SPECTACULAR KARST FORMATIONS AND SCENERY OF SOUTHERN CHINA

SOUTH CHINA KARST

Karst rock formations in China China has the most extensive and diversified karst terrain in the world and most of them are rich in caves and dolines (sinkholes, usually funnel-shaped and sometimes very large).The fengcong (cone karst) and fenglin (tower karst) formations associated with the Guilin-Li River-Yangshuo area are world famous and are among the most sought out destinations by tourists traveling in China.

The South China Karst was designated a UNESCO World Heritage Site in 2014. According to UNESCO: South China Karst is one of the world’s most spectacular examples of humid tropical to subtropical karst landscapes. It is a serial site spread over the provinces of Guizhou, Guangxi, Yunnan and Chongqing and covers 176,228 hectares. It contains the most significant types of karst landforms, including tower karst, pinnacle karst and cone karst formations, along with other spectacular characteristics such as natural bridges, gorges and large cave systems. The stone forests of Shilin are considered superlative natural phenomena and a world reference. The cone and tower karsts of Libo, also considered the world reference site for these types of karst, form a distinctive and beautiful landscape. Wulong Karst has been inscribed for its giant dolines, natural bridges and caves.

“The huge karst area of South China is about 550,000 square kilometers in extent. The karst terrain displays a geomorphic transition as the terrain gradually descends about 2000 meters over 700 kilometers from the western Yunnan-Guizhou Plateau (averaging 2100 meters elevation) to the eastern Guangxi Basin (averaging 110 meters elevation). The region is recognized as the world’s type area for karst landform development in the humid tropics and subtropics. The World Heritage Property of South China Karst is a serial property that includes seven karst clusters in four Provinces: Shilin Karst, Libo Karst, Wulong Karst, Guilin Karst, Shibing Karst, Jinfoshan Karst, and Huanjiang Karst. The total area is 97,125 hectares, with a buffer zone of 176,228 hectares. The property was inscribed in two phases.

“The property contains the most spectacular, scientifically significant and representative series of karst landforms and landscapes of South China from interior high plateau to lowland plains and constitutes the world’s premier example of humid tropical to subtropical karst: one of our planet’s great landscapes. It complements sites that are also present in neighbouring countries, including Viet Nam, where several World Heritage properties also exhibit karst formations. Phase I inscribed in 2007, include three clusters totalling 47,588 hectares, with buffer zones totalling 98,428 hectares.Phase II inscribed in 2014 includes four clusters totaling 49,537 hectares, and buffer zones totaling 77,800 hectares. The property’s forest cover and natural vegetation is mainly intact, providing seasonal variation to the landscape and further enhancing the property’s very high aesthetic value. Intact forest cover also provides important habitat for rare and endangered species, and several components have very high biodiversity conservation value.

“The South China Karst World Heritage property includes spectacular karst features and landscapes, which are both exceptional phenomena, and of outstanding aesthetic quality. It includes the stone forests of Shilin, superlative natural phenomena which include the Naigu stone forest occurring on dolomitic limestone and the Suyishan stone forest arising from a lake, the remarkable fengcong and fenglin karsts of Libo, and the Wulong Karst, which includes giant collapse depressions, called Tiankeng, and exceptionally high natural bridges between them, with long stretches of deep unroofed caves.

“It also includes Guilin, which displays spectacular tower karst and internationally acclaimed fenglin riverine landscapes, Shibing Karst, which has the best known example of subtropical fengcong karst in dolomite, deep gorges and spine-like hills often draped with cloud and mist, and Jinfoshan Karst, which is an isolated island long detached from the Yunnan-Guizhou plateau, surrounded by precipitous cliffs and punctured by ancient caves. Huanjiang Karst provides a natural extension to Libo Karst, contains outstanding fengcong features and is covered in almost pristine monsoon forest.”

Geology and Geomorphology of the South China Karst

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The South China Karst World Heritage property protects a diversity of spectacular and iconic continental karst landscapes, including tower karst (fenglin), pinnacle karst (shilin) and cone karst (fengcong), as well as other karst phenomena such as Tiankeng karst (giant dolines), table mountains and gorges. The property also includes many large cave systems with rich speleothem deposits. The karst features and geomorphological diversity of the South China Karst are widely recognized as among the best in the world. The region can be considered the global type-site for three karst landform styles: fenglin (tower karst), fengcong (cone karst), and shilin (stone forest or pinnacle karst).The landscape also retains most of its natural vegetation, which results in seasonal variations and adds to the outstanding aesthetic value of the area.

