Hole 52 was discovered in 1998 by Everett Kissinger and other scientists of Tongass National Forest. They reported it to cavers of the Tongass Cave Project, who mapped the cave and discovered an extensive bone deposit inside. The cave is located on the mainland side of Blake Passage not far from Lawyer's Cave, but much higher up the mountainside in the same band of marble. Dr. Heaton spent three days in September of 1999 doing a preliminary investigation of the cave with Dave Love and Pete Smith of the TCP and Jackie de Montigny of the Tongass National Forest. The Forest Service provided boat transportation, food, and lodging on a floating wannigan near the cave. Additional funding was provided by grants from the National Science Foundation and the National Geographic Society.
Hole 52 exhibits an interesting combination of features of a den site and a natural trap. The entrance is a large sinkhole, but it is easy to enter from the sloping side. The cave itself contains a series of horizontal passages and vertical pits. Bears, porcupines, and other mammals have used the horizontal passages at the bottom of the sinkhole as dens, but frequently then have fallen down pits inside the cave and been killed or trapped.
Hole 52 originates in a large sinkhole on a karst terrace. At the bottom of the sinkhole are several entrances to the horizontal passages and vertical pits of the cave. Even from the sinkhole, the loud roar of a waterfall inside the cave can be heard.
A porcupine skeleton and a large brown bear skull were found in organic sediments near the cave entrance. The porcupine appeared to be very recent, but the bear skull was radiocarbon dated at 10,350 years old. The horizontal passage in which these bones were found continues for 15 meters then abruptly drops off a 20-meter-deep pit. In the photo at the right, Dave Love sits at the edge of the pit. The bottom of the pit, and even a ledge half way down, is littered with bones of bears and porcupines. Many of them have been crushed or buried by subsequent rock fall. Two black bear crania were collected from the bottom of the pit and were radiocarbon dated at 10,930 and 4,845 years old.
Very little sediment is present at the bottom of the pit. Water is always dripping down the pit, and during rain storms it becomes a roaring shower. This water tends to wash sediments away to a lower level of the cave, where it accumulates in a bedded silt deposit. A small amount of sediment is present at the base of the pit in shallow pockets, and these pockets are loaded with micromammal remains (see photos below). Large numbers of remains were found of porcupine (Erethizon dorsatum), deer mouse (Peromyscus), red-backed vole (Clethrionomys), long-tailed vole (Microtus longicaudus), shrew (Sorex), and bat (Myotis). Single teeth were recovered of ermine (Mustela erminea), river otter (Lontra canadensis), hoary marmot (Marmota caligata), flying squirrel (Glaucomys), and meadow vole (Microtus pennsylvanicus). This represents the greatest rodent diversity of any site found thus far in Southeast Alaska. Even On Your Knees Cave, whose fossils span 50,000 years and several major climatic shifts (and which were excavated for seven years), does not have as much rodent diversity as Hole 52! Yet the fossils of Hole 52 have only been briefly sampled.
The most fossiliferous sediments of the cave were found in shallow pockets at the bottom of a 20-meter-deep pit. At left caver Dave Love examines one of these sediment pockets. A porcupine skull is exposed in the sediment pocket above.
Another long passage begins at the bottom of the pit. It slopes downward to a sedimentary deposit that turns into a lake during rain storms. A small test pit was dug in this deposit by Pete Smith, and the sediments contained micromammal fossils. A horizontal traverse across this low, sloping passage leads to another horizontal crawlway that contains bones of black bear and porcupine. Another complex passage leads to this place also, so it is uncertain how the animals arrived there. A black bear canine exposed at the surface was radiocarbon dated at 11,460 years old (the oldest date from the cave). Two additional black bear bones buried in shallow sediment were dated to 10,420 and 10,080 years old. A porcupine skeleton strewn along the crawlway was dated at 4,395 years old.
Clearly Hole 52 has enormous potential for elucidating the postglacial history of the Alaskan mainland. This site, like Lawyer's Cave, will help to establish the time of arrival of land mammals following deglaciation, which in turn will help to answer questions about the origin and diversity of island mammals. So far these mainland caves have not produced any fossils that date to the Last Glacial Maximum or before. These caves were almost certainly under glacial ice during much of the Ice Age. But deeper sediments in these caves have potential for holding fossils from the Middle Wisconsin Interglacial period, and finding such fossils will be a prime objective when these caves are excavated.