Reconstruction of a toposequence on volcanic material in the Honje Mountains, Ujung Kulon Peninsula, West Java

Soil formation on weathered acid tuffs was studied in the National Park of the Ujung Kulon Peninsula, West Java, Indonesia. In a toposequence in the Honje Mountains, five principal types of materials (layers) were distinguished based on micromorphology, mineralogy and chemistry. The deepest part of all profiles corresponds to a saprolite derived from Tertiary and Pleistocene volcanic deposits, locally showing the influence of pedoplasmation. The overlying layer also contains saprolite fragments, but later, pedogenic processes are indicated by striated b-fabrics and strong clay illuviation. In most profiles, formation of plinthite partly postdates clay illuviation. A transition layer separates this part of the profile from the top layer, which is characterised by a more open microstructure, an undifferentiated b-fabric and the presence of pumice gravel, feldspars and pyroxenes, originating from the Krakatau ash fall. After the uplift of the Mio-Pliocene Banten tuffs, deep ferrallitic weathering was followed by a period of erosion during which stone lines were formed. Hitherto these have been attributed to occasional coarser tephra falls. In a subsequent period of stability weathering and processes of pedoplasmation, clay illuviation and plinthitisation were active. During the eruption of the nearby Mount Krakatau in 1883, the area was covered by a layer of fresh ash, which affected the composition and microfabric of the top layer, leading to more andic properties. No important erosion event followed the ash fall.