Geography of Algeria
Algeria comprises 2,381,741 square kilometers of land, more than four-fifths of, desert, in northern Africa, between Morocco and Tunisia. It is the largest country in Africa, its Arabic name, Al Jazair, derives from the name of the capital Algiers, after the small islands found in its harbor. It has a long Mediterranean coastline; the northern portion, an area of mountains and plateaus between the Mediterranean Sea and the Sahara Desert, forms an integral part of the section of North Africa known as the Maghreb. This area includes Morocco and the northwestern portion of Libya known as Tripolitania. Land boundaries:Total: 6,764 km Border countries: Libya 989 km, Mali 1,359 km, Mauritania 460 km, Morocco 1,559 km, Niger 951 km, Tunisia 1,034 km, Western Sahara 41 km. Area – comparative: 3.5 times the size of Texas and twice the size of Ontario. Coastline: 1,622 km Maritime claims:Exclusive fishing zone: 32–52 nmi Territorial sea: 12 nmi Stretching from the Moroccan border the Tell Atlas, including the Djebel Babor formation, is the dominant northwestern mountain range.
Stretching more than 600 kilometers eastward from the Moroccan border, the high plateau area consist of undulating, steppe-like plains lying between the Tell and Saharan Atlas ranges. The elevation averages between 1,100–1,300 metres in elevation in the west, dropping to 400 metres in the east; the climate is so dry. The plateau area is covered by alluvial debris formed. An occasional ridge projects through the alluvial cover to interrupt the monotony of the landscape. Higher and more continuous than the Tell Atlas, the Sahara Atlas range is formed of three massifs: the Ksour Range near the Moroccan border, the Amour Range, the Ouled-Naïl Range south of Algiers; the mountains, which receive more rainfall than those of the High Plateaus, include some good grazing land. Watercourses on the southern slopes of these massifs disappear into the desert but supply the wells of numerous oases along the northern edge of the desert, of which Biskra, Béchar are the most prominent. Eastern Algeria consists of a massive area extensively dissected into mountains and basins.
It differs from the western portion of the country in that its prominent topographic features do not parallel the coast. In its southern sector, the steep cliffs and long ridges of the Aurès Mountains create an impenetrable refuge that has played an important part in the history of the Maghrib since Roman times. Near the northern coast, the Petite Kabylie Mountains are separated from the Grande Kabylie range at the eastward limits of the Tell by the Soummam River; the coast is predominantly mountainous in the far eastern part of the country, but limited plains provide hinterlands for the port cities of Bejaïa, Annaba. In the interior of the region, extensive high plains mark the region around Constantine. Near Constantine, salt marshes offer seasonal grazing grounds to seminomadic sheep herders; the Algerian portion of the Sahara extends south of the Saharan Atlas for 1,500 kilometres to the Niger and Mali frontiers. The desert is an otherworldly place, scarcely considered an integral part of the country.
Far from being covered wholly by sweeps of sand, however, it is a region of great diversity. Immense areas of sand dunes called areg occupy about one-quarter of the territory; the largest such region is the Grand Erg Oriental, where enormous dunes two to five metres high are spaced about 40 metres apart. Much of the remainder of the desert is covered by rocky platforms called humud, the entire southeastern quarter is taken up by the high, complex mass of the Ahaggar and Tassili n'Ajjer highlands, some parts of which reach more than 2,000 metres. Surrounding the Ahaggar are sandstone plateaus, cut into deep gorges by ancient rivers, to the west a desert of pebbles stretches to the Mali frontier; the desert consists of distinguishable northern and southern sectors, the northern sector extending southward a little less than half the distance to the Niger and Mali frontiers. The north, less arid than the south, supports most of the few persons who live in the region and contains most of the desert's oases.
