“ZANJONES”: WHAT ARE THEY AND HOW DO THEY DIFFER FROM REGULAR SINKHOLES

Puerto Rico karst topography consist in mogotes, sinkholes, caves, streams and zanjónes, among other formations. The term zanjónes was defined by Monroe in 1964 as a solution trench that can range from 1 m to kilometers of length with a width and depth of few meters. Currently, many karsts scientists use zanjónes-like as a karst landform based on this definition. Monroe described the zanjónes to be only in the north karst belt of Puerto Rico specifically in the Lares Limestone Formation. One of the sites discovered was the “Las Cabachuelas Nature Reserve at Morovis”, Puerto Rico. Our study proposes to find the zanjónes and characterize them using raster digital elevation model obtained from USGS (2018 USGS Lidar DEM: Post Hurricane Maria – Puerto Rico downloaded from NOAA Digital Coast). Our study developed a workflow using ArcGIS Pro to distinguish between a karst negative depression such as sinkhole and zanjónes. The workflow was developed from previous methods for sinkhole detections. The workflow uses fill-sink routines to show differences in the topography and geometrical properties of sinkholes and possible zanjónes. After the preliminary detection, a grid of elevation profiles was obtained to verify the depth of the zanjónes. In situ measurements for at least one zanjón was obtained to validate the model. The result of this study will provide a georeferenced map of zanjónes at the Nature Reserve. This study was part of the Undergraduate Research Opportunities in Cave and Karst Science (UROCKS) sponsored by NSF (2050819) at James Madison University.