The impact of the Mount Kelud eruption on soil characteristics and classifications

Mount Kelud is located in the eastern part of Java in Indonesia, and an eruption occurred there in 2014. This eruption produced volcanic materials, particularly distributed on the northeast and southern slopes. This Plinian eruption and the new pyroclastic materials could possibly have influenced changes to the soil development and classification but to date there have been no investigations to determine the nature of such changes. The main objectives of this study were to determine these changes in soil characteristics and classification affected by pyroclastic materials which were thicker on the north-east compared to the south slopes. For each slope, north-east (PTL) and south (PS), five slope positions were studied, i.e., top (1), upper slope (2), middle slope (3), lower slope (4) and plains (5). The results show that the thickness of the new pyroclastic material is less than 50 cm (in fact always less than 30 cm occurred in field measurements), but having slight variations in thickness depending on the sequence concerned. Hence the definitional requirement for a buried soil of 50 cm was not found following the 2014 eruption. Compared to the south (PS) slopes where no C horizon was developed, on the northeast (PTL) a varying thickness but less than 30 cm of new materials was found. This new pyroclastic material had a loose, single structure, light soil colour, high bulk density in the top layers but coarse texture, low organic carbon content and was low in exchangeable cations. The andic properties as defined in Soil Taxonomy (Soil Survey Staff, 2014) were not met in these new deposits. However based on this study, classification differences have occurred in the Upper Slope (PTL-2 Vitrandic Humudepts and PS-2 Humic Udivitrands), and in the Middle Slope (PTL-3 Vitrandic Humudepts and PS-3 Typic Udivitrands). The Lower Slope (PTL-4) and Plains (PS-5) were Fluvaquentic Endoaquepts and Fluvaquentic Humaquents respectively.