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Arjuno-Welirang Mountain is located in East Java province, which is a type of stratovolcano with an altitude of 3,339 m for Arjuno and 3,156 m for Welirang. The Arjuno-Welirang geothermal system is a volcanic geothermal system. Magnetotelluric is the most commonly used geothermal exploration method because of its deep penetration and sensitivity to conductive zones. The Magnetotelluric method measures 103 MT points in the field of geothermal systems in the South of Mount Arjuno-Welirang. In this study, the 3D inversion model of Magnetotelluric data was used to reduce the ambiguity of 2D Magnetotelluric inversion data. 3D Model Inversion uses WinGlink and 3DModEM. The steps of Magnetotelluric processing consist of time-domain conversion to the frequency domain, cross power selection, data smoothing, static effect correction, 2D and static strips, interpolation, masking, 3D inversion, and interpretation of inversion models. The 3D model inversion consists of 3D mesh grid parameters used by the NonLinear Conjugate Gradient Algorithm. 2D Inversion Modelling was done by the NLCG method, which produces a 2D model with an RMS error of 1.7%. 3D Inversion modeling was done by the NLCG method producing a 2D model with a value of RMS error of 2.83%. The geothermal system of the Arjuno-Welirang geothermal region consists of a layer of veil rock with a type of resistivity value of 5-11 Ωm, a middle resistivity zone with a value range of 11-76 m acting as a reservoir, and a high resistivity zone with a range of 76-500 Ωm or commonly called heat source. The results of the 3D inversion model indicated a range of low resistance types (hood rock layers) that have a thickness of 1200 - 1700 m, the value of this type of resistance is below the surface with a thickness of ±500-600 m. Thus, the Mt. Arjuno-Welirang is a geothermal prospect area.

Water is natural resources that is very essential for living creatures and the environment. Along with the increase of population , will increase the water demand and reduce the area of free land / open green space for the formation of ground water. By considering soil water conservation aspects, it is necessary to conduct a study of the recharge area on water basin soil in Pasuruan. This study was to determine the condition of the recharge area in the Basin Groundwater Pasuruan in 2003 and 2014. So it will be k[1]nown the changes of the vegetations density and land cover in the recharge area that can affect infiltration process in order to conserve water resources in CAT Pasuruan. From these changes it would be able to make the prediction of future conditions in the recharge area in CAT Pasuruan. This study uses Remote Sensing using Satellite imagery Landsat and Geographic Information System (GIS). Studies to determine the recharge area is influenced by several parameters, that is slope of land, lithology and Rainfall. Processing results obtained vegetation density changes of the recharge area in 2003-2014, high vegetation density decreased by 4330,89 Ha, so that changes in the high vegetation density in 2025 is predicted to be 52305,39 Ha and become 52176,78 Ha in 2030. While land cover changes produce changes in forest land cover increased by 569,88 Ha , so that changes in forest land cover in 2025 is predicted to be 37563,88 Ha and became 38720,494 Ha in 2030. The relationship between vegetation density and land cover of the recharge area in 2003 - 2014 obtained high vegetation density that experienced an increase area, which is on garden land cover amounting to 1144,80 Ha, 943,02 Ha of forest, 947,79 Ha of settlements land cover and 262,53 Ha of vacant land. And that experienced an increase with low vegetation density are the fields amounting to 943,02 Ha and 277,47 Ha of vacant land. Land cover vegetations that dominates throughout the recharge area is a mahogany tree vegetation, and sengon.