Abstract Near the South Pole, a large subglacial lake exists beneath the East Antarctic Ice Sheet less than 10 km from where the bed temperature is inferred to be −9°C. A thermodynamic model was used to investigate the apparent contradiction of basal water existing in the vicinity of a cold bed. Model results indicate that South Pole Lake is freezing and that neither present-day geothermal flux nor ice flow is capable of producing the necessary heat to sustain basal water at this location. We hypothesize that the lake comprises relict water formed during a different configuration of ice dynamics when significant frictional heating from ice sliding was available. Additional modelling of assumed basal sliding shows frictional heating was capable of producing the necessary heat to fill South Pole Lake. Independent evidence of englacial structures measured by airborne radar revel ice-sheet flow was more dynamic in the past. Ice sliding is estimated to have ceased between 16.8 and 10.7 ka based on an ice chronology from a nearby borehole. These findings reveal major post-Last Glacial Maximum ice-dynamic change within the interior of East Antarctica, demonstrating that the present interior ice flow is different than that under full glacial conditions.

Abstract A large volume of the East Antarctic Ice Sheet drains through the Totten Glacier (TG) and is thought to be a potential source of substantial global sea-level rise over the coming centuries. We show that the surface velocity and height of the floating part of the TG, which buttresses the grounded component, have varied substantially over two decades (1989–2011), with variations in surface height strongly anti-correlated with simulated basal melt rates ( r = 0.70, p < 0.05). Coupled glacier–ice shelf simulations confirm that ice flow and thickness respond to both basal melting of the ice shelf and grounding on bed obstacles. We conclude the observed variability of the TG is primarily ocean-driven. Ocean warming in this region will lead to enhanced ice-sheet dynamism and loss of upstream grounded ice.

Geoexchange systems utilize the heat capacity of the ground to provide efficient heating and cooling of buildings. West Chester University is developing a 16 MW district geoexchange system in southeast Pennsylvania. The system currently includes 529 borehole heat exchangers installed in fractured gneiss, with an anticipated 1400 borehole heat exchangers when complete. Borefield temperature, heat flux, and electric demand were recorded at 5 min intervals. Mean annual borefield temperature increased 2.1 °C yr −1 between 2011 and 2014, resulting from unbalanced cooling demand from high-occupancy buildings. The greatest recorded daily mean borefield temperature was 34.4 °C, which is significantly greater than ambient ground temperature of 12.8 °C and close to the maximum efficient design temperature of 41 °C for geothermal heat pumps. West Chester University is mitigating this unsustainable increase in temperature by installing a 738 kW cooling tower and heated sidewalks for snow removal. Inverse modeling of borefield temperature revealed an effective thermal conductivity between 1.3 and 1.4 W m −1 °C −1 , which is significantly less than the 2.9 W m −1 °C −1 of the formation, indicating that heat exchange is limited by borehole construction. Despite this performance issue, the system is operating with a coefficient of performance of 3.4 and 4.9 for heating and cooling, respectively. We conclude that thermogeologic investigation of borefield response could lead to significant improvements in efficiency and reduction in the number of wells required to maintain system performance.

Thermal response tests are the industry standard for borehole heat exchanger design in ground-coupled heat pump systems. Two previously conducted thermal response tests in phase 2 of the district-scale ground-coupled heat pump system at Ball State University (BSU) measured a bulk “formation” thermal conductivity K T between 2.6 and 3.0 W m −1 K −1 . Meanwhile, K T from a core recovered near BSU averages 2.2 ± 0.006 and 3.5 ± 0.086 W m −1 K −1 for dry and water-saturated samples, respectively. The range in K T data from saturated samples (1.8–7.2 W m −1 K −1 ) leads to the conclusion that thermal response tests do not capture the vertical and horizontal heterogeneity of heat flux in layered sedimentary aquifers. Characterization of the hydrogeologic environment can be one tool to tune district-scale ground-coupled heat pump systems to the specific on-site conditions that may influence the magnitude and mode of heat transfer. At BSU, temperature ( T ) changes in the groundwater environment at the active phase 1 field through October 2013 support this notion. After constant heat loading, a T increase of 14–18 °C was observed in the central monitoring well. The vertical structure in the T profile of this well may correlate to “thermofacies.” For example, a T spike between 14 and 19.5 m in depth may correspond to a sand and gravel zone in the surficial glacial till, and a T dip at a depth of 70 m agrees with the position of the Brainard Shale—zones of higher permeability and lower measured K T (2.0 W m −1 K −1 ), respectively. Higher measured K T zones, such as the low siliciclastic Silurian Salamonie Limestone and the Ordovician Whitewater Formation, may be target thermofacies for heat deposition and extraction. In contrast, sand and gravel zones within the glacial till may allow for significant thermal loading; however, groundwater advection may reduce the fraction of recoverable thermal load.

