This paper studies the geothermal prospects of new manifestations and hot springs distributed in Kenya. Geothermal resource prospecting begins with geochemical sampling and analysis. The concentrations of the chemical species were used as a basis geo-thermometer of the reservoir. In addition, the paper updates the geothermal map of Kenya, and provides geochemical analyses of six hot springs. The recorded hot springs range between 30 to 75°C, pH values are 7-8, and conductivities are 18.4-2,370 m-s/m. The study aimed to map new geothermal prospects, classify the hot springs water, and determine the potential resource application in the region. The water samples were analyzed for significant anions, cations, silica, and trace elements. Then reservoir temperatures were estimated using silica and cations geothermometry in the range of 80-247°C. The Homa Hills prospect exhibits characteristics of Na-HCO₃ waters with high sulphate and chloride species concentrations. From Piper ternary diagrams, all the hot spring waters can be classified as peripheral carbonated waters. Apart from Kakdhimu hot spring, the rest are significantly diluted by groundwater, and therefore, their chemical constituents are in small concentrations, giving little or no information about their origin. The Mulotʼs hot springs water has a soda taste due to the high concentration of HCO₃^-1. Considering their low temperatures, the hot springs could be suitable for direct use; e.g., aquaculture, spa, and greenhouse warming.

Little is known about the impact of vapor emitted from cooling towers on vegetation around geothermal power plants. In this study, the growth status of Fagus crenata saplings, placed at the site with different concentration levels of hydrogen sulfide (H₂S) emitted from volcanic gas fumaroles, was confirmed by visual observation of leaves and branches and by a vegetation index (NDVI) calculated from multispectral images. The results showed that during the four-month experimental period from late May to mid-September, the onset of leaf necrosis and a decrease in the vegetation index was observed at the site with the highest H₂S concentration. This was considered an effect of H₂S absorbed by the leaves of the saplings, due to the high sulfur content in the leaves. On the other hand, no detrimental signs on the leaves were observed at sites with similar H₂S exposure conditions to those around geothermal power plants, suggesting that the concentration levels of H₂S measured around geothermal power plants have no impact on vegetation. No detrimental signs on the leaves were also observed for the trees naturally grown around fumaroles, even at the sites with higher H₂S concentrations than those around geothermal power plants. This result suggests that the trees naturally grown in the local environment may be more tolerant to H₂S than the saplings used in the experiment because they might have already obtained the form suited to the higher H₂S concentrations.

In this study, for the purpose of demonstrating the effectiveness of thermal conductivity profiling using heating cable and multi-point temperature sensor (TCP using heating cable) inserted into the geological boreholes in designing ground-source heat pump (GSHP) systems, TCPs using heating cable at a depth of 50 m were conducted at 47 sites in Fukushima Prefecture, Japan. After conduction of TCPs using heating cable at 27 sites, a 50 m-deep borehole heat exchanger (BHE) was installed at the same locations and conventional TRT and TCP using optical fiber sensors inserted into the U-tubes of BHEs (TCP using heat transfer medium) were conducted.

The temperature profiles and apparent thermal conductivity (λ) values of both TCPs were consistent each other at many sites. On the other hand, at a few sites, several range of λ values of the TCP using heat transfer medium were extremely higher than that of the TCP using heating cable. The same section of temperature profiles of the TCP using heat transfer medium showed that the temperature recovered rapidly, suggesting that crossflow may be occurring in the annulus area in the BHEs. Since the TCP using heating cable can be tested in a borehole with a smaller annulus area than the BHEs, it was also confirmed that the risk (e.g., crossflow) of ground modification on the estimation of λ value can be minimized.

The 2,187 λ values by depth for TCPs using heating cable obtained at 47 sites were classified by geology, and their statistics for each geology were obtained. Comparison of the median λ values by geology with representative values of effective thermal conductivity in the literature was consistent for many geologies.

In order to use the λ values estimated from TCP using heating cable for the design of GSHP systems, the averaging method of λ values by depth for TCP using heating cable was investigated: the arithmetic mean calculated after correcting λ value over 4 W/(m·K) to 4, and the arithmetic mean values calculated after excluding λ values above 5 W/(m·K) were consistent with the λ value of the conventional TRT at the same site, respectively. However, since the section of borehole with large λ value has high heat exchange capacity, it is considered more suitable to use the arithmetic mean λ value correcting large λ values for the design rather than excluding the values.

Vapor-dominated geothermal resources were the first to be utilized for geothermal power generation. However, since there are few examples, its characteristics, actual conditions and issues are not well known to the general public. This review intends to provide an overview of the current understanding of the vapordominated geothermal resources, the phenomena that have occurred during steam production, the responses to these phenomena, and the issues that remain unresolved. This review is divided into three parts. In the third part, we will review, phenomena related to long-term steam production and remaining questions on the vapordominated geothermal resources.