“The South China Karst World Heritage property reveals the complex evolutionary history of one of the world’s most outstanding landscapes. Shilin and Libo are global reference areas for the karst features and landscapes that they exhibit. The stone forests of Shilin developed over 270 million years during four major geological time periods from the Permian to present, illustrating the episodic nature of the evolution of these karst features. Libo contains carbonate outcrops of different ages shaped over millions of years by erosive processes into impressive Fengcong and Fenglin karsts. Libo also contains a combination of numerous tall karst peaks, deep dolines, sinking streams and long river caves. Wulong represents high inland karst plateaus that have experienced considerable uplift, with giant dolines and bridges. Wulong's landscapes contain evidence for the history of one of the world's great river systems, the Yangtze and its tributaries. Huanjiang Karst is an extension of the Libo Karst component. Together the two sites provide an outstanding example of fengcong karst and also preserve and display a rich diversity of surface and underground karst features.

“Guilin Karst is considered the best known example of continental fenglin and provides a perfect geomorphic expression of the end stage of karst evolution in South China. Guilin is a basin at a relatively low altitude and receives abundant allogenic (rainfed) water from surrounding hills, leading to a fluvial component that aids fenglin development, resulting in fenglin and fengcong karst side-by-side over a large area. Scientific study of karst development in the region has resulted in the generation of the ‘Guilin model’ of fengcong and fenglin karst evolution. Shibing Karst provides a spectacular fengcong landscape, which is also exceptional because it developed in relatively insoluble dolomite rocks. Shibing also contains a range of minor karst features including karren, tufa deposits and caves. Jinfoshan Karst is a unique karst table mountain surrounded by massive towering cliffs. It represents a piece of dissected plateau karst isolated from the Yunnan-Guizhou-Chonqing plateau by deep fluvial incision. An ancient planation surface remains on the summit, with an ancient weathering crust. Beneath the plateau surface are dismembered horizontal cave systems that appear at high altitude on cliff faces. Jinfoshan records the process of dissection of the high elevation karst plateau and contains evidence of the region’s intermittent uplift and karstification since the Cenozoic. It is a superlative type-site of a karst table mountain.”

Fengcong and Fenglin Karst Features in China

Tony Waltham wrote in Cave and Karst Science: Fengcong and fenglin are the two major types of karst terrain as defined in Chinese literature. They correlate only loosely with the Western terms of cone and tower karst respectively. With its isolated towers rising from a karst plain, fenglin is the most extreme form of karst landscape, and much of it may evolve from fengcong where tectonic uplift is critically slow. The other widely-known Chinese term, shilin, translates to stone forest, and applies to a giant form of micro-relief; it is essentially a large form of karren or pinnacle karst that forms the surface texture superimposed on many of the fengcong and fenglin profiles. Chinese geomorphologists distinguish their karst types (in the warm and wet environments) not by the shape of their hills but by the presence or not of a karst plain between the hills. The origins of the terms lie buried in a karst literature that stretches back for 1200 years, though the fenglin term was probably formalized only by Xu Xiake in 1637. [Source: Tony Waltham, Cave and Karst Science 35(3):77-88 · January 2008]

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Fengcong (pronounced fungtsung and translating as peak cluster) is a karst with roughly conical hills separated by deep closed depressions, all standing on a common bedrock base so that it forms a continuous terrain of steep slopes and significant relief. It is also known as fengcong-depression or fengcong-doline topography, and a variant is fengcong-valley karst, where there is more interconnection between the dolines. Only when the early scientists started to travel abroad did they see a difference in the tropical karst regions, where individual hills were more distinctive than the intervening depressions.

The incredibly dramatic landscapes of almost vertical-sided limestone hills in Guangxi were glimpsed enough to generate their description as tower karst. The best examples are in the Yangshuo region, though they were (and are) commonly ascribed to Guilin, the larger city that lies not far away in a rather more subdued variety of karst landscape The city of Guilin, Guangxi, stands on areas of alluvial plain between the limestone towers of its well-known fenglin karst.

