Keywords:Initial soil formation, primary succsession, organo-mineral interaction, soil organic matter, volcanic ash soil, Miyake Island
Mt. Oyama in Miyake Island erupted with large amounts of volcanic ash in 2000. Large areas of the island were severely damaged by the volcanic ash, debris flow and volcanic gas. The areas from the mountain top (new crater) to mountain side on western part of the Island (Igaya area) were buried by thick volcanic ash deposition followed by primary succession of plant-soil system. The research on the initial soil forming process on fresh volcanic ash under natural environment is important to understand the development of volcanic ash soil (Andosols) and ecosystem in volcanic region. Co-variation between vegetation growth and accumulation of organic matter is especially important. We conducted soil profile investigation and sampling in the vegetation monitoring sites at Igaya area in 2007, 2011, 2015 and 2017. We examined the changes in the soil profile morphology and soil physico-chemical properties in the time series. Organo-mineral particle was separated by the combination of density and particle size fractionation and the recovered fractions were observed by scanning transmission X-ray microscopy (STXM) and near-edge X-ray absorption fine structure (NEXAFS). We will discuss on the concurrent development of soil-vegetation system and the accumulation of soil organic matter in the initial soil formation.