Guilin's landscape is the best in the world, but what makes it the best?

The Mid-Autumn Festival holiday is coming, and traveling has become a good choice for many friends. When it comes to the mountains and rivers of our motherland, I believe that many people will immediately think of a sentence: Guilin's landscape is the best in the world.

In September 2024, at the 37th International Geological Congress held in Busan, South Korea, Guilin Karst in Guangxi was successfully selected into the second batch of 100 World Geological Heritage Sites with its unique geological landscape and scientific research value, along with the Inner Mongolia Botanical Pompeii-Wuda Permian Vegetation Fossil Origin and the Dashanpu Dinosaur Fossil Site in Zigong, Sichuan. This is another world-class business card obtained after Guilin Karst was selected into the World Heritage List in June 2014. Guilin, a land known for its "best landscapes in the world", where is the "best"? What mysteries are hidden in its karst landforms waiting for us to explore?

The scenery of the Li River photographed in Xingping Town, Yangshuo County, Guangxi (Photo source: Xinhua News Agency)

01The past and present of karst

Speaking of Guilin, the first thing that comes to mind is the beautiful Li River, which is known as the "Hundred Miles of Art Gallery" for the green mountains, beautiful waters, strange caves and beautiful stones where it flows through; some people may think of the famous Elephant Trunk Hill, named because its shape resembles an elephant drinking water by the river, which is considered to be the iconic landscape of Guilin; others may think of the Moon Hill in Yangshuo County (there is a naturally formed large hole on the top of the mountain that resembles a full moon), the Sword Testing Stone on Fubo Hill (legend has it that it is the mark left by Ma Yuan, the Fubo General of the Eastern Han Dynasty, when he tested his sword), etc. These many rare natural wonders attract tourists from all over the world and show the magic and charm of this land to the world.

Elephant Trunk Hill in Guilin (Photo: Ma Zhifei)

In fact, the above-mentioned landscapes are closely related to karst landforms.

Karst landform, also known as karst landform , is a special geological phenomenon that mainly occurs in areas where soluble rocks (such as limestone, dolomite , etc.) are distributed. In 1893, Serbian scholar Jovan Cvijic (1865-1927) first proposed the term "karst" when studying the karst plateau landforms of the Istrian Peninsula in the former Yugoslavia. The transliteration is "karst", which was gradually widely accepted and applied by the geological community. It refers to the geological action of water on soluble rocks such as limestone, which is mainly chemical dissolution, supplemented by erosion, subsidence and collapse of flowing water, as well as the general term for the phenomena caused by these actions.

The karst plateau is composed of a large number of thick layers of limestone . Although limestone is almost insoluble in pure water, it is easily dissolved by water containing a small amount of carbonic acid. The local climate is characterized by hot and dry summers and warm and rainy winters. A small amount of carbon dioxide in the air and produced by plant decay is dissolved in the rain, which is weakly acidic. They come into contact with the limestone along the joints and cracks in the rock and react with the calcite in the rock, dissolving into calcium ions and bicarbonate ions and being carried away, thus forming funnels, karst grooves, stone buds, etc. on the surface, and dark rivers and karst caves underground.

Later, as geologists continued to study, they found that karst landforms are widely distributed, from tropical to temperate zones, from mountainous areas to plains, almost all over the world. Guilin Karst is a typical example.

02 Characteristics of Guilin Karst

The formation of Guilin Karst can be traced back to the geological history period of more than 300 million years ago (Devonian-Carboniferous). At that time, the place where Guilin is located was still a vast ocean. With multiple tectonic movements, the sea water gradually receded, leaving behind a 3,000-meter-thick limestone sedimentary layer with a gentle occurrence and huge, thick and pure rock layers. It is these ancient rocks that created the material basis for the formation of karst landforms.

Climate conditions are also an important factor in the formation of karst landforms. Guilin is located in a low-latitude zone with a subtropical monsoon climate . The climate in the area is hot and humid, with abundant rainfall. Karstification is very intense and develops rapidly. Karstification is more favorable in areas with thick limestone layers, many faults, and developed fissures. Geologists call this karst phenomenon in South China tropical monsoon karst, which is characterized by the development of a large number of cone-shaped and tubular peaks and layered caves.

In contrast, the temperate monsoon karst is located in a relatively dry climate, with only heavy rain in summer, so the development of karst landforms is limited to a certain extent. Its main characteristics are that huge canyons and layered caves often appear in areas with gentle occurrence and thick limestone development, while small pagoda-shaped peaks and cone-shaped peaks appear in mountainous areas, which are more typical in the Taihang Mountains (Langya Mountain) in North China, the Western Hills of Beijing (Yunshui Cave in Shangfang Mountain and the East and West Longmen Streams of Zhaitang) and the Yanshan area.

In short, over the long years, the limestone has been subjected to continuous erosion and dissolution by surface water and groundwater, gradually forming the unique landforms we see today, which are mainly manifested in the following aspects:

(1) Tall and majestic peaks : Although the mountains in Guilin are not very high, they have been eroded for a long time to form steep mountains and sharp peaks. They are tall and beautiful in various shapes, including tall and isolated peaks and rolling peaks.

A mountain overlooking Guilin (Source: Xinhua News Agency)

(2) Deep caves : Guilin Karst area has abundant karst cave resources. These caves have vast interior spaces and a variety of stalactite landscapes such as stalagmites, stone curtains, and stone flowers. The temperature inside the caves is constant and the humidity is suitable, providing a unique living environment for many organisms.

