Memories of Alan Edward Beck (1928–2020)

This is article providing a brief description of the life and scientific achievements of Alan Edward Beck, emeritus Professor of Western University. He was born in England on January 27, 1928 and passed away on December 1st, 2020 at his home in London (Ontario), Canada. He will be remembered not only for his significant contributions in Geophysics but also his active participation in activities of the International Heat Flow Commission- IHFC. In 1958 he was a founding faculty member of the Department of Geophysics of the University of Western Ontario, London, Canada. Shortly thereafter became Acting Head (1961), and then Head (1963) of the Department of Geophysics. He was a founding member of the International Heat Flow Commission, Vice Chairman for the period of 1979 to 1983 and then Chairman during 1983 to 1987. He retired in 1993 but continued to be active with participation in several international organizations. Beck was honored with the J. Tuzo Wilson Award of the Canadian Geophysical Union in 1993.

Editorial to the fourth issue of “International Journal of Terrestrial Heat Flow and Applied Geothermics”

Editorial

Inversion results appended with estimates from vegetation changes in assessment of Ground Surface Temperatures for the Amazon Region, Brazil

Estimates have been made of ground surface temperature (GST) variations for 25 localities in the region of Manaus (province of Amazon in Brazil) making use of both forward and inverse models. The work is based on analysis of borehole temperature logs as well as remote sensing data concerning changes in vegetation cover. Results of functional space inversion (FSI) of borehole temperature data reveal the occurrence of a cooling event, with a decrease in temperature of slightly less than 1oC, for the period of 1600 to 1850 AD. This episode coincides roughly with the period of “little ice age” in the southern hemisphere. It was followed by a warming event, with magnitudes varying from 2 to 3oC, that lasted until recent times. Integration of these results with estimates based on changes in normalized index of vegetation cover (NVDI) of the last decade points to continuation of climate warming over the last decade. This event is found to be prominent in areas of deforestation in central parts of the Amazon region.

Land Development and Role of Evapotranspiration in Climate Change

Analyses of underground temperatures have been used to obtain ground surface temperature (GST) histories. At individual sites, changes in the GST over time are synchronous with development which altered the evapotranspiration. At different, closely spaced sites, measured differences in GST between sites depend on the relative amounts of evaporation and transpiration at each site. These observations prove that a significant portion of the climate change observed on land is caused by changes in the amounts of evapotranspiration at each location. The magnitudes of GST changes vary from 0.6 to 2.6 C, for developments occurring from 8 to 52 years ago. In the temperate zone of Canada, these differences occur primarily in the summer. Our development, including urbanization and development of agricultural land, has produced a significant warming. It is best defined from underground temperature data.

Short- and long-term variations in groundwater temperature caused by changes in vegetation cover

Several comparative studies of the earth's surface provide evidence that vegetation and other bio-physical processes at the earth's surface can directly affect the atmospheric boundary layer, leading to changes in temperature and precipitation patterns. In this study, we demonstrate how vegetation cover can be responsible for the subsurface temperature variation as well as how this temperature variation can be related to past events. A linear decrease of 0.0407 K/year was estimated, and a decrease of 2 mK was observed in subsurface temperature when the surface temperature exceeded 9 oC. This diurnal temperature variation occurs during the phenological growing season of the vegetation. The transient temperature shows an annual cycle at a depth of 40 m. Model calculation applying a linear decrease in surface temperature of 2 K as a boundary condition was simulated. Comparing the results with the trend it is realistic to assume that when an apparent thermal diffusivity of 1.8*10-6 m²/s is applied an event starting between 10 and 20 years ago is responsible for the detected decrease in temperature. However, with this thermal diffusivity the conductive annual temperature variation reaches an amplitude of 1.1 mK instead of the measured 5.4 mK at 40 m. In conclusion, beside the vegetation causing additional convective heat transport triggered by the annual surface temperature, the influence of reduced solar incoming heat radiation reaching the ground caused by the increased shadowing effect of vegetation cover might be responsible for a continuous decrease in local temperature of 2 K being active approximately 20 years after plantation.

Effects of Near-Surface Air Temperature on Sub-Surface Geothermal Gradient and Heat Flow in Bornu-Chad Basin, Nigeria

A study of the effect of near-surface temperature on fields of subsurface geothermal gradient and heat flow has been carried out in the Bornu-Chad Basin, Nigeria, using corrected Bottom-Hole Temperatures (BHTc) lithologic-log data from 9 oil wells. The geothermal gradient using only BHTs ranges from 15.9oCkm-1 to 38.2oCkm-1 with an average of 26.9+/-3.5oCkm-1, while that computed with mean annual temperature and BHTs ranges from 28.2oCkm-1 to 51.5oCkm-1with an average of 37.5+/-2.5oCkm-1. The geothermal gradient using the mean annual temperature and BHTs in the Bornu-Chad is higher than using only BHTs by 7.0oCkm-1. Heatflow ranges from a minimum of 61 mWm-2 to a maximum of 114mWm-2 with an average of 68+/-5.89mWm-2. The isotherm maps exhibit an increasing SW-NE trend. An average heat flow of 68+/-5.9mWm-2 deduced from Bornu-Chad basin is normal for a continental passive margin with age of about 100My. Geothermal gradient results show a distinct and direct relationship with near-surface conditions. There are indications that surface heat flow is controlled by lithology, geothermal gradient and near-surface solar radiation conditions in the Bornu-Chad basin. Consequently, it is recommended that the mean surface temperature be used in geothermal gradients and heatflows estimations. The knowledge of geothermal properties is very important in the search for geothermal energy in the area of study.

