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relief,in sculpture, three-dimensional projection from a flat background. In alto-relievo, or high relief, the protrusion is great; basso-relievo, or bas-relief, protrudes only slightly; and mezzo-relievo is intermediate between the two. Ancient Egyptians and Etruscans also used cavo relievo, intagliointaglio
, design cut into stone or other material or etched or engraved in a metal plate, producing a concave, instead of a convex, effect. It is the reverse of a relief or cameo. The term also designates a gem so cut.
..... Click the link for more information. , or sunken relief, in which the design is incised deeper than the background. High relief, although also used in ancient times, reached its climax in the baroque period. Bas-relief is commonly employed on coins and on medals.
a work of sculpture on a flat surface. A relief is specifically characterized by a continuous connection with the surface, which serves as the physical base and background of the sculptural representation. The medium’s most expressive qualities are the unfolding of the composition on a flat surface, the use of a spatial perspective, the illusion of rounded three-dimensional forms, and the subtle modeling of figures. These factors make it possible to render in relief architecture, landscapes, and scenes with many figures. Reliefs can be incorporated into the composition of a wall, arch, or piece of sculpture. A relief may also be an independent work.
Reliefs are either sunken or raised. Sunk, or coelanaglyphic, relief, in which the outlines of modeled forms are incised in a plane surface, was used primarily in ancient Egyptian architecture and in ancient Greek, Roman, and Oriental glyptics. A variation of sunk relief is intaglio—the exact reverse of raised relief. Intaglio was intended as a means to achieve a miniature low relief.
Raised relief, which includes low relief and high relief, is much more common than sunk relief. It was used in the Paleolithic and, later, in Egypt, Assyria, India, and China. Raised relief was widely used to embellish Greek temples (pediments, metopes, and friezes) and Roman triumphal arches and columns. High relief also flourished during the Renaissance and in the sculpture of subsequent periods.
(geography), the irregularities on the land surface and ocean floor, differing in their configurations, dimensions, origin, age, and history of development. The relief is composed of combined forms—three-dimensional bodies that are formed in definite portions of the earth’s crust. They are bounded by two-dimensional elements or limiting surfaces such as slopes and horizontal and subhorizontal surfaces.
Relief forms may be positive (convex), such as uplands and mountains, or negative (concave), for example, basins and river valleys. They are also characterized as simple or complex (complicated by secondary irregularities). Several types of relief may be distinguished depending on the size of the forms: megarelief, which includes both global forms (for example, continental prominences and the ocean floor) and forms of a somewhat lesser order (mountain systems, plains regions); macrorelief (mountain ranges, intermontane basins, uplands, and lowlands); mesorelief (canyons, submarine canyons, hills); micro-relief (karst sinks, steppe depressions); and nanorelief (minute sinks, mole and marmot hills, termite mounds). This division of relief is arbitrary because no precise quantitative boundaries between these categories have been established.
External, or morphographic, relief features characterize the shape of slopes and their combinations, the length and orientation of the most important orographic units, and quantitative characteristics of the relief. Such external features cannot always serve as a reliable basis for a comprehensive description of the relief because forms with identical external characteristics often have a different origin and develop differently. In mor-phogenetic analysis a distinction should be made between endogenous relief-forming factors, caused by the internal forces of the earth (primarily tectonic movements and volcanic activity), and exogenous factors, related to the radiant energy of the sun (flowing water, glaciers, wind, wave action on the shores of seas and lakes, differential weathering). Gravitational processes (landslides, rock falls) occur under the direct influence of the force of gravity on the earth’s surface. Human activity also plays a significant part in shaping the relief.
As a component of the geographic environment and a cause of major changes in many climatic features, in the nature and distribution of surface subterranean waters, and in the soil and vegetation, the relief determines the conditions of its further development.
Endogenous and exogenous processes act on the earth’s surface simultaneously, but with varying intensity over time and space. Where endogenous processes play the leading role, major (structural) relief forms usually develop both on dry land and on the sea floor.
The formation of the largest (global) forms is also related to cosmic forces, such as the rotation of the earth and solar-lunar attraction. Exogenous processes usually mold the smaller (sculptural) forms, which are irregularities of larger forms. Depending on the prevalence of a particular exogenous factor, relief forms are classified as fluvial forms, which owe their appearance to the action of rivers and ephemeral streams; glacial forms, caused by the activity of modern and ancient glaciers; permafrost, or cryogenic forms; and arid forms, created chiefly by physical weathering and wind action.