Sand dunes are the most prominent features of this area's topography, but between the desert areas of the Grand Erg Oriental and the Grand Erg Occidental and extending north to the Atlas Saharien are plateaus, including the Tademaït and a complex limestone structure called the M'zab where the Mozabite Berbers have settled. The southern zone of the Sahara is totally arid and is inhabited only by the Tuareg nomads and by oil camp workers. Barren rock predominates, but in some parts of Ahaggar and Tassili n'Ajjer alluvial deposits permit garden farming. Northern Algeria enjoys a mild, Mediterranean climate, it lies within the same latitudes as southern California and has somewhat similar climatic conditions. Its broken topography, provides sharp local contrasts in both prevailing temperatures and incidence of rainfall. Year-to-year variations in climatic conditions are common; this area, the most inhabited in Algeria, is referred to as the Tell. In the Tell, temperatures in summer average between 21 and 42 °C (
The great Congo River known as the Zaire River under the Mobutu regime, is the second longest river in Africa, shorter only than the Nile, as well as the second largest river in the world by discharge volume, following only the Amazon. It is the world's deepest recorded river, with measured depths in excess of 220 m; the Congo-Lualaba-Chambeshi River system has an overall length of 4,700 km, which makes it the world's ninth-longest river. The Chambeshi is a tributary of the Lualaba River, Lualaba is the name of the Congo River upstream of Boyoma Falls, extending for 1,800 km. Measured along with the Lualaba, the main tributary, the Congo River has a total length of 4,370 km, it is the only river to cross the equator twice. The Congo Basin has a total area of 13 % of the entire African landmass; the name Congo/Kongo river originates from the Kingdom of Kongo once located on the southern bank of the river. The kingdom in turn was named for the indigenous Bantu Kongo people, known in the 17th century as "Esikongo".
South of the Kingdom of Kongo proper lay the named Kakongo kingdom, mentioned in 1535. Abraham Ortelius in his world map of 1564 labeled as "Manicongo" the city at the mouth of the river; the tribal names in Kongo derive from a word for a public gathering or tribal assembly. The modern name of the Kongo people or Bakongo was introduced in the early 20th century; the name Zaire is from a Portuguese adaptation of a Kikongo word, nzere, a truncation of nzadi o nzere. The river was known as Zaire during the 17th centuries; the Democratic Republic of the Congo and the Republic of the Congo are named after it, as was the previous Republic of the Congo which had gained independence in 1960 from the Belgian Congo. The Republic of Zaire during 1971–1997 was named after the river, after its name in French and Portuguese; the Congo's drainage basin covers an area larger than India. The Congo's discharge at its mouth ranges from 23,000 to 75,000 cubic metres per second, with an average of 41,000 cubic metres per second.
The river and its tributaries flow through the Congo Rainforest, the second largest rain forest area in the world, second only to the Amazon Rainforest in South America. The river has the second-largest flow in the world, behind the Amazon; because its drainage basin includes areas both north and south of the equator, its flow is stable, as there is always at least one part of the river experiencing a rainy season. The sources of the Congo are in the highlands and mountains of the East African Rift, as well as Lake Tanganyika and Lake Mweru, which feed the Lualaba River, which becomes the Congo below Boyoma Falls; the Chambeshi River in Zambia is taken as the source of the Congo in line with the accepted practice worldwide of using the longest tributary, as with the Nile River. The Congo flows toward the northwest from Kisangani just below the Boyoma falls gradually bends southwestwards, passing by Mbandaka, joining with the Ubangi River, running into the Pool Malebo. Kinshasa and Brazzaville are on opposite sides of the river at the Pool, where the river narrows and falls through a number of cataracts in deep canyons, running by Matadi and Boma, into the sea at the small town of Muanda.
The Congo River Basin is one of the distinct physiographic sections of the larger Mid-African province, which in turn is part of the larger African massive physiographic division. The drainage basin of the Congo River includes most of Central Africa; the main river and tributaries are:Sorted in order from the mouth heading upstream. Lower Congo Downstream of Kinshasa, from the river mouth at Banana, there are a few major tributaries, all on the left side. Mpozo Kwilu InkisiMiddle Congo Kwa-Kassai – 2150 km – 881,900 km2, 9,900 m3/s Fimi Lukenie Kwango Sankuru Lefini Sangha – 1,400 km, 213,400 km2, 750 m3/s Kadéï Ubangi/ – 2,270 km, 772,800 km2, 4,000 m3/s Mbomou Uele Tshuapa or Ruki River – 1,000 km Lomami River – 1,400 kmUpper Congo Upstream of Boyoma Falls near Kisangani, the river Congo is known as the Lualaba River. Luvua Luapula Chambeshi Although the Livingstone Falls prevent access from the sea, nearly the entire Congo above them is navigable in sections between Kinshasa and Kisangani.
