http://kickass.to/national-geographic-m ... 93238.html
A production of the National Geographic Channel in conjunction with Chinese television CCTV-9.
For additional maps, cross-sections, and photographs of Mawangdong Cave, Bandong Tienkeng, and the through-cave photographed in this movie, see page 3 of the Leye-Fengshan Geopark, Sanmenhai Karst Tourguide:
http://www.naturalarches.org/files/Leye ... kChina.pdf
NOTE: National Geographic Channel (NGC) is jointly owned by Fox Cable Networks and National Geographic Television & Film. They are acknowledged as producing documentaries with factual content and "pseudo-scientific entertainment programming" on NGC (Wikipedia). This film appears to be a documentary enhanced with exaggerated mystery and danger.
I have been asked to provide some clarification for the US caving community about the use of the term "tiankeng". This is pronounced "Tee-ann Kung" in Mandarin. As many of you know, I have been leading karst-focused tours for geologists and cavers and have first-hand knowledge of Chinese karst since 1993. The cavers staring in the film have clearly had a wonderful time in a spectacular area courtesy of National Geographic. The film does a good job of explaining the area to the general public, and conveying the wonder and excitement of exploring the karst of SW China.
This is a spectacular and interesting film of the huge collapse dolines and high-relief karst near Leye, SW China. It is also contains some unnecessary (in my opinion) exaggeration and self-promotion from Fox Cable and the National Geographic Channel. Anyone in the caving community who has been to the spectacular karst areas of China recognizes the hyperbole. The writers/producers seem either to have done a poor research job (unlikely) or made a deliberate decision to add additional "mystery" and danger to some of the most spectacular karst on Earth. These are clearly world-class caves.
Cave scientists have understood how these huge pits are created for over a hundred years. First described from the Dinaric Karst (Škocjanske jame) in the Balkans, known in China since 1992, explored in China by the Cave Research Foundation Expedition in 1993 (that was before the Funny Word "tienkeng" had been coined), and explored extensively in China by the Hong Meigui Cave Exploration Society (Erin Lynch) since 2001, the British Cave Research Association, and others. Large limestone pits like these are not common, but have been found in many places. At the time of this writing approximately 50 are known to exist in China (which is a VERY big country) and over 35 in other countries.
Simply, they are unusually large collapse dolines. That is the term I prefer to use to describe these features, not the funny Chinese word "tiankeng". The huge volume of limestone that has been removed must have gone somewhere. In most cases there is obviously a good-sized underground river beneath the collapsing doline which keeps removing the breakdown blocks as they fall underground. In this part of China there is stratigraphically over 7 1/2 miles (total thickness) of soluble limestone, high topographic relief, and it rains a whole lot to produce the groundwater that dissolves the limestone. Fracture traces in the limestone likely relate to the specific location of these pits, just as they do for millions of other cave passages around the world.
The public perception and misunderstanding about tienkengs has been caused by a prominent Chinese geologist who arbitrarily made up the word "tienkeng" (Sky Hole or Heavenly Pit) for exceptionally large collapse dolines. He defined them as collapse dolines that are more than 100 meters wide and deep. This is a completely arbitrary term. It is just like using the word "skyscraper" for tall buildings and "megabuilding" for the very tallest one. Then you can claim that your city has the only megabuilding in the world. It has allowed the Chinese to make a Big Deal out of the fact that they do, indeed, have a lot of impressively gigantic collapse dolines in their country. Applying the term to a specific collapse doine has encountered problems about whether a specific feature is really a "tiankeng" of "just" a large collapse doline. They are ALL just collapse dolines! Some of which are unusually big.
Note that the Chinese typically measure the size of the pits at their maximum dimensions and depth (from the highest point around the rim), where western cavers usually measure the depth from the lowest spot on the rim (shortest distance from top to bottom if you were actually going to rappel in). This further confuses the "depth" and "size" issues.
