Tibesti Mountains
The Tibesti Mountains are a mountain range in the central Sahara, primarily located in the extreme north of Chad, with a small portion located in southern Libya. The highest peak in the range, Emi Koussi, lies to the south at a height of and is the highest point in both Chad and the Sahara. Bikku Bitti, the highest peak in Libya, is located in the north of the range. The central third of the Tibesti is of volcanic origin and consists of five volcanoes topped by large depressions: Emi Koussi, Tarso Toon, Tarso Voon, Tarso Yega and Toussidé. Major lava flows have formed vast plateaus that overlie Paleozoic sandstone. The volcanic activity was the result of a continental hotspot that arose during the Oligocene and continued in some places until the Holocene, creating fumaroles, hot springs, mud pools and deposits of natron and sulfur. Erosion has shaped volcanic spires and carved an extensive network of canyons through which run rivers subject to highly irregular flows that are rapidly lost to the desert sands.
Tibesti, which means "place where the mountain people live", is the domain of the Toubou people. The Toubou live mainly along the wadis, on rare oases where palm trees and limited grains grow. They harness the water that collects in gueltas, the supply of which is highly variable from year-to-year and decade-to-decade. The plateaus are used to graze livestock in the winter and harvest grain in the summer. Temperatures are high, although the altitude ensures that the range is cooler than the surrounding desert. The Toubou, who were settled in the range by the 5th century BC, adapted to these conditions and turned the range into a large natural fortress. They arrived in several waves, taking refuge in times of conflict and dispersing in times of prosperity, although not without intense internal hostility at times.
The Toubou came into contact with the Carthaginians, Berbers, Tuaregs, Ottomans and the Arabs, as well as the French colonists who first entered the range in 1914 and took control of the area in 1929. The independent spirit of the Toubou and the geopolitics of the region has complicated the exploration of the range as well as the ascent of its peaks. Tensions continued after Chad and Libya gained independence in the mid-20th century, with hostage-taking and armed struggles occurring amid disputes over the allocation of natural resources. The geopolitical situation and the lack of infrastructure has hampered the development of tourism.
The Saharomontane flora and fauna, which include the rhim gazelle and Barbary sheep, have adapted to the mountains, yet the climate has not always been as harsh. Greater biodiversity existed in the past, as evidenced by scenes portrayed in rock and parietal art found throughout the range, which date back several millennia, even before the arrival of the Toubou. The isolation of the Tibesti has sparked the cultural imagination in both art and literature.
Toponymy
The Tibesti Mountains are named for the Toubou people, also written Tibu or Tubu, that inhabit the area. In the Kanuri language, tu means "rocks" or "mountain" and bu means "a person" or "dweller," and thus Toubou roughly translates to "people of the mountains" and Tibesti to the "place where the mountain people live".Most of the mountain names are derived from Arabic as well as the Tedaga and Dazaga languages. The term ehi precedes the names of peaks and rocky hills, emi precedes those of larger mountains, and tarso precedes high plateaus and gently-sloping mountainsides. For example, the Ehi Mousgou is a stratovolcano near Tarso Voon. The name Toussidé means "that which killed the Tou," as in the Toubou, reflecting the danger of the still active volcano. The name of Bardaï, the principal town in the range, means "cold" in Chadian Arabic. In the Tedaga language, the town is known as Goumodi, which means "red pass," signifying the color of the mountains at dusk.
Geography
Location
The mountains lie on the border between Chad and Libya, straddling the Chadian region of Tibesti and the Libyan districts of Murzuq and Kufra, around north of N'djamena and south-southeast of Tripoli. The range is adjacent to Niger and located approximately halfway between the Gulf of Sidra and Lake Chad, just south of the Tropic of Cancer. The East African Rift is to the east and the Cameroon line lies to the southwest.The range is in length, in width, and spans. It draws a large triangle with sides of and vertices facing south, northwest and northeast in the heart of the Sahara, making it the largest mountain range of the desert.
