Hammada al-Hamra
The Hammada al-Hamra (also written Hamadet el-Hamra ; Arabic الحمادة الحمراء, DMG al-ḥammāda al-ḥamrāʾ ) is a stony plateau in the northwestern Libyan Sahara .
The Arabic name "Red Hammada " has its origin in the laterite red coloration of the gravel and gravel soils caused by iron oxides in the loess dust . The Hammada al-Hamra extends over an area of around 84,000 square kilometers with an extension of around 440 km in an east-west direction and around 190 km in a north-south direction. Their wide barren areas have only a very low hydraulic gradient and are therefore only crossed by a few dry valleys ( wadis ). In the south, Hammada al-Hamra is the deeper Wadi ash-Shati and Dschebel al-Hasawana ( 28 ° 0 ' N , 14 ° 0' O ) is limited, in the southwest by the Ubari - Sandsee . In the north and east the plateau runs out almost flat. The highest peaks of the Hammada al-Hamra reach up to 825 m .
Settlement and traffic
In the hope of being able to restore the former productivity of the springs by digging wells and to reawaken the fertility of the oases, an English company laid a narrow-gauge railway from Farschud over the wide Hammada to the large oasis around 1910 and cleaned numerous old silted up wells there . The fields created in this way are quickly salty and silted up, the railway was bought by the government, the capital invested by the trading company was replaced, whereupon there was no longer any interest in maintaining operations.
Almost the entire Hammada al-Hamra, apart from a few oil drilling camps, is now permanently uninhabited. Their few fertile valleys are used as grazing ground for wildly grazing camels. The only year-round water-bearing well is Tehmet Burschada in a small wadi on the southern edge of the Hammada al-Hamra. Its position is not noted on the usual maps and is only known to those who are familiar with the area. In terms of mineral resources, the Hammada al-Hamra harbors significant oil deposits in its north and north-west. These were established in 1976 and have been developed economically since 1980. The companies Wintershall and Schlumberger are significantly involved in these projects . In addition, small amounts of phosphates were found.
Due to the favorable soil conditions for transport, the Hammada al-Hamra is now used as a transit route for the route from Ghadames to Sabha . Until the late 19th century, the Hammada al-Hamra was crossed on foot and by camels in its eastern area, especially by slave caravans on the route from Lake Chad to the Cyrenaica ports. The section of the route leading through the Hammada al-Hamra was still called Darb al-Attasch , the “path of thirst”, in Heinrich Barth's time due to the extreme dryness, the shadowless terrain and the enormous burdens associated with it for travelers . Even today, human skeletons can sometimes be found along this remote route.
History of origin
The Hammada al-Hamra plateau consists of fossil marine dolomite and other limestone sediments that are rich in flint inclusions . It rests on a 20 to 100 m thick sandstone formation that covers clay marl and gypsum inclusions in some places . Geologically, the Hammada plateau was only separated from a larger network, to which the Dar al-Gani plateau also belonged, in the Pleistocene by river terracing. Its present barren shape was formed in the Holocene . It is largely the result of wind erosion from the northeast wind that blows almost all year round. The surface grains of 10 to 100 mm are the result of chemical and mechanical weathering processes that still affect the underlying marine limestone and dolomite limestone sediments today, but which may have had a much stronger effect in the past humid climatic phases. It is believed that until around 3000 years ago, the Hammada al-Hamra was covered over long stretches by a layer of topsoil that was bound by a continuous savannah vegetation of trees, shrubs and grasses. Due to the increasingly arid climate for about 3000 years , the vegetation withdrew almost completely from the Hammada al-Hamra and the exposed soils became a victim of wind erosion. Remnants of the mineral-rich soils from the humid climatic phases can be found as a matrix between the exposed boulders and in the lee of bumps and individual elevations.
particularities
Together with certain other regions of the Northwest and Central Sahara (in Algeria: Acfer and Tanezrouft , in Libya: Dar al-Gani) the Hammada al-Hamra is one of the rare meteorite aggregation areas. In particular, due to the low gradient of their surfaces and the soil cover in humid climatic phases, favorable conditions existed here for the conservation of fallen meteorites during the individual humid periods. With an increasingly arid climate, the soil eroded and the sedimented meteorites emerged on the wind erosion areas, where they can be collected today. The Hammada al-Hamra is also located in the lee of the Jebel al Aswad, which is further east . This acts as a barrier against the flight of sand from the eastern sand lakes, which in other areas of the Sahara has a negative effect on the natural conservation of meteorites due to the associated abrasion. Due to the slightly basic dolomite subsoil, the dark desert varnish , which is otherwise often found on the surface rocks of the Sahara and which makes the optical detection of meteorites almost impossible, has hardly formed on the Hammada al-Hamra. The usually black meteorites therefore stand out relatively well on the beige-red background and can be seen from a distance of up to 50 m from the vehicle in good light conditions. To date, around 400 different, i.e. H. meteorites from different cases are recovered. The vast majority of them in the south and southeast of the Hammada al-Hamra.
literature
- S. Buhl: The Hammadah al-Hamra Meteorite Field after 20 Years of Prospecting. In: Meteorite Magazine. Auckland 11.2004, 37-48. ISSN 1173-2245
- Detlef Busche: The central Sahara. Surface shapes changing. Perthes, Gotha 1998. ISBN 3-623-00550-9
- F. Woller: Explanatory Booklet of the Geological Map of Libya 1: 250 000, sheet Al Fuqaha, NG 33.3. Industrial Research Center, Tripoli 1984.
- J. Schlueter et al. a .: The Dar al Gani meteorite field . In: Meteoritics & Planetary Science . Lawrence Kan 37.2002, 1079-1093. ISSN 1086-9379
Web links
Individual evidence
- ↑ Johannes Walther: To the fight in the desert on the Sinai and Nile. Observations and experiences. Verl. Quelle & Meyer, Leipzig, 1916. Page 48 and Page 49 .
Coordinates: 28 ° 18 ' N , 14 ° 0' E