Understanding Physical Geography: Key Concepts and Terms
Physical Geography. The general physical geography studies the landscape as it would be found without the intervention of human groups (natural landscapes). It includes the study of climate, water, relief forms, and living beings in their distribution and significance for landscapes.
Map Scale. The scale is the relationship between the dimensions of the map and the actual dimensions of the surface it represents. For example, a 1:100,000 scale indicates that one inch on the map represents a real mile (100,000 times). The larger the area represented, the larger the scale. The topographic map of Spain, for example, is on a scale of 1:50,000.
Parallel. The parallels are circles of diminishing radius as they approach the poles. Among the parallels, two of them are particularly important: the Tropic of Cancer and the Tropic of Capricorn, located at 23° 27’N and S of Ecuador, respectively. The Iberian Peninsula is between the parallels of 44° and 36° N latitude, while the Canary Islands are located approximately between latitudes 29° and 27° N.
Latitude. Latitude is the angular distance between any point on Earth’s surface and Ecuador. It is established through parallels (concentric imaginary lines parallel to each other and to Ecuador). It is measured in degrees, from 0° to 90°, from Ecuador northward and southward.
Meridian. Meridians are imaginary circles that pass through the poles, thus being perpendicular to Ecuador. All points on the same meridian have the same longitude and experience the same solar time at noon. As a result of rotation, the solar time is different for each meridian; the reference meridian, 0°, is that of Greenwich.
Longitude. The longitude of a place is the angle between the plane of the meridian of that place and the plane of the prime meridian or Greenwich meridian. Longitude is measured in degrees from 0° to 180° from the Greenwich meridian to the east and west. The time difference between the meridian of that place and Greenwich allows for the determination of longitude: if a city is at 12:00 while in Greenwich it is 11:00, it will be at 15° E longitude; conversely, if it is 14:00 in Greenwich and 16:00 in that city, it would be located at 30° W longitude.
Fault. A fault is a line of fracture and discontinuity between two blocks, through which they move, either vertically or horizontally. Faults usually coincide with areas of high seismic and volcanic activity. The old beds, made of very rigid materials, do not bend but break. The reliefs are the accidental result of these massive ancient formations characterized by horsts and grabens. The fault scarps are caused by a very complex evolution, and erosion is also favored by the presence of faults.
Altitude. Altitude is the height of a point above sea level. To represent them on maps, contour lines are used, which are closed lines connecting points of equal height. Spain has a high average altitude (660 m), which is due in large part to the massive interior of the plateau. Land below 200 m altitude represents less than 11% of the total mainland.
Peneplain. Peneplains are landforms that often occupy large areas and, through erosion, have a gently undulating surface, with little difference in height between the valleys and watersheds. They consist of ancient and eroded materials. In Spain, they are located in the northwest of the central plains. The Extremadura peneplain is a great extension that has an altitude between 300 and 500 m and consists of a basement crossed by the river Guadiana.
Socket. A socket is a geological crust belonging to very ancient, very hard formations that form the basis of an orogen or rise. The stiffness of the material explains the fragmentation into blocks forming a Germanic relief or fractured landscape. Much of the current plateau is formed by a hardened socket.
Crease. A crease is a deformation of geological layers, shaped like waves. Folds arise as a result of tectonic pressure in plastic rocks, rather than fracturing. A fold is formed by all anticlinal-synclinal structures. Folds may be upright, inclined, or recumbent, depending on the dip of the axial plane, and have varying degrees of curvature.
Depression. A depression is a recessed area of land. It can occur for several reasons: sunken blocks due to plate tectonics, synclinal depressions linked to rivers, sunken areas, or the effect of glacial erosion caused by the dissolution of limestone by water.
Allochthonous Ranges. If compression causes very intense folding, folds may tilt or topple in the direction of thrust. When the folds are uprooted, they are called allochthonous, and the transported materials are thrust nappes.
Appalachian Relief. This relief is the result of a long evolution: old folded chains are transformed into peneplains by erosion, and have subsequently been raised again and eroded. Some examples in Spain can be seen in the mountains between Asturias and Galicia, and in the Montes de Toledo.