Fenglin (pronounced funglin and translating as peak forest) is a karst with isolated hills rising from a plain that is normally formed of limestone bedrock overlain by a veneer of alluvium. It is also known as fenglin-plain topography, and fenglin-polje, fenglin-valley and fenglin-basin are variants determined by the type and extent of the plain between the hills. Slope angles and individual profiles of the hills are again irrelevant. The best known fenglin is that with vertica-sided towers rising from the alluvial plains, but many fenglin hills are more truly conical in profile. The Chinese perception of fenglin also extends to terrains with isolated hills that have very low conical profiles.

Fengcong and Fenglin Landscapes

Tony Waltham wrote in Cave and Karst Science: Typical fengcong terrain consists of roughly equally-spaced conical hills and deep dolines, with local relief that is anything from 30 meters to over 300 meters. This has commonly been labelled as egg-box topography, a conveniently descriptive term for the crowded hills with intervening depressions largely devoid of integrated valley systems, but this degree of perfection is rarely attained. The best examples are found in the Guizhou karst in China, where huge swathes of land are formed of very well developed cones that are close to symmetrical and rise to relatively sharp summits. Detailed measurements across large sectors of the fengcong in western Guizhou revealed remarkably uniform slope angles of 45–47° on cones of all sizes. However mean cone slopes in the fengcong are steeper than 50° in the Shuicheng area, and many are 55–60° in the Anshun area, both also in Guizhou. Variations in slope angles and cone profiles are created by contrasts within the bedrock lithology. Many cones, even in Guizhou, have more ragged or stepped profiles influenced by stronger beds within the limestone sequences, and some in the Guilin karst have asymmetrical escarpment profiles in steeply-dipping limestones. Guizhou cones of weaker, shale-rich limestones have rather lower slope angles. [Source: Tony Waltham, Cave and Karst Science 35(3):77-88 · January 2008]

Karst margin fenglin describes terrains with isolated towers that lie between areas of fengcong and non-karst, reflecting the significance of allogenic sediment in the development of fenglin (see below). Drainage in fenglin is primarily on the alluviated plains between the towers, where substantial dendritic systems of surface rivers can survive. Within the limestone, a relatively stable water table is maintained at the level of these rivers. It is likely that there is significant phreatic flow through the limestones beneath the plains, in the style of underflow (Worthington, 2004), though there are few large risings in the fenglin that could indicate any degree of maturity in such flooded caves. Foot caves abound within the towers, which are also penetrated by some caves that happen to carry the plain’s rivers through them. Vadose (underground water above the water table.) drains within the towers are close to vertical, and commonly intersect old, high-level passages that originated as foot caves at past plain levels. The famously spectacular fenglin karst of the Guilin-Yangshuo region in eastern Guangxi is already recognized as the definitive example of fenglin.

Most fenglin towers do have sides steeper than are found on most fengcong cones. There is, however, a transition through many fenglin towers that have more irregular profiles, but are still distinguished from fengcong by having the alluviated karst plain between them. There is also a transition through towers that have multiple peaks and through very small clusters of hills in the middle of a karst plain; the latter have been described as insular fengcong. Lithology influences profiles, creating asymmetrical or even conical towers in steeply-dipping limestones and lower profiles in weaker rocks, whereas the vertical-sided towers can only survive in strong and almost horizontally-bedded limestone. Fenglin karst can exist with low conical hills, commonly due to lithological influences. That in Guizhou is mainly formed in thinly-bedded dolomite carbonates.

Fengcong and Fenglin Geology and Evolution

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Fengcong are typically formed in carbonate rocks that are continuous and pure over a stratigraphic thickness of more than 200-300 meters, where the adjacent surface rivers are deeply entrenched, where the vadose zone is more than 100-300 meters deep, and where the climate is humid and rainy. The most marked hydrogeological feature is a well-developed subterranean river system, and the lack of surface rivers.