Large river steamers worked the river until quite recently. The Congo River still is a lifeline in a land with few railways. Railways now bypass the three major falls, much of the trade of Central Africa passes along the river, including copper, palm oil, sugar and cotton; the river is potentially valuable for hydroelectric power, the Inga Dams below Pool Malebo are first to exploit the Congo river. The Congo River is the most powerful river in Africa. During the rainy season over 50,000 cubic metres of water per second flow into the Atlantic Ocean. Opportunities for the Congo River and its tributaries to generate hydropower are th
Lake Tanganyika is an African Great Lake. It is the second oldest freshwater lake in the world, the second largest by volume, the second deepest, in all cases after Lake Baikal in Siberia, it is the world's longest freshwater lake. The lake is divided among four countries – Tanzania, Democratic Republic of the Congo and Zambia, with Tanzania and DRC possessing the majority of the lake; the water flows into the Congo River system and into the Atlantic Ocean. The name'Tanganyika' refers to'the great lake spreading out like a plain', or'plain-like lake'." Lake Tanganyika is situated within the Albertine Rift, the western branch of the East African Rift, is confined by the mountainous walls of the valley. It is the second largest lake by volume in the world, it is the deepest lake in Africa and holds the greatest volume of fresh water, accounting for 16% of the world's available fresh water. It extends for 676 km in averages 50 km in width; the lake covers 32,900 km2, with a shoreline of 1,828 km, a mean depth of 570 m and a maximum depth of 1,470 m.
It holds an estimated 18,900 cubic kilometres. The catchment area of the lake is 231,000 km2. Two main rivers streams. There is the Lukuga River, which empties into the Congo River drainage; the major river flowing into the lake is the Ruzizi River, formed about 10,000 years ago, which enters the north of the lake from Lake Kivu. The Malagarasi River, Tanzania's second largest river, enters the east side of Lake Tanganyika; the Malagarasi is older than Lake Tanganyika and, before the lake was formed, directly drained into the Congo River. The lake has a complex history of changing flow patterns, due to its high altitude, great depth, slow rate of refill and mountainous location in a turbulently volcanic area that has undergone climate changes, it has in the past had an outflow to the sea. It has been described as'practically endorheic' for this reason; the lake's connection to the sea is dependent on a high water level allowing water to overflow out of the lake through the Lukunga into the Congo.
Due to the lake's tropical location, it has a high rate of evaporation. Thus it depends on a high inflow through the Ruzizi out of Lake Kivu to keep the lake high enough to overflow; this outflow is not more than 12,000 years old, resulted from lava flows blocking and diverting the Kivu basin's previous outflow into Lake Edward and the Nile system, diverting it to Lake Tanganyika. Signs of ancient shorelines indicate that at times Tanganyika may have been up to 300 m lower than its present surface level, with no outlet to the sea, its current outlet is intermittent and thus may not have been operating when first visited by Western explorers in 1858. The lake may have at times had different inflows and outflows: inward flows from a higher Lake Rukwa, access to Lake Malawi and an exit route to the Nile have all been proposed to have existed at some point in the lake's history. Lake Tanganyika is an ancient lake, its three basins, which in periods with much lower water levels were separate lakes, are of different ages.
The central began to form 9 -- 12 million years ago, the northern 7 -- the southern 2 -- 4 mya. There are several islands in Lake Tanganyika; the most important of them are: Kavala Island Mamba-Kayenda Islands Milima Island Kibishie Island Mutondwe Island Kumbula Island The lake's water is alkaline with a pH of around 9 at depths of 0–100 m. Below this it is around 8.7 decreasing to 8.3—8.5 in the deepest parts of Tanganyika. A similar pattern can be seen in the electric conductivity, ranging from about 670 μS/cm in the upper part to 690 μS/cm in the deepest. Surface temperatures range from about 24 °C in the southern part of the lake in early August to 28–29 °C in the late rainy season in March—April. At depths greater than 400 m the temperature is stable at 23.1–23.4 °C. The water has warmed since the 1800s and this has accelerated with global warming since the 1950s; the lake is stratified and seasonal mixing does not extend beyond depths of 150 m. The mixing occurs as upwellings in the south and is wind-driven, but to a lesser extent there are up- and downwellings elsewhere in the lake.
