Process and Mineralogy of Volcanic Materials on the South Side of the Old Lawu Volcano in Java Island

Abstract

Activities of Old Lawu volcano in the past resulted in various soil development in the south side of the volcano, especially in the area of the east side of Wonogiri and west side of Ponorogo, that located in the Java island. This area is also famous as herbal crops producer for raw materials of traditional herbal medicine industry. The purpose of this research is to identify the process of exposure of the parent materials in the Old Lawu volcanic environment, the development of the soil parent materials, and the mineralogy variation.\xa0 Four Sites with different geological formation were observed, and each Site was selected for soil profile identification on the process of weathering of rocks.\xa0 All layers of each profile were then sampled and then sand fraction of the fine earth particle was determined for the mineral type using X-ray diffraction (XRD).\xa0 The results showed that materials of the Old Lawu volcanic activity that was of quaternary period had sized material of gravel, sand, silt, and clay. These materials were then exposed and undergone the process of weathering, transportation, and sedimentation according to the landform at that period. The development of soil as geoheritage in this region was influenced by the material size, landform, and settling process. There are four typologies of the environment on the soil development at the present study, there are: (1) Soil that developed in the inter-fluvial basins is characterized by thick soil and a clear horizon differentiation process as a feature of maturity stage of soil development. (2) Soil developed on the slope of hill area is characterized by shallow in solum and it is in early-stage soil development. (3) Soil developed on the volcanic materials that were transported and sedimented in the river environment is characterized by the thick soil above the layered fine size parent material with a variety of color. (4) Soil developed on the tertiary breccia showed early soil development.