Tony Waltham wrote in Cave and Karst Science: A key process in fenglin karst is the enhanced rock dissolution that takes place due to the chemically aggressive water occurring at the water table. This level has very little vertical variation either side of the level of the alluvial plain, in the style of the level control (known by the German term Vorfluter) that has long been recognized as critical to the lateral growth of the flat floors in karst poljes. The effect of this is to undercut any rising slopes marginal to the alluviated plain, by the creation of dissolutional notches and foot caves. With subsequent collapse over these undercuts, cliff retreat is accelerated at lower elevations, and the whole process effectively turns a cone into a tower. [Source: Tony Waltham, Cave and Karst Science 35(3):77-88 · January 2008]

Lateral planation at the expense of reducing hill profiles creates the commensurate extension of the base level plain, and so constitutes a transition from fengcong to fenglin. This does, however, require a stable base level and water table, and the processes in nature are greatly complicated by the common normal situation of a slowly falling base level. Critical are the relative rates of base level decline, dissolutional lowering of the rock surface beneath the alluvial plain, surface denudation on the karst hills, and sediment input that maintains the evolving alluvial plain. The underlying factor of base level decline is a function of both regional denudation and tectonic uplift.

Debate continues over the early evolution of fenglin, but it is recognized that, whatever its origins, fenglin karst only exists where a number of independent factors combine to create the right environment. The rarity of the perfect combination accounts for the scarcity of mature fenglin worldwide. These factors may be listed: 1) – Limestone that is pure, compact and strong; 2) A huge thickness of limestone, sufficient to allow massive surface lowering, without reaching the base of the limestone, which gives time and space for the karst landscapes to evolve to maturity; 3) A veneer of alluvium overlying the bedrock limestone of a karst plain; 4) A karst water table that is stable and is maintained at the level of the karst plain.

It is clear that the mature forms of fengcong and fenglin, particularly as seen in the karst terrains of Guizhou and Guangxi, have both evolved over very long periods, and there are implications that the fenglin probably has the longer timescale of the two. Some evidence for the lengths of these timescales comes from dated materials in the caves of the fenglin karst around Guilin. Most of these caves are richly decorated with massive deposits of calcite, and stalagmites in the caves of Maomaotou Hill, in the suburbs of Guilin, yield dates ranging from 41 to more than 350 thousand years, with deposition in both warm and cold stages through the Pleistocene (Wang, 1986). The karst is clearly much older. An important record has come from palaeomagnetic studies of clays in a tiered series of caves within a single tower, known as Chuan Shan or Tunnel Hill, which rises on the east bank of the Li River in the southern suburbs of Guilin (Williams, 1987). These cave deposits indicated a mean rate of plain lowering, and therefore of tower emergence, of not more than 23 millimeters per thousand years.

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Factors that influence fenglin and fencong development include: 1) Major inflows of allogenic water and clastic sediment that can recharge and maintain the alluvial plain as it evolves through surface and bedrock denudation; 2) Slow tectonic uplift that matches surface denudation and thereby maintains the karst plain as it is lowered through the limestone profile; 3) A hot and wet climate with significant rates of carbonate dissolution in a regime of abundant biogenic carbon dioxide; and 4) Equilibrium between rates of surface lowering and lateral planation that allows maintenance of the residual towers while the karst plain is lowered around them.

In simple terms, fenglin is a very mature form of karst terrain that can only evolve during surface lowering through a great thickness of limestone; furthermore it requires long-term lowering of an alluviated karst plain, which is only possible where slow tectonic uplift is matched by both its own bedrock denudation and sediment supplies that maintain its alluvial cover. There has been considerable debate over whether fengcong and fenglin evolve separately or whether fenglin evolves from fengcong. Most early ideas focussed on separate origins, dependent on bedrock porosity, bedrock fractures, depth of the karst or superficial cover. More recent studies recognize fenglin that is both evolved from fengcong and separate from it, though with the evolved style dominant in the Guilin area. The separate style includes various types of non-tropical, geologically-guided tower karst. The more isolated karst hills in Jamaica are ascribed to development where there is more insoluble sediment (analogous to the input of gravel where fenglin evolves), and this is claimed to be independent of development of the more widespread fengcong cone karst (Day, 2004); however the evidence is not conclusive.

