Analogue modeling of instabilities in crater lake hydrothermal systems

Abstract

[1] We carried out analogue experiments on two-phase boiling systems, using a porous vertical cylinder, saturated with water. The base of the cylinder was heated, and the top was cooled, as in a natural hydrothermal system. Previous work had shown that once the two-phase zone reached a certain level, thermal instabilities would develop. We made measurements of the acoustic energy related to boiling, and we found that high levels of acoustic noise were associated with the part of the cycle in which there was upward water movement. We repeated our experiments with a cooling water tank at the top of the system, representing a crater lake. This showed that periodic thermal instabilities still developed in this situation. We then compared our analogue measurements to two natural systems known to exhibit periodic behavior. There is good agreement between the thermal and acoustic cycling seen in our model and the observations made at Inferno Crater Lake in the Waimangu Geothermal area, New Zealand, whose level cycles by nearly 10 m, with a typical period of 38 days. Particularly notable is how in both systems high levels of acoustic noise are associated with rising water level. The much larger Ruapehu Crater Lake, also in New Zealand, cycled with a period of several months to a year for over a decade prior to the 1995 eruption. Strong acoustic and seismic energy usually occurred just before the lake temperature started to rise. This suggests a slightly different model, in which the increasing two-phase flow zone triggers more general convection once it reaches the base of the lake.

A water flow model of the active crater lake at Aso volcano, Japan: fluctuations of magmatic gas and groundwater fluxes from the underlying hydrothermal system

“…As in the case of Yudamari, simultaneous emissions of liquid water and steam are necessary at the Poás and Ruapehu crater lakes based on mass, energy, and Mg and Cl balances (Stevenson 1992). The system is similar to an analogue model that involves a two-phase boiling system, using a porous vertical cylinder saturated with water (Vandemeulebrouck et al 2005). The base of the cylinder is heated and the top is cooled, as in a natural hydrothermal system.…”

“…Based on analyses of chemical components, seismicity, and heat budgets, some crater lakes are regarded as a constituent part of their hydrothermal systems (e.g., Poás volcano in Costa Rica: Rowe et al 1992;Stevenson 1992; KusatsuShirane volcano in Japan: Ohba et al 1994). Laboratory experiments investigating changes in water level at Inferno Crater Lake in the Waimangu Geothermal Field, New Zealand, revealed that the cyclic changes in water level were caused by periodic thermal instability in porous media (Vandemeulebrouck et al 2005). Because volcanic activity such as continuous tremor can occur as a result of steamwater flow instability (Iwamura and Kaneshima 2005), monitoring the hydrothermal system beneath an active crater would provide information useful for understanding the mechanisms of these phenomena and for forecasting volcanic activity.…”

Precise remote-monitoring technique of water volume and temperature of a crater lake in Aso volcano, Japan: implications for a sensitive window of a volcanic hydrothermal system

“…Based on analyses of the chemistry, seismicity and heat-material budgets, some crater lakes, such as Poas volcano (Rowe et al, 1992), Kusatsu-Shirane volcano (Ohba et al, 1994), are considered to be constituent parts of a hydrothermal system. A laboratory experiment modeling the change in the water level of the Waimangu geothermal field suggested a hydrothermal instability ( Vandemeulebrouck et al, 2005). Nakadake in the Aso caldera ( Fig.…”

Volcanic Lakes

“…Lakes are approximated by a box of which the volume and temperature variations depend on heat and water entering (meteoric recharge, surface runoff, fluid input from the volcano) or exiting (evaporation, seepage, overflow) the lake. Fluid geochemistry is a common tool to study volcanic lakes, whereas subsurface processes may also be investigated by geophysical surveys (Rymer et al 2000(Rymer et al , 2009Vandemeulebrouck et al 2005;Fournier et al 2009;Caudron et al 2012), numerical modeling (Christenson et al 2010;Todesco et al 2012, this issue;Christenson and Tassi, this issue), and hydrogeology (Mazza et al, …”