Geography Reference
In-Depth Information
physical principles underlying meteorological processes, and they
routinely used elementary statistics in summarizing their data. It
was therefore less of a conceptual or practical leap for climatology
to focus on processes. The result was explanations for climatic
patterns based on the general circulation of the atmosphere,
driven by energy from the Sun and incorporating smaller-scale
circulation patterns, such as the mid-latitude depressions, and
modifi ed by regional and local effects, such as topography and
surface characteristics. Today, the knowledge of such processes
is being used as essential inputs to understanding the climatic
changes that are occurring at the beginning of the 21st century (as
discussed in Chapters 4 and 6).
Soil geography illustrates well the importance of processes to
physical geography by linking the different types of soil to the
different environments in which they form. Several soil-forming
processes transform the unconsolidated material cover of the
Earth's surface (the regolith) into productive soil. Each involves a
set of physical, chemical, and/or biological transformations, and
their effectiveness varies in different parts of the world. Leaching,
for example, refers to the removal of soluble constituents from
upper soil horizons: it requires downward percolation of water
through the soil and commonly occurs where rainfall exceeds
evaporation. Eluviation, the mobilization of clay in the upper
horizons and its redeposition in the subsoil, is best developed in
humid climates with a dry season. In contrast, upward movement
of soluble salts (salinization) and their accumulation in the soil
profi le is characteristic of arid and semi-arid lands where there
is insuffi cient rainfall to wash them out. The salts are drawn up
in groundwater by capillary action and left behind as the water
evaporates. Little understanding of the variability of the world's
soils is possible without knowledge of these processes going on
in the soil. Furthermore, the greater our understanding of soil-
forming processes, the more likely it is that soil management and
conservation will be effective, soil productivity maintained, and
soil degradation minimized.