Guilin, Li River and Yanghshuo Karsts

Tony Waltham wrote in Cave and Karst Science: The finest of the fenglin is the dramatic landscape of isolated, steep-sided towers rising from an alluviated plain, which is commonly covered in rice paddies. The fenglin of Yangshuo, at the southern end of the Guilin karst, represents the geomorphological extreme that has so often been the subject of traditional Chinese paintings and drawings. Numerous individual towers are well over 100 meters tall. Balázs defined his Yangshuo type of karst hills as having a diameter/height ratio of greater than 1.5, but many in the area have ratios of less than 0.5, so that they are two or three times as tall as they are wide, and thereby form one of the world’s most spectacular landscapes. Many towers do have vertical sides and are the more dramatic when they lack any aprons of talus around their bases; some of those around Yangshuo, nearby Fuli and Qifeng (near Guilin) are among the finest anywhere. Others in the same areas are more truly conical, notably in the immediate vicinity of Yangshuo town. Measured profiles in a small sample area of the fenglin near Yangshuo revealed a mean slope angle of 75°. The same survey found no significant difference between slope angles in the fenglin and fengcong (in sample areas between Guilin and Yangshuo); this could have been due to the locations and small sizes of the sample areas, as it is not supported by visual observation that is admittedly non-quantitative. [Source: Tony Waltham, Cave and Karst Science 35(3):77-88 · January 2008]

Large swathes of Guangxi have been described sweepingly as tower karst, whereas fenglin forms only 15 percent of the karst area within the province (and even only 50 percent within the Yangshuo area), the remainder being fengcong. Some of the very crowded fengcong just west of the Li River in the Guilin karst, in Guangxi, has slope profiles steeper than 60°. Towards its margin this area west of Caoping has hills with nearly vertical sides rising from low pediments that keep them apart; morphologically this provides almost the perfect transition from fengcong cones to fenglin towers, though the genetic relationship is perhaps clouded by lithological influences.

The drainage of fengcong karst is almost entirely underground, entering either by fissure percolation or through open sinks at the ends of short ephemeral stream courses within the dolines. Water tables commonly lie far beneath the doline floors, and long vadose cave passages can form dendritic systems. It is noticeable but not surprising that, where long caves have been mapped through fengcong karst, the passages lie beneath both dolines and cone hills with no correlation to the surface topography.

Phreatic loops do occur within the fengcong caves, and survive until development of graded profiles, whereas old passages are commonly abandoned and perhaps subsequently intersected at multiple high levels. The laterally extensive, vadose, cave drainage further distinguishes fengcong from fenglin. The extensive and spectacular fengcong karst of Guizhou (and northwestern Guangxi) is already recognized as the definitive example of its type.

It does not take very long in the field to appreciate the enormous variety of detail in the karst landscapes of Guangxi and Guizhou. It is very clear that multiple factors have been influential, and that not all have been operating at the same time at each site. Consequently there is no simple pattern in the distribution of fenglin and fengcong. On the largest scale, fengcong dominates the uplifted karst of the Guizhou plateau, whereas fenglin is largely restricted to the more stable lowlands of Guangxi. Both fengcong and fenglin occur within the relatively small karst in the Guilin-Yangshuo basin. Many of the fenglin areas are associated with sediment fans of rivers derived from the adjacent non-carbonate hills, while the lower gradient of the trunk Li River precludes its ability to transport sediment so that it has entrenched a gorge through the finest of the fengcong karst. On a smaller scale, a valley within the heart of the fengcong karst of Anshun, in Guizhou, contains two perfectly formed towers on an alluvial flat; this small patch of fenglin clearly developed where there was sediment input, as tectonics could have had no influence at this scale.

Xiaozhai Tiankeng

Tiankengs (Large Sinkholes)

A tiankeng (is a type of very large collapse or sinkhole that has evolved by roof collapse over a large cave chamber where a huge mass of breakdown debris has been removed by a substantial cave river. Tiankeng is Mandarin for “Heavenly Pit.” Zhu Xuewen and Chen Weihai wrote: Tiankengs are giant dolines sometimes found in areas of the cone karst. More than fifty tiankengs have been discovered in the cone karst in southern China, notably in the provinces of Chongqing, Guangxi, Sichuan and Guizhou. Current research indicates that tiankengs develop in specific environments of geomorphology, geology and hydrogeology, and are therefore distinguished from normal karst dolines.[Source:Zhu Xuewen and Chen Weihai, Speleogenesis, 2022]

In carbonate rock terrains, one kind of negative karstlandform has not previously been recorded because it is relatively rare and occurs only in more remote regions. It is the great or giant doline, with steep walls and several hundred metres in depth and diameter; it is a collapse doline distinguished by its very large size. This landform was first observed by geologists in China in the early 1980s, in the Xingwen karst in Sichuan, in an area that was being developed for tourism. It was not mentioned in the hydrogeological investigation reports throughout China in 1970s-1980s, and therefore had no scientific explanation.

