The Geochemistry and Potential Fertility of Volcanic Ash Discharged by Alaid and Ebeko Volcanoes, Kuril Islands

• Published in: Journal of volcanology and seismology 2021-09, Vol.15 (5), p.333-348
• Main Authors: Zakharikhina, L. V., Rashidov, V. A., Anikin, L. P.
• Format: Article
• Language: English
• Subjects: Ashes; Basicity; Chemical composition; Comparative analysis; Deficient elements; Discharge; Earth and Environmental Science; Earth Sciences; Ejecta; Eruptions; Europium; Fertility; Fertilizers; Fractionation; Geochemistry; Geology; Geophysics/Geodesy; Inspection; Islands; Nickel; Niobium; Radioisotopes; Rare earth elements; Rivers; Silicon; Silver; Streams; Surface water; Thorium; Time factors; Tin; Trace elements; Volcanic activity; Volcanic ash; Volcanic eruptions; Volcanic rocks; Volcanoes
• ISSN: 0742-0463; 1819-7108
• DOI: 10.1134/S0742046321050079

We have found out the general patterns in the elemental composition of ash ejected by the Kuril volcanoes Alaid and Ebeko. The ashes show persistent exceedances in the concentrations of K, Bi, U, Cs, Th, Na, and Yb relative to the mean concentrations for the respective types of volcanic rock. The deficient elements (Kk < 1) include Mg, Ag, Sn, Nb, Ta, Ni, and Cr. Inspection of the range of ashes ejected by different volcanoes of Kamchatka (Klyuchevskoi, Tolbachik, Ksudach, Bezymyannyi, Koryaksky, Shiveluch, and Kizimen) showed that the ejecta of Shiveluch and Kizimen are the most similar in elemental composition to the ashes discharged by the volcanoes of the Kuril Islands studied here. The ashes of Alaid and Ebeko volcanoes differ from most Kamchatka ashes in having higher concentrations of radioactive elements (U, Th). We have found a comparatively high potential of biological productivity for the Kuril ashes. The potential fertility index considered here (PFI) when compared with the most productive ash on the Kamchatka Peninsula whose PFI was taken to be unity is 0.72 and 0.66 for Alaid and Ebeko, respectively. The PFI shows a persistent dependence on the concentration of silicon in the ashes: the higher the basicity of an ash, the greater is its potential fertility. It is for the first time that we have discovered fractionation of rare earth elements occurring in all volcanic ashes under study here (both those for the Kuril Islands and for Kamchatka) in the form of a positive europium anomaly with E/Er* varying between 1.2 and 1.8. The estimation of the elemental composition for the surface waters of a brook that flowed on Ebeko Volcano did not reveal any tendency of active transfer of radioactive elements from ashes to naturally occurring solutions. A comparative analysis of the waters of this brook and the streams around the Kamchatka volcanoes studied here showed that the relationship between their compositions is largely controlled by the time factor. Streams near different volcanoes show similarities at the time of an eruption, and their water very actively receives rare earth elements (REE), their concentrations in brooks exceed the mean REE concentrations for fresh waters in continents by two orders of magnitude. When the volcanic event comes to an end, the relationship between the geochemical compositions of water in areas of ashfalls due to different volcanoes becomes weaker. The waters of small streams near volcanoes during eruptions can be r