Desertification is a type of land degradation in drylands in which biological productivity is lost due to natural processes or induced by human activities whereby fertile areas become arid. It is the spread of arid areas caused by a variety of factors,such as overexploitation of soil as a result of human activity and the effects of climate change. Geographic areas most affected include the Sahel region in Africa,the Gobi Desert and Mongolia in Asia as well as parts of South America. Drylands occupy approximately 40–41% of Earth's land area and are home to more than 2 billion people.
Erosion is the action of surface processes that removes soil,rock,or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited. Erosion is distinct from weathering which involves no movement. Removal of rock or soil as clastic sediment is referred to as physical or mechanical erosion;this contrasts with chemical erosion,where soil or rock material is removed from an area by dissolution. Eroded sediment or solutes may be transported just a few millimetres,or for thousands of kilometres.
A monsoon is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscillation of the Intertropical Convergence Zone (ITCZ) between its limits to the north and south of the equator. Usually,the term monsoon is used to refer to the rainy phase of a seasonally changing pattern,although technically there is also a dry phase. The term is also sometimes used to describe locally heavy but short-term rains.
Soil erosion is the denudation or wearing away of the upper layer of soil. It is a form of soil degradation. This natural process is caused by the dynamic activity of erosive agents,that is,water,ice (glaciers),snow,air (wind),plants,and animals. In accordance with these agents,erosion is sometimes divided into water erosion,glacial erosion,snow erosion,wind (aeolian) erosion,zoogenic erosion and anthropogenic erosion such as tillage erosion. Soil erosion may be a slow process that continues relatively unnoticed,or it may occur at an alarming rate causing a serious loss of topsoil. The loss of soil from farmland may be reflected in reduced crop production potential,lower surface water quality and damaged drainage networks. Soil erosion could also cause sinkholes.
Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil or as sediment mixed in suspension with water. Silt usually has a floury feel when dry,and lacks plasticity when wet. Silt can also be felt by the tongue as granular when placed on the front teeth.
A loess is a clastic,predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loesses or similar deposits.
The Interior Plains is a vast physiographic region that spreads across the Laurentian craton of central North America,extending along the east flank of the Rocky Mountains from the Gulf Coast region to the Arctic Beaufort Sea. In Canada,it encompasses the Canadian Prairies separating the Canadian Rockies from the Canadian Shield,as well as the Boreal Plains and Taiga Plains east of the Mackenzie and Richardson Mountains;while in the United States,it includes the Great Plains of the West/Midwest and the tallgrass prairie region to the south of the Great Lakes extending east to the Appalachian Plateau region.
The Tibetan Plateau,also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau or as the Himalayan Plateau in India,is a vast elevated plateau located at the intersection of Central,South,and East Asia covering most of the Tibet Autonomous Region,most of Qinghai,western half of Sichuan,Southern Gansu provinces in Western China,southern Xinjiang,Bhutan,the Indian regions of Ladakh and Lahaul and Spiti as well as Gilgit-Baltistan in Pakistan,northwestern Nepal,eastern Tajikistan and southern Kyrgyzstan. It stretches approximately 1,000 kilometres (620 mi) north to south and 2,500 kilometres (1,600 mi) east to west. It is the world's highest and largest plateau above sea level,with an area of 2,500,000 square kilometres (970,000 sq mi). With an average elevation exceeding 4,500 metres (14,800 ft) and being surrounded by imposing mountain ranges that harbor the world's two highest summits,Mount Everest and K2,the Tibetan Plateau is often referred to as "the Roof of the World".
Aeolian processes,also spelled eolian,pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth. Winds may erode,transport,and deposit materials and are effective agents in regions with sparse vegetation,a lack of soil moisture and a large supply of unconsolidated sediments. Although water is a much more powerful eroding force than wind,aeolian processes are important in arid environments such as deserts.
The East Asian Monsoon is a monsoonal flow that carries moist air from the Indian Ocean and Pacific Ocean to East Asia. It affects approximately one-third of the global population,influencing the climate of Japan,the Korean Peninsula,Taiwan,China,the Philippines and Mainland Southeast Asia but most significantly Vietnam. It is driven by temperature differences between the East Asian continent and the Pacific Ocean. The East Asian monsoon is divided into a warm and wet summer monsoon and a cold and dry winter monsoon. This cold and dry winter monsoon is responsible for the aeolian dust deposition and pedogenesis that resulted in the creation of the Loess Plateau. The monsoon influences weather patterns as far north as Siberia,causing wet summers that contrast with the cold and dry winters caused by the Siberian High,which counterbalances the monsoon's effect on northerly latitudes.
