The chemistry of sublimates collected directly from lava fountains at Kilauea Volcano, Hawaii

Abstract

During 1970, it was occasionally feasible to collect sublimate from directly above the lava fountain in the crater of Mauna Ulu on the east rift zone of Kilauea Volcano, when the level of the lava pool had dropped within the crater. Collecting equipment was suspended down the steep wall to a position above the fountain. Collections were made on quartz wool held within open-ended quartz tubes and, for silica detection, on stainless steel wool in a stainless steel tube. The main components in the sublimate were, in order of decreasing concentration for the best sample, Na, Ca, Al, Fe, Mg, K, B, Si, Ti, Zn, H +, NH 4 +, Cu, Ni in the form of sulfates, chlorides and fluorides. In order to investigate the forms in which the sublimate ions occur under different conditions of temperature and oxidation, the equilibrium compositions of the compounds most likely to be present were calculated. This was done for those important components for which thermodynamic data are available, using a computer program to calculate the minimum free energy for the mixture. The results indicate that, for primary conditions of high temperature and low oxygen partial pressure, the halides were the most likely form of the metallic compounds. Particulate sulfates appear under increasing oxidizing conditions caused by the access of air. These conclusions were reinforced by collections made from holes drilled through the thin crust of a lava lake formed during the same eruption.