IDENTIFYING PRESENT-DAY SLOPE INSTABILITY IN THE LANDSLIDES OF BLACK MESA, RIO GRANDE GORGE, NEW MEXICO, USING INSAR TIME-SERIES ANALYSIS

At the upstream end of White Rock Canyon, landslides have dynamically altered the landscape, forming several temporary lakes that flooded the Española Basin by damming the Rio Grande at least four times during the late Pleistocene. A similar landslide complex exists upstream of the Española Basin along the eastern flank of Black Mesa. However, the current state of movement activity of these landslides is unknown. Therefore, this study aims to delineate the mass wasting boundaries using a 2014 high-resolution LiDAR DEM and to identify the present-day slope instability of the Black Mesa landslide complex.

Leveraging Interferometric Synthetic Aperture Radar (InSAR) time series from Sentinel-1 satellite data (2017-2023), we quantified present-day slope movement. A Persistent Scatterer (PS) technique was implemented on 101 descending and 114 ascending Sentinel-1 data sets with VV polarization using ENVI SARScape software to construct the InSAR time series. 12 landslide bodies were delineated through visual interpretation of LiDAR hill-and-slopeshade models. The InSAR time series identified significant slope movement, with areas in landslides experiencing subsidence cumulatively exceeding 40 mm over the last six years. PS points with coherence greater than 0.76 over the entire analysis period were used to detect landslide movement.

To measure the average movement of the PS points with greater certainty, those with an average velocity > 1 STD (active PS points) were filtered from the results, and an Index of Activity was calculated on 250m grids based on the number of active PS points present in each 250m grid. Results indicate that landslide activity is greatest along the lower toe regions, while areas near the head scarps exhibit limited movement. It is unknown whether the Black Mesa landslide complex is characterized by catastrophic, incremental (creeping), or both failure speeds. The PS InSAR analysis indicates that, at present, portions of these rotational-to-translational deep-seated landslides are creeping downslope towards the river.