras. The crag is Paleozoic, of dark color, which, together with the vegetation (jara), gives it its name.

3. The Cordilleras Outside of the Plateau

External ridges, the Pyrenees and the Betic Cordillera, formed in the Alpine orogeny of the Tertiary when folded materials were deposited in trenches between former Betic and Pyrenean massifs that act as buffers. Folds and steep peaks dominate, and erosion has not had time to soften the forms.

• The Pyrenees have a rocky Paleozoic axial zone, belonging to the ancient Hercynian massif of Aquitaine, rejuvenated with the Alpine orogeny. It is the highest area and is steep (Montes Damned).

To the south are distinguished from one Pre-Pyrenees limestone, less high and more gentle, structured in two aligned parallel to the axial area. The Pyrenees have as an extension to the Basque Mountains and the Catalan Ranges.

• The Basque Mountains are an extension of the western Pyrenees. The crag is secondary. They have low height and smooth, undulating forms.
• The Catalan Ranges are a transformation of the eastern Pyrenees. The northern half consists of Paleozoic material, remnants of the old Hercynian massif of the Ebro raised in the Alpine orogeny. The southern half consists of limy side folded in the Alpine orogeny. The ranges are divided into two teams: one along the coast, of low height (Altos del Garraf), and a higher internal (Montseny, Montserrat). Both are separated by a longitudinal depression or graben, which was filled with tertiary and quaternary materials, leading to a relief of soft hills and valleys.
• The Betic Cordilleras are structured into two sets. The Penibética Cordillera runs along the coast. It consists of material from the ancient Paleozoic Hercynian massif Betic-Rif orogeny raised in Alpine (Sierra Nevada). The ridge Subbética, inside, is of secondary materials (Sierras of Grazalema, Ubrique, and Cazorla). Between them is the depression Intrabético fragmented in several small depressions (basins of Ronda, Antequera, Guadix, and Baza).

4. The Depressions Outside of the Plateau

These were pre-Alpine basins or trenches, following the Tertiary orogeny, were among the Alpine ranges and ancient massifs. They were filled by Tertiary and Quaternary sediments and are now almost horizontal reliefs; the open valleys and rivers have left in highlight tabular platforms.

• The Iberian Ebro depression is parallel to the Pyrenees. It is closed by them, the Iberian Range, and the Catalan Ranges. It was first occupied by the sea, but then it closed, turning into a big lake. Therefore, it has marine deposits (marl and limestone) and continental (Pyrenees conglomerates, clays, and sands). Where the rocks are more resistant (limestone, sandstone, and conglomerates), the horizontal reliefs (molars and foothills) dominate. Where soft materials (marl) dominate, relief gullies or badlands arise.
• The depression of the Guadalquivir, or Andalusia, parallel to the Betic Cordilleras, was first opened to the sea. Then it became a lake shore or lagoon and later, by sedimentation, into swampy marshes. It was filled with fine sediments, leading to mild forms (ridges and hills).

Insular Units and Dynamic Stresses

1. Balearic Islands

Geologically, this is a link between the two Alpine ranges in the Mediterranean, the Betic and Costero Catalana. Mallorca and Ibiza are fragments of the Betic Cordilleras, together with those underwater through a narrow strip of shallow sea. Menorca is linked to the Catalan Coastal Range.

• Ibiza has small mountain ranges.
• Mallorca has three sets:
  • The West saw, or Tramontana, is abrupt, rocky, and limestone.
  • The central depression has a rocky relief of soft clay.
  • The Sierra de Levante, which is less than 500 m, refers to the sea and is rocky limestone.
• In Menorca, the northern half has a line of mountains to the coast, making this area virtually inaccessible, while the southern half is flat.
• In Formentera, the plain dominates.

2. The Canary Islands

The whole of the Canary Islands is volcanic. It originated in the Tertiary when the Alpine orogeny broke the bottom of the Atlantic, and through the fractures reached masses of volcanic rocks that led to the islands.

The general evolution of the relief is divided into magmatic cycles of different magnitudes. Each begins with basaltic emissions and results in various forms in relation to the fluidity of the first material and the viscosity of the past. By age and position, there are three major groups:

• The islands are based on an outcrop of oceanic crust or basement complex, consisting of Mesozoic materials and submarine lavas, which constitute the oldest materials in the archipelago, easily recognizable basal complex in the north of La Gomera, La Palma (inside of the Caldera and the gorge of Sorrows) and Fuerteventura, which characterizes a relatively large sector of the island.
• The massive old (independent term regular use for the mountains of base) is formed by superposition of fluid basaltic lava old and are the foundation of almost all the islands. Deep incisions have received torrents and have led to coastal cliffs. Among the most prominent are the Teno and Anaga in Tenerife.
• The ridges are volcanic alignments for most recent fissure eruptions. At the summit, craters are aligned pyroclastic (fragmented volcanic material deposits and loose), and flanks, the lava flows. Stresses the dorsal Pedro Gil in Tenerife and the Cumbre Vieja on La Palma. El Hierro is set by the confluence of three ridges that clearly contribute to its triangular shape.