In the past 20 years, many more of these great karst dolines have been discovered in southern China. Some, including Xiaozhai, Dashiwei, Qingkou and Haolong, have been found by vigorous tourism development that has been searching for spectacular features in the more remote karst areas. Others have been found during explorations by the China Caves Project, and this has led to considerable research to identify the special features of the giant dolines that distinguish them from normal, smaller, dolines.

In the world's karst literature there is extensive discussion on normal doline development, but there is little on the development of giant dolines. This kind of giant doline is distinguished from normal dolines by its size, and also by major differences in basic characteristics, geomorphic evolution and hydrogeological conditions. The understanding of its geomorphology and its importance matured through the 1990s. In October 2001, it was proposed that this giant doline could be distinguished from normal dolines, and a new term, tiankeng, was proposed for the karst literature. Tiankengs have also been recorded as giant dolines outside China, including Crveno jezero in Croatia, Minyé in Papua New Guinea, Garden of Eden in Malaysia, and El Sotano in Mexico.

There are two types of tiankeng - collapse tiankengs and erosion tiankengs. The former developed by dynamic underground water flow, while the latter were formed by allogenic surface drainage that fed into an underground river in the karst. Collapse tiankengs are much more widespread and more numerous than the erosional forms.

Current records show that the tiankengs in the karst of China are mainly in the south of the country, especially in the cone karst terrain, although some lie outside this core zone. The distinctive cone karst of southern China covers an area of about 150,000 square kilometers, mainly in northern and western Guangxi, southern Guizhou, around the Yangtze Gorges, and across southeastern Chongqing, northern Guizhou, southeastern Sichuan, western Hunan and western Hubei, as well as in southeastern Yunnan.

Relationships between tiankeng development and the intense erosional power of underground water explain the spatial relationship between tiankengs and large underground river systems, especially in cone karst areas where cave river systems are very well developed. According to the national hydrogeological investigation in China in the 1970s-1980s, there are 2836 underground rivers within Guangxi, Guizhou, Sichuan, Chongqing, Hunan, Hubei and Yunnan, with a theoretical total length of 13,919 km. It appears that a very important condition for the development of tiankengs is the development of both cone karst and major cave river systems.

Inside Xiaozhai Tiankeng

Cone karst is one of the important environments for development of collapse tiankengs, but this does not imply that tiankengs are formed in all cone karst terrains with cave river systems. Tiankeng development is restricted to sites with favourable hydrogeological conditions and favourable geological structure. The erosion tiankeng is developed by an allogenic surface river where there is a deep vadose zone in carbonate rocks, with good drainage through the karst. Worldwide, tiankengs are rare because large cave river systems in cone karst are less common than they are in the Chinese karst.

Heaven Pit — the World’s Largest Sinkhole — and Major Tiankengs in China

Zhu Xuewen and Chen Weihai wrote: Except for the Xiaoyanwan and Dayanwan tiankengs in the Xingwen stone forest tourism area in Sichuan Province, which have been known for many years, the important discoveries of tiankengs have occurred since 1994. In that year, the largest tiankeng, Xiaozhai, was discovered near the Yangtze Gorges during the search for a new exploration site for British cavers in the China Caves Project. In 2001, a group of 26 tiankengs was discovered in the Leye karst in Guangxi during investigations for karst tourism resources and the search for another venue for cavers on the China Caves Project. The discoveries of this special karst feature generated interest in scientific research, which was pursued in subsequent years. Almost at the same time, Qingkou Tiankeng was discovered by the senior author in the Wulong karst, and was later explored by the Hongmeigui Cave Club. Around its vertical walls there are several hanging waterfalls and these converge on the floor and flow into a large cave passage. Qingkou Tiankeng was the first erosional tainkeng to be recognised. [Source: Zhu Xuewen and Chen Weihai, Speleogenesis, 2022]

Tiankengs are best described as collapse dolines that are more than about 100 m wide and deep, and this is recommended as the internationally accepted definition of a tiankeng (Zhu & Waltham, this volume). There are however many more features that are between 50 m and 100 m deep and wide, and these are already widely known as tiankengs within China; they have been referred to as "small tiankengs" (Zhu, 2001). These include three small tiankengs in the Mengzi basin, within the karst of Yunnan. Though many of these smaller features are very significant karst landforms, they are all omitted from Table 1 and the descriptions that follow.

