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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2016)

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.

    Cover page: Dynamics of Geyser systems, El Tatio, Atacama
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2018)
    El Tatio in northern Chile is one of the best-studied geothermal fields in South America. However, there remain open questions about the mass and energy budgets, water recharge rates and residence time in the subsurface, origin of dissolved solutes, and processes affecting the phase and chemical composition of groundwater and surface water. We measured and sampled surface manifestations of the geothermal system (geysers, perpetual spouters, mud pools/volcanoes, and non-eruptive hot springs) and meteoric water. From the isotopic composition we infer that the thermal water has a meteoric origin that is different from the composition of local meteoric water. The absence of detectable tritium in thermal waters indicates that most of the recharge occurred pre-1950. Boiling and steam separation from the deep reservoir appear to be the main subsurface processes affecting the thermal fluids. A large amount of heat is lost to the atmosphere by evaporation from surface water and by steam emitted from erupting geysers. Using the chloride inventory method, we estimate thermal water discharge to be 218 to 234 L/s, and the advective heat flow to be 120 to 170 MW.
      Cover page: Hydrothermal discharge from the El Tatio basin, Atacama, Chile
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2015)
      We compare and contrast data collected in 2012 and 2014 from the El Tatio geyser field, Chile. We identify geyser systems that evolve over time, including changes in the interval between eruptions, development of new thermal features, and interactions between geysers. We study three different cases: (a) an isolated geyser, which is periodic and has nearly identical eruptions every cycle; (b) a geyser and coupled noneruptive pool, where the geyser has nonregular cycles and several preplay eruptions before the main eruption; and (c) two geysers and a mud volcano, which have nonregular cycles and are all interacting. 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. The episodic addition of heat may govern the periodicity, while the depth where heat is added dictates the eruption style: conduits with deeper heat input are more likely to show preplay or minor eruptions. The interactions between thermal features can be explained by pressure transmission in subsurface permeable layers between geyser conduits. Key Points Geysers can be hydraulically connected through permeable pathways to other hot springs The level of complexity of geyser eruptions may be controlled by the underground geometry Over time geysers change periodicity, develop new thermal features, and shift interactions
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2015)
        Despite more than 200. years of scientific study, the internal dynamics of geyser systems remain poorly characterized. As a consequence, there remain fundamental questions about what processes initiate and terminate eruptions, and where eruptions begin. Over a one-week period in October 2012, we collected down-hole measurements of pressure and temperature in the conduit of an exceptionally regular geyser (132. s/cycle) located in the Chilean desert. We identified four stages in the geyser cycle: (1) recharge of water into the conduit after an eruption, driven by the pressure difference between water in the conduit and in a deeper reservoir; (2) a pre-eruptive stage that follows the recharge and is dominated by addition of steam from below; (3) the eruption, which occurs by rapid boiling of a large mass of water at the top of the water column, and decompression that propagates boiling conditions downward; and (4) a relaxation stage during which pressure and temperature decrease until conditions preceding the recharge stage are restored. 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 reservoir. 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 probably also Earth tides).
          Cover page: Dynamics within geyser conduits, and sensitivity to environmental perturbations: Insights from a periodic geyser in the El Tatio geyser field, Atacama Desert, Chile
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2016)
          In order to better understand the diverse discharge styles and eruption intervals observed at geothermal features, we performed three series of laboratory experiments with differing plumbing geometries. A single, straight conduit that connects a hot water bath (flask) to a vent (funnel) can originate geyser-like periodic eruptions, continuous discharge like a boiling spring, and fumarole-like steam discharge, depending on the conduit length and radius. The balance between the heat loss from the conduit walls and the heat supplied from the bottom determines whether and where water can condense which in turn controls discharge style. Next, we connected the conduit to a cold water reservoir through a branch, simulating the inflow from an external water source. Colder water located at a higher elevation than a branching point can flow into the conduit to stop the boiling in the flask, controlling the periodicity of the eruption. When an additional branch is connected to a second cold water reservoir, the two cold reservoirs can interact. Our experiments show that branching allows new processes to occur, such as recharge of colder water and escape of steam from side channels, leading to greater variation in discharge styles and eruption intervals. This model is consistent with the fact that eruption duration is not controlled by emptying reservoirs. We show how differences in plumbing geometries can explain various discharge styles and eruption intervals observed in El Tatio, Chile, and Yellowstone, USA.
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2016)
            Sinters are siliceous, sedimentary deposits that form in geothermal areas. Formation occurs in two steps. Hot water circulates in the subsurface and dissolves silica from the host rock, usually rhyolites. Silica then precipitates after hot water is discharged and cools. Extensive sinter formations are linked to up-flow areas of fluids originating from high temperature (> 175 °C) deep reservoirs. Fluid geochemistry, microbial communities, and environmental conditions of deposition determine the texture of sinter and pore framework. Porosity strongly influences physical and hydraulic properties of rocks. To better understand the properties controlling the transport of fluids, and interpret geophysical observations in geothermal systems, we studied 17 samples of modern geyserite sinter deposits (< 10 ka) from the active El Tatio geothermal field in northern Chile. We measured the physical properties (hydraulic, seismic, and electrical), and internal microstructure (using μX-Ray computed tomography). We find that the pore structure, and thus hydraulic and physical properties, is controlled by the distribution of microbial matter. Based on velocity-porosity relationships, permeability-porosity scaling, and image analysis of the 3D pore structure; we find that the physical and hydraulic properties of sinter more closely resemble those of vesicular volcanic rocks and other material formed by precipitation in geothermal settings (i.e., travertine) than clastic sedimentary rocks.
              Cover page: Physical and hydraulic properties of modern sinter deposits: El Tatio, Atacama
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2019)
              Broadband seismic data were recorded on the ground surface around an exceptionally regular eruptive system, geyser El Jefe, in the El Tatio geyser field, Chile. We identify two stages in the eruption, recharge and discharge, characterized by a radial expansion and contraction, respectively, of the surface around the geyser. We model the deformation with spherical sources that vary in size, location, and pressure, constrained by pressure observations inside the conduit that are highly correlated with deformation signals. We find that in order to fit the data, the subsurface pressure sources must be laterally offset from the geyser vent during the recharge phase and that they must migrate upward toward the vent during the eruption phase. This pattern is consistent with models in which ascending fluids accumulate and then are released from a bubble trap that is horizontally offset from the shallow conduit of the geyser.
                Cover page: Geometry of Geyser Plumbing Inferred From Ground Deformation
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