Douglas Vance

Geomorphology of China

Introduction

China is a vast country with many different climate zones, landforms, and topographic

areas. The country is one of the largest in the world and contains most of the geomorphologic

processes scientists have been able to study. Three regions of the country are particularly

interesting. They have been chosen because they demonstrate unique processes and involve

different climactic zones. These include the Gobi Desert, the karst landforms in the Yunnan

province in southeast China, and the Yangtze River. The Gobi Desert is mainly located in

Mongolia but extends into the northern part of China. It is important to China because of the

features that help create the desert environment. The karst landforms in southern China are

among the most amazing views in the world. This area is home to the largest area of karst

landscape than any other in the world. The limestone in this area has been eroded to form these

features into two main types, cone karst and tower karst. The Yangtze River is the most

important river in China as it spans almost the entire length of the country and benefits the

country in many different ways including agriculture and transportation. However, many risks

are involved with the river as it yields the consequences of the sub-tropical climate in southern

and eastern China. These three geographic features are very different in their processes and

effects on the landscape but they also affect each other. Each area discussed is connected in

erosional and climatic regards.

The overall purpose of this paper is to study the geomorphological processes responsible

for three main geographic features of China.

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The Gobi Desert, the karst landforms in southern China, and the Yangtze River all have different

geomorphologic features that created them, but they also affect each other in many ways.

Understanding this is important because of how large the country is. Many people believe there

is no way a river can affect a desert hundreds of miles north, and this is mostly true, however

similar forces are acting on both at the same time. So although the area is vast, the land is

changing all the time and each change causes a ripple effect that creates and alters landforms in

other areas. First, we must understand China as a whole, its location in the world, extent, and

other physical features. Next, each of the three geomorphologic areas will be explored. The Gobi

Desert, the karst landforms, and the Yangtze River are to be discussed respectively. Finally, the

information will be discussed and conclusions about the areas will be reached.

Background

China is undoubtedly a large country to cover. It spans more than 3 million square miles

and lies between about 18 degrees and 54 degrees north latitude and 73 degrees and 135 degrees

east longitude (Figure 1). The country is mostly mountainous mainly in the western part of the

country due to the Tibetan plateau. China has a west to east strike overall as the country levels

off and becomes flat as it approaches the ocean to the east and southeast. The total relief of

China is around 5 thousand meters in the west to 2 hundred meters in the east (Praeger, 1969).

This basic geographic information is relevant for many reasons. First, mountains, in general, tend

to create a rain shadow desert on one side especially if the raised land extends across deeper into

the landmass. Second, mountains create water runoff which is crucial in producing a river.

Finally, the creation of these mountains in particular, was due to the India continent colliding

with the Asia continent. This caused the orogenesis with land and sea based materials. The ocean

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material formed limestone and this is the basis for the karst features in southern and southeastern

China.

(Figure 1- This is a geographic map of China that shows the elements discussed in this paper

such as the Tibetan Plateau and Yangtze River. Source

http://www.freeworldmaps.net/asia/china/china-map-physical.jpg)

The Gobi Desert

The first feature we will look into is the Gobi Desert. The Gobi Desert is part of a greater

desert area known as the Central Asian Desert that stretches for more than 2000 miles. Another

part of this is the Taklamakan Desert. These deserts together span from western and northern

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China into Mongolia. More specifically, The Gobi Desert extends about 1000 miles across Asia

and is mainly composed of salt basins (Quilici, 1969). To understand the formation and

geomorphology of this region, three factors need to be explored. First is the soil history and

present soil. Next is the overall location of the desert. Finally, the weather, past and present, that

affect the arid climate.

First, the desert is obviously dry now but when did it become arid? Evidence can be

found in the soil history. Clues are available for an arid climate as early as the Paleozoic but the

soil gives the concrete evidence beginning in the Cretaceous and Tertiary ages. The soil shows

that the deposits from this area switch from coals, bauxites and iron-manganese ores to red

deposits with salts and gypsums. This evidence is important because the salts are deposited under

conditions of intense evaporation and water deficits, supporting the development of an arid

climate. Today’s soils are created by a process known as carbonate accumulation. This forms

desert limestone which has a gray-brown color. The southern part is the most desert-like part of

the region and is often called a stony desert. This is due to the aeolian processes that carry fine

sediments away and leave behind coarse material sitting on bedrock (Praeger, 1969).

The Gobi Desert is relatively flat because it is in a fold or valley but is almost completely

surrounded by mountains to the west, south, and east sides (Figure 2). The most significant of

these are the Qilian Mountains to the south. They are part of the Tibetan plateau and the

Himalayas.