As a consequence of the stratification, the deep sections contain "fossil water". This means that there is no oxygen in the deeper parts limiting fish and other aerobic organisms to the upper part. There are some geographical variations in this limit, but it is at depths of around 100 m in the northern part of the lake and 240–250 m in the south; the oxygen-devoid deepest sections contain high levels of toxic hydrogen sulphide and are lifeless, except for bacteria. Lake Tanganyika and associated wetlands are home to Nile crocodiles, Zambian hinged terrapins, serrated hinged terrapins and pan hinged terrapins; the Storm's water cobra, a threatened subspecies of banded water cobra that feeds on fish, is only found in Lake Tanganyika where it prefers rocky shores. The lake holds at least 250 species of cichlid fish and undescribe
Geography of Africa
Africa is a continent comprising 63 political territories, representing the largest of the great southward projections from the main mass of Earth's surface. Within its regular outline, it comprises an area excluding adjacent islands, its highest mountain is Mount Kilimanjaro, its largest lake is Lake Victoria Separated from Europe by the Mediterranean Sea and from much of Asia by the Red Sea, Africa is joined to Asia at its northeast extremity by the Isthmus of Suez, 130 km wide. For geopolitical purposes, the Sinai Peninsula of Egypt – east on the Suez Canal – is considered part of Africa. From the most northerly point, Ras ben Sakka in Tunisia, at 37°21′ N, to the more southerly point, Cape Agulhas in South Africa, 34°51′15″ S, is a distance of 8,000 km; the main structural lines of the continent show both the east-to-west direction characteristic, at least in the eastern hemisphere, of the more northern parts of the world, the north-to-south direction seen in the southern peninsulas. Africa is thus composed of two segments at right angles, the northern running from east to west, the southern from north to south.
The average elevation of the continent approximates to 600 m above sea level near to the mean elevation of both North and South America, but less than that of Asia, 950 m. In contrast with other continents, it is marked by the comparatively small area of either high or low ground, lands under 180 m occupying an unusually small part of the surface. Moderately elevated tablelands are thus the characteristic feature of the continent, though the surface of these is broken by higher peaks and ridges; as a general rule, the higher tablelands lie to the east and south, while a progressive diminution in altitude towards the west and north is observable. Apart from the lowlands and the Atlas mountain range, the continent may be divided into two regions of higher and lower plateaus, the dividing line running from the middle of the Red Sea to about 6 deg. S. on the west coast. Africa can be divided into a number of geographic zones: The coastal plains — fringed seawards by mangrove swamps — never stretching far from the coast, apart from the lower courses of streams.
Recent alluvial flats are found chiefly in the delta of the more important rivers. Elsewhere, the coastal lowlands form the lowest steps of the system of terraces that constitutes the ascent to the inner plateaus; the Atlas range — orthographically distinct from the rest of the continent, being unconnected with and separated from the south by a depressed and desert area. The high southern and eastern plateaus falling below 600 m, have a mean elevation of about 1,000 m; the South African Plateau, as far as about 12° S, is bounded east and south by bands of high ground which fall steeply to the coasts. On this account South Africa has a general resemblance to an inverted saucer. Due south, the plateau rim is formed by three parallel steps with level ground between them; the largest of these level areas, the Great Karoo, is a dry, barren region, a large tract of the plateau proper is of a still more arid character and is known as the Kalahari Desert. The South African Plateau is connected towards East African plateau, with a greater average elevation, marked by some distinct features.
It is formed by a widening out of the eastern axis of high ground, which becomes subdivided into a number of zones running north and south and consisting in turn of ranges and depressions. The most striking feature is the existence of two great lines of depression, due to the subsidence of whole segments of the Earth's crust, the lowest parts of which are occupied by vast lakes. Towards the south the two lines converge and give place to one great valley, the southern part of, less distinctly due to rifting and subsidence than the rest of the system. Farther north the western hollow, known as the Albertine Rift, is occupied for more than half its length by water, forming the Great Lakes of Tanganyika, Lake Edward and Lake Albert, the first-named over 400 miles long and the longest freshwater lake in the world. Associated with these great valleys are a number of volcanic peaks, the greatest of which occur on a meridional line east of the eastern trough; the eastern branch of the East African Rift, contains much smaller lakes, many of them brackish and without outlet, the only one comparable to those of the western trough being Lake Turkana or Basso Norok.
