Energetics of gas-driven limnic and volcanic eruptions

This paper lays the foundation for the rigorous treatment of the energetics of gas exsolution from a gas-containing liquid, which powers gas-driven volcanic and limnic eruptions. Various exsolution processes (reversible or irreversible, slow or rapid) are discussed, and the maximum amount of kinetic energy derivable from a reversible gas exsolution process is obtained. The concept of dynamic irreversibility is proposed for discussing the kinetic energy available from irreversible gas exsolution processes. The changes of thermodynamic properties during gas exsolution processes are derived. Density–pressure relations for gas–liquid mixtures are presented, including empirical relations for irreversible gas exsolution. The energetics of gas-driven eruptions through both fluid and rigid media, including the role of buoyancy and the role of magma chamber expansion work, are investigated. For reversible processes, the energetics can be used to discuss the dynamics of gas-driven eruptions, leading to maximum erupting velocities and maximum eruptible fractions. For irreversible processes, empirical relations and parameters must be employed. The exit velocities of the Lake Nyos eruption and the 18 May 1980 eruption of Mount St. Helens are modeled by incorporating possible irreversibility.