Combining TDEM and ERT for Robust Characterization of a Fumarolic System in a Stratovolcano Dome

The Cerro Machín Volcano (CMV) in Colombia, classified as a stratovolcano, is one of the most dangerous and active volcanoes in the region due to its dacitic composition, its proximity to populated areas, and the magnitude of past eruptions. An active fumarolic field at the summit of the dome is one of the clearest signs of this activity. This study combines Electrical Resistivity Tomography (ERT) and Transient Electromagnetic (TEM) methods to characterize the fumarolic system.

Six ERT lines were acquired to cover the fumarolic field, and a TEM profile was acquired at the center of one of the tomography lines. The ERT results reveal a high-resistivity gas reservoir likely associated with volcanic gas accumulation that feeds surface fumaroles. Shallow resistivity variations correspond to active fumarolic zones, emphasizing strong connections between gas pathways and hydrothermal activity. However, ERT’s limited depth penetration restricts the full delineation of the reservoir. TEM data suggest the reservoir extends to a depth of approximately 70 meters, providing a more detailed understanding of its dimensions. Our preliminary results demonstrate that combining TEM and ERT allows for robust constraints on the dominant features of hydrothermal systems, even in highly challenging terrains like the dome of an active volcano.