Bottom pressure signals at the TAG deep-sea hydrothermal field : evidence for short-period, flow-induced ground deformation

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L19301, doi:10.1029/2009GL040006.Bottom pressure measurements acquired from the TAG hydrothermal field on the Mid-Atlantic Ridge (26°N) contain clusters of narrowband spectral peaks centered at periods from 22 to 53.2 minutes. The strongest signal at 53.2 min corresponds to 13 mm of water depth variation. Smaller, but statistically significant, signals were also observed at periods of 22, 26.5, 33.4, and 37.7 min (1–4 mm amplitude). These kinds of signals have not previously been observed in the ocean, and they appear to represent vertical motion of the seafloor in response to hydrothermal flow - similar in many ways to periodic terrestrial geysers. We demonstrate that displacements of 13 mm can be produced by relatively small flow-induced pressures (several kPa) if the source region is less than ∼100 m below the seafloor. We suggest that the periodic nature of the signals results from a non-linear relationship between fluid pore pressure and crustal permeability

Hydrothermal origin of halogens at Home Plate, Gusev Crater

In the Inner Basin of the Columbia Hills, Gusev Crater is Home Plate, an 80 m platform of layered clastic rocks of the Barnhill class with microscopic and macroscopic textures, including a bomb sag, suggestive of a phreatomagmatic origin. We present data acquired by the Spirit Mars Exploration Rover by Alpha Particle X-Ray Spectrometer (APXS), Mössbauer Spectrometer, Miniature Thermal Emission Spectrometer (Mini- TES), and Panoramic Camera (Pancam) for the Barnhill class rocks and nearby vesicular Irvine class basalts. In major element concentrations (e.g., SiO2, Al2O3, MgO, and FeO*), the two rock classes are similar, suggesting that they are derived from a similar magmatic source. The Barnhill class, however, has higher abundances of Cl, Br, Zn, and Ge with comparable SO3 to the Irvine basalts. Nanophase ferric oxide (np ox) and volcanic glass were detected in the Barnhill class rocks by Mössbauer and Mini-TES, respectively, and imply greater alteration and cooling rates in the Barnhill than in the Irvine class rocks. The high volatile elements in the Barnhill class agree with volcanic textures that imply interaction with a briny groundwater during eruption and (or) by later alteration. Differences in composition between the Barnhill and Irvine classes allow the fingerprinting of a Na-Mg-Zn-Ge-Cl-Br (±Fe ± Ca ± CO2) brine with low S. Nearby sulfate salt soils of fumarolic origin may reflect fractionation of an acidic S-rich vapor during boiling of a hydrothermal brine at depth. Persistent groundwater was likely present during and after the formation of Home Plate

Flow near the critical point: Examination of some pressure-enthalpy paths

Quantitative flow modeling of fluids at elevated temperatures and pressures has generally been limited to consideration of either single-phase flow or two-phase flow at conditions below the critical point of water. In this paper, we introduce a version of the GEOTHER model that can simulate both multiphase flow and flow above the critical point, and demonstrate its capabilities by simulating flow in the vicinity of the critical point. GEOTHER2 is a multiphase, finite-difference model that simulates three-dimensional flow of pure water and heat at temperatures ranging from 0{degree} to 1,200{degree}C and pressures ranging from 0.5 to 10,000 bars. The governing equations are expressions of mass and energy conservation that are posed in terms of pressure and enthalpy. A series of one-dimensional experiments indicates that permeability is a pivotal factor in determining pressure-enthalpy/temperature trajectories near the critical point. At low permeabilities (10{sup -16} m{sup 2}), advective heat transport dominates, and the pressure-enthalpy trajectory maintains a constant "flowing enthalpy"

Annotated bibliography : hydrogeology of Kilauea Volcano, Hawaii

"Prepared in cooperation with the U.S. Department of Energy"Open-File Report 93-551-

Numerical Simulations of the Hydrothermal System at Lassen Volcanic National Park

The hydrothermal system in the vicinity of Lassen Volcanic National Park contains a central region of fluid upflow in which steam and liquid phases separate, with steam rising through a parasitic vapor-dominated zone and liquid flowing laterally toward areas of hot spring discharge south of the Park. A simplified numerical model was used to simulate the 10,000-20,000 year evolution of this system and to show that under certain circumstances fluid withdrawal from hot-water reservoirs south of the Park could significantly alter the discharge of steam from thermal areas within the Park

The Influence of Episodic Shallow Magma Degassing on Heat and Chemical Transport in Volcanic Hydrothermal Systems

International audienceSprings at La Soufrière of Guadeloupe have been monitored for nearly four decades since the phreatic eruption and associated seismic activity in 1976. We conceptualize degassing vapor/gas mixtures as square-wave sources of chloride and heat and apply a new semianalytic solution to demonstrate that chloride and heat pulses with the same timing and duration result in good matches between measured and simulated spring temperatures and concentrations. While the concentration of chloride pulses is variable, the local boiling temperature of 96°C was assigned to all thermal pulses. Because chloride is a conservative tracer, chloride breakthrough is only affected by one-dimensional advection and dispersion. The thermal tracer is damped and lagged relative to chloride due to conductive heat exchange with the overlying and underlying strata. Joint analysis of temperature and chloride allows estimation of the onset and duration of degassing pulses, refining the chronology of recent magmatic intrusion