ABSTRACT: The upper two of a series of four fan surfaces in the Kokoda
Valley, Papua and New Guinea, are covered with volcanic ash. Soils on these two
surfaces have fine-grained textures and well-developed structural characteristics.
The plasma of these soils is isotropic in thin section. Differences in color and in
the kinds of clay minerals present in these two soils are attributed to the drainage
conditions of the underlying material.
The lower two of the four fan surfaces have soils developed mainly from
alluvium. Some soil profiles on the older of these two surfaces are partially derived
from reworked volcanic ash. The alluvial soils are coarser grained and shallower
than the volcanic ash soils. The plasma of the alluvial soils exhibits increasing
birefringence with decreasing amounts of volcanic ash.
The soil pattern proved useful in interpreting aspects of the geomorphic history
of the study area