Mineral dust is atmospheric aerosol originated from the suspension of minerals constituting the soil,composed of various oxides and carbonates. Human activities lead to 30% of the airborne dust (particulates) load in the atmosphere. The Sahara Desert is the major source of mineral dust,which subsequently spreads across the Mediterranean and Caribbean seas into northern South America,Central America,and eastern North America,and Europe. Additionally,it plays a significant role in the nutrient inflow to the Amazon rainforest. The Gobi Desert is another source of dust in the atmosphere,which affects eastern Asia and western North America.
The Great Green Wall,officially known as the Three-North Shelter Forest Program,also known as the Three-North Shelterbelt Program,is a series of human-planted windbreaking forest strips (shelterbelts) in China,designed to hold back the expansion of the Gobi Desert,and provide timber to the local population. The program started in 1978,and is planned to be completed around 2050,at which point it will be 4,500 kilometres (2,800 mi) long.
A pediment,also known as a concave slope or waning slope,is a very gently sloping (0.5°–7°) inclined bedrock surface. It is typically a concave surface sloping down from the base of a steeper retreating desert cliff,escarpment,or surrounding a monadnock or inselberg,but may persist after the higher terrain has eroded away.
Aeolian landforms are produced by either the erosive or depositive action of wind. These features may be built up from sand or snow,or eroded into rock,snow,or ice.
A desert is a landscape where little precipitation occurs and,consequently,living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the land surface of the Earth is arid or semi-arid. This includes much of the polar regions,where little precipitation occurs,and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls,by the temperature that prevails,by the causes of desertification or by their geographical location.
Paha are elongated landforms composed either of only loess or till capped by loess. In Iowa,paha are prominent hills that are oriented from northwest to southeast,formed during the period of mass erosion that developed the Iowan surface,and they are considered erosional remnants since they often preserve buried soils. Paha generally rise above the surrounding landscape more than 6.1 metres (20 ft). The word paha means hill in Dakota Sioux. Well known pahas include the hill on which the town of Mount Vernon,Iowa developed,Casey's Paha in Tama County,Iowa,and the Kirkwood Paha,home of Kirkwood Community College's campus. These features are found in other regions of the United States and in Europe,where they are known as greda.
The Gobi Desert is a large,cold desert and grassland region in northern China and southern Mongolia and is the sixth largest desert in the world. The name of the desert comes from the Mongolian word Gobi,used to refer to all of the waterless regions in the Mongolian Plateau,while in Chinese Gobi is used to refer to rocky,semi-deserts such as the Gobi itself rather than sandy deserts.
The Mu Us Desert,also known as the Maowusu Desert,is a desert in the northern Ordos Plateau in Inner Mongolia,Northwest China. Its southeastern end is crossed by the Ming Great Wall,and it forms the southern portion of the Ordos Desert. The Wuding River drains the area,and then flows into the Ordos Loop of the Yellow River.
Zhuye Lake is the terminal lake of the Shiyang River,which is located in the east of the Hexi Corridor in Gansu Province,China. Zhuye Lake is located in the marginal area of the Asian monsoon and is affected by both the Asian monsoon system and the Westerly jet. By understanding the Holocene record in Zhuye Lake,the interaction of different climate systems during the Holocene can be studied. At the same time,the Asian monsoon system is climatically dynamic;changes in its sphere of influence can result in severe drought or flood over large,densely populated,regions. In addition,Zhuye Lake and the surrounding area in arid NW China are in ecological imbalance –a consequence of human impacts and climate. Understanding the environmental history here can assist climatological forecasting of the Asian monsoon system and ecosystem reconstruction.
Cima volcanic field is a volcanic field in San Bernardino County,California,close to the border with Nevada. The volcanic field covers a surface area of 600 km2 (230 sq mi) within the Mojave National Preserve west of the Cima Dome and consists of about 40 volcanic cones with about 60 lava flows. The volcanic cones range from simple cones over multi-cratered mountains to eroded hills,and lava flows are up to 9.1 km (5.7 mi) long. At least one lava tube exists in the field and can be visited.
