Dynamics of Lake Eruptions and Possible Ocean Eruptions

Dissolved gas in liquid is able to power violent eruptions. Two kinds of such gas-driven eruptions are known in nature: explosive volcanic eruptions driven by dissolved H2O in magma at high temperatures and lake eruptions driven by dissolved CO2 in water at low temperatures. There are two known occurrences of lake eruptions, one in 1984 (Lake Monoun) and one in 1986 (Lake Nyos), both in Cameroon, Africa. The erupted CO2 gas asphyxiated ∼1700 people in the Lake Nyos eruption and 37 people at Lake Monoun. Here we review experimental simulations of CO2-driven water eruptions and dynamic models of such eruptions, and a bubble plume theory is applied to the dynamics of lake eruptions. Field evidence, experimental results, and theoretical models show that lake eruptions can be violent, and theoretical calculations are consistent with the high exit velocities and eruption columns inferred from observations. Furthermore, the dynamics of lake degassing experiments are consistent with theoretical models. Other kinds of gas-driven eruptions are possible and may have occurred in nature in the past. A concentrated and large release of methane gas or hydrate from marine sediment may result in an ocean eruption. Furthermore, injection of liquid CO2 into oceans might also lead to ocean eruptions if care is not taken. The various kinetic and dynamic processes involved are examined and quantified. 293 First published online as a Review in Advance on January 16, 2006 A nn u. R ev . E ar th . P la ne t. Sc i. D ow nl oa de d fr om a rj ou rn al s. an nu al re vi ew s. or g by U ni ve rs ity o f M ic hi ga n on 0 2/ 01 /0 6. F or p er so na l u se o nl y. ANRV273-EA34-10 ARI 29 December 2005 20:35 INTRODUCTION TO GAS-DRIVEN ERUPTIONS No sight on Earth is more inspiring than that of an explosive volcanic eruption column ascending tremendously into the sky. Explosive eruptions are one kind of gas-driven eruptions, and they were the only kind known to science before 1984. Since that time, however, lake eruptions have been recognized (Freeth & Kay 1987; Kling et al. 1987, 1989; Sigurdsson et al. 1987; Sigvaldason 1989; Tazieff 1989; Freeth 1990; Freeth et al. 1990; Giggenbach 1990; Sabroux et al. 1990), and other types of gas-driven eruptions have been proposed (Chivas et al. 1987, Crawford & Stevenson 1988, Ryskin 2003, Zhang 2003). This paper reviews the dynamics of gas-driven eruptions, focusing on lake eruptions and possible ocean eruptions. Gas-driven eruptions are powered by the rapid exsolution of initially dissolved gas in a liquid. At high system pressures, the gas component is dissolved in the liquid. As the system pressure decreases, the solubility of the gas in the liquid decreases. Once supersaturation of the gas is reached, bubbles nucleate and grow, leading to large volume expansion. The expansion either drives the bubbly liquid upward through a solid medium (as in volcanic eruptions), or leads to the buoyant rise of a bubble plume in a fluid medium (as in lake eruptions). The dynamics of gas-driven eruptions depend on the gas-liquid system, whether the eruption is through a solid conduit or a fluid medium, and the initial and boundary conditions. Small-scale gas-driven eruptions may also be encountered during daily life. For example, champagne and beer may erupt when opened, especially if previously shaken. However, if opened carefully these liquids may not violently erupt because nucleation of bubbles is a difficult process. That is, for a system with a small degree of supersaturation, slow nucleation may suppress eruption. In such a case, addition of nucleation sites would facilitate eruptions. For example, if you enjoy beer and cigarettes (which we do not encourage), you may try the following “trick.” Open a bottle of cold beer, without shaking it, and place it on a table. Although beer is oversaturated with CO2, few bubbles would form and grow because nucleation requires some activation energy. Ask if your friends are able to drink it without touching the bottle by hand. When no one can accomplish this, light a cigarette and tap some cigarette ash into the beer. The ash particles provide nucleation sites and bubbles nucleate and grow. The resulting volume expansion drives bubbly beer to flow from the bottle mouth, where it can be consumed without touching the bottle.