Geothermal energy depends on high subsurface temperature, adequate permeability and fracture volume, and accessible groundwater supply to support heat exchange with surrounding rock. Some regions may have adequate thermal resources but lack the necessary permeability or deep circulating water. Exploitation of such areas for geothermal energy could occur if permeability can be enhanced enough to provide the necessary heat exchange. These improvements to the geothermal reservoir would produce what is termed an “enhanced geothermal system” (EGS). The Snake River Plain (SRP) in southern Idaho is a geological region with high heat flux (~110 mW/m 2 ) that has been recommended as an EGS target. In this study, we consider how the geologic and thermal history of the SRP might influence its EGS potential. We describe the fracture distribution (mean = 28.63 fractures/10 m) in a welded tuff core recovered from one of the few deep boreholes located on the SRP and provide a preliminary discussion of the likely geomechanical behavior under in situ stress. Spatial autocorrelation of fracture features is defined with geostatistical techniques and used in a stochastic simulation of possible structures in other welded tuff reservoirs. Autocorrelation scales for the continuous date are on the order of 70 meters with high subsample scale variability (56 m). Results should aid in designing criteria for a hydraulic fracturing plan that would augment the permeability and connectivity of an SRP reservoir's preexisting fracture network.

Abstract The HOTSAT multiplatform system for the analysis of infrared data from satellites provides a framework that allows the detection of volcanic hotspots and an output of their associated radiative power. This multiplatform system can operate on both Moderate Resolution Imaging Spectroradiometer and Spinning Enhanced Visible and Infrared Imager data. The new version of the system is now implemented on graphics processing units and its interface is available on the internet under restricted access conditions. Combining the estimation of time-varying discharge rates using HOTSAT with the MAGFLOW physics-based model to simulate lava flow paths resulted in the first operational system in which satellite observations drive the modelling of lava flow emplacement. This allows the timely definition of the parameters and maps essential for hazard assessment, including the propagation time of lava flows and the maximum run-out distance. The system was first used in an operational context during the paroxysmal episode at Mt Etna on 12–13 January 2011, when we produced real-time predictions of the areas likely to be inundated by lava flows while the eruption was still ongoing. This allowed key at-risk areas to be rapidly and appropriately identified.

Abstract Infrared (IR) satellite-based sensors allow the detection and quantification of volcanic hot spots. Sensors flown on geostationary satellites are particularly helpful in the early warning and continuous tracking of effusive activity. Development of operational monitoring and dissemination systems is essential to achieve the real-time ingestion and processing of IR data for a timely response during volcanic crises. HOTVOLC is a web-based satellite-data-driven monitoring system developed at the Observatoire de Physique du Globe de Clermont-Ferrand (Clermont-Ferrand), designed to achieve near-real-time monitoring of volcanic activity using on-site ingestion of geostationary satellite data (e.g. MSG-SEVIRI, MTSAT, GOES-Imager). Here we present the characteristics of the HOTVOLC system for the monitoring of effusive activity. The system comprises two acquisition stations and secure databases (i.e. mirrored archives). The detection of volcanic hot spots uses a contextual algorithm that is based on a modified form of the Normalized Thermal Index (NTI*) and VAST. Raster images and numerical data are available to open-access on a Web-GIS interface. Tests are carried out and presented here, particularly for the 12–13 January 2011 eruption of Mount Etna, to show the capability of the system to provide quantitative information such as lava volume and time-averaged discharge rate. Examples of operational application reveal the ability of the HOTVOLC system to provide timely thermal information about volcanic hot spot activity.

