Distribution of Fe and Al Forms In Soufriere Hills Volcanic Ash and Volcanic Ash-Derived Soil.

Soufriere Hills volcano is an active volcano that lies in the south central part of the volcanic island of Montserrat, West Indies.  Volcanic ash and volcanic ash-derived soils were found to contain three major elements, Fe, Al, and Si. Selective dissolution methods were utilized to characterize Fe and Al forms in volcanic ash and distribution of these forms in the soil profile. Three common dissolution procedures which include  ammonium oxalate (Fe_o/Al_o), sodium pyrophosphate (Fe_p/Al_p) and dithionite –citrate –carbonate (Fe_d/Al_d) extractions indicate significant differences in the distribution of different forms of Fe and Al in soils highly affected by the volcano compared to areas minimally affected. Greater proportion of Fe_o  was found in volcanic ash samples. The crystallinity of the iron oxides was determined by the ratio of Fe_o / Fe_d.  The ratio varied between 0.63-3.25 depending on the location and depth of soil from highly affected areas. Greater proportion of non-crystalline Fe forms and allophane were observed in soils minimally affected by the volcano. Distribution of allophane in soils of highly affected areas in the volcanic region varied with the soil depth.