Geoelectrical characterization of fumarolic zones in the Cerro Machín volcanic dome

Cerro Machín Volcano (Tolima, Colombia) is considered one of the most hazardous volcanic systems in the country due to its eruptive potential and the presence of an active fumarolic field on the central dome. Characterizing these surface manifestations is essential to understand the hydrothermal dynamics and the potential pressurization mechanisms associated with volcanic activity.

In this study, a geoelectrical characterization of the fumarolic field was carried out through the integrated application of Electrical Resistivity Tomography (ERT), Time-Domain Induced Polarization (IP), and Transient Electromagnetic Soundings (TEM). Data acquisition included three ERT+IP profiles using a Schlumberger configuration with 5 m electrode spacing (profile lengths of 255 m, 315 m, and 310 m), together with two TEM soundings performed along two of the profiles.

ERT sections allowed the delineation of the electrical resistivity distribution, revealing a deep high-resistivity body, a laterally extensive low-resistivity and high-chargeability zone surrounding this body, and localized high-chargeability anomalies in the vicinity of the fumaroles. TEM results were consistent with the ERT sections, confirming the presence of the deep resistive body and increasing confidence in the inferred subsurface structure. IP data further complemented the interpretation by identifying electrochemical contrasts associated with altered materials and chargeable minerals.

The integrated interpretation of ERT, IP, and TEM data supports a geoelectrical model consistent with the fumarolic dynamics of the Cerro Machín dome. This study represents the first geoelectrical characterization of the Cerro Machín fumarolic system and provides a baseline for monitoring and future investigations of its evolution.