Aesthetic value of aeolian geomorphosites in the Kumtagh Desert, China

JinFeng Wu , Xin Wang, Feng Guo, Lei Li

College of Tourism and Environment, Shaanxi Normal University, Xi’an, Shaanxi 710062, China

1 Introduction

Aeolian geomorphosites are one type of geomorphic entities, formed and developed under wind action, possessing special external morphology and internal structure, and are of great value in terms of aesthetics, social economy and science. The value of geomorphology used by society is very important to geomorphological resources. The identification and discovery of special aeolian geomorphological resources is important for the development of tourist areas, such as Shapotou District in the southeast edge of Tengger Desert. The discovery of singing sand and scientific connotation of sand dunes bestowed on the Shapotou Desert Experiment site by the Chinese Academy Sciences through years of research has made Shapotou District the first 5A-grade scenic spot in China. Besides, many tourism attractions in China often have a theme of dunes or aeolian geomorphology, such as Sand Lake of Ningxia, Kubuqi Desert and Badain Jaran Desert of Inner Mongolia, Singing Sand Mountain, Crescent Moon Spring, Yardang National Geological Park in Dunhuang, Gansu Province, and even the coastal areas of Changli Golden Coast, Hebei Province. With the expansion of global and Chinese tourism, the value of aeolian geomorphosites becomes increasingly important. The establishment of geological parks with a desert theme, such as Alxa Desert Geopark and Dunhuang Yardang Geopark, fully embodies the value of aeolian geomorphosites. Worldwide research about geomorphosites is at its beginning stage (Panizza, 2001; Panizza and Piacente,2003). The sixth International Geomorphology Conference was held in Spain in August 2005, and the fourth working group was set up to discuss academic issues about the evaluation of geomorphosites and tourism geomorphology. Vocabularies, such as geomorphological resources and geomorphosites have been widely used in a number of countries in Europe and North America, while relatively rare in other countries (Waele and Melis, 2009). With an improvement of living standards, the development of modern transportation and communication technology,and diverse travel modes, desert tourism is on the rise and has a bright future. Therefore, aeolian geomorphosites as a natural heritage are the result of social development. The study of aeolian geomorphosites and tourism development are not only important aspects of aeolian geomorphology service for human society, but also the expansion of this field has essential scientific significance and application.

Kumtagh (sand hill in Uyghur) Desert is the fourth largest mobile desert in China (Qu, 2010). It is located in the south rim of Luobupo Depression which is in the east of Tarim Basin, lying at the northern foot of the Altyn Mountains, close to Aqike Valley in the northern direction, and stretching to the west of Dunhuang city in Gansu Province in the eastern direction. The widest point between north and south of the Kumtagh Desert is 120 km, and the longest length from east to west is 350 km. Its area is about 24,243 km2, including the main part of the Kumtagh Desert (22,785 km2), the desert of Singing Sand Mountain area which is to the east of Dang River(633 km2), the sporadic, and sheet-like flat sand and dune lands of Aqike Valley (475 km2), as well as the interior gobi of Kumtagh Desert (350 km2), which is approximately in the region between 39°00′N–40°47′N and 90°27′E–94°52′E. In the perspective of administrative division, the main part of the Kumtagh Desert is in the east of Ruoqiang County of Xinjiang Uygur Autonomous Region, and is mainly distributed in Dunhuang City, Aksai Kazakh Autonomous County and Subei Mongolia Autonomous County in Gansu Province. The main part of the desert covers an alluvial-diluvial, stony clinoplains and fluvial-lacustrine plains of the northern foot of the Altyn Mountains.Dune distribution is from the piedmont belt with an altitude of 2,000 m, to the plain (or valley) with an altitude of 800 m, such that the surface gradually declines from south to north (Xiaoet al., 2010).Kumtagh Desert is gradually becoming a resort for adventure tourism. Aesthetic appreciation and experience is what tourists can obtain from the Kumtagh Desert, and one of the primary components that attract tourist is aeolian geomorphosites. The famous poem written by Wei Wang of the Tang Dynasty,"Straight lonely smoke rises in the desert, a grand long river reflects the round setting sun", vividly describes the aesthetic value of deserts. This paper adopts some qualitative research methods including field observation, descriptive method, expert assessment, and systematic investigation (Gao and Zhang, 2006; Zhang, 2006; Duan, 2010) to analyze and evaluate the aesthetic value from three aspects of"Beauty of Morphology", "Beauty of Color" and"Beauty of Forms", which aims to provide a solid foundation for tourism development of the aeolian geomorphosites in the Kumtagh Desert.