A short distance east of this rift-valley is Mount Kilimanjaro — with its two peaks Kibo and Mawenzi, the latter being 5,889 m, the culminating point of the whole continent — and Mount Kenya, 5,184 m. Hardly less important is the Ruwenzori Range, over 5,060 m, which lies east of the western trough. Other volcanic peaks rise from the floor of the valleys, some of the Kirunga group, north of Lake Kivu, being still
Burundi the Republic of Burundi, is a landlocked country amid the African Great Lakes region where East and Central Africa converge. The capital is Gitega, having moved from Bujumbura in February 2019; the southwestern border is adjacent to Lake Tanganyika. The Twa and Tutsi peoples have lived in Burundi for at least 500 years. For more than 200 of those years, Burundi was an independent kingdom, until the beginning of the 20th century, when Germany colonised the region. After the First World War and Germany's defeat, it ceded the territory to Belgium. Both Germans and Belgians ruled Rwanda as a European colony known as Ruanda-Urundi. Despite common misconceptions and Rwanda had never been under common rule until the time of European colonisation. Burundi gained independence in 1962 and had a monarchy, but a series of assassinations, coups and a general climate of regional instability culminated in the establishment of a republic and one-party state in 1966. Bouts of ethnic cleansing and two civil wars and genocides during the 1970s and again in the 1990s left the country undeveloped and its population as one of the world's poorest.
The presidents of Rwanda and Burundi, both Hutus, died together when their aeroplane was shot down in April 1994. 2015 witnessed large-scale political strife as President Pierre Nkurunziza opted to run for a third term in office, a coup attempt failed and the country's parliamentary and presidential elections were broadly criticised by members of the international community. The sovereign state of Burundi political system is that of a presidential representative democratic republic based upon a multi-party state; the President of Burundi is the head of head of government. There are 21 registered parties in Burundi. On 13 March 1992, Tutsi coup leader Pierre Buyoya established a constitution, which provided for a multi-party political process and reflected multi-party competition. Six years on 6 June 1998, the constitution was changed, broadening National Assembly's seats and making provisions for two vice-presidents; because of the Arusha Accord, Burundi enacted a transitional government in 2000.
In October 2016, Burundi informed the UN of its intention to withdraw from the International Criminal Court. Burundi remains an overwhelmingly rural society, with just 13% of the population living in urban areas in 2013; the population density of around 315 people per square kilometre is the second highest in Sub-Saharan Africa. 85% of the population are of Hutu ethnic origin, 15% are Tutsi, fewer than 1% are indigenous Twa. The official languages of Burundi are Kirundi and English, Kirundi being recognised as the sole national language. One of the smallest countries in Africa, Burundi has an equatorial climate. Burundi is a part of the western extension of the East African Rift; the country lies on a rolling plateau in the centre of Africa. The highest peak, Mount Heha at 2,685 m, lies to the southeast of Bujumbura; the most distant source of the River Nile is the Ruvyironza River in the Bururi Province of Burundi, the Nile is linked from Lake Victoria to its headwaters via the Kagera River to the Ruvyironza River.
Another major lake is Lake Tanganyika, located in much of Burundi's southwestern corner. There are two national parks, Kibira National Park to the northwest, Ruvubu National Park to the northeast. Both were established in 1982 to conserve wildlife populations. Burundi's lands are agricultural or pasture. Settlement by rural populations has led to soil erosion and habitat loss. Deforestation of the entire country is completely due to overpopulation, with a mere 600 km2 remaining and an ongoing loss of about 9% per annum. In addition to poverty, Burundians have to deal with corruption, weak infrastructure, poor access to health and education services, hunger. Burundi is densely populated and has had substantial emigration as young people seek opportunities elsewhere; the World Happiness Report 2018 ranked Burundi as the world's least happy nation with a rank of 156. Burundi is one of the few countries in Africa, along with its neighbour Rwanda among others, to be a direct territorial continuation of a pre-colonial era African state.
The early history of Burundi, the role and nature of the country's three dominant ethnic groups. However, it is important to note that the nature of culture and ethnic groups is always fluid and changing. While the groups might have migrated to the area at different times and as distinctly different ethnic groups, the current distinctions are contemporary socio-cultural constructs; the different ethnic groups lived together in relative peace. The first conflicts between ethnic groups can be dated back to the 17th century, when land was becoming more scarce because of the continuous growth in population; the first evidence of the Burundian state dates back to the late 16th century where it emerged on the eastern foothills. Over the following centuries it expanded; the Kingdom of Burundi, or Urundi, in the Great Lakes region was a polity ruled by a traditional monarch with several princes beneath him. The king, known as the mwami headed a princely aristocracy which owned most of the land and required a tribute, or tax, from
Geography of Cape Verde
Cape Verde is a group of arid Atlantic islands which are home to a number of birds and reptiles and constitute a unique ecoregion in the World Wildlife Fund classification. The Cape Verde Islands are located in the mid-Atlantic Ocean some 570 km off the west coast of the continent of Africa; the landscape varies from dry plains to high active volcanoes with cliffs rising steeply from the ocean. The climate is arid; the archipelago consists of ten islands and five islets, divided into the windward and leeward groups. The six islands in the Barlavento group are Santo Antão, São Vicente, Santa Luzia, São Nicolau and Boa Vista; the islands in the Sotavento group are Maio, Santiago and Brava. All but Santa Luzia are inhabited. Three islands – Sal, Boa Vista, Maio – are level and lack natural water supplies. Mountains higher than 1,280 metres are found on Santiago, Santo Antão, São Nicolau. Sand carried by high winds has caused erosion on all islands the windward ones. Sheer, jagged cliffs rise from the sea on several of the mountainous islands.
