Geotechnical and geophysical evaluation of the remarkable Chunchi landslide of 2021 in the Andean Ecuador

Landslides in the Northern Andes of Ecuador appear frequently due to the geological conditions of the area, like the strong movement that occurred on February 12, 2021 in the Chunchi canton. This landslide event has been one of the largest in the region, as it covered an approximate area of 115.35 ha, based on a combination of movements. The present investigation focuses on two main objectives, of which the first consisted of evaluating the main landslide characteristics together with the lithological identification of the affected area using non-destructive tests and by collecting samples that were subsequently tested in the laboratory. The second objective aims to identify the main triggering factors through the analysis of the given precipitation in the period of 2016–2021 and the analysis of pre-event earthquakes near the study area. We were able to establish that the movement was rotational, crawling and flow, classifying the soil as a type D profile, which is considered rigid. Furthermore, we encountered degraded surface material, being identified as materials of volcanic and volcano-sedimentary origin within the matrix. On the surface of the landslide, silty sand, clayey sand and volcanic ash deposits were observed between 1 and 2 m of depth. It was also determined that the soils were saturated from a depth of 3.92 m as a result of severe rainfall and agricultural activities, generating an increase in the hydrostatic load and therefore in the pore pressure, which resulted to be the main trigger of this catastrophic event.