Heaven Pit and Ground Seam Scenic Spot (400 kilometers northeast of Chongqing, Coordinates: 108°53'-109°11' E / 31°30'-31°40' N) embraces 626-meter (2,054-foot) -long Xiaozhai Tiankeng, or Heavenly Pit, the largest tiankeng-type sinkhole in the world.

Heaven Pit and Ground Seam Scenic Spot was nominated to be a UNESCO World Heritage site in. 2001. According to a report submitted to UNESCO: Xiaozhai Heaven Pit is actually a "heaven window" of the underground river on the lower reaches of this karst hydrogeological system, and is called karst tunnel. Xiaozhai Heaven Pit is close to the edge of the precipitous cliff on the right bank of deep-cut Daxi River. The elevation of the pit mouth is 1330 meters, and the elevation of the river bed in a shortest distance is 300 meters, the relative height difference between them exceeds 1000 meters.

Tainkeng with an Ancient Rainforest at the Bottom found in China

In March 2022, a team of Chinese scientists announced that they had discovered a giant new sinkhole with a forest at its bottom. The sinkhole is 192 meters (630 feet) deep, deep enough to engulf the St. Louis' Gateway Arch. A team of speleologists and spelunkers rappelled into the sinkhole and discovered that there are three cave entrances in the chasm, as well as ancient trees 40 meters (131 feet) tall, with branches angled the sunlight that pierces through the sinkhole opening. "This is cool news," said George Veni, the executive director of the National Cave and Karst Research Institute (NCKRI), and organization involved in the exploration with the Institute of Karst Geology of the China Geological Surve. [Source: Stephanie Pappas, Live Science, May 11, 2022

Stephanie Pappas wrote in Live Science: “ The discovery is no surprise, Veni told Live Science, because southern China is home to karst topography, a landscape prone to dramatic sinkholes and otherworldly caves. Karst landscapes are formed primarily by the dissolution of bedrock, Veni said. Rainwater, which is slightly acidic, picks up carbon dioxide as it runs through the soil, becoming more acidic. It then trickles, rushes and flows through cracks in the bedrock, slowly widening them into tunnels and voids. Over time, if a cave chamber gets large enough, the ceiling can gradually collapse, opening up huge sinkholes. "Because of local differences in geology, climate and other factors, the way karst appears at the surface can be dramatically different," he said. "So in China you have this incredibly visually spectacular karst with enormous sinkholes and giant cave entrances and so forth. In other parts of the world you walk out on the karst and you really don't notice anything. Sinkholes might be quite subdued, only a meter or two in diameter. Cave entrances might be very small, so you have to squeeze your way into them."

The new discovery took place in the Guangxi Zhuang Autonomous Region, near Ping'e village in the county of Leye, according to Xinhua. The sinkhole's interior is 306 meters (1,004 feet) long and 150 meters (492 feet) wide. Zhang Yuanhai, a senior engineer with the Institute of Karst Geology, told Xinhua the bottom of the sinkhole did indeed seem like another world. Chen Lixin, who led the cave expedition team, told Xinhua that the dense undergrowth on the sinkhole floor was as high as a person's shoulders. Karst caves and sinkholes can provide an oasis for life, Veni said. "I wouldn't be surprised to know that there are species found in these caves that have never been reported or described by science until now," Lixin said.

The new discovery brings the number of sinkholes in Leye County to 30, according to Xinhua. The same researchers have previously discovered dozens of sinkholes in Northwest China's Shaanxi province and a cluster of interconnected sinkholes in Guangxi, China Daily reported. A tiankengin Luoquanyan Village of Xuan'en County, central China's Hubei Province also has many plants growing at the bottom

Image Sources: Wikimedia Commons

Text Sources: CNTO (China National Tourist Organization), China.org, UNESCO, reports submitted to UNESCO, Wikipedia, Lonely Planet guides, New York Times, Washington Post, Los Angeles Times, National Geographic, China Daily, Xinhua, Global Times, The New Yorker, Time, Newsweek, Bloomberg, Reuters, Associated Press, AFP, Compton's Encyclopedia and various books and other publications.

Updated in June 2022