2 Beauty of morphology

The beauty of morphology of aeolian geomorphosites refers to the general characteristics of long-term interaction of wind, water, geological structure and plants in the special geographical environment of the Kumtagh Desert. Its basic image, variation and defective characteristics of natural beauty can be summarized as magnificent, odd, secluded and broad.

2.1 Magnificent beauty

Magnificent beauty of aeolian geomorphosites of the Kumtagh Desert is mainly reflected in the image of large sandy hills in the Altyn Mountains and Kumtagh Desert. Relative height is a primary factor of magnificent beauty. The Altyn Mountains, located in the south of the Kumtagh Desert, comprise the northern edge of the Tibet Plateau, and experienced a strong uplift during the Quaternary Period. The average height of the mountains is currently 3,000–4,000 m.However, located in the north of the desert is the Lop-Nor Depression which is a relatively sunken geological unit, whose altitude is below 800 m (Donget al., 2008). The Kumtagh Desert, in the middle of these two geological units, has great elevation differences from north to south. Although the wind regime of Kumtagh Desert is complex, its trend overall is from north to south, which supplies sand cover over the foot of the Altyn Mountains, forming climbing dunes. Seen from a distance, the sand-covered piedmont appears to be a sandy hill, which is above the northern low dunes and Gobi area and seems extremely majestic. In terms of aeolian geomorphology, sandy hills are higher than 100 m. Thus the name of Kumtagh Desert comes from its magnificent beauty. The lofty sandy hills are mainly distributed in the south of the Kumtagh Desert, which makes its grand beauty more prominent. There is great elevation difference between star sandy hills of Singing Sand Mountain regions and oasis of Dunhuang in the north. From Dunhuang City to the west, along provincial highway 215, there is also great elevation difference between the southern star sandy hills and the northern low Gobi. Walking through Xitugou along provincial highway 215, sandy hills on both sides show the grand beauty of the Kumtagh Desert.

2.2 Odd Beauty

Odd beauty of aeolian geomorphosites in the Kumtagh Desert is mainly reflected in its bizarre and unpredictable shapes. The area of Kumtagh Desert is ranked fourth in Chinese mobile deserts. However, the desert is famous as a museum of diverse aeolian geomorphology. The diversity is reflected in aspect of spatial scale. The height of the smallest aeolian landform, the sand ripple, is several millimeters, while the height of the largest aeolian landform, lofty sandy hill,is over a hundred meters. The odd features of ventifacts, Desert Rose Stone and Yardang landforms are particularly prominent in aeolian geomorphosites of the Kumtagh Desert.

2.2.1 Ventifact and desert rose stone

During long periods of geological history, many peculiar ventifacts are shaped by strong winds in the Kumtagh Desert, which become a wonder of the desert.Ventifacts vary in size, and small silicalite can be always seen, such as silicon fossils, agate, chalcedony and quartz rocks, which are dense and hard. They have various colors, including white, yellow, red, gray,black and mixed colors (Li, 1993). Beauty of ventifacts mainly lies in their forms. Ventifacts are angular and vivid with rugged changeable gesture. They are solid like jade from its texture and feel smooth, which give them special visual and tactile effects. Some ventifacts with odd shapes are extremely exquisite as crystals, some of which are perfectly round, simple and unsophisticated, while some are vividly human-shaped, producing endless imagination. Ventifacts have become a member of the family of ornamental stones, which is popular among people (Jia,2008). An important feature of ventifacts is that they are formed naturally without artificial carving, and their beauty lies in their tough character. The windward side of ventifacts is smooth as a mirror, but the rocks are angular as a whole, reflecting its strong-willed character, which gives one a sense of inspiration and encouragement.

