File:Giant canyon passage (Dismal Hollow, Mammoth Cave, Kentucky, USA) (37638225960).jpg
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(park service poster; original photo by Gary Berdeaux) Western Kentucky's Mammoth Cave is the longest cave system on Earth, with 412 miles known and mapped. The name does not refer to the early discovery of fossil mastodon or mammoth bones here. Rather, the name refers to the immense size of many rooms and passages. The system is famous for having giant canyon passages. Canyons are taller than they are wide. Giant canyons often have a boxy or rectangular cross-section because they are significantly filled with sediments and breakdown - often more than 50% filled. At one site (at least), about 80 feet worth of fill is present. Shown above is Dismal Hollow, a short stretch of impressive giant canyon passage that is the original downstream continuation of Audubon Avenue, one of my favorite sections of Mammoth Cave. The view seen here is looking in the old upstream direction. A subterranean river used to flow through here. The floor-to-ceiling height varies, but was measured to be 30 feet at one spot. Dismal Hollow and Audubon Avenue are at level B in the Mammoth Cave system, which is the 2nd-oldest and the 2nd-elevationally highest set of passages. Level B passages started forming during the Pliocene, 2 to 4 million years ago. The ceiling and walls of Dismal Hollow and Audubon Avenue consist of marine limestones of the Girkin Limestone (lower Upper Mississippian). The ceiling here is basal Beaver Bend Member limestones. The dark, slightly-recessed, relatively thin interval in the upper walls, just below the ceiling, is the Bethel Member, which consists of argillaceous limestones. In the Flint Ridge part of the cave system, the Bethel is a shale unit. The middle and lower walls are Paoli Member limestones. The photograph was taken near the top of a large pile of rocks, called a breakdown pile, that blocks this giant canyon passage. The rock pile is called Lookout Mountain. It corresponds to a surface sinkhole. The passage formerly continued to the old Green River (= heading behind the photographer). Note: "Dismal Hollow" is also a place name for a cave passage next to Sandstone Avenue, near Mammoth Cave's Carmichael Entrance. Locality: Dismal Hollow & Lookout Mountain (just south of Rafinesque Hall), Mammoth Cave, Kentucky, USA |
| Date | |
| Source | Giant canyon passage (Dismal Hollow, Mammoth Cave, Kentucky, USA) |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/37638225960. It was reviewed on 13 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 17:36, 13 October 2019 | | 4,000 × 3,000 (7.09 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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