Mountain Soils - Mountain Geography: Physical and Human Dimensions - page 305

becomes part of the geologic record. If a mountain has been severely eroded by glaci-
ers, its surfaces may have been scraped to bare rock. Where soil has been removed or
buried, time starts at zero.
A number of studies have documented the relative rate of soil development on young-
er features such as glacial moraines and mudflows (Mahaney 1990; Morisada and Oh-
sumi 1993; Douglass and Bockheim 2006; Haugland and Burns 2006). Although the rate
of soil formation is variable, evidence of the early stages of soil development usually
appears within a century or so. In the moist tropics, the rate is greatly telescoped, par-
ticularly on volcanic parent material, so that a soil may begin to develop within dec-
ades; in mid-latitude and polar mountains, it may take thousands of years. The erup-
tion of the Indonesian island volcano Krakatoa in 1883 deposited a new land surface
on the remnant island, Rakata. Today, Rakata is covered with lush tropical vegetation
and relatively well-developed soil. By contrast, in many areas in mid- and high-latitude
mountains, several millennia of exposure to the elements have failed to result in a well-
developed soil. One investigation of glacial deposits in the subalpine zone of the Indian
Peaks region, Colorado Rockies, estimated that over 2,000 years were required for the
soil to develop distinctive horizons and achieve a steady pH (Retzer 1974). Soil develop-
ment is limited by low moisture as well as by low temperatures: In maritime mountains,
where moisture is plentiful, soil would develop faster than in arid mountains. On Mount
Kenya, soil depth, degree of horizon development, surface color, and grade of soil struc-
ture are closely associated with the age of the Pleistocene and Holocene parent material
deposits (Mahaney 1990). Soil horizons in the Afroalpine developed slowly: A “B” hori-
zon formed within about 2,000 years (Fig. 6.4). Deposits near active glaciers or volca-
noes provide excellent sites for studying the early stages of soil development (Douglass
and Bockheim 2006). In Switzerland, Egli et al. (2001) used radiocarbon dating to de-
termine the ages of six soils, ranging from 150 years to 10,000 years, and then studied
chemical changes in the soil profiles over time. A useful aspect of the relationship of soil
development to time is that, once rates of weathering and soil development have been
determined in an area, the degree of soil development can be used to estimate the age
of nearby surfaces.