Relief-Portugal

Relief-Portugal

Less than one-eighth of Portugal rises above 2,300 feet (700 metres). Most of the country’s mountains are north of the Tagus River, which flows northeast to southwest and divides the country. North of the Tagus, more than nine-tenths of the land rises above 1,300 feet (400 metres); in the south, only one range, São Mamede, surpasses 3,200 feet (1,000 metres).

NORTH

In the northwest the mountains of the Minho province, surmounted by the Larouco Mountains, which rise to 5,010 feet (1,527 metres), form an amphitheatre facing the Atlantic Ocean. The area is composed of metamorphic rocks (crystalline schists, slates, and quartzites) and intrusive or granitic rocks, marked by fault lines that give rise to hot springs. Rolling plateaus and deeply entrenched streams characterize the relatively fertile granitic regions; the schist outcrops offer poor soils. Between the ridges, rivers such as the Lima and the Cávado flow through deep gorges or in flat-floored valleys. The narrow coastal strip is backed by hills that rise steeply to 1,000 to 2,000 feet (300 to 600 metres).

NORTHERN INTERIOR

Beyond the mountains of the Minho is Trás-os-Montes, which is bordered on two sides by Spain. In the region south of the Douro, which is also the western extension of the Spanish Meseta, are Beira Alta and Beira Baixa.

In the north of the northern interior region are high plateaus (terra fria [“cold country”]) at 2,000 to 2,600 feet (600 to 800 metres) that are heavily faulted and composed largely of ancient Precambrian rock (more than 540 million years old), such as granites, schists, and slates. They form a rolling topography. The rivers follow lines of structural weakness and run northwest-southeast. After rejuvenation in the past 5 million years, they now flow in deep valleys and canyons that reach depths of as much as 1,600 feet (500 metres) below sea level. The singular monadnock of the Nogueira Mountains rises to 4,330 feet (1,320 metres) above the general plateau level.

A similar pattern of relief and geology is found south of the Douro, but the sheltered valleys of dark-coloured schists trap the heat of a Mediterranean climate, creating a terra quente (“hot country”). The high Beiras plain is bounded on the northwest by the Caramulo (3,527 feet [1,075 metres]) and Montemuro mountains (4,531 feet [1,381 metres]) and their foothills; the plain is flanked to the south and southeast by the granite and schist escarpment of the Estrela Mountains, which, together with the lower Guardunha Mountains (4,026 feet [1,227 metres]), represent the continuation in Portugal of the Central Sierras of Spain. Between the two ridges, the Guarda plateau has an average elevation of 3,000 feet (900 metres). The mountain chain extends southwestward to the Açor (4,652 feet [1,418 metres]) and Lousã mountains (3,953 feet [1,205 metres]). Farther south the eroded plateau of Beira Baixa drops from an elevation of 1,600 feet (500 metres) to 700 feet (200 metres) toward the Tagus River. It merges almost imperceptibly into the highlands of the Alto Alentejo.

SOUTH

Some three-fifths of Portugal’s land below 1,300 feet (400 metres) is found in the south. From the lower Douro to Lisbon and the lower Tagus, the plains—mainly Triassic sandstones—of the old western provinces of Beira Litoral and Estremadura descend to low-lying, sometimes marshy coasts. Shifting sands and dunes have been stabilized since the 19th century, but lagoons and salt marshes still characterize the river mouths (e.g., Aveiro Lagoon at the mouth of the Vouga River).

Inland, east and south of Leiria, Jurassic limestones interspersed with large areas of slightly younger Cretaceous sandstones and conglomerates have been eroded into rolling sandy hills and steep calcareous escarpments. Ancient volcanic activity has left basalt plateaus. Between the Tagus and the Guadiana, the Alto Alentejo is a continuation of the Spanish tablelands—a series of plateaus, either crystalline (Paleozoic Cambrian and Silurian schists), at 600 to 1,300 feet (180 to 400 metres) with poor soils except where outcrops of diorite have weathered into rich black soils, or limestone, with piedmont springs at their foot. North of Beja, in the Baixo Alentejo, ridges of quartz and marble oriented northwest-southeast account for a monotonously undulating relief between 300 and 600 feet (90 and 180 metres). This terminates in the east with the schistose Caldeirão Mountains (1,893 feet [577 metres]). Sheltered by the mountains from northern climatic influences are the more extensive scarps and hills of the Algarve. These are composed of limestones and sandstones of the Mesozoic Era. The Monchique Mountains, a dissected massif of intrusive igneous rock (syenite), rise to 2,959 feet (902 metres) at Mount Foia.

THE MADEIRA ISLANDS

The Madeira archipelago includes eight volcanic islands in the Atlantic, 600 miles (1,000 km) southwest of the mainland. Only two of these, Madeira and Porto Santo, are inhabited. Madeira forms an asymmetrical mountainous hump in midocean, rising to 6,109 feet (1,862 metres) in the interior, falling more steeply in the north. Thick layers of basalt alternating with beds of ash and scoriae create a stepped relief that has been deeply dissected into gorges and canyons. The cratorial Curral das Freiras is about 2,265 feet (690 metres) deep. Paul da Serra is a bleak high-level plateau. The eastern tip of Madeira, like the uninhabited Desertas Islands, is sandy. The island of Porto Santo is low-lying and flat.

THE AZORES

Nine islands constitute the Azores, which extend in three groups over 400 miles (650 km) in the mid-Atlantic. The easternmost island, Santa Maria, lies 875 miles (1,408 km) from the Portuguese mainland; the westernmost, Flores, is about 1,230 miles (1,980 km) from Cape Race, Newfoundland, Canada. The islands are volcanic, occasionally active. Their varied scenery includes crater lakes, plateaus at various elevations, mountainous massifs, flat-bottomed valleys, and rugged coastlines.