Mountain Soils - Mountain Geography: Physical and Human Dimensions - page 300

combined presence of fine material and moisture is favorable to the establishment of
plants. Wind-blown deposits are often alkaline and thus help counteract the natural
acidity of alpine soils (Delmas et al. 1996). Many mountain soils develop from wind-
borne deposits rather than through the breakdown of bedrock (Retzer 1965; Muhs and
Benedict 2006), especially where deposits of volcanic ash produce deep soils, as in Ice-
land, Japan, and the northern Andes (Buytaert et al. 2005).
FIGURE 6.1 Graphical portrayal of the combined effects of altitude, temperature, moisture, and time
in the La Sal Mountains, Utah. (From Richmond 1962.)
Climates change. During the past 900,000 years, glaciers in Europe and North Amer-
ica have advanced and retreated nearly 20 times. Midlatitude and polar mountains ex-
perienced the effects of these major climatic changes more acutely than lowlands, being
glacier-covered even when the surrounding lowlands were not. Consequently, soil sur-
faces in mountains such as the Alps or Rockies only began to form after the ice melted,
and thus are young (10,000-15,000 years). The climate has warmed since then, though
marked fluctuations have occurred. Surfaces that escaped direct glaciation provide
evidence of the soil-forming and geomorphic effects of these climatic events (Fig. 6.1).
In some cases, older soils persist and retain the characteristics that evolved under very
different climatic regimes. The Coast Range of northern Oregon contains ancient red-
dish lateritic soils ( Oxisols, highly weathered lowland tropical soils) formed during the
Miocene (20 million years ago). As the climate changed, its effect on soil development
also changed, so that older soils served as parent materials for modern soils.
A soil can develop under one climatic regime in the lowlands and then be uplifted
to higher elevations during mountain building. This probably happened in the Oregon
Coast Range, where the major uplift occurred during the Pliocene (10 million years