Cheryl Jaworowski

High-resolution mapping of river-hydrothermal water mixing: Yellowstone National Park

Thermal mixing in rivers is a common geophysical phenomenon that controls myriad processes, from aquatic ecological functions to stream and groundwater biogeochemistry. We present high-resolution remotely-sensed temperature distributions of thermal plumes discharging into rivers collected from Yellowstone National Park. Airborne (4 m pixel size) and ground-based (centimetre or better spatial resolution) images corroborate the presence of these mixing zones. They illustrate that thermal discharges in rivers may not be well-mixed with the bulk flow even after traversing distances corresponding to several stream widths. This allows for large thermal gradients (>30°C) to persist between the thermal discharge and the bulk flow. The plumes may have pronounced internal temperature gradients that vary in space and time. The images illustrate the potential of portable high-resolution sensors not only for acquiring observations needed for fundamental understanding of non-isothermal mixing processes but also for providing temperature distributions necessary for understanding many thermally-mediated processes.

Temporal and Seasonal Variations of the Hot Spring Basin Hydrothermal System, Yellowstone National Park, USA

Monitoring Yellowstone National Park’s hydrothermal systems and establishing hydrothermal baselines are the main goals of an ongoing collaborative effort between Yellowstone National Park’s Geology program and Utah State University’s Remote Sensing Services Laboratory. During the first years of this research effort, improvements were made in image acquisition, processing and calibration. In 2007, a broad-band, forward looking infrared (FLIR) camera (8–12 microns) provided reliable airborne images for a hydrothermal baseline of the Hot Spring Basin hydrothermal system. From 2008 to 2011, night-time, airborne thermal infrared image acquisitions during September yielded temperature maps that established the temporal variability of the hydrothermal system. A March 2012 airborne image acquisition provided an initial assessment of seasonal variability. The consistent, high-spatial resolution imagery (~1 m) demonstrates that the technique is robust and repeatable for generating corrected (atmosphere and emissivity) and calibrated temperature maps of the Hot Spring Basin hydrothermal system. Atmospheric conditions before and at flight-time determine the usefulness of the thermal infrared imagery for geohydrologic applications, such as hydrothermal monitoring. Although these ground-surface temperature maps are easily understood, quantification of radiative heat from the Hot Spring Basin hydrothermal system is an estimate of the system’s total energy output. Area is a key parameter for calculating the hydrothermal system’s heat output. Preliminary heat calculations suggest a radiative heat output of ~56 MW to 62 MW for the central Hot Spring Basin hydrothermal system. Challenges still remain in removing the latent solar component within the calibrated, atmospherically adjusted, and emissivity corrected night-time imagery.

Thermal remote sensing of snow cover to identify the extent of hydrothermal areas in Yellowstone National Park

High resolution airborne multispectral and thermal infrared imagery (1-meter pixel resolution) was acquired over several hydrothermal areas in Yellowstone National Park both in September of 2011 and in early March, during the winter of 2012, when snow cover was still present in most of the Park. The multi-temporal imagery was used to identify the extent of the geothermal areas, as snow accumulation is absent in hydrothermal areas. The presence or absence of snow depends on the heat flow generated at the surface as well as antecedent snow precipitation and temperature conditions. The paper describes the image processing and analysis methodology and examines temperature thresholds and conditions that result in the presence or absence of snow cover.

Geophysics and Geologic Hazards

Sinkholes in Florida pose significant geotechnical, engineering, and hydrogeological challenges for using the land in constructive ways. In some instances, the sinkholes may prove unstable, thus limiting the overburden stress that can be applied. Additionally, the sinkholes may provide a conduit for accelerated contaminant transport from surface activities. In this case study, we use electrical resistivity tomography (ERT) to understand the scope of sinkhole activity under a planned landfill. As part of their application, the landfill permit applicant submitted a dense network of parallel, twodimensional electrical resistivity profiles as described in the following. We provided an alternative, three dimensional analysis of this data set to enhance detection of subsurface sinkhole targets. Eighty five parallel resistivity lines spaced 6m (20ft) apart were coalesced into a large three-dimensional resistivity model to map the 14 hectare (35 acre) site. The results revealed that resistive sand-filled sinkholes could extend at least 30m (100ft) below ground surface with a diameter that ranged from 30 to 100m (100-300ft). The host conductive limestone was shown to have a complex undulating topography with eroded pinnacles. Using cone penetrometer technology (CPT), the edge of the limestone pinnacles were also shown to have significant raveling, which coincided with a narrow range of resistivity values. The implications of the correlation between direct characterization using CPT and indirect characterization with ERT suggest that raveling could cover as much as 17% of the site. Based on these findings, the site was determined to be ill suited for landfill construction.