Plate Tectonics. Plate tectonics is a geological theory that explains various geological phenomena from the movement of rigid lithospheric plates on the soft asthenosphere, movements that are due to convection currents in the mantle. This theory differs from Wegener’s continental drift in that plate theory does not believe in the autonomous movement of continents; rather, they are carried passively by lithospheric plates.
Hercynian. The Hercynian orogenic cycle developed during the Late Paleozoic, approximately between 400 and 230 million years ago. It affected central and southern Europe, resulting in a series of mountain ranges on the edge of the Precambrian and Caledonian massifs. Remains of these ranges are found in the Galician Massif and the Spanish Meseta, as well as in the Alpine mountain ranges (e.g., the Pyrenees).
Massif. A massif is a compound formed by ancient rock, sometimes primary, which has been eroded. Although the arrangement of the crag can be complicated (complex folds and tight), what remains of them is only the root of the folds; thus, the clumps are what remains of old folding chains. Today, the high plateau of ancient massifs are surfaces of erosion. The old beds are part of what geologists call sockets. In Spain, this form of relief can be seen on the Plateau.
Plateau. The origin of a plateau is usually a plain formed from an old sedimentary basin, elevated by tectonic movements or epirogenic accidents. These often result in large edges of the plateau forming folded mountains that separate it from the depressed areas outside. In the Iberian Peninsula, an example is the Spanish plateau, whose edges are the Galician Massif, the Cantabrian Mountains, the Iberian System, and Sierra Morena. The plateau is bisected by the Central System: the northern sub-plateau is drained by the Duero River, while the southern sub-plateau is watered by the Tagus and Guadiana rivers, divided into two basins by the Montes de Toledo.
Gully. Gullies in soft materials are formed by water from streams that, when there is adequate plant cover, attack the slopes, digging long furrows with sharp edges. Gullies or “badlands” frequently appear in clay relief because clay is an impermeable but soft rock. Examples of this model appear in the clay basins of the two plateaus or in the Ebro basin. In some of these cases, foresters try to limit the erosion of the watersheds through reforestation.
Karst. The term used to refer to the modeling of any region that evolves by dissolving limestone, which is hard but soluble in water. The origin of the term is Kars, a region northwest of the former Yugoslavia. This model is characterized by the appearance of narrow gorges, sinkholes, and caves in areas of flat terrain, known as Polje, where few rivers are lost in sinkholes and rock fluting forms long grooves that sometimes create sinkholes. In Spain, this type of modeling is quite common; the “Ciudad Encantada de Cuenca” is an example of karst in a very advanced state of destruction, and examples of sinkholes or torques exist in Antequera and Ronda.
Hoz. A hoz is a formation caused by rivers on limestone, which dig deep narrow valleys (also called gorges or canyons), surrounded by almost vertical walls. In Spain, examples include the Sickles of the Duratón River near Sepúlveda (Segovia) or the cross-Pyrenean rivers that carve limestone gorges, such as the rivers of the Cantabrian mountain range, where the Cares Gorge can be highlighted.
Dolina, Torque. The sinkhole, known in Spain as torques, are oval or circular depressions produced in karstic relief, with diameters ranging from a few meters to several hundred meters. As limestone usually contains some clay, the bottom can be rocky or sandy. One of the most important in Spain is the Torcal de Antequera, which originated in Jurassic limestone arranged in horizontal layers.
Polje. Poljes are closed basins, large seasonally flooded depressions in karstic relief, with a plain background where rivers appear embedded and sometimes get lost in sinks.
Berrocal. Also known as “chaos balls,” these are formed by the decomposition of granite, which is an impermeable rock, hard but very sensitive to chemical decomposition. The decomposition is particularly intense in the network of cracks (joints) that run through its thickness. Water seeps into cracks, and ice can pop the rock. This type of landscape is very common in the Central System, particularly notable in the “Pedriza” of the Manzanares.
Cerro Witness. A cerro witness is a remnant of a platform in a tabular relief, consisting of a set of hard and soft layers arranged horizontally, in which erosion has sculpted landscapes that are also horizontal. With increasing erosion by rivers in the soft layers, hills are formed, and if the plateau is attacked by erosion, “witness hills” with flat tops appear everywhere. These are quite common in the sedimentary basins of the two sub-plateaus and in the Ebro Depression.
