Landslides are important agents of landscape evolution and a major geohazard in populated mountainous regions. In the Ecuadorian Andes, steep relief, seasonal rainfall, heterogeneous volcanic and volcaniclastic materials, irrigation, and land-use changes can combine to produce conditions favorable to slope instability . The internal geometry of a landslide, zones of deformation, and preferential groundwater pathways are commonly difficult to assess from surface observations alone, which motivates the use of non-invasive geophysical methods together with geological constraints .

Electrical resistivity tomography (ERT) is widely used in landslide investigations because it images spatial contrasts in bulk electrical resistivity that may reflect changes in lithology, porosity, weathering, fracture condition, pore-water content, and pore-fluid conductivity . However, the relationship between resistivity and geological or geotechnical properties is not unique. Consequently, an ERT anomaly should not be interpreted as a slip surface, saturated zone, or mechanically weak layer without independent constraints. Studies that combine ERT with boreholes, penetration testing, laboratory measurements, geological mapping, or other geophysical data demonstrate that independent information can substantially reduce interpretive ambiguity . This need for independent constraints is especially important where borehole control is unavailable and the same conductive response may be produced by different combinations of lithology and water content . Time-lapse studies further show that resistivity patterns can vary seasonally as subsurface moisture conditions change .

The San José de Aloburo landslide provides a useful case for evaluating this integrated approach in a volcaniclastic Andean setting. The 2021 event affected agricultural land, roads, reservoirs, greenhouses, and houses, and was classified in the post-event assessment as a complex movement with a rotational component in the upper sector and flow-like behavior downslope . The field campaign was conducted after the event and focused on the upper and physically accessible part of the landslide, where ERT acquisition and stratigraphic observations could be performed safely. A recent Andean example from Chota–Cajamarca, Peru, likewise combines ERT with geological and geomorphological information to constrain landslide geometry, illustrating the regional relevance of integrated geoelectrical–geological workflows while also emphasizing that geological interpretation must remain site specific .

Recent low-cost and open-hardware resistivity systems demonstrate the importance of documenting the injected signal, current and voltage measurement chain, repeated or reciprocal measurements, calibration and validation procedures, and processing workflow when instrumentation itself is a principal contribution . The non-commercial system used at San José de Aloburo is not presented here as a new reproducible instrument design because equivalent archival metadata are incomplete. Instead, the contribution of this study is the integrated observational dataset and the transparent workflow used to combine ERT with stratigraphic constraints while explicitly carrying forward limitations arising from survey coverage, inversion non-uniqueness, seasonal hydrological variability, and incomplete acquisition and inversion metadata.

The objective of this study is therefore to evaluate how ERT, surface geology, stratigraphic observations, and local grain-size information can be combined to characterize the upper sector of the San José de Aloburo landslide. Specifically, the study aims to (i) describe the principal geoelectrical domains identified in four 2-D ERT profiles; (ii) evaluate whether selected geoelectrical boundaries are spatially consistent with potential instability-related contacts when constrained by field geology and morphology; (iii) compare the shallow ERT response with the available stratigraphic observations without assuming a one-to-one correspondence between resistivity contours and geological contacts; and (iv) explicitly assess the methodological limitations associated with survey geometry, Wenner-array resolution, inversion non-uniqueness, seasonality, the limited granulometric dataset, and the non-commercial acquisition system.

The study area is located in San José de Aloburo, Pimampiro, Imbabura Province, Ecuador (Fig. ). The principal landslide occurred on 23–24 November 2021, affecting approximately 25.17 ha and causing major economic and structural damage, including the destruction of 17 houses, 7 reservoirs, 5 greenhouses, and part of the main road. The post-event technical assessment classified the movement as a complex landslide, with a rotational component in the upper sector and a partial flow in the lower sector; the documented principal movement direction was NW–SE .

Regional mapping and local reports describe the area as a heterogeneous volcanic to volcaniclastic succession associated with the Angochagua Formation, including ash, pumice, tuffaceous material, breccia, and conglomeratic deposits . Slopes in the landslide sector are commonly between 25 and 35°. The climate is temperate humid, with annual precipitation reported between approximately 500 and 750 mm and wetter periods during April–May and October–December . Thus, the November 2021 failure occurred within one of the wetter seasonal windows identified for the area.

