Relations Between Soil Mass Movement and Relief in Humid Subtropical Low-Elevation Mountains

Abstract: Well-developed and undeveloped soils are present in tropical
and subtropical mountainous landscape. The soil types and mass
movement were determined by geomorphological processes. We studied
the relations between soil mass wasting and soil distribution and relief
in a subtropical low-elevation mountain in central Taiwan. Five soil profiles
located on different landscape sites with 5% to 30% slopes along
two transects were selected to evaluate soil mass wasting episodes by
estimating absolute soil ages according to predictive equations. From the
estimated absolute soil age, the soils in this mountain may have formed
in the early Pleistocene (ca. 1200È1500 ka). However, the soils of this
era were mass wasted during mid-Pleistocene (ca. 200È900 ka) and
were preserved only in the footslope areas as buried soils. The geomorphological
surface of the mid-Pleistocene was covered with colluvial
material in the backslope areas and exposed at the footslope sites. In
recent era, soils on the ridge were mass wasted and accumulated on the
backslope areas, which led to a new soil genesis direction; therefore,
soils located on the ridge and backslope are classified as Inceptisols or
Cambisols and those on the footslope area as Typic Hapludults or Acric
Nitisols. The variety of soil development and distribution based on relief
in this mountain forest in Taiwan show the key features of unstable Kcycle
phases and are best illustrated in the alternating (backslope) and
accreting (footslope) zones of the K-cycle. This study also presents that
iron activity (Feo/Fed) and crystallinity of iron (Fed j Feo/Fet) are good
indices to infer or predict soil ages in this area.