Characteristic of Soils Developed from Pyroclastic Materials Across the Dry Southwest Tambora’s Footslope

Abstract

Development of soils from newly deposited materials are of interest for investigation, especially when the environment has specific conditions as the leading factors of the soil formation and development. The Southwest Tambora’s footslope is part of the last Tambora’s pyroclastic deposition but this part has the driest climate. Despite this Southwest Tambora’s footslope in fact at macro scale has homogeneous specific conditions, the results of toposequential soil observation showed that this area composed of soils having significant differences, even differed one another at the higher order of classification. The common characteristic of the soils in this area is that they have sandy texture with 70 to 90 percent sand mostly with limited soil horizon development, only minority of the soils already have B horizon. Regardless the sandy texture as the common strong characteristic of the soils here, the formation of B horizon is the strongest differentiae among the soils and yet there are some other characteristics to show that even the soils of the same taxonomic class are not necessarily homogeneous. Previous geological studies of this part of Tambora’s footslope depicted different modes of the deposition of the last erupted pyroclastic materials, among others by transportation and sortation processes after the material eruption. This difference has resulted in different stratification of particle size and the level of compaction of the pyroclastic materials. So the soil formation here have been taken place from not a completely homogeneous parent material condition, under the limited weathering rate due to the dry climate.