Morphometric Analysis of Gypsum Depressions Using Drone Imagery at Sinkhole Flat, Eddy County, New Mexico, USA
Publication Date: 2026/09/01
Publication Volume: Journal of Cave and Karst Studies 88 #3
DOI Link: https://dx.doi.org/10.4311/2022ES0105
ABSTRACT:
Morphometric analysis is conducted on five karst depressions in Permian-age gypsum of southeast New Mexico. These depressions take on the form of classically shaped blind valleys and sinkholes. Blind valleys in this study are disappearing surface streams composed of multiple tributaries that connect to the main trunk channel leading to a cave entrance. A visible light (RGB) sensor mounted on a quadcopter is used to collect aerial imagery for karst depression mapping and analysis. Field measurements were taken for each depression for comparison with the drone imagery and its derivative layers such as digital elevation model (DEM) and slope. Drone flight elevations were set to 45 m above ground level (AGL) except for one site, which was 76 m AGL, resulting in a spatial resolution ranging from 0.78 to 2.37 cm. A total of 505 images were taken for all sites and mosaiced with photogrammetry software for geospatial analysis. The average field measured depth is 7.5 m and the average DEM measured depth is 5.48 m. DEM measured perimeter ranged from 77 to 675 m and volume ranged from 129 to 4,339 m³. All DEM measured slopes were less than field measured slopes with the differences ranging from −1° to −39°. Drone orthomosaics and DEM-derived layers make it possible to visualize and quantify the complex morphology of the karst depressions that are not clearly discernible from the ground. Drone imagery can be used to rapidly map and assess gypsum depressions in arid areas.
SIMPLE LANGUAGE SUMMARY:
In southeast New Mexico, much of the ground is gypsum, a soft mineral that dissolves in water. Over time this creates sinkholes (bowl-shaped holes in the ground) and “blind valleys,” where small streams flow into a hollow and disappear into a cave instead of continuing on the surface. This study measured five of these hollows at a place called Sinkhole Flat. The author flew a small drone with an ordinary camera about 45 meters (about 150 feet) above the ground and took 505 photos. Computer software stitched the photos together into detailed maps and 3D height models that show details as small as a few centimeters. The author then compared the drone measurements with measurements taken on foot. The drone models showed the hollows as somewhat shallower and less steep than the ground measurements did, but they made it possible to see and measure shapes that are hard to make out from the ground. The study shows that drones are a fast and useful way to map these features in dry areas.
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