This paper briefly analyzes the reasons why the Sahara Desert and kalahari desert push the two sides of the Taiwan Strait.

Kalahari desert, also known as the Kalahari Basin.

Dry inland areas of southern Africa. Also known as "Kalahari Basin", it is the main terrain area in south-central Africa. The total area is about 630,000 square kilometers.

It is a great basin-shaped plain on the inland plateau of southern Africa. It occupies almost all of Botswana, 65,438+0/3 in eastern Namibia and the northernmost part of Cape Province. In the southwest, it is mixed with Namibia's coastal desert nano ratio. Kalahari desert is about 65,438+0,600 kilometers (65,438+0,000 miles) from north to south and about 960 kilometers (600 miles) from east to west, with an estimated area of 930,000 square kilometers (360,000 square miles).

It borders Lake Ngami in the north and the Orange River in the south. It starts at about 26 east longitude in the east and reaches the Atlantic coast in the west. Mainly distributed in Botswana and Namibia, some of which belong to Angola and South Africa.

Geomorphologically, it belongs to a depressed basin on the African platform, with an altitude of 000m- 1 1,000 m, surrounded by mountains and highlands with an altitude of 1 1,500 m. The terrain in the basin is not undulating, and isolated islands and mountains occasionally appear. There are many dry ditches and fine sand on the ground. There are Kalahari dunes in Kalahari Basin, which is the largest dune area in the world.

There are rivers crossing the edge of the basin, whose starting point and ending point are outside the basin: there are Kuanduo River and the upper reaches of Zambezi River in the northeast; There is Cunene R in the northwest and Orange R in the low-lying valley in the south.

There are three main basins in South Africa: Okowango system enters the basin from the rainy north, forming a slender swamp belt of 16835 square kilometers. 1849, Livingstone discovered that the Okowango River flows into Ngami L. Although it has been dry for decades, it still exists on the map. Sometimes excess water flows into Kadi depression in Maccati. The smaller watershed in the northwest is called Etoshapan. There is a Molobo-Northob system in the south, which once flowed to the Orange River. There are many muddy areas formed in low-lying areas. These "salt fields" will accumulate rainwater and form a temporary lake until it evaporates and dries up.

Kalahari desert and the central Sahara desert have similar latitudes (only the difference between south latitude and north latitude) and similar climates, which are also influenced by the subtropical high system. The ground is dry all the year round, and the annual precipitation is 125-250 mm.

However, its climate and vegetation are not exactly the same as those of the Sahara desert, because there is a little more precipitation, so it is covered by some vegetation. Climate and vegetation change from southwest to northeast. The west is a desert, where succulents and shrubs grow on sand dunes as high as 100 meters. There is more rainfall in the north and northeast, which is tropical grassland and savanna. In the short rainy season, plants flourish, the ground is covered with fertile grassland, as well as dense shrubs and tall forests. Many antelopes and other tropical animals. But most of the year, the desert is short of water, and many rivers flowing through the desert dry up. Dry land is a real obstacle to exploration in this area.

Bakarahari and Bushmen live in this resource-poor land (rich in diamonds, copper, lead, zinc, nickel, vanadium and other minerals, but rarely exploited at present). Most of them are engaged in animal husbandry and some are engaged in hunting. There is little economic development except in the marginal areas of Kalahari. For example, there is a huge irrigation plan in the Okowango Delta, and the result is nothing. Today, Kalahari is still dry and short of water. When the pioneers of Dambre immigrants tried to cross this place at the end of19th century, they called it "the third place".

Kalahari extends westward into a foggy coastal desert called namib desert, which is very similar to the famous Atacama Desert.

Natural characteristics

(1) Physical geography and geological conditions. Kalahari desert has a flat surface, little fluctuation, and sand everywhere. The elevation of all places is above 900 meters (3,000 feet). The bedrock is only exposed in the low and upright hills, and the number is small, but it is conspicuous on the general ground. Except this hill group, three kinds of land cover all the features of kalahari desert: small sand plains, vertical sand dunes and shallow lakes (depressions). The depth of sand usually exceeds 60 meters (200 feet). In many areas, sand is red because it is covered with a thin layer of iron oxide.

The springbok in Kalahari Antelope National Park in South Africa is characterized by a long series of sand dunes, which generally extend north or northwest. This dune is at least 1.6 km (1 mile) long, about several hundred meters wide and 6? 60 meters (20? 200 feet). Each dune is separated from its adjacent hills by a wide and parallel pit, which is called "street" or "path" by locals because each pit is convenient for people to walk.

Shallow lakes or depressions are the most important characteristics of desert water system, and they are "dry lakes" at the end of extremely short streams. No water flows into the ocean from kalahari desert, but each stream ends in a slightly lower pit, where there is no exit. When the river dries up, the fine sediment particles brought by the slow-moving river are precipitated together with the soluble calcium minerals and salts condensed by evaporated water. As a result, these floors have no vegetation and shine white when they are dry. The gluing activity of soluble minerals makes them hard, and sometimes they are covered by shallow stagnant water. In places with low salt content, depressions may be covered with grass after rain.

(2) Water system. In the south and middle of kalahari desert, surface water only exists in small puddles which are widely distributed, and there is no surface water system. Almost all the rain disappears into the deep sand as soon as it falls. A large number of ancient water systems have been discovered in some places in southern and central kalahari desert-some on the ground and some by aerial photography. Even when the rainfall is the highest in a year, these water supply systems are no longer in operation today.

There is a very unusual water system in North kalahari desert. In summer, there will be heavy rain in the highlands of central Angola in the northwest of Kalahari. A large amount of runoff water flows into several streams flowing south, and these streams converge to form Okavango River and Kuando River. The Okavango River flows southeast into the northernmost part of kalahari desert, and finally divides into several distributary channels and flows into the vast swamp in northern Botswana. In Angola, after an unusually wet rainy season, excessive water flowed into the swamp, overflowing to Lake Ngami in the far south, and then flowing eastward through the Boteti River, into Lake Shao and Makgadikgadi salt marshes. Similarly, the Cuando River flows southward from Angola and partially flows into the northeast extension of the swamp. Therefore, in a long-term water shortage area, a large area of water surplus has been caused.

(3) soil. The soil in kalahari desert is mostly sandy, red in color and low in organic matter. Chemically, they are relatively alkaline and very dry. In or near salt marshes, soil often contains calcium or salt, which is toxic to most plants.

(4) climate. The moist air mass comes from the Indian Ocean, with the largest amount of water in the northeast (more than 500mm [20 inches] per year) and a decrease in the southwest (less than130mm [5 inches] at the southern edge of Kalahari). But the precipitation changes greatly. Rainfall mostly occurs during the summer thunder and lightning, and changes greatly every year. Winter is particularly dry and the humidity is extremely low, with 6? It didn't rain for eight months.

The daily and seasonal temperature changes greatly and regularly. In summer, the temperature in the shade still reaches 43? 46℃( 1 10? 1 15℉), but it can be reduced to 2 1? 27℃(70? 80℉); In winter nights, the temperature usually drops to freezing point, even as low as-12℃( 10℉).

(5) plants. Because a deep layer of sand covers most of the land, it greatly affects the growth of vegetation there. Shallow-rooted plants cannot survive for many years, although annual plants grow very fast after a good rain and can sow seeds to support the next good rainy season. Trees whose roots are deep enough to come into contact with permanently moist sand layers can grow well.