Abstract <p>A three-dimensional numerical thermohydrodynamic model of the Mutnovsky magma–hydrothermal system has been developed based on a comprehensive hydrogeological analysis. The model was implemented using TOUGH2 software with the EWASG state module. The study was conducted in two stages. The first stage simulated the natural state of the system driven only by the conduction heat flow (60&#xa0;mW/m²), which proved insufficient to account for the observed high temperatures of thermal manifestations. The second stage incorporated additional heat sources of magmatic origin, spatially constrained by Frac-Digger analysis of microearthquakes data (2013‒2025). The model with magmatic heat sources (total power 416 MW) shows good match with field data regarding the temperature and flow rate of the main thermal features. The results support the concept of hydrothermal circulation involving infiltration of meteoric water through the volcanic edifice, lateral transit and heating at depth, and subsequent ascent and discharge along fault zones.</p>