Geology of Libya

       In view of the general geological formations that make up the surface of the Libyan territory according to map,The oldest formations are in southern Libya, Generally, the pre-Cambrian, first (Paleozoic) and some second (Mizuzo) formations prevail in the south and center, in the northwest region, the formations of the second geological time (Mizuzwe) prevail, but In the plain of Sirte, the plain of Benghazi, the Green Mountain and the Marmerica plateau, the formations of the third geological time prevail, Ancient geological formations are also found in different parts of Libya covered by layers of sediment that have accumulated during the fourth and modern geological times, or under volcanic rocks resulting from volcanic eruptions at different times.

References:

 Al-Hajji, S. A. (1989): New Libya. Publications of Al-Fateh University Complex-Tripoli-Libya. (In Arabic)

Sharaf, A. T (1995) Geography of Libya. Third edition. Publisher: Alexandria Book Center. Egypt. (In Arabic)Hydrogeology of Libya https://earthwise.bgs.ac.uk/index.php/Hydrogeology_of_Libya

The absence of permanent surface waterways in Libya is due not only to the lack of rain, but also to the nature of the geological structure, which is one of the reasons for this phenomenon, especially in the northern mountains (Jabal Nafusa and Al-Jabal Al-Akhdar), which rain fall on some of its parts, may be sufficient to appear Rivers even if quarterly.

These mountains are composed of limestone rocks, with karst phenomena, so a large part of the rainwater falling on them seeps in the cracks of the rocks, and clustered in caves and basements, creating in some places a number of Springs, such as Bo Mansour, Dabbousieh, in Al-Jabal Al-Akhdar, Al-Ain Al-Zarqa in Jado in Jabal Nafusa, and remains of surface water gather in the valleys, which generally descend to the north.

Libya can be divided into two large basins, one open to the north and its waters drain to the Mediterranean, and the second is internal and includes most of the desert and its depressions, and most of its water drain internally in closed basins.

The water-dividing line between the two basins starts from the western end of the Nafusa mountain and extends with the axis of the mountain to the east until Jadu, and then deviates to the south, separating the Qibla region (which flows towards the Gulf of Sirte) from the Ghadames basin (which connects to the basin of southern Algeria and drains inland).

The line is then aligned with the eastern edges of Hamada al-Hamra, and then extends southward to approximately 28 d. N latitude. and then heads eastward along the mountains of Al-Soda and the Haroge hills, and then veers north-east, leaving the oases of Murada, Ujla, Gallo and Jakhrah to the south of it, and at the north-east of the oasis of Jakhrah, heading towards the northwest so that the empty valley leaves outside, and near Benghazi deviate eastward in line with the Green Mountain and the Betnan Plateau. The internal basin its northern borders starting from the ends of the former basin, and includes the central, and southern part of Libya, and It is bordered to the south by the mountains of Tibesti, the of Arde, Anedi, Arkno and Uwainat.

The internal basin includes basins (Fezzan, Al-Kufra, Al Jufrah, Al-Balat, Gallo, Ujla and Jakhrah). Surface water in northern Libya (north the latitude 28 d. N) is divided into seven areas as follows:

(1) The area extending from the Tunisian border to a longitude (13d.30 m. E), and from the Mediterranean coast to the northern slopes of Mount Nefoussa; the average rainfall in this region is between (100-300 mm per year).

The most important valleys: Wadi Al-Mejenin, Wadi Ghan, Wadi Zart, Wadi Nalut, Wadi Jado,Wadi Al-Danaji, Wadi Ghado, Wadi Al-Atal, Wadi Sakfal, Wadi Wazen.

All the valleys of this area end in the Jaffara plain, and do not reach the Mediterranean Sea, except Wadi Al-Mejenin.

(2) The area extending from Wadi El-Raml in the west to Al-Kararim in the east, between longitudes (30 d. -13 m. -15 d. 30 m. E), and the Mediterranean coast in the north and latitude (32 d. North). The average annual rainfall in this region ranges between (150-300 mm per year), and the amount of running water is large because it is mountainous.

The most important valleys:Wadi al-Raml, Wadi al-Mesid, Wadi Tartat, Wadi al-Amarin, Wadi Meqdal, Wadi Bin Jbara, Wadi Bsais, Wadi Ghonaima, Wadi Naqaza, Wadi Lebda, Wadi Ghogao, Wadi Kaam.

(3) The area extending from the Tunisian-Algerian border in the west, to a longitude (15 d. 30m. E), and from the southern slopes of the mountain of Nafusa to latitude (28 d. N) south.

The average rainfall of this region ranges between (25-100 mm per year), and waters of all valleys pour in desert.

The most important valleys are(Wadi Wams, Wadi Faisal, Wadi Marmouta, Wadi Tagalgo, Wadi Lalla, Wadi Ras Al-Tabl, Wadi Mursit and its tributaries, Wadi Soofejin and its tributaries and the most important ( Tinenai and Memon and Ghoobyn, Al-Blad, Tmaaslh).

(4) The area between longitudes (15 d. 30m. and 20 d. E) and between the Mediterranean Sea and latitude (28 d. N). With an average rainfall ranging between (25-175 mm annually), and all valleys pour into the sea and coastal marshes.

The most important valleys are (Wadi al-Weshka, Wadi al-Abadleh, Wadi Mraah, Wadi Tamet, Wadi Bi Al-Kabir, Wadi Tilal, Wadi Jarf, Wadi Bin Jawad, Wadi Harawah and Wadi Matratin).

(5) The area between longitudes (20 d. and 23 d. E), the Mediterranean and Al-Jabal Al-Akhdar, the average rainfall ranges between (150-500 mm per year) and therefore it is the richest areas in its surface waters and all its valleys go to the sea.

The total surface runoff of Jabal Al Akhdar is estimated at 70 million cubic meters for the north of Jabal Al Akhdar and 40 million cubic meters for the south.

The most important of these valleys: Wadi Al-Qatra – Wadi Zaza – Wadi Derna-Wadi Abu Mansour-Wadi Al Bab-Wadi Al Ramla-Wadi Al-Kuf-Wadi Al-Angel-Wadi Al-Mahboul-Wadi Al-Naqa-Wadi Al-Qalaa-Wadi Morcos-Wadi Samalous-Wadi Al-Khrouba.

(6) The area between the Egyptian border and longitude (20 d. E), the foothills of the southern green mountain and latitude (28 d. N), and the average rainfall between (25-200 mm per year). All valleys pour into to the Al-Balat, and the desert south, and its discharge is limited and irregular.

(7) The area between longitude (23 d. E) and the Egyptian border, and the Mediterranean Sea in north and latitude (30 d. N) in south. The average rainfall ranges between (25-150 mm annually), the most important valleys located in the coast of Tobruk: Wadi Al Jarfan , Wadi Janzour, Wadi Al Haniywa, Wadi Mursalik Wadi Al-Khalej, Wadi Al-Maalaaq, Wadi Al-Raheb.

 References:

 Sharaf, A. T (1995) Geography of Libya. Third edition. Publisher: Alexandria Book Center. Egypt. (In Arabic)

Zakry, Y. M. (2005) The Climate of Libya: An Applied Study of Physiological Climate Patterns Department of Urban Planning, Faculty of Earth Sciences, Geography and Urban Planning, Mentouri University – Constantine – Algeria (In Arabic)

Hydrogeology of Libya https://earthwise.bgs.ac.uk/index.php/Hydrogeology_of_Libya