Soil Development from Volcanic Ash Based on Different Pyroclastic Composition

Abstract

Potential volcano in several provinces in Indonesia played a significant role in the formation and quality of soil development. Soils that developed from the volcanic ashes are often thought to contribute greatly to improve soil fertility, without regard to the nature and composition of the volcanic ash produced. Volcanic ash generated from the results of volcanic activity has a different composition, there are basaltic, andesitic and granitic, thereby affecting the formation and characteristics of the soil. The objective of this study was to determine the soil development from different types of pyroclastic materials generated from the Lokon volcano in North Sulawesi. The study was carried out at the foot of Mount Lokon with three-point of coordinates, namely (1) 1o 21’18.0“ N and 124o 49' 20.2” E, (2) 1o 21’ 30.2“ N and 124o 49' 2.8” E, (3) 1o 24’ 23.70“ N and 124o 52' 17.30“ E. Arc-GIS 10.3 software was used for mapping the location of the study with the base maps of a regional geological map and the topography map. Soil characteristics including texture, pH, organic-C, Cation Exchange Capacity (CEC), and mineral contents were determined. The results show that there are two types of pyroclastic as the source of soil development from volcanic ash, namely; 1) basaltic pyroclastic with 43.26% SiO2 that is resulted from the first magmatic eruption and 2) andesitic pyroclastic with 5.09% SiO2 that is resulted from the late magmatic eruption. Basaltic pyroclastic contains Fe 37.63%, Al 11.35%, Ca 13.17% and Mg 5.69%, while andesitic pyroclastic contains Fe 38.35%, Al 6.87%, and Ca 8.61%. Rainfall ranges from 2000 to 3500 mm yr-1, which helped the soil formation and influenced the characteristics of the soil, such as sandy loam texture, soil organic-C content 3.08% , CEC 23.24 cmol (+) kg-1 and clay CEC 148.93 cmol(+) kg-1. The clay minerals in the soil consist of vermiculite, kaolinite and, halloysite. Cation supply from basaltic pyroclastic influences the formation of vermiculite mineral, whereas andesitic pyroclastic largely influences the formation of the kaolinite mineral. The formation of soil texture with a predominance of the sand fraction is more influenced by the type of andesitic pyroclastic that is more resistant to weathering processes.

Keywords

• andesitic
• kaolinite
• pyroclastic
• soil
• volcanic ash