Cirque. A cirque is one of the parts of glacial formations, shaped like amphitheaters filled with ice and dominated by high rock walls. In the Pyrenees, current glaciers are small, such as the cirque glaciers like the Aneto. In the Alps and other great mountain ranges, cirque glaciers extend through glacier tongues.
Moraine. Moraine is the material piled on the sides of the glacier tongue, which can also appear in the middle and at the end of the tongue.
Mountain Lakes. Mountain lakes are glacial lakes that can appear in what was once the cirque or in some parts of the tongue.
Estuary. An estuary is the bottom of a river valley that has been invaded by the sea with the tides, creating a swing between the sea and river. When the river valleys are of minor importance, they are called estuaries, as is the case in Galicia.
Spits. Spits are accumulations of sand in front of the coast; sometimes these deposits are based on capes or promontories. The arrows can isolate ponds in a former Gulf littoral, forming ridges as in the Mar Menor in Murcia or the Albufera of Valencia.
Isthmus. An isthmus is a narrow strip of land that connects an island to a continent. Examples of this landform can be seen in Ampurias, Gibraltar, or Peñíscola.
Marshes. Marshes are lowlands that are almost at the same level as the sea, developed to coat spits at the mouth of rivers. A great example is the Guadalquivir River.
Deltas. Deltas are formed at the mouths of rivers by the accumulation of materials that create a penetration of land into the sea, typically in a triangular shape. The most significant example in the Iberian Peninsula is the Delta del Ebro.
Weather
Weather. Weather refers to the types of weather that occur in a particular place and are repeated in cycles. The most important elements of climate are temperature and rainfall. The factors affecting climate include latitude, atmospheric circulation, marine and continental influence, altitude, and the provision of relief. Spain has a wide variety of climates, the most important being the Mediterranean (coastal and interior) and the oceanic.
Time. Time is the state of the atmosphere at a given place at a given time. To determine the type of weather, factors such as temperature, humidity, precipitation, wind, and atmospheric pressure are considered.
Albedo. Albedo is the energy of radiation reflected or scattered by a body. The atmosphere filters out sunlight and holds, on average, 57% of energy in the upper layer, while it reflects about 40%, and 10% of the solar flux is reflected by the soil surface.
Temperature Range. The temperature range is the difference between the maximum and minimum temperatures of an area. It can refer to the annual or daily temperature range, both of which increase within the reduced sea mitigating effect on temperatures. In Spain, the temperature range is high in both sub-plateaus and greatly reduced in the Cantabrian and Mediterranean coasts. Inversion. Inversion is a phenomenon that occurs primarily in winter when cold air, being heavier, accumulates in the bottom of the valleys. This is because the surface contact with the ground, at low temperatures, is higher in low-lying areas than in the mountains.
Isotherm. An isotherm is the line joining points with the same temperatures.
Air Masses. Air masses are large air cells that have the same characteristics of temperature (warm or cold), pressure (high or low), and moisture. Air masses can form anticyclones, which are centers of high pressure above 1015 mb, and cyclones, which are low-pressure centers below 1015 mb.
Wind. Wind is the movement of air from high to low pressure. Wind strength increases proportionally to the pressure gradient between two air masses. In Spain, the north and northeast winds tend to be cold and dry, while westerly winds are mild and moist. Northwest winds tend to be cold, and the south and southwest winds are warm and humid, while the southeast winds are warm and dry.
Isobar. An isobar is an imaginary line on weather maps that joins points with the same atmospheric pressure at a given time.
Anticyclone. An anticyclone is an area of high pressure (more than 1016 mb), surrounded by other low-pressure areas, with winds circulating in the northern hemisphere in a clockwise direction. Generally, this corresponds to times of stable weather on the surface. Among those affecting Spain are the Scandinavian and Azores anticyclones.
Cyclone. A cyclone is a low-pressure center, also known as a depression or storm. In the Northern Hemisphere, winds rotate in depressions in the opposite direction to clockwise. Major depressions affecting the Iberian Peninsula include the Depression of the Gulf of Rosas (especially important in autumn when it can coincide with the “cold drop”) and the Gulf of Cadiz, both seasonal.
