Harris
Robert N.
Harris
Robert N.
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ArticleObservations and modeling of a hydrothermal plume in Yellowstone Lake(American Geophysical Union, 2019-05-09) Sohn, Robert A. ; Luttrell, Karen M. ; Shroyer, Emily L. ; Stranne, Christian ; Harris, Robert N. ; Favorito, Julia E.Acoustic Doppler current profiler and conductivity‐temperature‐depth data acquired in Yellowstone Lake reveal the presence of a buoyant plume above the “Deep Hole” hydrothermal system, located southeast of Stevenson Island. Distributed venting in the ~200 × 200‐m hydrothermal field creates a plume with vertical velocities of ~10 cm/s in the mid‐water column. Salinity profiles indicate that during the period of strong summer stratification the plume rises to a neutral buoyancy horizon at ~45‐m depth, corresponding to a ~70‐m rise height, where it generates an anomaly of ~5% (−0.0014 psu) relative to background lake water. We simulate the plume with a numerical model and find that a heat flux of 28 MW reproduces the salinity and vertical velocity observations, corresponding to a mass flux of 1.4 × 103 kg/s. When observational uncertainties are considered, the heat flux could range between 20 to 50 MW.
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ArticleSpectral analysis of vertical temperature profile time-series data in Yellowstone Lake sediments(American Geophysical Union, 2021-03-17) Sohn, Robert A. ; Harris, Robert N.We use yearlong vertical temperature profile time-series (seven thermistors at evenly spaced depth intervals from 10 to 70 cm) from five sites in and around the Deep Hole thermal area, southeast of Stevenson Island, Yellowstone Lake, to investigate heat and mass fluxes across the lake floor. The records demonstrate that thermal gradients in surficial sediments are modulated by a rich spectrum of bottom water temperature variations generated by hydrodynamic processes, and that sites inside the thermal area also respond to hydrothermal variations. We develop and implement a new method for estimating the sediment effective thermal diffusivity and pore fluid vertical flow rate that exploits the full spectrum of observed temperature variations to generate the parameter estimates, uncertainties, and metrics to assess statistical significance. Sediments at sites outside thermal areas have gradients of ∼7.5°C/m, in situ thermal diffusivities of ∼1.6 × 10−7 m2/s consistent with highly porous (80–90%) siliceous sediments, and experience hypolentic flow in the upper ∼20 cm. Sites inside the Deep Hole thermal area exhibit considerable spatial and temporal variability, with gradients of 1–32°C/m, and higher thermal diffusivities of ∼2–12 × 10−7 m2/s, consistent with hydrothermal alteration of biogenic silica to clays, quartz, and pyrite. Upward pore fluid flow at these sites is observed across multiple depth intervals, with maximum values of ∼3 cm/day. The observed spatial and temporal variability within the thermal area is consistent with upward finger flow combined with short wavelength convection within the porous sediments above a steam reservoir.
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ArticleHeat flux from a vapor-dominated hydrothermal field beneath Yellowstone Lake(American Geophysical Union, 2021-05-14) Favorito, Julia E. ; Harris, Robert N. ; Sohn, Robert A. ; Hurwitz, Shaul ; Luttrell, Karen M.We report results from 149 heat flux measurements made over an ∼2-year interval at sites in and around a vapor-dominated geothermal field located at water depths of ∼100–120 m in Yellowstone Lake, Wyoming. Measurements of both in situ temperature and thermal conductivity as a function of depth were made with a 1 m probe via a remotely operated vehicle, and are combined to compute the vertical conductive heat flux. Inside the ∼55.5 × 103 m2 bathymetric depression demarcating the vapor-dominated field, the median conductive flux is 13 W m−2, with a conductive output of 0.72 MW. Outside the thermal field, the median conductive flux is 3.5 W m−2. We observed 49 active vents inside the thermal field, with an estimated mass discharge rate of 56 kg s−1, a median exit-fluid temperature of 132°C, and a total heat output of 29 MW. We find evidence for relatively weak secondary convection with a total output of 0.09 MW in thermal area lake floor sediments. Our data indicate that vapor beneath the thermal field is trapped by a low-permeability cap at a temperature of ∼189°C and a depth of ∼15 m below the lake floor. The thermal output of the Deep Hole is among the highest of any vapor-dominated field in Yellowstone, due in part to the high boiling temperatures associated with the elevated lake floor pressures.
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ArticleHeat flow and thermal regime in the Guaymas Basin, Gulf of California: Estimates of conductive and advective heat transport(Wiley, 2023) Neumann, Florian ; Negrete-Aranda, Raquel ; Harris, Robert N. ; Contreras, Juan ; Galerne, Christophe Y. ; Peña-Salinas, Manet S. ; Spelz, Ronald M. ; Teske, Andreas ; Lizarralde, Daniel ; Höfig, Tobias W. ; Expedition 385 ScientistsHeat flow is estimated at eight sites drilled int the Guaymas Basin, Gulf of California, during the International Ocean Discovery Program Expedition 385. The expedition sought to understand the thermal regime of the basin and heat transfer between off-axis sills intruding the organic-rich sediments of the Guaymas Basin, and the basin floor. The distinct sedimentation rates, active tectonics, and magmatism make the basin interesting for scientific discoveries. Results show that sedimentation corrected heat flow values range 119?221?mW/m2 in the basin and 257?1003?mW/m2 at the site of a young sill intrusion, denominated Ringvent. Thermal analysis shows that heat in the Guaymas Basin is being dissipated by conduction for plate ages >0.2 Ma, whereas younger plate ages are in a state of transient cooling by both conduction and advection. Drilling sites show that Ringvent is an active sill being cooled down slowly by circulating fluids with discharge velocities of 10?200?mm/yr. Possible recharge sites are located ca. 1 km away from the sill's border. Modelling of the heat output at Ringvent indicates a sill thickness of ca. 240?m. A simple order-of-magnitude model predicts that relatively small amounts of magma are needed to account for the elevated heat flow in non-volcanic, sediment-filled rifts like the central and northern Gulf of California in which heating of the upper crust is achieved via advection by sill emplacement and hydrothermal circulation. Multiple timescales of cooling control the crustal, chemical and biological evolution of the Guaymas Basin. Here, we recognize at least four timescales: the time interval between intrusions (ca. 103 yr), the thermal relaxation time of sills (ca. 104 yr), the characteristic cooling time of the sediments (ca. 105 yr), and the cooling of the entire crust at geologic timescales.