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Aspect (geography)
Encyclopedia
In physical geography
, aspect generally refers to the horizontal direction to which a mountain
slope faces. For example, a slope on the eastern edge of the Rockies
toward the Great Plains
is described as having an easterly aspect. A slope which falls down to a deep valley
on its western side and a shallower one on its eastern side has a westerly aspect or is a west-facing slope. The term can also be used to describe the shape or alignment of a coastline. Here, the aspect is the direction which the coastline is facing towards the sea. For example, a coastline with sea to the northeast (as in most of Queensland
) has a northeasterly aspect.
The aspect of a slope
can make very significant influences on its local climate
(microclimate
). For example, because the sun
's rays are in the west
at the hottest time of day in the afternoon, in most cases a west-facing slope will be warmer than a sheltered east-facing slope (unless large-scale rainfall influences dictate otherwise). This can have major effects on altitudinal and polar limits of tree growth and also on the distribution of vegetation that requires large quantities of moisture. In Australia
, for example, remnants of rainforest are almost always found on east-facing slopes which are protected from dry westerly wind
.
Similarly, in the northern hemisphere
a south-facing slope will accure before it becomes more open to sunlight and warm winds and snow will therefore generally be warmer and dryer due to higher levels of evapotranspiration
than a north-facing slope. This can be seen in the Swiss Alps
, where farming
is much more extensive on south-facing than on north-facing slopes. In the Himalayas, this effect can be seen to an extreme degree, with south-facing slopes being warm, wet and forested, and north-facing slopes cold, dry but much more heavily glaciated.
For a farmer, thus, choosing an aspect that will shelter from hot, dry winds or from cold can be critical to successful growth of crops. Most farming agencies will state in manuals whether a crop prefers a poleward or equatorward aspect (if this is important). Glaciology
is also influenced by aspect: unless precipitation
patterns dictate otherwise (as in Iceland
where glaciers accumulate on the much wetter southwestern side) glaciers always accumulate downwards on the poleward side of mountains.
levels and seasonal influences similar to level slopes at lower elevation whereas poleward aspects have soil development
similarities to level soils at higher elevations. Soils with a prevailing windward aspect will typically be shallower, and often with more developed subsoil characteristics, than adjacent soils on the leeward where decelerating winds tend to deposit more air-borne particulate material. Outside of the tropics, soils with an aspect directed toward an early afternoon solar position will typically have the lowest soil moisture content and lowest soil organic matter content relative to other available aspects in a locale. Aspect similarly influence seasonal soil biological
processes that are temperature dependent. Particulate laden winds often blow from a prevailing direction near solar early afternoon, the effects combine in pattern common to both hemispheres.
, but there they produce many unexpected climatic effects:
Physical geography
Physical geography is one of the two major subfields of geography. Physical geography is that branch of natural science which deals with the study of processes and patterns in the natural environment like the atmosphere, biosphere and geosphere, as opposed to the cultural or built environment, the...
, aspect generally refers to the horizontal direction to which a mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...
slope faces. For example, a slope on the eastern edge of the Rockies
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
toward the Great Plains
Great Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...
is described as having an easterly aspect. A slope which falls down to a deep valley
Valley
In geology, a valley or dale is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys...
on its western side and a shallower one on its eastern side has a westerly aspect or is a west-facing slope. The term can also be used to describe the shape or alignment of a coastline. Here, the aspect is the direction which the coastline is facing towards the sea. For example, a coastline with sea to the northeast (as in most of Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
) has a northeasterly aspect.
Importance of aspect
Aspect can be very influencing on temperature. This is so because the concentration of sun's rays at the equator are more in a shorter area. Whereas, in the polar regions the same amount of sun light is concentrated in a larger area, resulting in a colder temperature.The aspect of a slope
Slope
In mathematics, the slope or gradient of a line describes its steepness, incline, or grade. A higher slope value indicates a steeper incline....
can make very significant influences on its local climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
(microclimate
Microclimate
A microclimate is a local atmospheric zone where the climate differs from the surrounding area. The term may refer to areas as small as a few square feet or as large as many square miles...
). For example, because the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
's rays are in the west
West
West is a noun, adjective, or adverb indicating direction or geography.West is one of the four cardinal directions or compass points. It is the opposite of east and is perpendicular to north and south.By convention, the left side of a map is west....
at the hottest time of day in the afternoon, in most cases a west-facing slope will be warmer than a sheltered east-facing slope (unless large-scale rainfall influences dictate otherwise). This can have major effects on altitudinal and polar limits of tree growth and also on the distribution of vegetation that requires large quantities of moisture. In Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, for example, remnants of rainforest are almost always found on east-facing slopes which are protected from dry westerly wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
.
