Mountain Ranges, Deserts and Landforms of Eritrea

Geography

The Sahel spans 5,900 km (3,670 mi) from the Atlantic Ocean in the west to the Red Sea in the east, in a belt several hundred to a thousand kilometers (c. 600 miles) wide. It covers an area of 3,053,200 square kilometers (1,178,850 sq mi).

Representing a climatic and ecological transition zone with hot semi-desert and steppe conditions, the region borders the more humid Sudanian savannas to its south and the dry Sahara desert to the north. This ecoregion is also called the Sahelian acacia savanna in honour of its most prominent and very drought tolerant genus of tree.

The topography is mainly flat; most of the region lies between 200 and 400 meters (660 and 1,310 ft) in elevation.

History

Around 4000 BC, the climate of the Sahara and the Sahel started to become drier at an exceedingly fast pace. This climate change caused lakes and rivers to shrink significantly and caused increasing desertification. This in turn decreased the amount of land conducive to settlements and caused migrations of farming communities to the more humid climate of West Africa.

The larger Sahelian kingdoms emerged from 750 AD and founded several large cities in the Niger valley region, including Timbuktu, Gao and Djenné.

The kingdom of Alodia was a Christian Nubian Kingdom in the eastern Sahel that reached its zenith from the 9th to 12th century. It was first mentioned in 569, its capital Soba located near modern-day Khartoum.

Physical geography

The Highlands are divided into northwestern and southeastern portions by the Main Ethiopian Rift, which contains a number of salt lakes. The northwestern portion, known as the Abyssinian Massif, includes the Semien Mountains, part of which has been designated the Simien Mountains National Park. Its summit, Ras Dashen (4,550 m), is the highest peak in Ethiopia. Lake Tana, the source of the Blue Nile, also lies in the northwestern portion of the Ethiopian Highlands.

The southeastern portion is known as the Harar Massif. It's bounded in the west, by the fault line of the Rift Valley, in the east, by the Ogaden Lowlands and in the south, by the Elkerie and Borena Lowlands. Its highest peaks are located in the Bale Zone of Ethiopia's Oromia Region.

Geology

The Ethiopian Highlands began to rise 75 million years ago, as magma from the Earth's mantle uplifted a broad dome of the ancient rocks of the Arabian-Nubian Shield. The opening of the Great Rift Valley split the dome of the Ethiopian Highlands into three parts; the mountains of the southern Arabian Peninsula are geologically part of the ancient Ethiopian Highlands, separated by the rifting which created the Red Sea and Gulf of Aden and separated Africa from Arabia.

Around 30 million years ago, a flood basalt plateau began to form, piling layers upon layers of voluminous fissure-fed basaltic lava flows. Most of the flows were tholeiitic, save for a thin layer of alkali basalts and minor amounts of felsic (high-silica) volcanic rocks, such as rhyolite.

Climate

Spatial distribution of temperature in Ethiopia is determined primarily by altitude and latitude. Altitude is the main factor that determines the spatial distribution of temperature in Ethiopia. Ethiopia lies within the tropics, a zone of maximum insolation, where every place has overhead sun twice a year. However, considerable portions of Ethiopia are highland areas, and their altitudes give them non-tropical temperatures. Ethiopia's tropical climate occur in lowlands at the country's peripheries. The predominant climate of the Ethiopian Highlands is the Alpine climate.

Because the highlands elevate Ethiopia, located close to the equator, this has resulted in giving this country an unexpectedly temperate climate.

Ecology

The Ethiopian Highlands share a similar flora and fauna to other mountainous regions of Africa; this distinctive flora and fauna is known as Afromontane, but from the time of the last ice age the region has been populated with some Eurasian (palearctic) flora. The habitats are somewhat different on either side of the Great Rift Valley which splits the highlands.

At lower elevations, the highlands are surrounded by tropical savannas and grasslands, including the Sahelian acacia savanna to the northwest and the East Sudanian savanna to the west.

Geology

Local geology is characterized by volcanic and tectonic activity, various climate cycles, and discontinuous erosion. The basic geological structure of this area was caused by the movement of tectonic plates as Africa moved away from Asia. Mountain chains formed and were eroded again during the Paleozoic. Inundations by the sea caused the formation of layers of sandstone, and limestone was deposited further offshore. As the land rose again, further sandstone formed above the limestone. Further tectonic shifts caused lava to pour out of cracks and cover the sedimentary deposits.

The Danakil Desert has a number of lakes formed by lava flows that dammed up several valleys. Among these is Lake Afrera, which has thick saline crusts on its banks.

Climate

Dallol (92 metres below sea level), has the highest average temperature recorded on earth. Dallol features an extreme version of a hot desert climate (Köppen climate classification BWh) typical of the Danakil Desert. Dallol is the hottest place year-round on the planet and currently holds the record high average temperature for an inhabited location on Earth, where an average annual temperature of 34.6 °C (94.3 °F) was recorded between the years 1960 and 1966. The annual average high temperature is 41.2 °C (105.4 °F) and the hottest month has an average high of 46.7 °C (116.1 °F). The highest temperature ever recorded is 49 °C (121 °F).

Geography

Between 100 and 35 million years ago the area that is now the Eastern Desert was underwater, covered by the Tethys Ocean. During the Oligocene period, around 34 million years ago, the land began to tilt and the coastline was pushed back to the north and west. Concurrently, the basement complex to the east was uplifted, forming the mountain range of the Desert. In this same sequence of land movements, a rift which is now the Red Sea was opened up.

The mountain range of the Eastern Desert runs between 80 and 137 kilometres (50 and 85 mi) inland from and parallel to the Red Sea Coast. It has peaks around 1,500 metres (4,900 ft) above sea level. The southern mountains are predominantly composed of igneous rock while the mountains to the north are composed of limestone.

Climate

The Eastern Desert has a semi-arid/arid/hyper-arid climate. On average, the region usually receives less than 25 millimetres (0.98 in) of rainfall per year in infrequent patterns. Most of the rainfall occurs during the winter months around the mountains. The mountains can create a rain shadow for the rest of the Desert, contributing to the arid environment.

Average temperatures are between 14 and 21 °C (57 and 70 °F) in winter (November–March) and 23.1 and 23.1 °C (73.6 and 73.6 °F) in summer (May–September). The weather is typically sunny; however, sandstorms can occur, usually between March and June. The storms (khamsins) are caused by tropical air moving up from Sudan, accompanied by strong winds and higher temperatures.

History

The earliest signs of humans in the desert was found in the form of flint tools from 250,000 BC.

Around 25,000 BC, the land underwent significant climatic change which transformed the grassy plains into desert. This made the land much less habitable, driving nomads which had inhabited what is now the Eastern Desert towards the Nile River.

Trade routes from the Nile to the Red Sea were established through the Desert. Notably, there was a route between the Nile River and Mersa Gawasis, an ancient Egyptian port. There were also many mines and quarries along this route. Boats were carried in pieces across the desert through the wadis and then set up once they reached the port to embark on expeditions.