Underground cave (Source: Xinhua News Agency)

(3) Spectacular underground rivers : Guilin has a well-developed underground river system with undercurrents, forming many spectacular underground waterfalls and underground river landscapes. These underground rivers are not only an important part of the groundwater cycle, but also an important driving force of karstification.

03 Geomorphic manifestations at the end of karst evolution

Regarding the Guilin karst landform, geologists call it "the landform manifestation of the late stage of karst evolution in South China". How should we understand this?

Regarding the development stage of karst landforms, geologists believe that karst landforms begin to develop from rising karst highlands, and complete a development sequence through four stages: infancy , adulthood , late adulthood ( blind valley stage ) and old age ( quasi-plain stage ). Saying that Guilin Karst is a landform display of the late stage of karst evolution in South China does not mean that it has entered old age or is no longer developing. The "late stage" here refers more to the fact that in the process of karst landform development in this area, Guilin Karst has reached a relatively mature and stable stage, and its geomorphic characteristics and karstification process are representative and typical.

In fact, Guilin's karst landform is famous for its tall and isolated peaks, deep caves and winding underground rivers, which are typical manifestations of karst landforms in their prime . In this development stage, sinkholes, funnels and karst depressions are widely distributed on the ground, the underground cave system is intricate and interconnected, and surface water systems such as the Lijiang River flow through the karst area. Part of the river section turns underground to form underground rivers. These characteristics are consistent with the description of the prime stage.

Some scholars also divide the development of karst landforms into the early deposition stage, the beginning of dissolution stage, the intense dissolution stage, the landform stabilization stage and the later transformation stage according to the chronological order. The karst landform development process in Guilin Karst area fully demonstrates the characteristics of the above stages, especially the landform features of the intense dissolution stage and the landform stabilization stage are the most significant. These landform features not only have extremely high ornamental value, but also are an important reference for global karst research.

04 Peak forests and peak clusters

Peak forests and peak clusters are the two main types of Guilin karst landforms. Some scholars praise it as "a typical representative of continental tower-shaped karst, showing the Guilin model of coexistence and interaction of peak forest and peak cluster karst forms."

The so-called peak forest , also known as conical karst or tower karst, refers to the towering limestone peaks. Due to the dissolution, the surface rocks gradually lose their support and collapse and fall off to form isolated peaks. They appear scattered or in groups on the flat ground, and look like a forest from a distance, hence the name. The relative height difference of the peaks is 100 to 200 meters, and the slope is very steep, generally more than 45 degrees, with various shapes, some are steep and upright like swords pointing to the sky, and some are round and beautiful like green screens.

The so-called peak cluster refers to a series of peaks connected by dense peaks and interdependent with a relative height of 200 to 300 meters. A "U"-shaped saddle is formed between the peaks, and there are often karst depressions, funnels, sinkholes, etc. between the peak clusters, thus forming a combination of peak cluster depressions or peak cluster funnels .

Peak forest in Yangshuo County, Guilin City, Guangxi (Source: Xinhua News Agency)

Peak forest ( Picture from the Earth Science Dictionary )

Peaks on both sides of the Li River in Yangshuo County, Guilin City, Guangxi (Source: Xinhua News Agency)

Peak cluster ( Picture from the Earth Science Dictionary )

Karst peak cluster depression (Source: Xinhua News Agency)

In contrast, the peaks in the peak forest are relatively independent, with various shapes, and the landscape is more open and spectacular. For example, Yangshuo's Ten-Li Gallery is a typical representative of the peak forest landscape, where the peaks stand in rows, each with its own characteristics, like a flowing landscape painting; while the peaks in the peak cluster are closely connected, with a relatively uniform shape, and appear more compact and dense. For example, the continuous peaks on both sides of the Li River are a model of the peak cluster landscape. They are closely connected to form a magnificent natural barrier, adding infinite scenery to the Li River.

What is even more surprising is that at the foot of these peaks, there are intricate caves and underground rivers, which together "eat away" the mountain, sometimes destroying the stone peaks to the point where only an empty frame remains. The most famous is the Reed Flute Cave in Guangming Mountain in the northwest suburb of Guilin. This cave is about 240 meters long, 50-90 meters wide, and 10-18 meters high. In the deep and mysterious cave, stalagmites stand in rows and stalactites hang in various shapes and forms, just like a magnificent "immortal cave". From the ink wall books found on the cave walls, it is found that people have visited the cave at least since the 5th century AD.

The development process of stalactites ( Picture from the Dictionary of Tourism Geology )

Guilin's karst landform is not only a masterpiece of nature, but also a witness to the geological changes of the earth for billions of years. As its international reputation and influence gradually increase, its unique scientific research value, eco-tourism value, educational value and potential huge economic value will be further explored, providing a strong impetus for promoting local economic and social development and enhancing international cultural exchanges and cooperation.

Author: Ma Zhifei, a popular science writer and member of the Beijing Science Writers Association, has written more than 10 popular science books, including "A Dream of Red Mansions" and "Glass Earth". He has won the Ministry of Natural Resources' Excellent Popular Science Book Award, the Wu Dayou Popular Science Book Award, and the China Natural Resources Writers Association's "China Gem Literature Award" Popular Science Works Award.

Reviewer: Li Zhongdong, Deputy Director of Sichuan Geophysical Survey Institute, Chief Scientific Communication Expert of the Ministry of Natural Resources

Produced by: Science Popularization China

References:

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