Similarly, in the northern hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
a south-facing slope will accure before it becomes more open to sunlight and warm winds and snow will therefore generally be warmer and dryer due to higher levels of evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...
than a north-facing slope. This can be seen in the Swiss Alps
Swiss Alps
The Swiss Alps are the portion of the Alps mountain range that lies within Switzerland. Because of their central position within the entire Alpine range, they are also known as the Central Alps....
, where farming
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...
is much more extensive on south-facing than on north-facing slopes. In the Himalayas, this effect can be seen to an extreme degree, with south-facing slopes being warm, wet and forested, and north-facing slopes cold, dry but much more heavily glaciated.
For a farmer, thus, choosing an aspect that will shelter from hot, dry winds or from cold can be critical to successful growth of crops. Most farming agencies will state in manuals whether a crop prefers a poleward or equatorward aspect (if this is important). Glaciology
Glaciology
Glaciology Glaciology Glaciology (from Middle French dialect (Franco-Provençal): glace, "ice"; or Latin: glacies, "frost, ice"; and Greek: λόγος, logos, "speech" lit...
is also influenced by aspect: unless precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
patterns dictate otherwise (as in Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
where glaciers accumulate on the much wetter southwestern side) glaciers always accumulate downwards on the poleward side of mountains.
Soil aspects
In some locales there are patterns of soil differences related to differences in aspect. Strong slopes with equatorward aspects tend to have soil organic matterOrganic matter
Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds...
levels and seasonal influences similar to level slopes at lower elevation whereas poleward aspects have soil development
Pedogenesis
Pedogenesis is the science and study of the processes that lead to the formation of soil ' and first explored by the Russian geologist Vasily Dokuchaev , the so called grandfather of soil science, who determined that soil formed over time as a consequence of...
similarities to level soils at higher elevations. Soils with a prevailing windward aspect will typically be shallower, and often with more developed subsoil characteristics, than adjacent soils on the leeward where decelerating winds tend to deposit more air-borne particulate material. Outside of the tropics, soils with an aspect directed toward an early afternoon solar position will typically have the lowest soil moisture content and lowest soil organic matter content relative to other available aspects in a locale. Aspect similarly influence seasonal soil biological
Soil life
Soil life or soil biota is a collective term for all the organisms living within the soil.-Overview:In balanced soil, plants grow in an active and steady environment. The mineral content of the soil and its heartiful structure are important for their well-being, but it is the life in the earth that...
processes that are temperature dependent. Particulate laden winds often blow from a prevailing direction near solar early afternoon, the effects combine in pattern common to both hemispheres.
Coastal aspects
These are usually of importance only in the tropicsTropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
, but there they produce many unexpected climatic effects:
- The dryness of the Dahomey GapDahomey GapIn West Africa, the Dahomey Gap refers to the portion of the Guinean forest-savanna mosaic that extends all the way to the coast in Benin, Togo and Ghana, thus separating the forest zone that covers much of the south of the region into two separate parts...
, due to the rain-bearing winds moving parallel to the coast.
- The summer dryness of the Coromandel CoastCoromandel CoastThe Coromandel Coast is the name given to the southeastern coast of the Indian Subcontinent between Cape Comorin and False Divi Point...
due to the southerly monsoonMonsoonMonsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
flowing parallel to the coast. Its wetness during the northeast monsoon is similarly explained.
- The anomalous late autumn rainy seasons of central VietnamVietnamVietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
and the coastal zone of northeastern BrazilZona da Mata (coastal)The Zona da Mata is the narrow coastal plain between the Atlantic Ocean and the dry agreste and sertão regions in the northeastern Brazilian states of Maranhão, Piauí, Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe and Bahia....
for the same reason as above.
- The unusual dryness of Port MoresbyPort MoresbyPort Moresby , or Pot Mosbi in Tok Pisin, is the capital and largest city of Papua New Guinea . It is located on the shores of the Gulf of Papua, on the southeastern coast of the island of New Guinea, which made it a prime objective for conquest by the Imperial Japanese forces during 1942–43...
compared to the rest of New GuineaNew GuineaNew Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
is because the National Capital District lies parallel to the trade winds which have a drying effect. In Gulf Province and LaeLaeLae, the capital of Morobe Province, is the second-largest city in Papua New Guinea. It is located at the start of the Highlands Highway which is the main land transport corridor from the Highlands region to the coast...
, which receives their full force, rainfall during southern winter is exceedingly heavy.rain fall and thuder storms during the rainy season
- The relative dryness of the Queensland coast has the same cause as with Port Moresby.