Noble gases from the Earths mantle

The local He flux in volcanic lakes can be significantly higher than the He flux 

Identification of gases of mantle origin in lakes can contribute to the understanding of the distribution of other gases and in particular of CO2. The accumulation of CO2 in Lake Nyos led to lethal gas bursts. Based on He, He, and Ne measurements it could be demonstrated that the high CO2 concentrations were of mantle origin and that the CO2 flux from the mantle leads to critical conditions in Lake Nyos within about 20 to 30 years (Sano and Wakita 1987 Sano et al. 1990). 

---