Wednesday, November 7, 2007
288-6

Effect of Volcanic Ash Deposition on the Soils of Montserrat Island, West Indies.

Thilini D. Ranatunga1, Kamala N. Bhat2, Robert W. Taylor2, Richard April3, and Zachary N. Senwo2. (1) Department of Natural Resources and Environmental Science, Alabama A&M University, P.O. Box 1208, Normal, AL 35762, (2) Department of Plant and Soil Science, Alabama A&M University, P.O. Box 1208, Normal, AL 35762, (3) Department of Geology, Colgate University, Hamilton, NY 13346

Soufriere Hills Volcano is an active volcano that lies in the south-central part of the volcanic island of Montserrat, West Indies. Continued intermittent deposition of volcanic ash from Soufrière Hills volcano occurred since its major eruption in 1995. Heavy ash deposition along with the extremely high temperatures is believed to have effects on the chemistry of the soils beneath the ash. Thus, assessment of the impact of ash deposition on the soils of Montserrat was carried out by detailed chemical analysis of the ash and soils from areas severely affected by the volcano. Elements in volcanic ash determined by XRF measurements shows the presence of Si, Al, Ca, Fe, Na, Mg, K, Ti, Mn, and P as the major elements. High levels of extractable Al found in ash as well as ash-soil mixtures and soil itself is a significant concern because of potential Al toxicity to vegetation. In addition, elevated levels of extractable Fe and Mn were also found in soils which are of a concern. However, high levels of available Ca, Mg, and P present in ash should enhance the fertility of the soil-ash mixture as well as the resulting soil which will form. Sequential P extraction indicates that most of the P in ash is likely to exist as Ca-bound-P followed by Al- or Fe-bound-P with significant amount of residual P. Trace or heavy metals in ash and ash soil samples were significantly lower indicating that heavy metal contamination of soils by continuous ash deposition will be minimal.