The lack of natural vegetation in the uplands and coast contributes to soil erosion. Only the interior valleys support natural vegetation. Geographic coordinates 16°N 24°WArea Total: 4,072 km2 Land: 4,072 km2 Water: 0 km2Area – comparative US: larger than Rhode Island Canada: larger than the Queen Charlotte Islands UK: larger than Suffolk Coastline 965 km Maritime claims Measured from claimed archipelagic baselines Territorial sea: 12 nmi Contiguous zone: 24 nmi Exclusive economic zone: 200 nmi Exclusive economic zone EEZ area: 800,561 km2 Continental shelf: 5,591 km2 Coral reefs: 0.09% of world Sea mounts: 0.04% of world source: Sea Around Us Project's Countries' EEZ Terrain Steep, rocky, volcanic. Elevation extremes Lowest point: Atlantic Ocean 0 m Highest point: Mount Fogo 2,829 m Natural resources Salt, basalt rock, kaolin, clay, gypsum Land use Arable land: 11.66% Permanent crops: 0.74% Other: 87.59% Irrigated land 34.76 km2 Total renewable water resources 0.03 km3 Freshwater withdrawal total: 0.02 km3/yr per capita: 48.57 m3/yr Natural hazards Prolonged droughts.
Geography - note Strategic location 500 km from west coast of Africa near major north-south sea routes. Cabo Verde shares maritime boundaries with Senegal. Cabo Verde has signed treaties with Mauritania delimiting the specific boundaries. However, the two treaties conflict in their delimitation of the precise borders. A cold Atlantic current produces an arid atmosphere around the archipelago. December–June is cool and dry, with temperatures at sea level averaging 21 °C. Although some rain comes during the latter season, rainfall is sparse overall and erratic. Accumulations are around 130 mm annually in the northern islands and 300 mm in the south; the archipelago is subject to cyclical droughts. Rainfall is irregular causing periodic droughts and famines. Desalination plants now provide water to more than half the country's population. Experiments with fog collectors have been conducted since 1962, such collectors had not been expanded beyond the Serra Malagueta community of Santiago Island, as of 2009.
The average precipitation per year in Praia is 240 mm. During the winter, storms blowing from the Sahara sometimes form dense dust clouds that obscure the sun; the clearest skies are found between February and June, with little rainfall during these months. Saharan dust, Harmattan wind, laden dust come from the Sahara; this occurs between November and March and is similar to the "Calima" affecting the Canary Islands. The ocean near Cabo Verde is an area of tropical cyclone formation; the Cape Verde islands are a degradated area. Most islands do not always get a monsoon. In fact, it is not surprising that some atmospheric precipitation of islands are limited in tropical rain. If rain arrives, it is between August and October; the first "rainy season" brings high humidity that condenses as dew mountain. The other rainy season is between December and June, when the northeast trade winds are common during this season, only altitudes above 600m tend to receive regular rain; the island of Sal receives an average of 0.0mm in May.