Plutonism was widespread from mid-Mesozoic through Paleogene time in the Cordilleran Interior of the United States (CI, defined as the region underlain by broadly autochthonous ancient crust inland from the Sierra Nevada batholith). Intrusive activity here was broadly synchronous with intrusion of the coastal Sierra Nevada and Peninsular Ranges batholiths, but in detail, timing in the CI differed from that nearer the coast: Triassic plutons are absent in the CI, the Jurassic intrusive peak is less pronounced than in the Sierra Nevada, and the most intense plutonic activity occurred later than in the Sierra Nevada and Peninsular Ranges. Granitoid rocks of the CI, especially the younger ones, have clear isotopic signatures of ancient crustal source components and are commonly strongly peraluminous; both of these characteristics represent major contrasts with the coastal batholiths. The North American craton, which forms the basement of the CI and from which the plutons were to a considerable extent derived, underwent intense orogeny and high-grade metamorphism during the Early Proterozoic. For the next 1.5 b.y. the continent remained intact and free of orogenic modification. Compressional tectonics, manifested both by thin-skinned thrusting and ductile nappe formation, as well as plutonism, characterized Mesozoic reactivation. Emplacement of the dominant Cretaceous CI plutons was roughly synchronous with the major deformation. CI plutonism was distinctive in several respects: (1) although no continental collision and no apparent extensional tectonism were involved, it extended far inland (800 km at present; probably >400 km at the time of intrusion) in old, previously stable crust; (2) intermediate metaluminous (<65 percent SiO 2 ) as well as felsic peraluminous granitoids show clear isotopic evidence for major crustal input; (3) strongly peraluminous granitoids have moderate concentrations of large-ion lithophile elements and fairly high Sr contents, not the high LIL and low Sr that characterize such rocks in other belts in ancient crust. Although CI magmatism extended remarkably far inland and evidence for a major subcrustal component is in many cases absent, it almost certainly was directly related to a subduction-induced thermal regime. Crustal thickening by sediment accumulation or overthrusting was probably of little importance in inducing magmatism. The thermal regime necessary for extensive Cretaceous–early Paleogene anatexis was probably brought about by increased mantle heat flux, perhaps resulting from lithospheric erosion, and/or by emplacement of subcrustal magmas at deep levels.

During 1973 and 1974, precision temperatures (±0.02°C absolute) were measured in four drill holes, ranging in depth from 42 to 122 m, in Clear Lake, Lake County, California. The departure of the measured temperatures from their predrilling values was found to vary considerably among the holes. It is a function of the length of time after drilling that the buoy system supporting the plastic casing survived the storms on the lake, as well as the duration of the drilling disturbance. With one exception, CL-73-7, most of the holes were lost within a month after drilling. Thermal-conductivity measurements on the sediment cores from the holes were measured using the needle-probe technique. These measurements indicate that the sapropelic muds that underlie most of the main body of the lake and the peat of the southeast, or Highlands Arm, of the lake have thermal conductivities only slightly greater than that of water. Conductivities of the coarse-grained sediments associated with the deltaic deposits of Kelsey Creek are two to three times that of water and are not grouped as tightly as the fine-grained muds and peats. Heat flows calculated from the above measurements are 1.5 to 1.6 heat-flow units (HFU) in the main basin of Clear Lake and about 2.4 HFU in the Highlands Arm of the lake. These values are considerably lower than expected, based on heat-flow measurements in The Geysers 25 km south of Clear Lake. A correction for an average sedimentation rate in the lake of 0.68 mm/yr would raise the observed heat flows about 13 percent. Although the exact thickness of sediment is unknown, a correction for the refraction effect caused by the thermal conductivity contrast between the low-conductivity lake sediments and the higher conductivity surrounding rock would tend to increase the heat flow at depth in the main basin only slightly for any reasonable thickness of sediment. In the Highlands Arm of the lake, the geometry is different, and the correction could raise the observed heat flux at depth as much as three times that observed, again for reasonable sediment thicknesses. However interesting these numbers are, it should be cautioned that sediment composition and thickness below about 200 m in the lake are unknown, and large differences in conductivity could drastically change these corrections. The possibility of such high heat flows, though, is encouraging enough that future measurements at greater depths should be contemplated. Aside from the refraction effects there are other possible causes of the low heat flows: (1) Clear Lake is bounded by faults and at least one fault is inferred to pass beneath the main body of the lake—downward cold water movement along such faults could absorb heat and decrease the heat flux; and (2) water may be moving down through the sediments, although generally the permeability of lake sediments is rather low. Depending on the velocity of the movement, a substantial reduction in heat flow could result. The downward movement of water over such a large area (114 km 2 ) could be a source of recharge for The Geysers-Clear Lake geothermal system.