UC Berkeley

Geysers are hot springs that periodically or episodically erupt liquid water and vapour. They are uncommon because they require a combination of abundant water recharge, magmatism to supply heat and silica, and fractures or cavities to trap rising multiphase fluids. To better understand the dynamics inside of geyser conduits, interaction between geysers, properties of the surrounding rock, and the origin of the fluid, we collected data in the El Tatio geothermal field, Atacama Desert in Chile, during October 2012 and 2014. We monitored eruption intervals, durations, and discharge through measurements of pressure and temperature within geyser conduits. At the surface, we collected samples for petro-physical and geochemical analysis. We identify that geyser systems evolve over time, including changes in the interval between eruptions, development of new thermal features, and interactions between geysers. Though geysers erupt with different styles, we recognize some common features: the conduit recharges with liquid during the quiescent period, bubbles enter the conduit before eruptions, and eruptions occur when water boils in the upper part of the conduit. Eruptions are triggered by the episodic addition of steam coming from depth suggesting that the dynamics of the eruptions are dominated by geometrical and thermodynamic complexities in the conduit and deeper reservoir. The depth where heat is added dictates the eruption style: conduits with deeper heat input are more likely to show pre-play or minor eruptions. Further evidence favoring the dominance of internal processes in controlling periodicity is also provided by the absence of responses of the geyser to environmental perturbations (air pressure, temperature and Earth tides). The thermal features interact by pressure transmission through subsurface permeable layers, which is consistent with permeability measurements of sinter in the lab. Sinter closely resembles vesicular volcanic rocks and other material formed by precipitation in geothermal settings such as travertine. We find that in fresh geyserite sinter the pore structure, and thus hydrological and geophysical properties, is controlled by the distribution of microbial matter. The geochemistry of water indicates mixing of andesitic and meteoric water. Steam separation, and dilution underground occurs as fluids rise to the surface. Evaporation at the surface seems to affect thermal pools, fountain geysers, and water in discharge channels.