3.3. Weathering indices
Weathering indices were calculated from the geochemical concentration to see the relative weathering of the volcanic materials. Figure 12 shows Ruxton index, desilication index, base loss, and Ca loss. Most indices indicated a progressive weathering sequence from the least to most weathered soil: Anak Krakatau < Panjang < Rakata < Sebesi. Nevertheless, the Ruxton and desilication indices, which reflect the loss of SiO2 indicated the considerable variation in weathering degree in soils at the Sebesi island.
Both base cations loss and Ca/Ti ratio confirmed former finding of the most weathered soils in Sebesi and least weathered in Anak Krakatau.