Drilling of the volcanic conduit in the Unzen Scientific Drilling Project (USDP) was completed in 2004. Some conduit materials of the 1990–95 eruption were encountered at the bottom of Well USDP-4 (150 m below sea level), and a bottom temperature of about 200 °C was estimated using logging data, although before drilling a temperature of about 700 °C had been inferred. Accordingly, conduit cooling from the initial temperature (850 °C) to the estimated temperature (about 200 °C) was evaluated by numerical simulation. The drilling provides constraints for the numerical model. The drilling indicates that the N–S width of the conduit of the latest eruption is 20 to 30 m and that it occupies a zone of about 300 m, which includes conduits of past eruptions. The process of cooling in the conduit, from an initial temperature of 850 °C in 1995 (the end of the eruption) to 200 °C in 2004 (completion of the conduit drilling), was replicated in models with permeabilities of 1 and 10 mdarcys. This result demonstrates that a highly permeable volcanic body surrounding a small conduit is required to explain the estimated bottom temperature.Our study also aimed to use a numerical simulation to construct a comprehensive hydrothermal model beneath Unzen Volcano. There are four large geothermal systems in the Shimabara Peninsula (Obama hot springs, Unzen fumarolic field, Shimabara hot springs and the West Unzen High Temperature Body [WUHTB]). Three pressure sources (“Sources A”, “B” and “C” from shallow to the deep) were determined by geodetic data during the 1990–95 eruption. Source C is located at about 8 km deep at WUHTB, and is considered to be a magma body. We attempted to explain the existence of the four geothermal systems from the large-scale structures (the topography of the Shimabara Peninsula and Unzen Graben) and the various heat sources. We first set a heat source around Source C and changed its position and size. This numerical model produced the upflow zones at the Obama and Shimabara hot springs and WUHTB; however, the Unzen fumarolic field became a recharge area. This result indicates that another heat source is required to explain the Unzen fumarolic field and that two heat sources beneath WUHTB and the Unzen fumarolic field are involved in the formation of the four hydrothermal systems in the Shimabara Peninsula.

Drilling of the volcanic conduit in the Unzen Scientific Drilling Project (USDP) was completed in 2004. Some conduit materials of the 1990–95 eruption were encountered at the bottom of Well USDP-4 (150 m below sea level), and a bottom temperature of about 200 °C was estimated using logging data, although before drilling a temperature of about 700 °C had been inferred. Accordingly, conduit cooling from the initial temperature (850 °C) to the estimated temperature (about 200 °C) was evaluated by numerical simulation. The drilling provides constraints for the numerical model. The drilling indicates that the N–S width of the conduit of the latest eruption is 20 to 30 m and that it occupies a zone of about 300 m, which includes conduits of past eruptions. The process of cooling in the conduit, from an initial temperature of 850 °C in 1995 (the end of the eruption) to 200 °C in 2004 (completion of the conduit drilling), was replicated in models with permeabilities of 1 and 10 mdarcys. This result demonstrates that a highly permeable volcanic body surrounding a small conduit is required to explain the estimated bottom temperature.Our study also aimed to use a numerical simulation to construct a comprehensive hydrothermal model beneath Unzen Volcano. There are four large geothermal systems in the Shimabara Peninsula (Obama hot springs, Unzen fumarolic field, Shimabara hot springs and the West Unzen High Temperature Body [WUHTB]). Three pressure sources (“Sources A”, “B” and “C” from shallow to the deep) were determined by geodetic data during the 1990–95 eruption. Source C is located at about 8 km deep at WUHTB, and is considered to be a magma body. We attempted to explain the existence of the four geothermal systems from the large-scale structures (the topography of the Shimabara Peninsula and Unzen Graben) and the various heat sources. We first set a heat source around Source C and changed its position and size. This numerical model produced the upflow zones at the Obama and Shimabara hot springs and WUHTB; however, the Unzen fumarolic field became a recharge area. This result indicates that another heat source is required to explain the Unzen fumarolic field and that two heat sources beneath WUHTB and the Unzen fumarolic field are involved in the formation of the four hydrothermal systems in the Shimabara Peninsula.

The authors have been conducting demonstration and performance assessment of the ground-coupled heat pump (GCHP) system optimized for the air conditioning system of an experimental house in the artificial island in Fukuoka City, Japan, since 2005 to evaluate the subsurface thermal environmental changes caused by heat exchange with the ground. The authors monitored the underground temperature and groundwater level in some observation wells around the heat exchanging well, and performed numerical simulation of the underground temperature change with a groundwater simulator ldquoFEFLOWrdquo. The simulation result for a 20-year operation by using the numerical model, which had replicated the measured heat exchange rate during the 40-day heating operation from 15 December 2006, predicted that the cumulative increase or decrease of subsurface temperature will not be seen. Therefore, it is thought that there is little impact to the subsurface thermal environment around this GCHP system. [All rights reserved Elsevier].