The raster map panels reproduce the coordinate annotations present in the archived map exports. The corresponding GIS project files were not included in the manuscript source package available for this revision, so the underlying coordinate reference system cannot be independently re-derived from that archive. No unsupported numerical reprojection of the raster figures was therefore introduced; the map grids are used only for spatial context and are not used in the ERT inversion or quantitative calculations.

The area lies within the Mira River basin and Chota sub-basin. Irrigated agriculture is a dominant land use, and canals and reservoirs are common in the surrounding terrain . These hydrological and anthropogenic elements provide relevant context for infiltration and water redistribution, but the present study does not quantify their direct contribution to the 2021 failure.

The workflow combined geological field observations and ERT acquisition, followed by independent processing and subsequent joint interpretation. Geological information is used as a constraint on the interpretation of shallow geoelectrical patterns rather than as a direct conversion from resistivity to lithology.

The revised interpretation distinguishes electrical observations from geological inference. Bulk resistivity is controlled by several coupled factors, including mineralogy, grain size, porosity, degree of weathering, water content, and pore-fluid conductivity . Therefore, the 4–45 Ω m domains observed at San José de Aloburo cannot be uniquely assigned to saturation, fracturing, or low cohesion. Conversely, a fractured zone need not be conductive if fractures are relatively dry. ERT also does not measure cohesion directly. In this study, low-resistivity domains are consequently described as conductive geoelectrical zones that are consistent with increased moisture and/or electrically conductive volcaniclastic material where the field geology supports such an interpretation.

This cautious approach is consistent with integrated landslide studies in which ERT interpretations are strengthened by independent geological or geotechnical constraints. For example, combined 2-D/3-D ERT with penetration tests, boreholes, and laboratory analyses, and showed that wet- and dry-period surveys helped separate hydrological from lithological effects. used resistivity imaging to characterize the Montaguto landslide, while demonstrated the value of integrating ERT with geotechnical data for stability assessment. These studies underline an important limitation of the present dataset: the San José de Aloburo survey has stratigraphic control at shallow depth but no direct geotechnical verification of the deeper geoelectrical boundaries.

The geological columns are therefore used primarily to constrain the upper part of the ERT interpretation. Their maximum observed thickness is approximately 19 m, whereas the ERT sections extend to approximately 35–40 m. A direct one-to-one correlation between stratigraphic contacts and deeper iso-resistivity contours is not justified. Figure  illustrates the spatial comparison among the field exposure, geological sketch, Column A, and Profile 2. Panel (b) is a conceptual sketch and is not drawn to vertical scale; panel (c) records stratigraphic height from the base of the exposure; panel (d) is the independently inverted ERT section; and panel (e) shows their map relationship. The dashed connectors are intended to show approximate spatial correspondence in the shallow sector, not to imply that resistivity contours are geological layer boundaries.

The stratigraphy suggests a plausible hydrogeological contrast between coarser pumice/lapilli-rich units and finer ash-rich units. Coarser units may favor infiltration and drainage relative to finer layers, whereas finer units may locally impede vertical flow. Such contrasts could promote perched or laterally redirected water under wet conditions. However, this mechanism remains conceptual because hydraulic conductivity, pore pressure, and water content were not measured directly. The single quantitative grain-size analysis of ANG-TOP-B-01 further limits the strength of any site-wide sediment–resistivity correlation. Its coarse distribution is therefore treated as local sedimentological evidence only.

Seasonality is another important limitation. The principal landslide occurred during the October–December wetter period, whereas the ERT campaign represents later, comparatively drier post-event conditions. The resistivity models should therefore be regarded as a temporal snapshot rather than as a direct reconstruction of the hydrological conditions that prevailed during the November 2021 failure. Seasonal changes in water content and hydraulic connectivity could alter both the amplitude and spatial continuity of conductive anomalies. Time-lapse electrical studies on active landslides demonstrate that repeated surveys can separate persistent electrical structure from transient hydrological changes and can substantially improve interpretation of subsurface water circulation . In debris affected by reactivation, recent ERT work also illustrates both the value of conductive anomalies for identifying water-related zones and the interpretive difficulty that remains when direct subsurface validation is limited .