Geothermal Gradients in the Upper Amazon Basin derived from BHT data

The Upper Amazon Basin (UAB), present foredeep of the sub Andean retro-foreland basin. It comprises Putumayo area (southeastern part of Colombia), Oriente area (eastern Ecuador) and Marañón area (northeastern part of Peru). Bottom Hole Temperature (BHT) from a regional well log database (1076 wells and 2957 logs) were analyzed and data discriminated according to drilling operations (i.e., log acquisition operations, cementing, formation test, tools misreading values), topography and shallow subsurface weathering conditions (i.e., temperature data from wells with depths below 305 m. were avoided). A new normalized database has been setup (1021 wells and 1399 logs). Analysis of this data set has allowed better understanding of the regional distribution of geothermal gradient variations within the study area. The results indicate mean uncorrected geothermal gradient (UCGG) for the UAB of 20.4 °C/km. The UCGG is a first approach based on well data with sufficient information and is useful for comparison purposes with other basin where corrected data is limited. In addition, a new computer-generated contour Geothermal Gradient Map (GGM) has been created, using 56 locations (for which number of BHT at different depths ≥ 3, and temperatures in the range 23.4 to 44.4 °C). As for the locations 2 are in Colombia, 28 in Ecuador and 26 in Peru. This map is useful in analysis data of UCGG due to its wide distribution along the basin. Finally, correction based on Horner´s method was applied to these datasets (where number of BHT ≥3 at the same depth; time since circulation - TSC incremental), obtaining a Corrected Geothermal Gradient (HCGG) of 22.9 °C/km (46 wells and 153 logs). We recommend the use of this gradient for comparative reference purposes.

Numerical Model to Assess the State and Increase of Temperatures in Underground Mine Galleries: A Tool to Support Heat Recovery Projects

Underground mining is facing growing challenges related to the need to mine deeper and at higher temperatures, to operational expenditures associated with energy consumption, lower grade ores, environmental constraints, and social pressures. In this scenario, a new numerical model is proposed to estimate temperature increase inside mining galleries to provide specific criteria for heat recovery projects, which may consider heat extraction from abandoned mines using closed-loop geothermal systems or from operating mines using the exhaust ventilation air. This model couples different approaches from previous models and include key parameters unemployed until this moment, such as wall roughness and velocity profile modeling, what would allow for a more realistic estimation of convective heat transfer phenomena, which is critical to predicting heat exchange in ventilation air due to the turbulent nature of the airflow. The model also includes other heat sources that could be present inside galleries and should be accounted for, such as machinery, once the heat dissipated to the environment might be substantial depending on the equipment and gallery geometry. The general intention of this project is to account for every heat source that may contribute to increasing the temperature inside the gallery, so it becomes tangible to harness as much heat energy as possible, preventing energetic losses and stimulating an increase of thermodynamic efficiency in underground mining operations. The model is not validated yet with real temperature data, but preliminary results agree with the ones from previous models.

Method for estimating the depth of circulation of thermal and non-thermal waters in the upper crust

In this work we consider model formulations that allow better understandings of the relations between Darcy velocity and temperatures in coupled two-dimensional systems. The revised theoretical formulations are capable of accounting for the effects of heat transfer by fluid movements in horizontal and vertical directions. The models have been found useful in estimating the maximum and minimum depths of thermal and non-thermal waters in several geological units in Brazil. The best fitting values encountered are 1.8 to 2.7 km for the Paraná basin, 2.0 to 2.8 km for the Parnaiba basin, 1.6 to 2.3 km for the Amazon basins, 2.0 to 2.7 km for the San Francisco Province, 1.9 to 2.4 km for the Sergipe-Alagoas basins and 2.0 to 2.8 km for the Borborema Province. The models have also allowed estimation the average values of Péclet number and Darcy velocity for groundwater flows in these units. Note that higher horizontal velocities are associated with smaller depths of circulation. This is a natural consequence of the fact that in systems where horizontal velocities are high the quantities of vertical flows are less intense.

Influence of past vegetation changes on estimates of ground surface temperature histories GSTH obtained by inversion of borehole temperature logs: Example from the Western Canadian Sedimentary Basin

Functional space inversions (FSI) of precise temperature logs from 43 wells, located in low conductivity clastic sediments of the Western Canadian Sedimentary Basin, (WCSB), reveal evidence of extensive, recent ground surface temperature (GST) warming. Simultaneous inversion of log data acquired during the period of 1987-2005, as well as averaging of the individual site reconstructions of subsurface temperature signals, indicate evidence of high magnitude of warming of about 2°C (with standard deviations of 0.7°C). Magnitudes of such warning events exceeds 3-4 times that of globally averaged continental GST’s for the 20th century and is significantly higher than that of changes in surface air temperatures (SAT) based on instrumental records in the WCSB. Within this region, GST warming in the 20th century could have been at least partially caused by changes in vegetation cover. The temporary or permanent removal of vegetation, through deforestation, forest fires, and grassland conversion for agriculture occurred in the relatively young provinces of WCSB, during centennial long settlement and development programs. This might have significantly changed the surface properties of the area, since changes in surface albedo affects the radiation budget, while changes in the thermal, moisture and aerodynamic characteristics affect the energy balance. The results of our modelling for typical range of bedrock thermal diffusivities and assumed surface warming history for studied areas in WCSB show that a possible jump in ground surface temperature can easily be interpreted in the FSI results as a gradual warming event of large amplitude and attributed to SAT.