Desert rose stones are rose shaped gypsum crystals which grow in the depression of the desert. Because they contain iron and manganese, most of their colors are brown and brown-yellow. According to their growth morphology, it can be divided into monomer,conjoined shape, branched shape, and fasciculate shape. The diameters of monomer and conjoined shape is 1.5–10 cm and 10–50 cm or longer, respectively.Some crystals are arc-imbricate shape in groups, while others are rhombic tabular-imbricate shape (Gao,2008). Desert rose stones are rare flower-like minerals among natural stones, which are full of ornamental value.

2.2.2 Yardang landforms

Yardang landforms of the Kumtag Desert are famous for its different gesture, which is a unique landscape in the Gobi desert and known as a wonder of the world. Some large-scale Yardang groups resemble ancient cities, including city walls, streets, buildings,squares, churches and statues, while others are animal shaped. They are incomparably graceful and have extraordinary vigour (Liu, 2005). Some medium-scale Yardang groups have narrow wind-erosion valleys;however, their gesture are various, such as ravine,depression, peristele, mushroom stone, stalagmite, and pavilion stone, which form superimposed, erect and accumbent, well-proportioned, magnificent landscapes. The gesture of many Yardang landforms are in a row spreading in one direction.

Most of the Yardang landforms are "top-flat,body-steep". The huge mound is several-meters high;the sidewall is steep, while the other side in the prevailing wind direction is serpentine. Climbing on its flat top with wind whistling in ones ears, overlooking the mountain presents a savage picture, which makes people shudder. Yardang landforms are mysterious,some of which are like a deserted castle, standing on the ground. Every night, there is loud sound in the gale,giving one a sense of eeriness, thus it is famous worldwide as the "Devil town". In addition, Yardang landforms in the Kumtag Desert have a long history,such as relics of the Great Wall in the Han Dynasty, the world-famous Silk Road, as well as a large number of ancient city sites. This makes the Yardang landforms more mysterious when combining long history with ancient cultures.

2.3 Secluded beauty

Secluded beauty of the Kumtagh Desert is mainly reflected in its southern canyon, the northeastern Yardang canyon and Xihu wetland (Donget al., 2010).Due to the uplift of the mountains, seasonal rivers,originating from the Altyn Mountains in the south of the desert, form canyons through long term erosion.These canyons cut into the desert and stretch from west to east, including Hongliu, Xiaoquan, Suosuo, Balong,Xiaoduoba, Daduoba, Cuimu, and West, which are convoluted, deep and quiet. The walls are in-line, vertical, or interleaving in relation to the direction of sunlight, producing a wonderful phenomenon of alternately bright and dark, distinct gradation and varied shades. When the canyons split the bedrock, they sometimes become narrow, when they run through relatively soft Jiuquan and Yumen conglomerates they become broad at times, which give people the feeling of a sudden glimpse of hope in the dark mist of bewilderment. Due to faults, cliffs often appear in canyons such as Suosuo, Duoba, Cuimu and West, giving one a sense of deep solitude. Some of these canyons form small and rare sand falls in the desert. Due to the unique geographic environment and nature of the sediments, columnar sculpture groups are formed on both sides of the canyons with different gesture. A stretch of lofty sandy hills show rare and spectacular wonders on both sides of the canyons.

Yardang Valley in the north of Yardang Geological Park is deep and narrow due to long-term wind action,whose width is 50–200 m, and a length of 3 km. Both sides of this valley are steep, giving one a sense of awe.In addition, the Xihu wetland, taking Hala Lake and Hala’nuoer as the core in the eastern edge of the desert,is a green island in the Kumtagh Desert.

