Landforms and Coastal Features: A Comprehensive Overview
Morphostructural Units
Morphostructural units are the shape and internal arrangement adopted by the relief.
Erosion, Orogeny, and Sedimentation
Erosion is the wearing of relief by some agents that can be erosive, climatic, or atmospheric, and biological agents.
Orogeny is the process of creating mountains.
Sedimentation is the deposit on the Earth’s crust of material from the disintegration of rocks or substances in solution.
Rock Types and Geological Processes
Marl is a sedimentary rock composed mainly of limestone and clay, white in color.
Marine transgression is the progress of the sea over an area not occupied by it so far, produced by subsidence of the coast or by raising the water level.
Fracture is a fracture of the crust without separating the fractured blocks.
Fault is a breaking of the crust with separation of the fractured blocks.
Fold is a deformation of geological strata in the form of waves resulting from tectonic pressure.
Granite is a plutonic igneous rock, i.e., formed inside the Earth and solidified from a molten state by being forced to ascend to the surface. It is light in color.
Limestone is a sedimentary rock that is formed on the outside of the Earth from fragments of preexisting rocks or bodies.
Landforms
Coastal plains are the coastal strip of sedimentary rocks formed from the alluvial deposits by rivers due to the erosive power loss near the mouth or by the combined action of the sea and rivers.
Erosion surface is a flat extension resulting from the action of erosion.
Colmatation is a depression filled by the deposition of materials transported by water.
Glacial Landforms
Glaciers affect the highest mountain ranges. They give rise to two types of glaciers:
- Cirque glaciers are accumulations of ice at the head of the valleys. The melting ice breaks the rocks on the walls of the cirque, extending their steep forms.
- Valley glaciers are rivers of ice. They are formed when the thickness of ice in the cirque is great. Then the ice from the lower layers of the cirque moves outside and spreads downstream. Rock fragments containing ice widen the river valley.
Fluvial Landforms
Terraces are flat, raised bands on the fringes of a river. Their origin is due to Quaternary climate changes. In the cold glacial periods, river flow is low and water is found as ice in the mountains, its erosive force decreases and deposits materials on its banks. In the post-glacial periods, the river flow increases with increasing temperature and melting ice, its erosive power increases and deepens its bed, leaving the deposited materials suspended on its banks, which form the terraces. The repetition of these cycles creates stepped terraces.
Lenar or sinkholes are grooves or cavities separated by more or less acute walls. The grooves are formed by water runoff on the slopes or on flat surfaces with cracks. The cavities are formed in places where there are small cavities in which water is stored.
Gorges, ravines, or canyons are deep, narrow valleys, surrounded by steep slopes, caused by rivers.
Poljes are elongated depressions framed by steep slopes with a horizontal background. They are wholly or partly traversed by streams of water, suddenly disappearing from sinks or underground wells and continuing to circulate.
Sinkholes or torcas are large cavities formed in places where water stagnates. They can take many forms and join with other neighbors, forming cavities called uvalas with a complicated plot.
Caves are formed by infiltrating water and underground circular cracks in the ground by excavating limestone galleries.
Troughs are narrow openings that connect the surface with groundwater galleries.
Plateaus and Plains
Moors are structural surfaces that are flat and high, formed by hard layers of limestone. In these, river erosion has carved U-shaped valleys that intersect and separate into smaller tables. The moors are located in the northern and eastern basin of the central plains in the north and east of the southern sub-plateau.
The countryside consists of gently rolling lowlands traversed by rivers. They form where the moors have been eroded, and surface clays and marls of the lower levels. The most outstanding countryside areas are crossed by the Douro, Tagus, and Guadiana rivers.
Slopes are sloping areas between the moors and the countryside.
Coastal Features
Capes are projections deep into the sea coast, and gulfs are deep sea inlets into the coast.
Cliffs are coasts that enter the sea with a steep slope.
Beaches are flat expanses and low slopes of sand, gravel, or pebbles, located at sea level. They consist of continental and marine sediments.
Shallows are marine erosion platforms parallel to the coast that have been elevated above sea level.
Estuaries are coastal entrants resulting from the invasion by the sea in the final stretch of a river valley.
Marshes are plains of mud.
Lagoons are salty coastal lakes separated from the sea by a belt of sand that closes the bay.
Tombolos are sand bars that attach islets to the shore.
Deltas are coastal outgoings formed when the river contributes more sediment than the sea can redistribute because it is a quiet mass of water, without too strong currents or waves.
Dunes are mounds of sand typical of sandy shores.
Volcanic Landforms
Volcanic cones are conical elevations open at the top.
Calderas are large circular craters, caused by the explosion or collapse of a volcano.
Badlands are rough terrain formed by quickly solidified lava.
Dikes and necks are magma emission lines.
Ravines are steep, narrow valleys.