3.3.1 Geochemical concentration of major elements
Table 2 provides the average concentrations of major geochemical elements of the soils. As described in the previous section, these soils are still young with a very limited profile development, we combined data from all depth for data analysis. Anak Krakatau soil had higher contents of Al, Fe, Ca, Mg, S oxides, while Rakata soils have higher Si, and less Al, Fe, Ca, S, Mg compared to the other soils. The total alkali vs. silica showed two main composition clusters for the studied soils in the andesite and dacite fields (Figure 10). Soil samples from Rakata occupy the dacite field with SiO2 ranging from 71.1 to 75.5%, and these values were larger than those found in the Panjang and Anak Krakatau soils. Soils from Sebesi had a wider range of SiO2 content, and some had large K content. Soils of Anak Krakatau and Panjang had an andesitic composition.