Aspect (geography)
Compass direction of a slope or coastline.
Aspect, also called exposure, is the compass direction or azimuth that a terrain surface faces. It describes the orientation of a slope or coastline, such as an easterly aspect for a slope on the eastern edge of the Rockies toward the Great Plains. Aspect, together with grade or inclination angle, characterizes the surface gradient and influences physical and biotic features.
Quick Facts
- Field
- Physical geography, physical geology
- Known for
- Influence on temperature
- microclimate
- soil development
- and coastal climate
Facts from the source article.
Importance
Aspect strongly influences temperature because the Sun's angle in the Northern and Southern hemispheres is less than 90 degrees. In the Northern Hemisphere, north-facing slopes are often shaded, while southern slopes receive more solar radiation as they are tilted toward the Sun. The effect grows with latitude and proximity to winter solstice, and on steeper slopes; at 40° north on December 22, slopes steeper than 22.5° receive no energy. Aspect significantly affects local microclimate: west-facing slopes are generally warmer than east-facing ones because the Sun is in the west during the hottest afternoon period, unless large-scale rainfall patterns intervene. This influences tree growth limits and vegetation distribution; in Australia, rainforest remnants occur almost exclusively on east-facing slopes protected from dry westerly winds. In the Northern Hemisphere, south-facing slopes are warmer and drier due to higher evapotranspiration, as seen in the Swiss Alps where farming is more extensive on south-facing slopes. In the Himalayas, south-facing slopes are warm, wet, and forested, while north-facing slopes are cold, dry, and heavily glaciated.
Soil aspects
Soil differences can relate to aspect. Equatorward slopes often have soil organic matter and seasonal patterns similar to lower-elevation level slopes, while poleward slopes resemble higher-elevation level soils. Windward aspects typically yield shallower soils with more developed subsoil than leeward aspects, where winds deposit more airborne material. Outside the tropics, soils facing early afternoon solar positions tend to have the lowest moisture and organic matter content. Aspect also affects temperature-dependent seasonal soil biological processes.
Coastal aspects
Coastal aspects are mainly significant in the tropics, producing unexpected climatic effects. The Dahomey Gap's dryness results from rain-bearing winds moving parallel to the coast. The Coromandel Coast is dry during the southerly monsoon due to parallel flow, yet wet during the northeast monsoon. Central Vietnam and northeastern Brazil experience anomalous late autumn rainy seasons from similar causes. Port Moresby's unusual dryness compared to the rest of New Guinea arises because it lies parallel to drying trade winds, while Gulf Province and Lae receive heavy rainfall and thunderstorms during the rainy season. The Queensland coast's relative dryness shares this cause.
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