Turbulent bubble plumes and CO2-driven lake eruptions

We examine the motion of turbulent bubble plumes within lakes containing large quantities of dissolved CO2 such as Lake Nyos, Cameroon. First we describe some new laboratory experiments in which we examine the dynamics of turbulent bubbles plumes produced by electrolysis in an aqueous solution. These experiments were analysed to determine the entrainment rate into the plume. Using the experimental results, we then develop a model of the motion of a bubble plume through a CO2-rich lake. The model identifies that for a sufficient amount of dissolved CO2 in the lake or a sufficient flux of CO2 at the base of the lake, a turbulent bubble plume can rise through the lake and erupt at the surface. The model predicts that owing to the rapid entrainment of ambient fluid, the surface flux of CO2 may be 104–105 times greater than that at the base of the lake. We also show that the return flow in the lake acts to decrease the CO2 content at all depths as the CO2 is erupted at the surface, and that this eventually leads to termination of the activity. The model provides the first quantitative analysis that CO2 saturated lakes can overturn convectively and lead to rapid degassing events such as occurred at Lake Nyos in Cameroon in 1986.