When the rain comes, if it comes, it can be strong. Half of the rain in a particular year can fall into a single storm. Most of the Cape Verde islands are dry, but on islands with high mountains and farther away from the continental land mass, by orography, the humidity is much higher, giving a rainforest habitat degraded by the strong human presence. Northeastern slopes of high mountains receive a lot of rain and southwestern slopes do not; this is because they are umbria areas, situated in the north hillsides or slopes of the mountainous areas, oriented behind the sun in the Northern Hemisphere, in the shadyside orographic. So the amount of solar radiation that it receive is much lower than it would if it had without the
Tungsten, or wolfram, is a chemical element with symbol W and atomic number 74. The name tungsten comes from the former Swedish name for the tungstate mineral scheelite, tung sten or "heavy stone". Tungsten is a rare metal found on Earth exclusively combined with other elements in chemical compounds rather than alone, it was identified as a new element in 1781 and first isolated as a metal in 1783. Its important ores include scheelite; the free element is remarkable for its robustness the fact that it has the highest melting point of all the elements discovered, melting at 3422 °C. It has the highest boiling point, at 5930 °C, its density is 19.3 times that of water, comparable to that of uranium and gold, much higher than that of lead. Polycrystalline tungsten is an intrinsically hard material, making it difficult to work. However, pure single-crystalline tungsten can be cut with a hard-steel hacksaw. Tungsten's many alloys have numerous applications, including incandescent light bulb filaments, X-ray tubes, electrodes in gas tungsten arc welding and radiation shielding.
Tungsten's hardness and high density give it military applications in penetrating projectiles. Tungsten compounds are often used as industrial catalysts. Tungsten is the only metal from the third transition series, known to occur in biomolecules that are found in a few species of bacteria and archaea, it is the heaviest element known to be essential to any living organism. However, tungsten interferes with molybdenum and copper metabolism and is somewhat toxic to more familiar forms of animal life. In its raw form, tungsten is a hard steel-grey metal, brittle and hard to work. If made pure, tungsten retains its hardness, becomes malleable enough that it can be worked easily, it is worked by drawing, or extruding. Tungsten objects are commonly formed by sintering. Of all metals in pure form, tungsten has the highest melting point, lowest vapor pressure, the highest tensile strength. Although carbon remains solid at higher temperatures than tungsten, carbon sublimes at atmospheric pressure instead of melting, so it has no melting point.
Tungsten has the lowest coefficient of thermal expansion of any pure metal. The low thermal expansion and high melting point and tensile strength of tungsten originate from strong covalent bonds formed between tungsten atoms by the 5d electrons. Alloying small quantities of tungsten with steel increases its toughness. Tungsten exists in two major crystalline forms: α and β; the former is the more stable form. The structure of the β phase is called A15 cubic. Contrary to the α phase which crystallizes in isometric grains, the β form exhibits a columnar habit; the α phase has one third of the electrical resistivity and a much lower superconducting transition temperature TC relative to the β phase: ca. 0.015 K vs. 1–4 K. The TC value can be raised by alloying tungsten with another metal; such tungsten alloys are sometimes used in low-temperature superconducting circuits. Occurring tungsten consists of four stable isotopes and one long-lived radioisotope, 180W. Theoretically, all five can decay into isotopes of element 72 by alpha emission, but only 180W has been observed to do so, with a half-life of ×1018 years.
The other occurring isotopes have not been observed to decay, constraining their half-lives to be at least 4 × 1021 years. Another 30 artificial radioisotopes of tungsten have been characterized, the most stable of which are 181W with a half-life of 121.2 days, 185W with a half-life of 75.1 days, 188W with a half-life of 69.4 days, 178W with a half-life of 21.6 days, 187W with a half-life of 23.72 h. All of the remaining radioactive isotopes have half-lives of less than 3 hours, most of these have half-lives below 8 minutes. Tungsten has 11 meta states, with the most stable being 179mW. Elemental tungsten resists attack by oxygen and alkalis; the most common formal oxidation state of tungsten is +6, but it exhibits all oxidation states from −2 to +6. Tungsten combines with oxygen to form the yellow tungstic oxide, WO3, which dissolves in aqueous alkaline solutions to form tungstate ions, WO2−4. Tungsten carbides are produced by heating powdered tungsten with carbon. W2C is resistant to chemical attack, although it reacts with chlorine to form tungsten hexachloride.
In aqueous solution, tungstate gives the heteropoly acids and polyoxometalate anions under neutral and acidic conditions. As tungstate is progressively treated with acid, it first yields the soluble, metastable "paratungstate A" anion, W7O6–24, which over time converts to the less soluble "paratungstate B" anion, H2W12O10–42. Further acidification produces the soluble metatungstate anion, H2W12O6–40, after which equilibrium is reached; the metatungstate ion exists as a symmetric cluster of twelve tungsten-oxygen octahedra known as the Keggin anion. Many other polyoxometalate anions exist as metastable species; the inclusion of a different atom such as phosphorus in place of the two central hydrogens in metatungstate produces a wide v