Highlights • The KGF is a geothermal field with the longest history of utilization in Indonesia. • Introduces new technology for geothermal monitoring using absolute gravimeter. • Evaluates previous gravity monitoring of relative gravity measurement at KGF. • Provide precise gravity change data to clarify mass variation in the subsurface. • The absolute measurements at KGF provide good base lines for future monitoring. Abstract In more than 25 years, repeated gravity measurements (RGM) for geothermal monitoring have been applied in the Kamojang Geothermal Field (KGF), Indonesia. Pertamina has carried out RGM using relative gravimeters at more than 50 benchmarks at KGF since 1984. They used LaCoste-Romberg type G 653, G 655, and Scintrex CG-3 gravimeters to estimate gravity variation. In 2009, we introduced a new microgravity network using A10 (#017) micro-g, a portable absolute gravimeter, which we re-occupied in 2010 and 2011. We identify gravity value changes in production and injection area of KGF as well as changes at the reference station. A linear trend of declining mass of about −17.9 μGal/year at PG48A, a benchmark far from production and injection wells, reveal the temporal gravity variation outside of geothermal reservoirs. The series of monitoring in this present research shows the distribution of large negative gravity changes up to −80 μGal. The large mass loss stays continues to maintain massive production throughout 200 MWe installed capacities at KGF. The absolute gravity measurements improve the result of gravity change data for monitoring. This present study introduces new technology that will enhance the method of reservoir monitoring using repeated precisely-gravity measurements. The use of absolute gravimeter is the best way to account for regional effect, and correct for changes at the base and reference station over time.

Highlights • Subsidence around the Hatchobaru geothermal field was estimated by PS-INSAR. • Space adaptive filtering was used to elaborate the spatial pattern of displacements. • Spatial dense mapping of displacement revealed sharp boundaries of displacements. • The sharp boundaries of displacements likely correspond to fault traces. • Temporal trend interpretation with AIC revealed the decay of the subsidence velocity. Abstract We estimated surface displacements using persistent scatterer SAR interferometry (PS-InSAR) around the Hatchobaru geothermal field, Japan, from 18 ALOS/PALSAR images acquired from July 2007 to December 2010. Generally, geothermal fields, covered with natural targets such as rocky terrain and vegetation, have been one of the difficult targets for PS-InSAR analysis. However, we applied space adaptive filtering to increase the number of pixels for measuring surface displacement. The results of our analysis demonstrate ground subsidence with decaying velocity over the observation period around the geothermal field. The spatial pattern of ground subsidence includes sharp boundaries of subsidence that can be interpreted as fault traces. We demonstrated the usefulness of PS-InSAR analysis with the space adaptive filtering to estimate surface displacements with high spatial resolution and high spatial density around a geothermal field.

Abstract Thermal activity monitoring in and around active volcanic areas using remote sensing is an essential part of volcanology nowadays. Three identical approaches were used for thermal activity exploration at Aso volcanic area in Japan using Landsat ETM + images. First, the conventional methods for hydrothermal alteration mapping were applied to find the most active thermal region after exploring geothermal indicator minerals. Second, we found some thermally highly anomalous regions around Nakadake crater using land surface temperature estimation. Then, the Stefan-Boltzmann equation was used for estimating and also monitoring radiative heat flux (RHF) from the most active region of about 8 km 2 in and around Nakadake crater in the central part of the Aso volcano. To fulfill the required parameter in the Stefan-Boltzmann equation for radiative heat flux, the NDVI (Normalized differential vegetation index) method was used for spectral emissivity, and the mono-window algorithm was used for land surface temperature of this study area. The NDVI value was used to divide land-cover in the study area into four types: water, bare ground, mixed and vegetated land. The bare land was found within the most active region. Vegetation coverage area showed an inverse relationship with total RHF in this study as health of thermally stressed vegetation supports this relationship. The spatial distribution of spectral emissivity ranged from 0.94 to 0.99 in our study. Land surface temperature was estimated using a mono-window algorithm and was highest LST in 2008 and lowest in 2011. The results of RHF showed that the highest pixel RHF was found to be about 296 W/m 2 in 2008. Total RHF was obtained of about 607 MW in 2002 and the lowest was about 354 MW in 2008. The RHF anomaly area was found the highest in 2002 and was lowest in 2011. The highest total heat discharge rate (HDR) obtained about 3918 MW in 2002 and lowest total HDR about 2289 MW in 2008 from this study area. But in the case of Nakadake crater alone, the higher thermal activity was observed in 2008 and was less in 2004. The study showed that Landsat thermal infrared is the best option for thermal activity exploration and monitoring at Aso volcano as well as in any active volcano region considering high efficiency and low cost. Highlights • The most active volcanic zone is identified using alteration and thermal anomaly. • The highest land surface temperature is obtained in 2008 about 62 °C in this study. • Total RHF is obtained highest 606 MW in 2002 and lowest 354 MW in 2008. • Vegetated area is more or less inversely correlated with total heat flow. • The Nakadake crater was most active in 2008 and less in 2004 in the study period.

Highlights • A Python-based stochastic library is presented for assessing geothermal potential. • The geothermal potential is the amount of thermal energy stored in the reservoir. • The library applies the volumetric method in a liquid-dominated reservoir. • The library employs the Monte Carlo simulation for assessing geothermal potential. • Hot spring data from the municipality of Nombre de Jesus, El Salvador are used. Abstract We present a Python-based stochastic library for assessing geothermal power potential using the volumetric method in a liquid-dominated reservoir. The specific aims of this study are to use the volumetric method, “heat in place,” to estimate electrical energy production ability from a geothermal liquid-dominated reservoir, and to build a Python-based stochastic library with useful methods for running such simulations. Although licensed software is available, we selected the open-source programming language Python for this task. The Geothermal Power Potential Evaluation stochastic library (GPPeval) is structured as three essential objects including a geothermal power plant module, a Monte Carlo simulation module, and a tools module. In this study, we use hot spring data from the municipality of Nombre de Jesus, El Salvador, to demonstrate how the GPPeval can be used to assess geothermal power potential. Frequency distribution results from the stochastic simulation shows that this area could initially support a 9.16-MWe power plant for 25 years, with a possible expansion to 17.1 MWe. Further investigations into the geothermal power potential will be conducted to validate the new data.