Topography
The highest peak in the Tibesti Mountains, as well as the highest point in Chad and the Sahara Desert, is the Emi Koussi, located at the southern end of the range. Other prominent peaks include Pic Toussidé at and the Timi on its western side, the Tarso Yega, the Tarso Tieroko, the Ehi Mousgou, the Tarso Voon, the Ehi Sunni, and the Ehi Yéy near the center of the range. The high Tarso Ahon rises north of Emi Koussi. The Mouskorbé is a peak notable for its height in the northeastern part of the mountain range. The Bikku Bitti, the highest point in Libya, is nearby, on the other side of the border. The average elevation of the Tibesti Mountains is about ; sixty percent of its area exceeds in elevation.The range includes five shield volcanoes with broad bases whose diameter can reach : Emi Koussi; Tarso Toon, which rises above sea level; Tarso Voon; Tarso Yega; and Tarso Toussidé, which culminates in the peak of the same name. Several of these peaks are topped with large calderas. Tarso Yega has the largest caldera, with a diameter of and a depth of approximately, while Tarso Voon has the deepest caldera, with a depth of approximately and a diameter of. They are complemented by four large lava dome complexes, high and several km wide, all located in the central part of the mountain range: Tarso Tieroko; Ehi Yéy; Ehi Mousgou; and Tarso Abeki, which rises to above sea level. These volcanic complexes are now considered inactive, but according to the Smithsonian Institution were active during the Holocene. Tarso Toussidé is an active volcano that has spewed lava over the past two millennia. Gases escaping from fumaroles on Toussidé are visible when evaporation is low. The volcano's crater, Trou au Natron, is in diameter and deep. On the northwest side of Tarso Voon is the Soborom geothermal field, which contains mud pools and fumaroles that vent sulfuric acid. The sulfur has stained the surrounding soil bright colors. Fumaroles are also present at the Yi Yerra hot springs on Emi Koussi. Tarso Tôh was an active volcano in the early Holocene. The volcanic area of the Tibesti Mountains is located entirely in Chad; it covers about a third of the total area of the Tibesti Mountains and is responsible for between of rock.
The rest of the Tibesti Mountains consists of volcanic plateaus, located between elevation, as well as lava fields and ejecta deposits. The plateaus are larger and more numerous in the east: the Tarso Emi Chi, the Tarso Aozi, the Tarso Ahon to the north of Emi Koussi, and the Tarso Mohi. In the center is Tarso Ourari at about. To the west, in the vicinity of Tarso Toussidé, is the aforementioned Tarso Tôh, a small plateau at just, and the even smaller Tarso Tamertiou at. The plateaus are strewn with volcanic spires and are separated by canyons that have been formed by the irregular flow of wadis. After often-violent rains, they see the formation of ephemeral streams and flora. The southern, southwestern and eastern slopes of the mountain range have a gentle rise, while the northern slope of the range is a cliff overlooking the vast Libyan desert pavement known as the Serir Tibesti.
Hydrology
Five rivers in the northern half of the Tibesti Mountains flow to Libya, while the southern half belongs to the endorheic basin of Lake Chad. However, none of the rivers travel long distances, as the water evaporates in the desert heat or seeps into the ground, although the latter may flow great distances through subterranean aquifers.The wadis in the Tibesti are called enneris. The water mainly originates from the storms that periodically rage over the mountains. Their flow is highly variable. For example, the largest wadi, named Bardagué and located in the northern part of the range, recorded a flow of in 1954, yet over the next nine years it experienced four years of total drought, four years of flow less than and one year where three different flow rates were measured:.
File:GueltaCamels.jpg|thumb|left|alt=A guelta on the Ennedi Plateau, southeast of the Tibesti|A guelta on the Ennedi Plateau, southeast of the Tibesti
Other major rivers cut into the mountains: the Enneri Yebige flows northward until its riverbed disappears on the Serir Tibesti, while Enneri Touaoul joins the south-flowing Enneri Ke to form Enneri Miski, which then disappears in the plains of Borkou. Their basins are separated by an high watershed that runs from Tarso Tieroko in the west to Tarso Mohi in the east. The Enneri Tijitinga is the longest wadi in the range, flowing some southward. It forms in the west of the range and peters out in the Bodélé Depression, as does Enneri Miski a little further to the east, along with other wadis such as the Enneri Korom and Enneri Aouei. Several rivers flow radially on the southern slopes of the Emi Koussi before seeping into the sands of Borkou and then reemerging at escarpments up to south of the summit, near the Ennedi Plateau.
At the bottom of many canyons are gueltas, wetlands that accumulate water mainly during storms. Above, enneri beds sometimes contain sequential pools of water that. The water is replenished several times a year during flooding, and salinity levels are low. The Mare de Zoui is a small permanent body of water above sea level, located in the northern part of the mountains in the wadi of the Enneri Bardagué, east of Bardaï. Supplied by sources upstream of the wadi, in heavy rains it overflows and spills into small wetlands.
The Yi Yerra hot springs is located on the southern flank of Emi Koussi at about elevation. Water emerges from the springs at. A dozen hot springs are also located at the Soborom geothermal field on the northwest side of Tarso Voon, where water emerges at temperatures ranging between.