The Iberian Peninsula: Geography, Relief, and Coastal Features

Posted on May 30, 2024 in Geology

Location of the Iberian Peninsula

The Iberian Peninsula is located at the westernmost point of Europe. It is one of the three peninsulas in the southern part of the continent and presents a more solid landmass.

The peninsula’s geographical position facilitates easy communication and trade with Europe. However, the mountain ranges were never an obstacle to contact between the people who live in this area, nor were they able to stop the invasions of the past. Additionally, the mountain passes, though not too many, were not always easily accessible.

To the south, only 14 miles separate Gibraltar from Africa. For centuries, people crossed the strait from one bank to another, and over time there has been active commercial and cultural exchange, especially of animal and plant species. Some say this strait separates Europe from Africa, but other authors consider it a bridge between two continents.

The Mediterranean Sea encloses the Iberian Peninsula. This inland sea has strategic importance for navigation, particularly for controlling passage through the Strait of Gibraltar.

Spanish Peninsular Relief

The solid form of the peninsula is determined by the width and length of its coastlines. Most of the coastal perimeter has a rectilinear shape, except for small stretches. The rectilinear layout of the mainland coast offers few natural harbors for navigation.

The high altitude is due to two factors: the existence of a vast central plateau, which occupies three-quarters of the Iberian Peninsula, and the many and varied mountain ranges that cross the territory. The elevation of the peninsula and the steep slopes prevent the formation of soils suitable for agriculture, make communications difficult, and influence weather conditions.

The peripheral relief of the peninsula hinders access to the plateau. One must climb a steep slope to reach the central plains. This, together with the breadth of the peninsula, prevents the influence of the sea climate from reaching the interior lands, resulting in extreme winters and summers.

The diversity of the peninsula’s relief and the variety of climates create very different natural units.

The Plateau

The main unit of Spanish relief, the plateau occupies the central area of the Iberian Peninsula and represents 45% of its surface. During the Alpine orogeny, it was fractured into two major groups:

The Northern Sub-plateau has an average altitude of 800-850 m; it appears almost completely surrounded by mountains and is bisected east to west by the Duero river network. The rivers of the Northern Sub-plateau, beyond the divide that exists between the plateau and the peneplain, descend to the sea, cutting through the hard Hercynian materials, forming cliffs and gorges.
The Southern Sub-plateau has an average altitude of 500-700 meters and comprises two plateaus separated by the Toledo Mountains: the plateau of the Tagus River Basin and the plateau of the Guadiana Basin. The Southern Sub-plateau slopes gently toward the Atlantic, and the rivers here flow peacefully to the mouth. Between these two plateaus extends the plain of La Mancha, which has the largest surface area in Spain.

The Mountainous Interior of the Plateau

These are the Central Mountains and the Toledo Mountains, both oriented east to west. As they are part of the old bedrock, the rocks that form them are granites, slates, and gneisses. The profiles of these ranges present soft and rounded shapes. There are also sharp ridges of quartzite, more resistant to erosion.

The Central System

This system practically divides the plateau into two halves and is composed of different ranges of significant altitude. Between the mountain ranges of the Central System, there are submerged valleys and high mountain passes, often snow-covered, making communications difficult, especially during winter. The most important pass is the Somosierra, which connects the two plateaus.

The Cantabrian Mountains

These mountains form a linear chain that presents very strong and sharp slopes on the Cantabrian side, less accentuated on the inner slope. Features:

In the western part of the range, the Asturian Massif gives rise to a series of dislocated Paleozoic blocks. In this part, there are the largest coal deposits in Spain, plus a variety of metals such as iron, mercury, and antimony. Access between the plateau and Asturias is difficult, due to the altitude and the rugged topography, with few mountain passes.
In the eastern part, or Cantabrian Mountains, the peaks lose altitude. Here, folded structures dominate, with abundant sedimentary materials, including sandstone and conglomerates, especially calcareous ones, which, due to their size, hardness, and strong inclination, are key to explaining the energy of this relief, which is embossed with ridges and foothills.

The Pyrenees

The Pyrenees Mountains form a continuous alignment of approximately 440 km long, stretching from the Gulf of Biscay to Cap de Creus, drawing the boundary with the rest of Europe. The range, with widths of over 100 km, forms a series of parallel alignments that descend in the form of colossal steps from the central or axial Pyrenees.

