Understanding Iberian Peninsula’s Geography: Aridity, Basins, Lakes, and Geology
Aridity and Climate Sectors
As aridity increases, there are four sectors:
- Northeast Sector (Peninsular Catalan): Wetter, with a higher risk of frost due to cold continental air from the north.
- Valencian-Balearic: Less influence of oceanic air masses, temperatures increase southward, and precipitation decreases.
- Southeastern Peninsular Mediterranean: Semiarid, with the minimum precipitation on the peninsula, experiencing year-round drought. Air masses are influenced by the Alboran Sea. The south coast has the highest average temperatures and strong winds, causing precipitation in the southwest during winter and autumn.
Peninsular Basins
Pronged Peninsular Basins: There are three. Those on the Cantabrian side are short, rising in mountains near the coast. They have great erosive power, which would be even greater if the slopes were not protected by vegetation. Cantabrian rivers are flowing, with regulated flow due to abundant precipitation. Atlantic basins are long, originating near the Mediterranean and flowing into the Atlantic. They have an irregular regime, with summer droughts and autumn/spring floods. Mediterranean slopes are short (except for the Ebro). Gullied rivers erode deforested slopes, with a very irregular regime, summer droughts, and catastrophic autumn floods due to heavy rainfall.
Lakes
Types of Lakes:
- Endogenous Lakes: Caused by forces within the earth. These include tectonic lakes formed on land that sunk due to tectonic activity (e.g., La Janda in Cadiz) and volcanic lakes housed in old craters.
- Exogenous Lakes: Formed by external forces.
- Glacial Lakes: Formed by glacial erosion (e.g., Pyrenean lakes).
- Karst Lakes: Originate in basins created by limestone dissolution. These are common in arid regions.
- Wind-Dug Lakes: Excavated by wind action on soft materials.
- Coastal Lakes: Salty lakes separated from the sea.
Geological Areas
Siliceous Area
Composed of ancient rocks from the Precambrian and Primary eras. It is located in the western mainland and extends to the western Cantabrian mountain range, the Central System, the Montes de Toledo, and Sierra Morena. The prevailing rock is granite, which can be chemically altered by water. Crystal decomposition creates thick, brownish-yellow sand deposits in valleys and low-slope areas. Alteration occurs along joint networks. In high mountain areas, water seeping into fractures freezes, causing rock breakage and the formation of sharp peaks and scree. Flaking of granite due to parallel joints creates an undulating landscape. Perpendicular joints result in scree piles and tors.
Limestone Area
Formed by secondary fold sediments, with limestone soils extending across the Pyrenees and near the Cantabrian Mountains. The predominant rock is limestone, which cracks but dissolves easily with rainwater, especially along joints, creating karst relief. Features include:
- Lapies (Sinkholes): Furrows formed by water runoff on slopes. Narrow grooves are separated by sharp partitions, while wider spacing creates flat surfaces between sinkholes.
- Gorges, Canyons, or Sickles: Narrow, deep valleys formed by rivers.
- Poljes: Depressions or horizontal valleys.
- Temporary Ponds or Torcas: Cavities formed where water stagnates, with circular or funnel shapes.
- Caves: Created when water infiltrates limestone fissures.
- Potholes: Narrow openings connecting to underground systems.
Clay Area
Consists of less resistant sedimentary materials deposited in the late Tertiary and Quaternary periods. It includes parts of the Ebro and Guadalquivir depressions and the Mediterranean coastal plains. The relief is mostly horizontal fields, not affected by folding but susceptible to rapid erosion due to the softness of the materials. Long periods of dry heat alternating with torrential rain and lack of plant protection lead to deep gullies and erosion of stream sides.