A great deal of melted snow water from the Altyn Mountains infiltrates into the underground, and seeps from low-altitude areas through groundwater runoff,forming different sized marshes, such as reed, sedge,and cattails. Meadows grow around the marshes, such as reed,Achnatherum splendens(Trin.) Nevski,Calamagrostis epigejos(L.) Roth,Leymusgrass, andIris ensataThunb. Psammophytes grow in patchy sand-gather areas, such asArtemisia ordosicaKrasch.,Nitraria tangutorumBobrov, and tamarix. Compared with desert canyons, walking through these over-head grasslands give one a sense of quiet spirit. During spring and summer, the surface of the wetlands ripples with lush vegetation where various birds gather together. This region contains federally protected species such as 34 kinds of wild animals like black storks,red-crowned cranes, and wild camels, and four kinds of plants such asGymnocarpos przewalskiiMaxim.,Populus euphraticaOliv., along with various medical cash plants such asApocynum venetumL.,Cynomorium songaricumRupr., andEphedra(Wanget al., 2009).

2.4 Broad beauty

Broad beauty of the Kumtagh Desert is mainly reflected in its flat terrain and broad prospect, giving one a relaxed and happy aesthetic feeling. Because of the open feature of the desert as a whole, the southern Altyn Mountains and lofty sandy hills, and the northern North Mountain can be observed in the far distance of the desert. People usually describe the open desert as an endless sea of sand, which aptly describes the Kumtagh Desert. Among various types of aeolian geomorphology, the gobi eroded by wind and the northern linear dunes can show the boundless and open feature of the Kumtagh Desert best.

The broad beauty of the gobi landscape is reflected in "the empty beauty" because of its vast, open and remote feature, which include three other forms, illusory beauty, hazy beauty, and quiet beauty (Zhang,2003). This openness gives one a feeling of sudden enlightenment, peace of mind, and happy heart. The vast and remote feature of the gobi is represented by Yumenguan site and Beacon Tower site of the Great Wall. Illusory beauty is reflected in the mirage which can easily appear in the gobi. The mirage is a natural phenomenon caused by the atmosphere refracting light,producing an illusionary appearance of some feature,giving one a sense of nothingness, disillusionment and unachievable goals. Mirages are dreamlike and mysterious, which can stimulate the curiosity. In cloudless and hot summer days, the mirage can commonly be seen on both sides of the roads from Dunhuang to Yang Guan and Yumen Pass, such as the surging sea, high mountains, neat buildings and elaborately arranged cities. Hazy beauty is reflected in uncertain and blurred scenery presented by the mirages. Sometimes, they connect the sky with the gobi, producing implicit beauty that is easy to realize and hard to express. Quiet beauty is reflected in the silence of the gobi. When there is no wind, the desolate gobi is soundless, seems void under the blue sky, and it looks as if the air is static. Therefore, standing in the gobi, people can feel the world by sound, which frees the spirit, disconnects one from modern society, and produces a closer relationship with nature.

2.5 Variation characteristics

Compared with various aeolian sediment landforms, aeolian geomorphologies are changeable and unpredictable. Sand ripple are most susceptible to aeolian action, and its size, shape and arrangement is easily modified by wind. Under steady wind direction and force, sand ripples present ordered, alternate,dark/white stripes that are vertical with wind direction.On flat land surfaces, these orderly stripes can extend tens of meters, which are considered as a classic case of self-organization in a complicated system. Under changeable wind forces, sand ripples will constantly merge from small to large, or form composite ripples from secondary ripples superimposed on larger ripples.Under wind directions with complex changes, sand ripples will form intricate shapes, such as crescent,branched, pyramidal, and reticular, which correspond to the type of dunes. The formation mechanism of sand ripples and dunes is different in aeolian geomorphology, however, sand ripples are considered as miniature dunes in morphology. Therefore, if dunes cannot be appreciated, tourists can experience and enjoy the type and morphology of dunes by viewing various sand ripples.

The climatic environment of the Kumtagh Desert is extreme drought, with the hinterland almost devoid of vegetation cover except for depression areas and gullies. The fluidness of the dunes is strong, especially smaller dunes, producing changeable forms and land surfaces. For example, the morphology of dunes shifts,forming new dunes under strong winds. In the northern linear dunes area, the windward and leeward slopes of dunes alternate under changeable wind direction,producing slope variation on both sides of the dunes in different seasons. Desert vehicles in some areas can easily steer from south to north, while in other areas they cannot. These are the peculiar characteristics of aeolian geomorphology in the Kumtagh Desert.

