ROLE OF EVAPORITE KARST IN HYDROLOGY AND MORPHOLOGIC EVOLUTION OF THE LOWER PECOS VALLEY, NEW MEXICO, USA

A north-south chain of cenotes, or sinkhole lakes, occurs at Bottomless Lakes State Park, along the east side of the Pecos River floodplain in southeastern New Mexico. The cenotes, formed in gypsum and mudstone of the Permian Artesia Group, are fed by spring discharge from the underlying San Andres artesian aquifer, and represent the discharge end of the regional hydrologic system within the Roswell Artesian Basin. Upward seepage of ground water from the artesian aquifer has caused dissolution of evaporites within the overlying Artesia Group, localized subsidence, and upward propagation of collapse chimneys, which ultimately formed the cenotes. An increase in discharge in recent years from Lea Lake, the largest of the cenotes, reflects the combined effects of gradually rising water levels in the artesian aquifer and enhanced spring flow due to mass wasting processes along the steep eastern margin of the lake. Although the Bottomless Lakes cenotes probably formed during the Pleistocene, catastrophic solution collapse processes are still active along this portion of the lower Pecos, demonstrating the dynamic role of evaporite karst phenomena in the regional hydrologic framework of the lower Pecos Valley.