The Central Pyrenees: Where the altitude is most remarkable, as in the peaks of Aneto, Maladeta massif, Mont Perdu, and Pica d’Estats. Because of its altitude, mountain passes are scarce and difficult. The central part is formed basically by Hercynian materials, resulting in massive and high peaks. Here, you can still find the last remnants of glaciers, thanks to the high-altitude climate.
The Pre-Pyrenees: Of lesser elevation and gentler slopes, the two alignments are mountain ranges parallel to the axial zone, formed by secondary materials and limestone: the Inner Sierras, reaching over 2500 meters in altitude, such as Guara and Peña Oroel; and the Outer Sierras, such as Cadí, Montsec, with more modest elevations. Between both groups, the Middle Depression of the Pyrenees opens up, long, narrow, and interrupted by other reliefs.

The Cordillera Bética

The Cordillera Bética mountains were formed during the Alpine orogeny due to the strong pressure exerted on the sedimentary material accumulated on the seabed. The system is formed by the Penibética Range and the Subbética Range, separated by a discontinuous series of depressions.

The Penibética Range, located near the coast, is composed of materials from the ancient Hercynian massif, elevated by the Alpine orogeny.
The Subbética Range is a great folded structure, extending from the Rock of Gibraltar to the end of the range, where it plunges into the sea and later resurfaces to form part of the relief of the Balearic Islands. In the mountains of this range, there are alternating layers of marls, hard limestone, and soft limestone, which offer a broken and irregular relief.

The Depressions Outside the Plateau

The Ebro Depression is wedged between the foothills of the Pyrenees, the Iberian Range, and the Catalan Coastal Range. It has a length of about 380 km and a maximum width of 150 km. At the time of its formation, the depression was occupied by the sea, but it was later closed off, and a lake formed, slowly filled with materials provided by the continental rivers.
The Guadalquivir Depression lies between the steep edge of Sierra Morena and the Cordillera Bética. It is a flat, triangular-shaped area, about 330 km long by 200 km wide at the coast, which gradually narrows inland. The altitude ranges between 150 and 250 m.

The Mountains on the Coast

The Pre-Coastal Range is an inner alignment with important peaks such as those found in the Guilleries, Montseny, Prades, and Ports de Beceite. This alignment is formed by material accumulated at the mouths of ancient rivers. These deposits, which have formed conglomerates, have been elevated due to the resistance they presented to erosion when the water was lowering the surrounding lands. This is the case of Montserrat (1236 m) and Montsant (1166 m).
The Coastal Range is gently undulating, without significant elevation: Montnegre (759 m), Collserola (512 m), and Monzón (762 m). Some of its peaks approach the coast, forming cliffs, as in the case of Garraf. This range gradually declines to sea level at the edge of Vendrell, where the Pre-Coastal Range reaches the sea.

Central Catalan Depression

The Central Catalan Depression originated as the eastern part of the Ebro Basin, but it is drained by rivers such as the Llobregat, Francolí, and Ter, which flow into the Mediterranean Sea, unlike the Ebro River. This large depression, which extends between the Pyrenees and the Coastal Range, was once occupied by the sea and emerged slowly due to the sedimentation of materials of marine and fluvial origin. The sedimentary areas of fluvial origin deposited heavier materials at the foot of the mountains, where they formed conglomerates.

The Central Catalan Depression is shaped like a large amphitheater, sloping gently towards Lleida, Tárrega, and Calaf, where the layers are more recent, and until a few years ago, there were wetlands.

Catalan Coasts

The granite massif of Cap de Creus, the Gulf of Roses in the plains of Empordà, and the Costa Brava, with small coves between rocky foothills, lend attractiveness and variety to the northern coast. After this, the coast continues straight and monotonous due to the existence of the coastal plain, narrow in El Maresme and wider in El Camp de Tarragona, with some rivers that form small deltas at their mouths. This pattern is interrupted when some relief reaches the sea, as in the case of the Garraf massif.

The coastal plain has been formed by the active alluvium of the Mediterranean rivers and materials brought by sea currents. However, the fault that runs along the coast has caused some areas to sink into the sea. This explains why the plain is narrow near the rivers and small deltas form.

The population density is high on the coastal plain because the soil is fertile, the climate is mild, there are many economic activities, and there are good communication routes—ports, roads, and airports—making it an ideal location to attract tourism.