A wet-season ERT survey acquired with the same geometry would consequently provide valuable complementary information. Comparison of wet- and dry-season models could test whether low-resistivity domains expand or become more continuous during infiltration, whether conductive zones persist through both seasons, and whether the interpreted potential instability-related boundaries are spatially stable. No such repeated dataset is available here, so lithological and hydrological contributions cannot be separated quantitatively.

The Wenner configuration also influences the achievable resolution. Its strong signal response is advantageous for manual field acquisition, but its comparatively limited lateral resolution can smooth narrow or steeply dipping structures. In addition, inversion regularization and decreasing sensitivity with depth can broaden or suppress thin units. The approximately 1.3 m layer observed in the stratigraphic record but not resolved in the ERT section should therefore not be interpreted as absent. Its thickness relative to the 5–7.5 m base electrode spacing, potentially limited electrical contrast with adjacent material, and inversion smoothing all provide plausible reasons why it may not appear as a distinct electrical layer.

Recent integrated landslide investigations provide useful context for the level of inference supported by the present dataset. At Montescaglioso, geological observations were combined with multiple geophysical methods to refine the internal landslide architecture , whereas geophysical–geotechnical integration in residual soils demonstrates how direct mechanical control can strengthen slip-surface interpretation . In the Andes, the Laguna del Amor study in Peru provides a geographically relevant example of ERT integrated with field geology and geomorphology . These studies support the integrated strategy used here, but they also highlight why the present manuscript limits its conclusions where borehole, geotechnical, or repeated hydrological measurements are unavailable.

Finally, the non-commercial ERT system is an important practical component of the study, but its archived metadata are incomplete. The available records document the general acquisition configuration and the measured quantities used to compute apparent resistivity, whereas several electronic specifications and calibration details requested during review cannot be recovered reliably. Consequently, the absolute measurement accuracy cannot be independently reassessed from the archived material, and the missing metadata constitute an unquantified source of instrumental uncertainty. Fully documented low-cost systems provide useful benchmarks for the level of signal characterization, repeatability testing, validation, and open processing that is desirable when instrumentation itself is the principal methodological contribution . The system used here is therefore presented as the acquisition platform for this case study, not as a fully reproducible instrument design or metrological benchmark, and no performance equivalence with those systems is claimed.

The four ERT profiles resolve broad geoelectrical domains in the upper and accessible sector of the San José de Aloburo landslide to approximately 35–40 m depth. Low-resistivity domains of approximately 4–45 Ω m are prominent, but they cannot be uniquely interpreted as saturated, fractured, or low-cohesion material. Their geological meaning is constrained by field morphology and stratigraphy, and selected strong resistivity gradients in Profiles 1, 2, and 4 are interpreted as potential instability-related boundaries rather than mechanically verified rupture planes.

The stratigraphic columns document alternating ash and pumice/lapilli-rich volcaniclastic units and provide direct geological control only within the shallow observed interval, up to approximately 19 m. The quantitative grain-size analysis of ANG-TOP-B-01 confirms a locally coarse-grained volcaniclastic unit but does not validate a general resistivity–grain-size relationship for the whole landslide. The comparison of stratigraphy and ERT is therefore interpretive and spatial, not a one-to-one correspondence between geological layers and iso-resistivity contours.

The survey geometry is concentrated in the crown and upper accessible sector, so the present dataset does not determine the full depth, volume, or complete 3-D geometry of the approximately 25 ha landslide. The 3-D representation is a fence diagram of independent 2-D inversions, not a 3-D inversion. The principal scientific product of this work is therefore the integrated observational ERT–geology dataset and an uncertainty-aware interpretation workflow, rather than a new instrumental benchmark or a complete geotechnical model of the landslide. Future work should prioritize repeated wet- and dry-season ERT using fixed geometry, additional profiles across the central and lower landslide body, and independent borehole, geotechnical, hydrological, or inclinometer control. Such data would allow more rigorous testing of the proposed hydrological and instability-boundary interpretations.