Growth-zoned gypsum stalactite from the Kawah Ijen volcanic lake, Indonesia, records a >40-year record of volcanic activity

Abstract

Volcanic crater lakes represent both a significant hazard and an opportunity to monitor the activity of their host volcano. Unfortunately monitoring efforts, especially of lake water composition, are commonly limited by the lack of a historical record. Here we report the results of a study on the Kawah Ijen crater lake in eastern Java, Indonesia that uses growth-zoned gypsum precipitated from lake water seepage as a proxy record of lake water chemistry. Absolute ages for gypsum growth zones were determined from 210Pb radionuclide dating with a newly developed Ar-Kr-Xe correction for variations in the volcanic flux. The resulting 40-year time series of gypsum composition shows that periods of unrest are recorded by large compositional variance, whereas quiescence is characterized by low concentrations and low variance. Gypsum associated with the 1817 phreato-magmatic eruption of Kawah Ijen is similar in most elements, but it has markedly higher ratios of Cu over Sb, As and Tl, which is interpreted to represent a volcanic gas signal. These results show that gypsum holds great promise to provide the missing historical record of lake chemistry and unrest at Kawah Ijen volcano, and this approach can be extended to other volcanoes hosting crater lakes where gypsum is present.