Front. A front is the interface between two air masses. This surface is never vertical but tilted because the thicker and heavier air tends to enter as a wedge below the lighter air. This is what happens with the polar front that separates tropical air from polar air in the temperate zone.
Polar Front. The polar front is the front that separates polar air masses from warm air from the south. It is located around 60 degrees north latitude. Storms associated with the polar front define the humid climate of the Cantabrian coast and are responsible for affecting much of the Iberian Peninsula at certain times of the year, especially in the fall.
Stormy. Also called “barometric depression,” this is the area under the effect of atmospheric pressure below normal (1016 mb), causing unstable weather. Storms are generally formed in families of three to five, moving from west to east, and result mainly in the western edges of rainy and windy weather. On isobar maps, they are represented by two circular arcs, symbolizing the path at low levels of the warm front and the cold front. In Spain, they are more frequent in late autumn and winter.
Jet Stream. The jet stream is a stream of westerly winds at an altitude of over 8,000 meters (between cold air masses and warm) and a speed of between 150 and 600 km/h. When the undulations slow down, they can produce deep valleys that sometimes cause the phenomenon known as “cold drop.” In winter, it is located between 30° and 45° N latitude, and in spring, it moves northward. The jet stream determines the atmospheric circulation of the temperate zone; the polar front, for example, is a reflection of this powerful current.
Relative Humidity. Relative humidity is the percentage of water vapor in the atmosphere concerning the maximum value that corresponds to the saturation level (the maximum amount of water vapor that can be retained by an air mass at a given temperature). When this level is exceeded, the excess water precipitates. The moisture level is determined by temperature, proximity to the sea, relief, and vegetation cover.
Condensation. Condensation is the process of changing from a gaseous state to a liquid state. When a mass of moist air cools, it condenses and precipitates, producing rain. The temperature at which water vapor condenses in the air depends on the vapor content.
Fog. Fog forms when soil temperature drops below the temperature of the lower layer of air, and if the humidity is sufficient, it condenses, forming fog.
Cold Drop. A cold drop is a meteorological phenomenon that occurs when a package of very dense cold air moves through the “jet stream,” leaving a large pocket of cold air at high pressure in the hot air and low pressure. Being heavier, it falls, taking the place of the surrounding warm air. This leads to strong vertical motions and heavy rainfall. In Spain, it is relatively common in Levantine autumns.
Isohyet. An isohyet is a line on weather maps used to connect points with the same rainfall in millimeters.
Windward. Windward refers to the part of the land where the wind blows. The opposite term is leeward.
Steppe. A steppe is a formation of thorny shrubs and low vegetation that reveals much of the soil. Typical species of the steppe include thyme, esparto, and asparagus. In areas near the coast, the palm is also common. This vegetation is characteristic of the Almeria area and Los Monegros in Aragon.
Dehesa. A dehesa is a type of anthropogenic landscape in forests of oak, cork, and holm oak that have been “cleared” to create grassland areas used for livestock. The pasture in cork is very common in Extremadura and Salamanca, where it is used for pig farming.
Landa. Landa refers to vegetation of the temperate zone, characteristic of European areas with an oceanic climate. It occurs in northern Spain on the upper floors of the relief, as a result of deciduous forest degradation. Representative species include heather, gorse, broom, bracken, and gorse.
Prairie. A prairie is a herbaceous formation that grows where conditions are too arid (hot and dry) for trees. The prairie can be a natural formation where the climate prevents tree development, or it can be human-made when pastures replace forests after being cleared by humans.
Conifer. Conifers are arboreal species characterized by having a conical crown and small needle-like leaves. The understory is usually low due to soil acidification from the needles. Conifers can adapt to extremes of humidity or dryness, cold or heat. In Spain, the most prevalent species include pine, fir, black pine, Scots pine, Aleppo pine, and juniper or pinsapo.
Protected Natural Area. A protected natural area is a region dominated by natural elements or having special biological or landscape characteristics. Currently, there are more than 500 protected natural areas in Spain, the largest number being protected natural parks such as the Sierra de Grazalema or the Tables of Coldstream.
