Abstract
The unsaturated zone is a critical component of karstic groundwater systems and is shown to provide substantial storage capacities. Understanding the spatial patterns and controls on flow path activation is often a challenge. Previous research focused on remotely sensed data or inferential analyses to quantify these patterns. Here, we use two cave systems—one in Arizona, USA and a second in Kentucky, USA—to show the value of the cave survey and inventory data in the direct observation of speleogenesis and unsaturated zone processes. Using geospatial statistical analyses, we show that passage size varies with distance from some faults, indicating that these faults play a major role in transporting fluid into the limestone and creating increased permeability in the form of cave passages. Additionally, the close relationship between water, calcite resources and geology provide clear evidence for the activation of unsaturated zone flow paths through these cave systems. While both cave systems represent a large area of greatly increased permeability, only isolated sections of the caves show evidence of this active flow. In both cases, modern vadose zone flow occurs proximal to faults and contacts with overlying insoluble lithology. These results suggest that an expanded use of cave survey and inventory data may provide a greater insight into unsaturated zone processes.
Highlights
Understanding unsaturated zone processes is critical to improving our ability to mitigate contamination [1], predict vadose groundwater flow paths and storage capacity [2], and protect fragile cave resources [3]
Cave entrance locations are oriented either adjacent to or directly across the canyon from one another and are completely devoid of active water flow, indicating that these caves are older than the Grand Canyon and are the result of older groundwater systems; they are suggested to be of hypogene origin [7]
The results show a decrease in passage size with an increased distance from the Leandras fault and Halogen fault, suggesting that they may have been the source of the hypogene fluids which created the Bopper cave system
Summary
Understanding unsaturated zone processes is critical to improving our ability to mitigate contamination [1], predict vadose groundwater flow paths and storage capacity [2], and protect fragile cave resources [3]. To understand these processes, a wide variety of techniques are implemented. Recent advances in lidar and photogrammetry techniques produce high resolution models of subsurface conduits that allow for the interactive analysis of cave features after data collection [8,9,10] While these modeling efforts provide substantial insight into unsaturated zone groundwater flow, these methods either rely on remote assessment of these processes or can only be applied to isolated sections of a conduit. Direct observations of conduit features and flow paths and their physical characteristics in the unsaturated zone may provide substantial information for documenting groundwater flow through this component of the critical zone
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