Numerical assessment of the potential for future limnic eruptions at lakes Nyos and Monoun, Cameroon, based on regular monitoring data

We assessed the potential for limnic eruptions at lakes Nyos and Monoun, Cameroon on the basis of numerical modelling and CO₂ profiles obtained by regular monitoring of the lakes. The change through time of the profiles suggests one particular scenario for producing an eruption: a supply of CO₂-undersaturated fluid from the lake bottom that induces upwards growth of the CO₂-rich bottom layer, leading eventually to CO₂ saturation at mid-depths of the lake. By using a numerical model for the ascent of a plume of CO₂ bubbles, we found that under realistic conditions (e.g. a profile of CO₂ as deduced from the regular monitoring data), a bubble plume generated from the middle depths of the lake can reach the lake surface with a high flux of CO₂, which corresponds to a limnic eruption. In addition, we developed a numerical model to investigate how changes in the CO₂ concentration at the lake bottom affect the dynamics of a two-phase flow in the controlled degassing pipe, using the recently observed CO₂ profiles. This model enables us to estimate the CO₂ concentrations at the lake bottom from the heights of fountains that are observable at the lake surface.