In-Cave and Surface Geophysics to Detect a “Lost” River in the Upper Levels of the Mammoth Cave System

In early 1960, explorers accessed a signifi cant underground river through a crawlspace beneath a ledge in Swinnerton Avenue southeast of the Duck-Under. However, later expeditions failed to fi nd this crawlspace. Instead, the level of sediment in the passage is now generally at or above the rock ledge, leaving no openings to lower level passages other than the Duck-Under itself. Apparently recent organic material (leaves, twigs, etc.) observed in passages just below the Duck-Under may be related to open channel fl ow from storm events which could theoretically provide local sediment transport. Therefore we have used in-cave spontaneous potential (SP), ground penetrating radar (GPR), and acoustic profi ling, as well as surface mise-a-la-masse resistivity profi ling, in an attempt to locate the river itself rather than the missing crawlway. Incave dye studies and additional geophysical profi ling are needed to work out the detailed 3-D hydraulics of this region of the cave system. Background and Purpose At least two cave explorers recall accessing a signifi cant underground river through a crawlway beneath a ledge in Swinnerton Avenue on the upper level of the Mammoth Cave system just southwest of the DuckUnder on January 2 and March 19, 1960 (see Figure 1). Recent expeditions to Swinnerton Avenue (in the 1980s and 2000s) failed to fi nd this crawlway. Instead, the rock ledge in the area where the explorers recall the crawlway is at or only slightly above the level of sediment in the passage. Previous expeditions in 2007 and 2010 failed to fi nd the crawlway, but did identify sediment transport features (ripple marks with gypsum fl uff in the troughs, and gravelly rills; see Figure 2). However for sedimentation to have concealed the crawlway, it must have occurred between the 1960s and 1980s, and cosmogenic dating of sediments at the level of Swinnerton indicates that they have been underground for about 2.5 million years (Granger et al, 2001). In addition, according to records of the USGS gauging station BRKN2 just south of Mammoth Cave at Brownsville, KY, the largest fl ood since 1905 occurred on January 24, 1937 and raised the Green River 44.94 feet above normal pool (NOAA, 2013). This is far less than the 200 or more foot rise (Palmer 1981) necessary to backfl ood Swinnerton Avenue. However, the authors have observed recent organic material in passages just below Swinnerton in 2003, 2007, and 2010, as well as fl owing water in a narrow (impassable) channel obliquely crossing Swinnerton north of the Duck-Under, suggesting open channel fl ow of infi ltrating surface water. Such fl ow, particularly if it is intense during and/or after storm events could have moved sediments within the cave. Alternatively localized aeolian sediment transport within the upper levels of Mammoth may be indicated by a famous set of “dunes” 82 Mammoth Cave National Park's 10th Research Symposium: Celebrating the Diversity of Research in the Mammoth Cave Region in Turner Avenue, and by the preferential occurrence of gypsum fl uff in the troughs of ripple marks as observed in Swinnerton itself (Figure 2). The purpose of this investigation was to determine whether there is evidence in Swinnerton of recent sediment transport that could explain the apparent disappearance of the entrance to the “Lost River”. In addition, while preparing for this study, the authors became aware of the “Three Springs Conundrum” formulated by Meiman et al (2001) based on dye tracing that showed that the disappearing stream fed by Three Springs has not been found underground, and that shallow and deep fl ow pathways may go in diff erent directions. The volume and direction of fl ow in the “Lost River” as recalled by early explorers even before formulation of the Conudrum is consistent with a likely explanation for the Conundrum – that is, the Lost River is in the right place and fl owing the right direction to represent the swallowed Three Springs water. Thus, a second complementary purpose became collection of data that might indicate the path taken by water that emerges at Three Springs, and is quickly lost again into the Mammoth plumbing system. 2010 Spontaneous Potential Survey In order to check for evidence of relatively recent water fl ow in Swinnerton Avenue, an expedition was undertaken in August 2010 to perform spontaneous potential (SP) measurements in Swinnerton Avenue southwestward from the Duck-Under. The SP method involves measuring the Figure 1: Eyewitness sketches of the crawlway to the “Lost River”. For orientation, the slot is labeled S in each view, and the shelf or ledge is