PDF: /pdf/seka_pdf9548.pdf

Abstract:

The karst of Xingwen, China, contains the Xiaoyanwan tiankeng, alongside the degraded tiankeng of Dayanwan and also the potential collapse chambers in the Zhucaojing cave system. These three sites appear to represent an evolutionary sequence, whereby a tiankeng develops from multiple cave collapses, and subsequently degrades to the profile of a large doline.

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  PDF: /pdf/seka_pdf9549.pdf

White W.B. and White E.L.

Abstract: Development of large collapse structures in karstic terrain requires an interaction between mechanical instability and chemical removal of collapsed rock. Upward migration of pre-existing voids can choke out if there is no mechanism for the efficient removal of fallen blocks. Rates of dissolution, size of initial cavity, and overlying bedrock characteristics determine the size of the final surface landform. Collapse features range in scale from small sinkholes to hundreds of meters in such features as the Golondrinas collapse pit in Mexico. Tiankengs are interpreted as end members features on a continuous scale.

  PDF: /pdf/seka_pdf9546.pdf

Some large dolines in the Dinaric karst

Kranjc Andrej

Abstract: The main characteristics of the Dinaric karst are all kind of depressions, not only poljes and dolines, but also collapse dolines and similar forms. Some examples of such forms of large dimensions are located on the higher karst plateaus (Pokljuka, Jelovica, Sne?nik in Slovenia), on the contact karst (Škocjanske Jame), on the levels above poljes (Crveno Jezero above the Imotsko Polje), and behind large karst springs (Unška Koliševka above the springs of Malni). Slovene terms for karst depressions are defined.

  PDF: /pdf/seka_pdf9547.pdf

Hydraulic processes in the origin of tiankengs

Palmer Arthur N. and Palmer Margaret V.

Abstract: Tiankengs are formed most commonly by the collapse of bedrock into underlying caves that contain active rivers. The collapse propagates itself by blocking and diverting the underground streams, so that hydraulic gradients become steeper and the solutional and erosional capacities are enhanced. Most of the volume of a tiankeng is produced by removal of mass by the cave streams. A large and fluctuating discharge is most favorable. As diversion passages form and enlarge, they foster further collapse and diversion. Stress release around the collapse encourages the opening of new fractures with trends that differ from regional fracture patterns. These processes account for the large scale of tiankengs in comparison to the original cave passages.

  PDF: /pdf/seka_pdf9545.pdf

Cave un-roofing as a large-scale geomorphic process

Klimchouk Alexander

Abstract: A morphogenetic approach appears to be the most sensible in defining the tiankeng as a typological category. Tiankengs are giant collapse dolines formed over large river caves, with continuous precipitous perimeter and a diameter-to-depth ratio between 0.5 and 2. The term bears an evolutionary meaning, referring to the youthful stage of open collapse doline development, and the relationship of tiankengs to large underground rivers. The latter criterion separates tiankengs from other types of giant collapse features, such as caprock collapses over evaporates or large collapses over hydrothermal cavities. The South China karst offers evidence that un-roofing of caves is a large-scale geomorphic process playing an important role in the formation of cone and tower karst. It is probably the major process in the origin of large depressions, gorges and valleys in tropical karst, although other geomorphic processes contribute to shaping and maturation of a landscape and eventually obscure the origin in unroofed caves. Many saddles between hills and towers in fengcong and fenglin karst may owe their origin to cave un-roofing.

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in Miscellaneous by Super User
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in Miscellaneous by News Manager
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