Rockport and Presque Isle Inland Sinkholes, Michigan

Back in Rockport State Recreation Area forest near Alpena Michigan lies 12 relatively un-explored Devonian Era sinkhole karst features — flooded sinkholes that might contain archaeological clues from the last Holocene and the possibility of dormant cave passage. Certified cave divers Adam Haydock, Chris Parks, and Mike Apke brought gear to the Big Sink for an initial checkout dive. I stayed topside while Mike and Chris descended. Visibility 20ft at surface to 25-40ft depth. Two types of plant growth at the bottom. Bass swimming about. 90-degree vertical wall surrounding inner sink contour dropped from 40ft to max depth 59ft — significantly colder water and visibility dropped to 3-5ft at the organic sediment cloud inside. Silt bottom compacted at max depth — could not push deeper. Upright trees with tops pointing back up the slope suggest land sliding into the sink. No cave passage found — the theory holds that these are flooded tubular-collapse rubble piles where gypsum and sulfate layers in the Detroit Group strata dissolved away. About 13 sinkholes in the area. The underwater springs in Lake Huron with sulfur vents and cyanobacteria mats give clues to Devonian era conditions and possibly extraterrestrial biology. With Chris Parks and Mike Apke.