Hazardous Crater Lakes

Abstract

Geochemistry of crater lakes can provide information about deep magmatic activity and shallow volcano-fluid interactions because the lakes act as condensers, traps, and calorimeters for magmatic volatiles and heat supplied through the volcanic conduits. Such information is only available through long-term monitoring. Some recent results obtained by geochemical monitoring are reviewed with special emphasis on mitigation of crater-lake related disasters. Currently applied geochemical and geophysical monitoring methods of crater lakes include variations in Mg/CI ratios, polythionate speciation, acoustic survey, and mass balance calculations, which together provide useful insights on what is going on within and beneath the active crater lakes. Crater lakes hosted by dormant volcanoes can sometimes be hazardous, and examples include Lakes Nyos and Monoun (Cameroon) where CO2 stored in the lakes suddenly burst out, killing close to 1800 people in 1984 and 1986. More than 7 years continuous monitoring of the lakes has revealed that a tremendous amount of CO2 still remains in the lakes, that it is increasing at an alarming rate (ca. 0.2 Gmol/year for Lake Nyos and 0.02 Gmol/year for Lake Monoun) especially within the bottom layers, and that a permanent, subbottom recharge system exists which provides dissolved CO2 as well as various chemical species and heat to the lakes in the form of warm springs. Recurrence of the gas bursts is highly probable and remedial measures such as reduction of CO2 through controlled degassing of these lakes are strongly recommended.