About the geography of the Kalahari Desert?

Kalahari Desert

Kalahari Desert

Kalahari

Also translated as Kalahari Desert, also known as Kalahari Basin.

The dry interior area of ??southern Africa. Also known as the "Kalahari Basin", it is the main terrain area in central and southern Africa. The total area is approximately 630,000 square kilometers.

It is a large, basin-like plain in the interior plateau of southern Africa. It occupies almost all of Botswana, eastern 1/3 of Namibia and the far north of the Cape Province of South Africa. In the southwest it blends with Namibia, the coastal desert of Namibia. The longest distance from north to south of the Kalahari Desert is about 1,600 kilometers (1,000 miles), and the maximum distance from east to west is about 960 kilometers (600 miles). Its area is estimated to be 930,000 square kilometers (360,000 square miles).

It is bounded by Lake Ngami to the north and the Orange River to the south. It starts from about 26° east longitude in the east and ends near the Atlantic coast in the west. Mainly in Botswana and Namibia, part of it belongs to Angola and South Africa.

Geomorphologically, it is a depressed basin on the African platform, with an altitude of 700-1,000 meters, surrounded by mountains and highlands with a height of 1,500 meters. The terrain in the basin is not undulating, with occasional isolated islands and mountains appearing. There are many dry ditches and fine sand on the ground. The Kalahari Basin contains the Kalahari Sand Dunes, the largest sand dune area in the world.

There are rivers crossing the edge of the basin, and their starting and ending points are outside the basin: there are the Kwando River (Kwando R.) and the upper reaches of the Zambezi River (Zambezi R.) in the northeast; The Cunene River (Cunene R.) and the Orange River (Orange R.) occupy the low-lying valley in the south.

There are three main drainage basins in the South African landform basin: the Okovango system enters the basin from the rainy north, forming an elongated swamp belt of 16,835 square kilometers. In 1849, Livingstone discovered that the Okovango River flows into Lake Ngami (Ngami L.). Although it has dried up for decades, it is still on the map. Sometimes excess water flows into the Makgadikgadi depression. The smaller watershed in the northwest is called the Etosha Pan. To the south is the Molopo-Nossob system, which once flowed to the Orange River. There are many muddy areas formed by low-lying areas. These "salt lands" collect rainwater and form a temporary lake until it evaporates and dries up.

The Kalahari Desert and the central Sahara Desert have similar latitudes (only the difference between southern and northern latitudes), similar climates, and are also affected by the subtropical high pressure system. The ground is dry all year round, with annual precipitation of 125-250mm.

But its climate and vegetation are not exactly the same as those of the Sahara Desert. There is a certain amount of vegetation coverage due to slightly more precipitation. The climate and vegetation change from southwest to northeast. The west is a desert, with succulent plants and shrubs growing on sand dunes up to 100 meters high. There is more rainfall in the north and northeast, which are tropical steppes and tropical savannas. During the short rainy season, vegetation flourishes and the ground is covered with rich pastures and a thicket of scrub and tall woods. Many antelopes and other tropical animals. But water is scarce in the desert most of the year, and the beds of the many rivers that crisscross the desert are dry. Dry land is a real obstacle to exploration in this area.

The Bakarahari and Bushman people live in this resource-poor land (it is rich in diamond, copper, lead, zinc, nickel, vanadium and other mineral deposits, but it is rarely developed and utilized) Most of them are engaged in animal husbandry, and some also engage in hunting. There is little economic development except on the edge of the Kalahari. For example, there was a huge irrigation scheme in the Okavango Delta, but nothing happened. Today's Kalahari is still dry and lacks water. When the Boer immigrant pioneers attempted to cross here in the late 19th century, they called it "Thirstland".

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

Natural features

(1) Physical geography and geological conditions. The surface of the Kalahari Desert is not very undulating and is covered with sandy plains. The altitude everywhere is more than 900 meters (3,000 feet). The bedrock is exposed only in low, upright wall-like hills, which are few but conspicuous on the general ground. In addition to these small mountains, three types of surface cover all the characteristics of the Kalahari Desert: small sand plains, longitudinal dunes and shallow lakes (depressions). The depth of sand is generally more than 60 meters (200 feet). In many areas, the sand is red, the result of a thin layer of iron oxide covering the sand grains.

Springbok in Kalahari Oryx National Park, South Africa The entire western part of the Kalahari Desert is characterized by long chains of sand dunes that run roughly north or northwest. The dunes are at least 1.6 kilometers (1 mile) long, hundreds of meters wide, and 6 to 60 meters (20 to 200 feet) high. Each dune is separated from its neighbors by a wide, parallel depression, which is called a "street" or "path" by locals because each depression is convenient for people to travel.

Shallow lakes or depressions are the most distinctive features of desert water systems. They are "dry lakes" at the end of very short streams. No water ever flows from the Kalahari to the ocean, but each stream ends its course in a slightly lower depression from which there is no outlet. When the creek dries up, the fine silt particles carried by the slow water settle out along with soluble calcium minerals and salts that condense from evaporated water. The result is surfaces that are devoid of vegetation, gleaming white when dry, hardened by the cementing activity of soluble minerals, and sometimes covered by a shallow sheet of stagnant water. In areas with low salt content, depressions may become covered with grass after rain.

(2) Water system. In the southern and central Kalahari Desert, surface water is only found in widely distributed small puddles, 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 found in certain parts of the southern and central Kalahari Desert - some on the ground and others detected through aerial photography. Even during the rainiest time of the year, these water systems are no longer functioning today.

There is a very unusual water system in the northern part of the Kalahari Desert. Heavy summer rains fall in torrents on the central highlands of Angola, far northwest of the Kalahari. Large amounts of runoff water flow into several south-flowing creeks, which join to form the Okavango and Kwando (Cuando or Kwando) rivers. The Okavango River flows southeast into the northernmost part of the Kalahari Desert, and eventually disperses into a number of distributary channels into the vast marshlands north of Botswana. In Angola, after an unusually wet rainfall season, excess water flowed into marshes and overflowed into Lake Ngami far to the south, then flowed eastward through the Boteti River into Lake Sao (Lake Xau) and Makgadikgadi Salt Marsh. Likewise, the Kuando River flows south from Angola, partially emptying into a swampy northeastern extension. As a result, an area with long-term water shortage has created a phenomenon of water surplus in a wide area.

(3)Soil. The soil of the Kalahari Desert is mostly sand-based, red in color, and low in organic matter. Chemically, they are relatively alkaline and extremely dry. In or near salt marshes, soils tend to be calcium or salty and toxic to most vegetation.

(4)Climate. Moist air masses come from the Indian Ocean, with the largest amounts of water in the northeast (annual average of more than 500 millimeters [20 inches]) and decreasing amounts in the southwest (less than 130 millimeters [5 inches] at the southern edge of the Kalahari). But precipitation varies greatly. Most rainfall occurs in the summer when there are thunder and lightning, and the weather varies greatly from year to year. Winter is extremely dry, with extremely low humidity, and there is no rain at all for 6 to 8 months.

The daily and seasonal temperature changes range over a wide range and regularly. In summer, the temperature in the shade still reaches 43-46℃ (110-115℉), but it can drop to 21-27℃ (70-80℉) on the same night; in winter, the temperature at night generally drops to freezing point or even as low as - 12℃(10℉).

(5) Plants. Because a deep layer of sand covers much of the land, it greatly affects the growth of vegetation there. Shallow-rooted plants will not survive on a perennial foundation, although annuals grow very quickly after a good rain and can be sown to support until the next good rain season. Trees with roots deep enough to reach the layer of permanently moist sand do well.