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(Figure 2- This map of the Gobi Desert shows the surrounding topography focusing on the

mountains in the area. Source http://commons.wikimedia.org/wiki/File:Gobi_desert_map.png)

These mountains create the rain shadow effect in which orogenic uplift causes all the moisture to

be dropped on the front side of the mountains. By the time the air mass crosses the mountains

and descends, it is completely dry and increasing in temperature. The temperature increases

because the air mass is quickly descending and expanding. The mountains to the east and west

have the same effect. Any air mass containing moisture that avoids the Tibetan Plateau will just

run into another mountain range that will deplete the available moisture. This entire region is

also located in the center of a continent therefore reducing the amount of moisture available

(Praeger, 1969).

The final component for this arid region is of course the weather. The mountains play a

large part in the weather of this area but another factor is also important. The continental

Mongolian-Siberian anticyclone located in Russia and Mongolia is an almost permanent high

pressure system that controls the region. High pressure systems are typical for sunny, dry

weather because it is a stable system. Moisture and rain is associated with low pressure systems

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and unstable weather. The high pressure is the source wind because wind moves from high to

low pressure; this helps keep undesirable weather away. The high pressure system is mainly in

control of this region in the winter as it advances southward. In the summer, the low pressure

system, The East Asian Monsoon, to the south that is the cause for the massive flooding in India

and along the Yangtze River is more prominent as it moves north. However, this does not affect

the Gobi Desert because of the rain shadow effect from the Tibetan Plateau and Himalayas. This

high pressure system is the final punch to create a sustained arid climate as this area receives less

than 100 mm of rainfall per year (Praeger, 1969).

Yunnan Province

The karst features of southern China seem other worldly and are among some of the most

amazing sights in the world according to Sweeting. Karst is the term used to describe a landscape

riddled with limestone that has been eroded by fluvial processes. Limestone dissolves when

water such as rain, rivers, and lakes act on it leaving behind caves, towers, and hills of remaining

limestone. Rain water is slightly acidic. Limestone breaks down when exposed to water and the

acidic nature of rain water accelerates the process. Yunnan is a province in south China that is

riddled with these unique landforms. This area is located on the China reference map where the

Mekong River flows out of the Tibetan Plateau. Karst dominates for many reasons. First is the

amount of limestone in the area. The limestone is more than 9000 feet thick and represents over

60 percent of the known strata in this region (Sweeting, 1973). The climate also plays a large

role. Yunnan has a sub-tropical climate where the western part of the province receives around

1500mm of rainfall annually and the east receives 600 mm. The area receives the effects of the

East Asian Monsoon which is the low pressure system that advances north in the summer. This

causes the area to receive more rainfall in the summer causing the erosion rate to increase. The

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last feature is the location in regards to the Tibetan Plateau. Yunnan is raised in elevation due to

the building of the Himalayas and contains many rivers that originate in the highlands. This leads

to fast flowing rivers that are high in sediment content. These rivers accelerate the erosional

fluvial processes that have formed this region (Praeger, 1969). There are two types of karst

features in southern China, cone karst and tower karst.

Cone karst is also known as Kegelkarst. These are limestone hills that resemble cones,

rising and falling in quick succession. They are mainly located in eastern Yunnan and can reach

as much as 300 feet high. They have a wide base anywhere between 300 and 600 feet and have a

moderate slope, usually anywhere between 40 and 60 degrees. Cone karst is typically formed

from water eroding on top of limestone bedrock. Rain or rivers can form channels in the blocks

of limestone and slowly erode over time to create a rounded hill of the original block. These are

located in eastern Yunnan where the topography is more level and the rivers are not as fast and

are not carrying a high sediment payload (Sweeting 273-281).

In contrast tower karst, known as Turmkarst, are steep sided limestone hills in groups.

They are almost always accompanied by a river or standing water. Lakes are a common site

around tower karst. The towers can rise to 300 meters high which is almost 1000 feet and have

anywhere between 70 and 90 degree slopes. They typically form in tropical regions so heavy

rainfall creates prime conditions for heavy flowing rivers with large amounts of sediment. These

towers are often riddled with caves because infiltrating rain forms channels in the limestone. The

caves can also be formed by past groundwater channels. Two factors play into the difference in

forming cone and tower karst. First is the more significant river flow, tower karst forms when

cone karst forming processes are accelerated such as faster rivers with more sediment. Second

are the joints in the limestone. They form as guidelines for the formation of water channels so

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they often serve as the point of erosion. Uplift can also rejuvenate the karst landscape with this

areas proximity to the Himalayas (Sweeting, 1973).

