Thermo-mechanical Model of Geysers (original) (raw)
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Fluid oscillations in a laboratory geyser with a bubble trap
Journal of Volcanology and Geothermal Research
Geysers are rare geologic features that episodically erupt water and steam. While it is understood that the eruptions are triggered by the conversion of thermal to kinetic energy during decompression of hot fluids, geysers commonly exhibit a range of dynamic behaviors in-between and during eruptions that have yet to be adequately explained. In-situ measurements of temperature and pressure as well as remote geophysical techniques have revealed oscillatory behavior across a range of timescales, ranging from eruption cycles to impulsive bubble collapse events. Many geysers, including Old faithful in Yellowstone National Park, USA, are believed to have offset subsurface reservoirs (referred to as a 'bubble trap') that can trap and accumulate noncondensable gas or steam entering the system. The impact of a bubble trap on the dynamic behaviors of the system, however, has not been fully established. We constructed a laboratory bubble trap and performed a series of experiments to study how fluids oscillate back and forth between the eruption conduit and laterally-offseet reservoir in-between eruptions. We present a new theoretical model based on Hamiltonian mechanics that successfully predicts the oscillation frequencies observed in our experiments based on the conduit system geometry, the amount of gas that has accumulated in the bubble trap, and the amount of liquid water in the system. We demonstrate that when scaled to Old Faithful Geyser, this mechanism is capable of producing oscillations at the observed frequencies.
1995
Geysers that discharge water and steam intermittently to the atmosphere are one of the rarest natural phenomena associated with geothermal systems. several approaches including laboratory experiments, field observations and mathematical and numerical modelling studies are used in the present study to explain the behaviour of geysers and the important parameters controlling the eruption of geysers. A particular study is made of three geysers at Rotorua geothermal field: Pohutu, Prince of Wales Feathers and Waikorohihi. The existing mathematical model (steinberg et al., 1981a) is studied and an improved mathematical model is developed to accommodate two-phase flow and the variation in fluid properties with temperature. Both the existing and the improved mathematical models are used to model pohutu and are able to reproduce not only the interval benveen eruptions but also the durations of the cavern filling and the duration of the pre-play stage observed by the author on the 20m of Aug...
About the Mechanism of Geyser Eruption
arXiv: Geophysics, 2012
Essentially new physical mechanism of geyser eruption based on instability in "water-vapor" system is proposed. Necessary and sufficient conditions of eruptions are received. For group of Kamchatka geysers a good accordance of theoretical model with empirical observations is shown.
An experimental study on violent geysers in vertical pipes
Journal of Hydraulic Research, 2018
This paper reports a laboratory study on violent geysers in a vertical pipe. Each geyser produced consists of a few consecutive violent eruptions within a time frame of a few seconds with heights that may exceed 30 m. Herein, the term violent is used to distinguish the present work from previous studies, which reported geyser heights that were relatively small compared to the present study. Previous work has speculated that the extreme behavior of geysers is driven by the buoyant rise of the air pocket in the vertical pipe. The present study shows that once the air pocket breaks through the free surface and produces a water spill, the horizontal pipe ow dynamics, in particular the rapidly changing pressure gradient following the rst weak eruption, is driving the entire geyser mechanism.
Numerical modelling of Pohutu geyser, Rotorua, New Zealand
Geothermics, 2016
The Rotorua geothermal field (RGF) in the North Island of New Zealand is renowned for an abundance of natural geothermal manifestations and contains one of New Zealand's last remaining areas of major geyser activity at Whakarewarewa. Close proximity of the geothermal resource to a population centre and ease of access for end-users resulted in intensive drilling and fluid abstraction from shallow bores for domestic and commercial usage from the 1950s onwards. Increasing concern about the effect of geothermal fluid withdrawal on the activity of springs and geysers led to the establishment of the Rotorua Geothermal Monitoring Programme (RGMP) in 1982. By 1986, aquifer pressures declined to the lowest levels since the monitoring programme began, and to prevent further deterioration of spring and geyser activity, a Bore Closure Programme was enforced. By 1988, the programme contributed to a 75% decrease in net withdrawal and an immediate increase in reservoir pressures was observed. During the ensuing years recovery of some surface features has also been observed. Thus, although the geysers at Rotorua, New Zealand have shown some natural variation in their behaviour, they have also been significantly affected by human interference. The aim of this study is to quantify the past response of geyser activity to human-induced changes in the state of the Rotorua geothermal reservoir and to provide a tool for predicting the future behaviour of the geysers. The study is based on a simple computer model of a geyser that consists of a chamber linked to cold recharge and deeper hot recharge. The chamber also has an outlet to the surface through a narrow channel. The TOUGH2 simulator is used to carry out many numerical experiments to determine how parameters such as the size of chamber, cold recharge pressure, hot recharge pressure and permeability of the channel affect whether or not the model produces geysering behaviour and how they affect the period of the eruptions. The model successfully matches the observations that: (i) geysering ceases if hot recharge diminishes, (ii) the frequency of eruption increases if hot recharge increases and (iii) if hot recharge increases enough, then geysering turns into continual spouting.