Regions of tectonic uplift and subsidence are influenced in morphologically opposite directions by external processes: the uplifted and rising segments of the earth’s crust disintegrate and are subjected to erosive denudation, whereas the subsiding sectors are filled with the products of disintegration and ablation, becoming accumulation areas.
According to W. Penck, the predominance of tectonic uplifts over the combined action of external forces results in an accelerating development of relief, characterized by an increase in absolute and relative elevations, in the depth of dissection, and in the steepness of slopes. River erosion and denudation processes are vigorous in areas of accelerating relief development. An example of such relief development is alpine type of relief characteristic of young mountain regions such as the Alps and the Himalayas.
A preponderance of destructive exogenous factors leads to the disintegration of positive relief elements, to declining development: a decrease in absolute and relative elevations, the appearance of concave slope forms, and a slackening of erosion and denudation processes. In mountain lands, declining development corresponds to mid-elevation relief, exemplified by the Urals and Appalachians. As they become lower, mid-elevation mountains are transformed into low-elevation relief, for example, certain sections of the Kazakh Melkosopochnik. Peneplains are formed in the final stage of the declining development of relief.
If tectonic subsidence occurs, depending on the intensity of the action of external forces, the depressions in the relief will either increase in size or level out through the accumulation of loose material carried from outside.
With the passage of geological time the correlation between the relief-forming factors in each segment of the earth’s surface changes often, leaving its mark on the relief. Contemporary land relief includes elements of different ages with traces of both accelerating and declining development. Therefore, for a better understanding of relief, it is customary to consider it in its paleogeographic aspect. Stratification of relief is an index of the alternation of accelerating and declining relief development in mountains over time, and its study helps clarify the history of development of the mountain country as a whole.
The combination of exogenous factors and the relative role of a particular exogenous factor in relief formation depend on climate. For this reason, the distribution on earth of relief forms created primarily by exogenous processes follows the law of geographic zonality. Within plains areas, there are clearly discernible morphoclimatic zones corresponding to the territorial differentiation of present-day exogenous processes.
In mountain country, owing to climatic differences caused by elevation, vertical morphological zonality is observed. Changes in climate, geographical zonality, and vertical zonality that occurred in the geological past are reflected in present-day relief because it preserves its features for some time under changed conditions. In the contemporary landscape, therefore, relict relief not typical of modern morphoclimatic conditions may be observed in places. The glacial relief forms on the East European Plain, for example, are a relict of Pleistocene glaciation. By identifying relict forms it is possible to predict the direction of the further development of relief.
Complexes of elementary forms that are similar in external appearance and origin and that recur regularly over a certain area are called genetic relief types. Their territorial isolation may be related to geological structure (for example, step-like relief), the predominant influence of some external relief-forming factor (glacial, water erosion, and eolian relief), or the preponderant influence of tectonic factors (primary tectonic relief).
One of the more complex current problems is the creation of a genetic classification of relief. Such a classification is necessary not only for theoretical generalization but also for geomor-phological mapping. The most widely used classification in the USSR is based on the identification of major genetic relief categories resulting from the predominant influence of endogenous or exogenous relief-forming processes.
Relief forms created primarily by endogenous processes are classified as morphostructures. Morphostructures clearly reflect the geological structures of the earth’s crust. Thus, platform geological structures with horizontal bedding correspond chiefly to plains areas, and folded structures are associated with mountain country. Smaller relief forms of predominantly exogenous origin, such as river valleys, canyons, barchans, and moraine ridges, are identified as morphosculptures.
The genesis of relief is studied in geomorphology. The results of studying relief are used in solving many problems relating to land improvement, engineering and technical investigation, and prospecting for useful minerals.
REFERENCESMarkov, K. K. Osnovnye problemy geomorfologii. Moscow, 1948.
Shchukin, I. S. Obshchaia geomorfologiia, 2nd ed., vols. 1–3. Moscow, 1960–74.
Nikolaev, N. I. Neotektonika i ee vyrazhenie ν strukture i rel’efe terrilorii SSSR. Moscow, 1962.
Meshcheriakov, Iu. A. Strukturnaia geomorfologiia ravninnykh stran. Moscow, 1965.
Meshcheriakov, Iu. A. Rel’ef SSSR (Morfostruktura i morfoskul’ptura). Moscow, 1972.
Rel’ef Zemli (Morfostruktura i morfoskul’ptura). Moscow, 1967.
Zvonkova, T. V. Prikladnaia geomorfologiia. Moscow, 1970.
Krivolutskii, A. E. Zhizn’ zemnoi poverkhnosti (Problemy geomorfologii). Moscow, 1971.
T. K. ZAKHAROVA