Located in Madison County, the M2 Blue cave system was discovered by Buford Pruitt in the early 1990s and initially explored by him with Mark Long and Fred Davis. Further exploration has occurred sporadically since then by several other teams. Most exploration prior to 2010 has concentrated on the upstream end of the cave which is shallower and has excellent visibility.
In the summer of 2010 the M2 Blue entrance cleared, and over several dives the downstream end of the line was extended significantly by our team and eventually connected to old cave line in an unknown cave system to the south. After some research, the unknown cave system was discovered to be originating in an offset sink known as Fannell’s Funnel. Although it had been previously explored for about 3000 feet of passage, no survey or map of this system was available. Subsequent survey by KUR showed that Fannell’s Funnel was indeed the unknown system connected to the downstream end of M2 Blue.
Further exploration in the area of the connection yielded an important discovery: a breakdown room at the junction of at least four passages, the most significant being a large siphon passage trending south at a depth considerably greater (150-160 feet) than the rest of the system (100 – 120 feet). Observations suggest that this deep siphon passage is draining a substantial portion of the water that traverses the upstream M2 system, the rest draining southeast to Fannell’s Funnel.
Subsequently Brett Hemphill, Andrew Pitkin and Michael Poucher explored the deep siphon passage, adding around 4500 feet of line at depths around 155 feet and ending at around 7200 feet from the entrance. Other parts of the system were pushed in 2011 (the Plonker Passage) but no further line was added to the downstream exploration.
Continued exploration of the system in 2015 by Andrew Pitkin and Charlie Roberson has pushed the downstream passage (the "Prehistoric Tunnel") out to 11,645 feet from the Fannell's Funnel entrance, trending south and currently about 9000 feet in a straight line from the northernmost extent of the surveyed Madison Blue system.
The Fannell's Funnel entrance is in the Withlacoochee River and in addition to siphoning strongly when river levels are anything other than very low, visibility in the hundred feet or so of entrance passage is typically no better than 2-3 feet. The cave water is at a constant temperature of 68F, but the river temperature varies from being in the 50s in the winter to the mid 80s in the summer. Since almost all the decompression is done in the river water, and decompression times of 6 hours and more are becoming necessary with extended bottom times for exploration, this site is very much a seasonal one with exploration occurring only in the summer.