Geomorphology of Catalonia: Pyrenees, Coastal Ranges, and Central Depression
The Geomorphology of Catalonia
The Catalan relief emphasizes four main units: the Pyrenees (Pyrenean foothills and axial), the Coastal Cordillera, the Central Depression, and the coastal plains. Catalonia has a mountainous setting with two large plains, l’Empordà and d’Urgell, and a rugged coastline, the waters of which flow into the Ebro Depression.
The Role of the Pyrenees
Of the 435 km of the Pyrenees, 250 km are in Catalan territory. From the Cinca River to Cape Creus, the Pyrenees occupy one-third of Catalonia and consist of two parallel mountain ranges:
- The Axial Pyrenees: Composed of old materials, culminating in the peaks of the Estatis and other high mountain areas. Some parts of these mountains have smooth forms with high plains, while others are ridges with flat bottoms and vertical walls.
- The Foothills: Folded and faulted sedimentary materials dominate, primarily limestone rocks. In Catalonia, these ranges are divided into two units: inner ranges and outer ranges, separated by depressions such as the Tremp basin.
The rivers flowing from the Pyrenees, encountering steep slopes and hard materials, carve gorges and canyons into the landscape. Narrow gorges between cliffs are called steps.
The Transverse Cordillera
This comprises a series of relays along the foothills of the Pyrenees, connecting them with the Catalan coastal ranges. These are tabular blocks (a type of relief with a flat surface and coastal borders). Some are higher, forming mountains, while others are sunken, like the Olot plain. The Olot volcanic field arose from over 40 vents.
The Coastal Ranges
This set is a double mountain range parallel to the coast, extending from the mouth of the Ter River to the Ebro Delta. These reliefs separate the interior from the coast. The mountains form a double alignment: the Interior Cordillera and the Coastal Cordillera, separated by depressions and faults.
The northern part, from Collserola to the Gavarres, consists of old mountains with modest altitudes and mild relief due to erosion. The mountains south of Barcelona originated from the folding of sedimentary rocks, predominantly limestone. Rivers that drain into the Mediterranean, such as the Ebro, the Llobregat, and the Francolí, have carved difficult passages through this relief. Rivers rising in these mountains, like the Gaià or Besòs, have short courses due to the proximity of the sea and irregular flow.
Interior or Pre-Coastal Mountain Range
This range forms a line with important peaks like the Montseny. Its relief consists of materials accumulated at the mouths of ancient rivers. These deposits, which have formed conglomerates, have been uplifted due to their resistance to erosion. This is the case of Montserrat.
Coastal Mountain Range
Gently undulating with no significant elevation. An example is the Collserola hills near Barcelona. Some of its slopes approach the coast, forming cliffs, as in the case of Garraf.
Between the two mountain ranges lies a wide corridor, the pre-coastal depression, formed by faults. This area now includes the provinces of La Selva and the Penedès.
The Central Catalan Depression
This is the eastern part of the Ebro Depression, with the peculiarity that some rivers, like the Ter and Llobregat, drain into it, while others do not drain into the Ebro. This depression, situated between the Pyrenees and the Coastal Cordillera, was once occupied by the sea and emerged slowly due to the sedimentation of marine and river materials. The central depression is shallow near Lleida, where the sediments are more recent and until recently formed wetlands. The alternation of soft and hard rocks has led to erosion by rivers, forming plateaus, terraces, and excavated basins. Large clayey plains extend in the center.
Catalan Coasts
The granite massif of Cap de Creus (a steep hill with a flat top), the Gulf of Roses, the flat l’Empordà plain, and the Costa Brava with its small coves between rocky outcrops are attractive features of the northern coast. Southward, the coast continues straight and monotonous due to the existence of the coastal plain, narrow near the Maresme and wider in the Tarragona area, with some rivers forming deltas at their mouths. This plain is interrupted where some reliefs reach the sea, such as the Garraf massif. The coastal plain is densely populated due to its rich soil, mild climate, diverse economic activities, and good maritime, land, and air communications, making it an ideal location for tourism.