Time as a factor

Abstract

As in physics, chemistry, and biology, it is common also in soil science to study changes with time as the independent variable, or x axis in a graphical representation. These kinds of relationships are called chrono-functions. Some processes of soil formation, such as podzolization, are simple and rapid enough to be studied by means of laboratory experiments (Fisher & Yam 1984). Most soil-forming processes are too slow for such an approach, and chronofunctions are derived by comparing changes in soils of different age. If such studies are to reflect purely the effect of time on soil formation, then all the studied soils should also be comparable in climate, organisms, topography, and parent material. Such a study set of soils is called a chronosequence. The best known kinds of chrono-sequences are on flights of terraces abandoned on valley walls by downcutting streams (Harden 1982a) and on concentric moraines dumped successively by retreating glaciers (Burke & Birkeland 1979). Chrono-sequence studies are also useful for estimating rates of deformation and recurrence intervals of earthquakes along faults. The security of large permanent engineering works, such as dams and nuclear power plants, in tectonically active areas depends on such studies of soils (Shlemon 1985).