Understanding the dynamics of a geyser from temporal monitoring of seismic source
2010
Old Faithful Geyser is the most popular geyser in Yellowstone National Park. The predictability, the repeatability and the short time lag, ~1 hour, between two eruptions make its study very convenient to apprehend its cycle and to make progress in the understanding of geyser's dynamics. The geyser's edifice is characterized by a diameter of 60 m, a height of 4m, with an opening of approximately 2 m x 1 m, a crack-like aperture. In 1992, Sharon Kedar deployed 96 geophones around the geyser vent in order to continuously record seismic signals during several eruptive cycles. The signal recorded at Old Faithful is characterized by small impulsive events, with durations of ~1s, related to bubble collapse in the boiling water column. We revisited the seismic signals recorded by Sharon Kedar in order to determine the locations of the source of these events during an entire cycle with the objective to monitor the temporal evolution of the system. An analysis of 2 hours of seismic ...
Near-Surface Phenomena in Geysers
The University Of Auckland Physics Dept MSc Thesis, 1977
Two New Zealand geysers, Okianga at Whakarewarewa and Taumatapuhipuhi at Tokaanu, were studied in order to learn about the hydrodynamics of their operation. Temperature, chemical composition, and flow data were collected from the geysers. Temperature profiles over time were logged for up to six depths between surface level and 2 metres depth in each geyser. These profiles indicated in each geyser the existence of pressure disturbances, the behaviour of convection currents, the depths at which inflows occurred, and in the case of Taumatapuhipuhi, regular temperature fluctuations of several degrees every two minutes. The water in both geysers boils at temperatures lower than would be expected for a hydrostatic head of hot water with bubbles in it. Possible causes of this are discussed and inferred to be probably due to either rising small parcels of hotter water or pressure disturbances associated with turbulence. Fluorescent dyes were used to measure dilution rates in the geysers but could not quantitatively indicate eruptive volumes. The dilution studies indicated in each geyser system the probable existence of two distinct volumes which are connected by slow two-way convective dispersal. Equations governing the behaviour of such a system are presented. The smaller volume, the immediate reservoir, directly feeds the outflow from the mouth of the geyser. Some recharge to the immediate reservoir comes directly and the remainder appears to circulate through the larger volume. A possible reason for the fluctuations in dilution rate during the eruptive cycle of Okianga is presented in terms of this model. Neither of the geysers studied was found to feed into surrounding springs during the course of the observations. Flows from the mouth of each geyser were also measured. Taumatapuhipuhi, which does not normally erupt, was found to have a two minute and a ten minute cycle of fluctuation in flow. A possible mechanism for this is discussed.
Experiments and Numerical Modeling of Field-Scale Geysers in Stormsewer Systems
38th IAHR World Congress - "Water: Connecting the World", 2019
This paper reports a laboratory and numerical study on violent geysers in a vertical pipe. The laboratory geysers produced consists of a few consecutive violent eruptions within a time frame of a few seconds with heights that may exceed 30 m and with characteristics resembling geysers that occur in actual stormsewer systems (e.g., strongest eruption is not the first one but few eruptions later). In general, the present study shows that once the air pocket breaks through the free surface and produces a water spill, the horizontal pipe flow dynamics, in particular the rapidly changing pressure gradient following the first weak eruption, is driving the entire geyser mechanism. This conference paper is based on the following