2.6 Defectiveness features

Defectiveness is a type of phenomenon that refers to the destruction and imperfection in the appearance of things. Researchers have applied defectiveness to aesthetics, called Defective Beauty (Duan, 2010;Zhang, 2010), which is a type of theory for sublimation of defective appearance in cognition. Defective beauty of the Kumtagh Desert can be seen everywhere, such as various Yardang landform shapes that are the result of long-term water and wind erosion. These shapes give free reign to the imagination and amazement.Defective beauty in the northern desert can be found in linear dunes, which can be long and straight, or sinuous and rolling, while others are short. The inter-dune corridors of these linear dunes are narrow or broad.Defective beauty in the southern desert can be found in the form of flood erosion. All these different forms are the result of aeolian geomorphology, giving one a sense of amazement such as the sudden appearance of linear dunes in inter-dune corridors, or dune discontinuity during the process of extension. Defective beauty can also produce curiosity in the origin of these landforms, such as which landforms are formed from which type of water or wind erosion.

3 Beauty of color

Beauty of color of aeolian geomorphosites in the Kumtagh Desert stems from sand grains composed of a variety of minerals with different colors. These geomorphosites can be enjoyed from two different levels, sand grains at the micro level, and desert at the macro level.

3.1 Color of sand grains

Sand grains produced by the weathering of rocks have different shapes and colors due to different mineral composition. These shapes and colors are stunningly beautiful and have high ornamental value. The sand of Singing Sand Mountain in Dunhuang has five colors,red, yellow, green, white and black, which glisten and are spotlessly clean, as beautiful as diamonds.

3.2 Color of desert

Aeolian geomorphological colors are caused by different colored sediment, with visual effects caused by sunlight. The Kumtagh Desert is the most colorful desert in China, with unique patterns formed by color disparity and spatial variation of the sediment. The feathery dunes are the most representative of the geomorphology (Donget al., 2008). In the northern linear dunes areas, flat and broad inter-dune corridors have stable beds with dark colored coarse grains,which are formed by long-term wind erosion. On the dark beds it occurs wind-drift sand with fine light colored grains, similar to the scene of wind blown sand passing over the surface of asphalt roads. When the wind abates, this sand accumulates and bright dune-like drifts are formed on the dark beds. Due to the resistance of both sides of the linear dunes to wind,the wind speed is faster in the center of inter-dune corridor, therefore, bright dune-like drifts are formed,protruding towards the southwest, which is a unique landscape in the Kumtagh Desert. The orderly bright dune-like drifts are very spectacular and show up in remote sensing images as feather-like projections protruding from linear dunes to both sides. This is why some researches called them feathery dunes by mistake.

Yardang landforms are composed of lacustrine sediment and dune sand interbed with fine light colored sand grains, while Yardang Valley and surrounding gobi are dark coarse sand and gravel left by long-term wind erosion. The colors between Yardang landforms and Yardang Valley are not only distinct,but also complementary to each other, which makes the Yardang landforms more beautiful and spectacular.The visual effect of the core scenic area in Yardang Geopark, named "fleet launching out", is caused by color contrast between Yardang landforms (the fleet)and Yardang Valley (the seawater). The special reflection of the sand to light makes the color of dunes extraordinarily beautiful in moonlight, sunrise and sunset.

4 Beauty of forms

Beauty of forms in the Kumtagh Desert is the regular combination features of aeolian geomorphology, which fits the rule of beauty of form; orderly,rhythmic and united.

4.1 Layer feature

The spatial structure Kumtagh Desert landscape can be enjoyed from three aspects, macro, medium and micro.

From the macro perspective, the Kumtagh Desert stretches as far as one can see, and is both serene and majestic. During a gale, the sand undulates in waves,similar to surging waves of the sea. There are patterns in the north of Kumtagh Desert with approximately 4,000 km2of like-feather structures, composed of vertical linear dunes and inter-dune drifts. The linear dunes are called "pteryla", and the inter-dune drifts are called "feathers". The whole desert, covering the diluvial-alluvial fan at the northern foot of Altyn Mountains, is like a large fan, which forms a unique landscape not found in other deserts. The broad inter-dune provides ample space for large-scale tourist activities.