The Yangtze River

The Yangtze River is the most important river in China in terms resources such as

irrigation for farmland and power production from dams. Its headwaters are located in the

Tibetan Plateau at around 5100 meters high and the river stretches 3600 miles across China until

it reaches the Pacific Ocean in the east (Rau, 1970). The Yangtze River is the third largest river

in the world in regards to length and water discharge and the fourth largest in terms of sediment

load (X.X. Luo, 2012).

(Figure 3 – This map shows the extent of the Yangtze River Basin. Source X.X. Luo, 2012)

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The Yangtze River basin stretches from about the midway point of the river to the mouth

at the Pacific Ocean and is essential to supporting life in this area (Praeger,1969) (see Figure 3).

The 180,000 square mile basin is home to about 450 million people and is a prime location for

human activity because of the rich floodplain soil (X.X. Luo, 2012). The soil was originally two

thirds yellow-cinnamonic soils but has been changed by farmers. This area is affected by the

tropical monsoon that fluctuates seasonally. So although the area is rich and great for agriculture,

it is also in danger of seasonal flooding. The floods are some of the most extensive in the world

and this has led to human action such as building dams (Praeger, 1969). Within the basin, around

50,000 dams have been built over history to combat the major flooding events. The most

significant dam in China is the Three Gorges Dam. It was built in 2006 and is the world’s largest

hydropower project. Although this dam produces more power than any other, it is controversial

for geological reasons. A common occurrence with dams is the reduction of sediment. Coarse

grained material can become trapped on the upstream side of the dam which allows only fine

grained material to pass through. This causes problems downstream. For example, this situation

can change a gravel based river to a sand based river. This change is controversial because it can

change the ecological processes of the river downstream from the dam causing problems in

erosion and even biological processes (X.X. Luo, 2012).

Discussion

Some of the key factors discussed are the importance of mountains in the formation of

each area. The rain shadow desert in the Gobi, the orogenisis and uplift of the land in forming

karst, and the headwaters of the Yangtze River are all due to the Tibetan Plateau and surrounding

mountains. Each area seems to be connected. The Tibetan plateau stops moisture from getting to

the Gobi Desert creating the arid environment. The limestone in Yunnan is there because of the

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formation of the Himalayan Mountains and the rain that falls on the plateau from the tropical low

pressure system is the source of many rivers that run through south China and carve the karst

landforms. Finally, the Yangtze River that provides for so many and is capable of destroying so

much is also created in these mountains. Even though they are all different processes, each is

affected by the others. The plateau is critical to each area. The Gobi Desert is formed from the

rain shadow desert effect. All the moisture is dropped on the plateau and creates some of the

rivers that run through China. These rivers carry sediment and pick up speed and cut through the

limestone in Yunnan. One of these rivers is the Yangtze, which provides for a mass of China’s

population. Overall we can conclude that each area relies on the Tibetan Plateau. Without it, each

geomorphological landform would change completely.

Conclusion

China is a large country and is home to many different types of geomorphological

landforms and processes. First, the Gobi Desert is the main desert in China. It is created by the

rain shadow effect caused by the Himalayas and the Tibetan Plateau and the Siberian-Mongolian

high pressure system located over Mongolia. Second, the karst landscape of the Yunnan

province. This landform is made of limestone that was formed by the oceanic materials from the

impact of India into Asia. The limestone is eroded by the high amount of rainfall and the

numerous rivers that cut through the tropical and sub-tropical regions of China. Third, the

Yangtze River’s headwaters flow from the Tibetan Plateau and carry sediment downstream

eroding and constantly changing the landscape. Without the Tibetan Plateau all of these regions

would dramatically change. The Gobi Desert would be exposed to the effects of the low pressure

system and receive enough rainfall to change the landscape. The limestone would not exist in

Yunnan without the orogenisis of the Himalayas therefore there would be no karst landforms.

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Finally, The Yangtze River would not be one the most impressive rivers in the world without the

rainfall and sediment from the plateau. Overall, the Tibetan Plateau creates each of these unique

processes and without it, none of the landforms would be the same.

References:

X.X. Luo, S.L. Yang, J. Zhang, The impact of the Three Gorges Dam on the downstream

distribution and texture of sediments along the middle and lower Yangtze River

(Changjiang) and its estuary, and subsequent sediment dispersal in the East China Sea,

Geomorphology, Volume 179, 15 December 2012, Pages 126-140, ISSN 0169-555X,

10.1016/j.geomorph.2012.05.034.

(http://www.sciencedirect.com/science/article/pii/S0169555X12003868)

Sweeting, Marjorie M. Karst Landforms. New York: Colombia University Press, 1973. Print

Rau, Margaret. The Yangtze River. New York: Julian Messner, 1970. Print

Quilici, Folco. The Great Deserts. London: Collins, 1969. Print

Praeger, Frederick A. The Physical Geography of China Volume 2. New York: 1969. Print

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