There are numerous references to these large pits in China that have been written over the last 20 years, some accurate, some with included hyperbole. Here is where to start:
Tiankengs: Definition and Description, 2006, Zhu Xuewen and Tony Waltham
http://www.speleogenesis.info/directory ... df9541.pdf
This is a summary paper that that defines the features. In regards to the proposed concept of a "tiankeng karst":
The concept of tiankeng karst has been considered within China as a term to describe an extremely mature type of karst landscape that has matured beyond normal fengcong karst with high relief. The term could be used to describe the Leye karst in Guangxi, China, and perhaps the Nakanai karst in New Britain, Papua New Guinea, both of which are distinguished by unusually large numbers of tiankengs. However, some mature karst terrains contain just a few tiankengs, notably just two in each of the karsts of Xingwen, Croatia and Mexico, and these question the applicability of the term. Tiankeng karst may be purely descriptive of the Leye and Nakanai terrains, but the term has not yet been shown to have any geomorphological status with reference to karst evolution.
Figure 1 of this 2006 report shows EXACTLY the "mystery cave" in the Leye Karst that this film is all about. Maoqui Dong is the "incipient tienkeng" that they first rappelled into. - There are all sorts of problems trying to translate Chinese language or idiograms into English, and then trying to figure out by reading the English translations if you are talking about the same place (are the names really the same in Chinese). The names "Bandong" and "Baidong" are likely the same when you read the Chinese characters or pronounce them in Mandarin. It would have not taken much research for the National Geographic explorers to have had a very good idea what they would find when they got to these collapse dolines China and to know how the features had formed.
For a list of 33 "tienkengs" and comparable features known to exist outside China in 2004 (including El Sotano and Golindrinas in Mexico):
http://www.speleogenesis.info/directory ... df9540.pdf
Special Issue: Tiankengs Transactions of the British Cave Research Association: Cave and Karst Science: V. 32, n. 2&3 (in one volume). Descriptions of the giant collapse dolines in China and the Wulong Karst World Heritage site.
The Mother Of All collapse Dolines is Xiaozhai, close to the Yangtzee River, just south of the first of the Three Gorges. Down-cutting by the Yangtze has created the great relief found in the area. Xiaozhai is 662 meters deep (measured by the Chinese to obtain maximum depth) and has a trail (with many steps) to the bottom, where a diversion tunnel for hydroelectric power has been constructed. See The Yangtze Gorges Expedition: China caves project 1994 - Guest Editorial by Andy Eavis, BCRA Cave and Karst Science Vol 22 (2) 1995. Description of the Xiaozhai area south of Fungjie and the Yangtze Gorges.
https://www.googledrive.com/host/0B0PLt ... %20065.pdf
The Yangtze Gorges Expedition: China caves project 1994 - Guest Editorial by Andy Eavis
BCRA Cave and Karst Science Vol 22 (2) 1995: 51
The Yangtze Gorges Expedition: China caves project 1994 - Expedition Report by Kev Senior (Ed.)
BCRA Cave and Karst Science Vol 22 (2) 1995: 53-90
Report of the China Caves Project 1994 expedition to Xinglong. Includes surveys, maps and photos.
So: It appears to me that the term "tienkeng" is proving itself to be a very effective public relations term for the Chinese, similar to the effectiveness of the term "spelunker" introduced by Clay Perry in 1939 and subsequently used widely by newspaper reporters. Both terms are likely to be around for quite some time to come. The geologist and expedition leader in this movie does an excellent job of explaining karst hydrology, even with the inclusion of enhanced mystery, and explaining the previously well-known understanding of how these giant pits develop. The whole tone of the movie (with enhanced mystery and danger) is similar to the one National Geographic produced a couple of years ago on what they claim to be the Biggest Cave in the World (Hang Son Doong in Vietnam: http://www.youtube.com/watch?v=aWaKRjTbZdI ), where he was also the team geologist.
That said, this film is about some of the most spectacular karst in the world and is worth watching.
My colleagues in China point out that the video is providing lots of publicity for the Leye-Fengshan Geopark, which is likely to make it easier for future expeditions to get permission to cave in those areas.