Solana. In mountainous areas, a solana is the side of an elevation facing the sun, while the opposite side is the shady side. It is usually warmer and drier, making it more suitable for crops and settlements.
Leeward Slope. The leeward slope is the mountainside exposed to the downward flow of wind, corresponding to areas of dry climate.
Windward. Windward refers to the part of the land where the wind blows. The “windward side” is the side of a mountain exposed to the wind flow.
Hydrology
Hydrography. Hydrography is the area of knowledge within geography that studies marine and inland waters; it is part of physical geography.
Watershed. A watershed is the territory watered by a main river and its tributaries, bounded by the slopes that form its boundary. The basin is symmetrical if the structure and number of tributaries are similar in both areas. The largest basin in Spain is the Douro.
Flow. The absolute flow is the amount of water measured in cubic meters evacuated by a river over a period of time, usually one second (m³/sec). The flow rate is the ratio between the average annual flow and the catchment area in km² (l/s/km²). The flow rate is usually higher at the mouth of the river, where there are no leaks or evaporation; flow decreases upstream. The flow rate also varies according to the season; Levantine rivers experience the most significant changes in flow, with the Douro being the largest river in Spain, evacuating 620 cubic meters per second.
Torrente. A torrente is a watercourse that is brash and violent, connected to torrential rains. The stream consists of three parts: the catchment area where erosion is severe, the drainage channel, and the alluvial fan. Floods are more common in the Canary Islands, where the lack of rain causes the appearance of gullies that channel rainwater, forming streams.
Drought. Drought refers to the decrease in river flow during the dry season due to low rainfall. It is also called the average level and lower or minimum flow in a river or stream, which can reach zero and serves as the starting point for measuring the height of the water. Almost all Mediterranean rivers suffer severe drought in the summer, leading some rivers to become completely dry wadi channels for much of the year, sometimes for several years until heavy rainfall brings some flow.
Rambla. A rambla is a generally dry channel that theoretically runs a river current. Las Ramblas (“torrent” in the Valencian Community) appear in rivers with a torrential regime because they have no flow for most of the year. In some cases, the absence of flow can last several years. Most rivers in Almeria are ramblas, as is the case in much of the Mediterranean coast, where notable examples include Benipila and Cervera gullies.
Meander. Meanders are sinuous curves in the middle-lower river. If bends are enclosed, the alluvial river deposits sediment on the convex side and digs into the concave side. In low plains, meanders develop in alluvium, and if a rise in the river occurs, it can cut off a bend, leaving a crescent-shaped residual lake (oxbow lake). In Spain, examples of meanders can be seen in the Ebro River, downstream of Zaragoza.
Alluvial Terraces. Alluvial terraces are the result of climatic variations during the Quaternary. Under dry conditions, vegetation is impoverished, and watersheds and rivers become aground, carrying an overload of sediment that prevents them from digging their beds. During wet conditions, rivers excavate their channels, leading to the formation of terraces.
Lake. Lakes are bodies of water of varying depth and size located in the interior of continents. In high mountain regions such as the Pyrenees, there are numerous small lakes (with diameters of only a few tens of meters), known as mountain lakes or glacial lakes.
Marshes. Marshes are saltwater wetlands located near the coast, often near river mouths. An example in Spain would be the marshes of the Guadalquivir.
Delta. Deltas are fluvial landforms, generally triangular in shape, generated by the accumulation of sediment at the mouth of a river, which fills with materials to form a penetration of land into the sea. A delta forms when a river contributes more sediment to the sea than it can absorb and redistribute. In the delta, the river opens into arms among which are marshy areas that eventually become islands due to increasing flooding. In Spain, the most remarkable delta for its breadth is the Ebro delta.
Albufera. Albuferas are coastal lagoons formed by sandbars. They are common on the Mediterranean coast, where sand availability facilitates the formation of barriers that close depressions, notably in Valencia and the Mar Menor.
Estuary. An estuary is a coastal landform at the mouth of a river, occurring when the bottom of the river valley is flooded by the sea. When the tide comes in, it pushes seawater into the river, while at low tide, river waters are evacuated. The term estuary is used only to describe this phenomenon in large rivers; in Spain, the submerged valleys are much smaller and are called estuaries, such as those found along the Galician coast.