Exploring Spain’s Diverse Landscapes: Plateaus, Coasts, and Islands

Posted on Nov 4, 2024 in Geology

Exploring Spain’s Diverse Landscapes

The Outer Ridges of the Plateau

Formed in the Alpine orogeny of the Tertiary period, these ridges are primarily composed of limestone.

A) The Pyrenees

These mountains exhibit a complex structure:

  • The Shaft: The ancient Hercynian massif of Aquitaine, rejuvenated during the Alpine orogeny, features rugged Paleozoic materials.
  • The Pyrenees (Tertiary): Formed by limestone, these mountains are softer and less elevated.
  • The Median Depression: A long, narrow depression located between the interior and exterior pre-Pyrenean mountain ranges.

B) The Basque Mountains

An extension of the Pyrenees, these mountains are characterized by gentle slopes, moderate altitude, and rocky limestone.

C) Catalan Coastal Range

The northern half consists of Paleozoic materials (Hercynian remnants of the Catalan-Balearic massif), while the southern half is formed by limestone terrain. It is divided into two sections: a coastal range and a higher inland range, separated by a tectonic depression.

D) The Betic Cordillera

This geologically complex region features two mountain ranges:

  • Penibética Mountain Range: Located along the coast, this range contains Paleozoic materials and the highest peaks.
  • Subbética Mountain Range: Situated inland, this range was formed in the Tertiary period by the folding of marine deposits.
  • Intrabético Depression: Fragmented into several smaller depressions, this area lies between the Penibética and Subbética mountain ranges.

Mainland Coastal Relief

Coastal Landforms

  • Capes: Portions of land that extend into the sea.
  • Gulfs: Deep inlets of the sea.
  • Cliffs: Steep rock faces by the sea, subject to erosion, forming arches and headlands.
  • Beaches: Flat expanses of sand and small pebbles formed by continental and marine sediments.
  • Shallow Platforms: Elevated marine erosion platforms parallel to the coast.
  • Estuaries: Coastal inlets formed by the sea invading river valleys.
  • Salt Marshes: Mud plains in shallow bays filled with river sediments.
  • Spits: Sand bars extending into bays. When a spit closes off a bay, it forms a barrier island.
  • Lagoons: Salty coastal lakes separated from the sea by sandbars.
  • Tombolos: Sand bars connecting islets to the shore.
  • Deltas: Formed where rivers deposit more sediment than the sea can redistribute.
  • Dunes: Mounds of sand formed by wind accumulation, with gentle windward slopes and steep leeward slopes.

Atlantic Coasts

  • Cantabrian Coast: Straight coast with cliffs, shallows, estuaries, beaches, and tombolos.
  • Galician Coast: Formed by the sea invading river valleys in the fractured Galician massif.
  • Andalusian Atlantic Coast: Features marshes, spits, and dune fields.

Mediterranean Coasts

  • Betic Sector: Cliffs, dunes, lagoons, and marine terraces.
  • Gulf of Valencia: Broad, sandy beaches, lagoons (e.g., Valencia lagoon), tombolos (e.g., El Peñón de Ifach), and small river deltas.
  • Catalan Coast: Coastal cliffs, beaches, small coastal plains, and some deltas.

Balearic Islands

A link between the two Alpine ranges in the Mediterranean.

  • Mallorca: Serra de Tramuntana (rocky limestone mountains in the north), Serres de Llevant (lower limestone mountains), and a central clay plain.
  • Ibiza and Formentera: Limestone mountains in northern Ibiza, a massif in eastern Formentera, and a plain between them.
  • Menorca: Low-lying Paleozoic mountains in the north and a flat, limestone southern half separated by a fault.

Balearic coasts feature cliffs and alternating sandy beaches.

Canary Islands

Volcanic islands with characteristic landforms:

  • Volcanic Cones: Conical elevations formed by volcanic material.
  • Calderas: Large circular craters formed by volcanic explosions.
  • Badlands: Rough terrain formed by solidified lava blocks.
  • Dikes and Volcanic Rocks: Solidified magma intrusions exposed by erosion.
  • Valleys and Gorges: Narrow valleys carved by streams.
  • Coasts: Renewed by volcanic eruptions.
  • High Cliffs: Characteristic of ancient massifs.
  • Beaches (Western Islands): Stretches of sand due to the narrow coastal shelf.

Limestone Areas

Composed of secondary rocks, predominantly limestone, these areas feature karst relief:

  • Lapies: Grooved and pitted rock surfaces.
  • Canyons: Deep, narrow valleys carved by rivers.
  • Poljes: Elongated depressions with steep sides.
  • Sinkholes: Large cavities formed by water stagnation, sometimes joining to form uvalas.
  • Caves: Formed by underground water dissolving limestone.
  • Potholes: Narrow openings connecting the surface with underground galleries.

Clay Areas

Composed of Tertiary and Quaternary sedimentary rocks, predominantly clay, these areas feature horizontal relief:

  • Rolling Plains: Gently undulating landscapes formed by river erosion.
  • Gullies: Narrow, deep channels formed by water erosion in dry periods.

Differential Erosion

  • Horizontal Strata: Rivers carve valleys, separating large platforms called mesas. Mesas erode into buttes and hills.
  • Gently Inclined Strata: Forms cuestas with steep escarpments and gentle backslopes.
  • Folded Strata:
    • Appalachian Relief: Alternating ridges and valleys formed by differential erosion of ancient mountains.
    • Jura Mountains Relief: Convex and concave folds with valleys perpendicular and parallel to the summits. Erosion can lead to relief inversion.

The Plateau

A high plateau (600-800m) formed in the Primary era by erosion of the Hesperian Massif. It comprises three units:

  • Paleozoic Basement: Outcrops in the west with granite, slate, and quartzite. Rugged peneplain with inselbergs.
  • Mountain Ranges: Central System and Montes de Toledo, formed by primary rocks (granite, slate, gneiss).
  • Internal Sedimentary Basins: Duero and Tajo basins, formed by the collapse of the plateau basement during the Alpine orogeny.

Landforms within Basins

  • Páramos: Flat, high structural surfaces of hard limestone, with U-shaped valleys carved by rivers.
  • Campiñas: Gently rolling lowlands of clay and marl.
  • Slopes: Transitional zones between páramos and campiñas.

Sub-Plateaus

  • Northern Sub-Plateau (Duero Basin): Higher elevation, single river basin.
  • Southern Sub-Plateau (Tajo Basin): Lower elevation, divided by Montes de Toledo into two watersheds.

Mountain Ridges of the Plateau

  • Galician Massif: Rounded, low-lying mountains with numerous faults.
  • Cantabrian Mountains:
    • Western Sector (Asturian Massif): Appalachian relief formed by uplift of the plateau basement.
    • Eastern Sector (Cantabrian Mountains): Formed by folding of secondary materials.
  • Iberian System: Medium-high range formed by folding of secondary materials. Northern sector with higher elevations (Demanda, Moncayo ranges).
  • Sierra Morena: Rugged plateau separating the Guadalquivir valley from the plateau, formed by uplift during the Alpine orogeny.

Depressions Outside the Plateau

  • Ebro Depression: Parallel to the Pyrenees, filled with marine and continental sediments. Arid climate.
    • Piedmont: Flat lands with conglomerates, mesas, and sinkholes.
    • Center: Horizontal strata of limestone, clay, marl, and gypsum.
  • Guadalquivir Depression: Parallel to the Betic Cordillera, filled with clay, limestone, and marl. Predominantly clay.