From the medium perspective, the dunes show various and wonderful shapes in the Kumtagh Desert.Parallel, linear "fake feathers" dunes present beauty of rhythm, while the different albedo of sediment with alternately dark and bright on the surface presents gentle beauty. The barchans, which are arc shaped dunes, are of moderate height, with white sand that shins like moonlight. The pyramid dunes, with meandering desert ridge lines, show the bright and dark interface in the sunshine. The angular golden dunes are exceptionally majestic under a clear blue sky. The Singing Sand Mountain is typical pyramid dunes.

From the micro perspective, the line beauty of sand ripples is aesthetically pleasing. There are five types of sand ripples, line, curve, chain, tongue and crescent,which are formed from wind action in the Kumtagh Desert. These beautiful lines witness the footprint of the wind, which show the beauty and grace of the desert.

4.2 Line feature

Line feature is one of the prominent characteristics of aeolian geomorphology and is also a crucial reason which attracts artists to consider aeolian geomorphology as a creation theme, and is reflected in the aforementioned poem by Wei Wang. Most types of aeolian geomorphology are named by their line features, such as crescent, linear, star, and pyramid dunes.Yardang means steep hill in Uyghur, and it highlights the vertical line feature. The line features of aeolian geomorphology in the Kumtagh Desert include horizontal, vertical, oblique and curved. Horizontal line is the main line feature at the top of Yardang landforms and linear dunes, which conveys a sense of ease. Vertical line is the main feature of Yardang walls and desert canyons, which have characteristics of growth and a stable center of gravity, conveying an impression of solemn, sublime feeling. Slash is the main feature of sand ridge lines of star dunes. Due to their fluidness,they present a feeling of movement and restlessness. If we look up from the bottom, it presents a sense of energy and optimism. If we look down from the top, it presents a sense of decline and disillusionment. Curve is the main feature of barchan, crescent, and compound barchan dunes with free and lively features, which gives one a sense of elegance and fullness.

The famous scenic spot, Crescent Moon Spring of Dunhuang, attracts a great number of tourists because of its crescent feature. Crescent Moon Spring, called sand drain in ancient times and commonly known as medicinal springs, is one of top eight scenic spots since the Han Dynasty (Zhang, 1987) and is called"Yue Quan Xiao Che (clear crescent spring)". The shape is like the crescent moon and is called "the No.1 spring of the desert". Its distance from north to south is about 100 m, and from west to east is about 25 m. The spring is shallower in its west side than in the east side and the deepest site is about 5 m. Dang River is the source of Crescent Moon Spring. As a result of the continuous filling of water, the spring is clear and beautiful in the surrounded yellow-sand,and does not dry up.

4.3 Auditory feature

The auditory features of aeolian geomorphology in the Kumtagh Desert lie in the singing sands of Singing Sand Mountain and the weird sounds of Yardang Geopark. Singing sand is worldwide, and can be found in Long Island, Massachusetts Bay and the West Bank of Wells of the United States, Bonn Herm Island of Denmark, Fort Cole of Poland, Brazil, Chile, Asia and the Middle East (Quet al., 2007). The Singing Sand Mountain of Dunhuang is one of the top four deserts in China. The other three deserts are Badain Jaran Desert of Inner Mongolia, Singing Sand Mountain of Shapotou on the bank of the Yellow River in Zhongwei County of Ningxia, and Xiangsha Bay on both sides of Hantaichuan in the Kubuqi Desert which is about 25 km south of Dalate County, Inner Mongolia.Singing Sand Mountain of Dunhuang produces a loud sound during a gale, described as "the sound of heaven and earth, the natural and tuneful sound". The sound during a breeze seems as if it is from favorite Chinese instruments, and its charm is represented in a Qing Dynasty poem by Lvji Su.

5 Conclusions

Aeolian geomorphosites have some unique aesthetic features and are important forms of natural beauty. The study of these aesthetic features can make the content of aesthetic research richer, provide some theoretical guidance for tourism development and has crucial theoretical and applied significance.

This research was supported by the National Natural Science Foundation of China (No. 41071090).

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