Lebanon is a small, mountainous country on the eastern shore of the Mediterranean, about 34° N and 35° E, bordered by Syria to the north and east and Israel to the south. It covers 10,452 km² and is only 32 to 88 km wide, yet it packs four parallel strips of land between the sea and Syria: a narrow coastal plain along 225 km of shore, the Mount Lebanon range, the Beqaa Valley, and the Anti-Lebanon range on the Syrian border. The highest point is Qurnat as Sawda’, 3,088 m, in the north of Mount Lebanon; Mount Hermon, 2,814 m, anchors the southern end of the Anti-Lebanon. The Litani, at more than 140 km, is the longest river that flows entirely within the country, while the Orontes rises in the northern Beqaa and flows north into Syria. Almost all of this terrain is built from limestone laid down in ancient seas and then pushed up along the fault system that separates the African and Arabian plates. Read in order of age, the rocks tell how the country was made.
Gondwana’s Northern Shore and the Jurassic Dolomite of the Kesrouane
The deep foundations of Lebanon are still poorly known. No rock older than the Early Jurassic, roughly 200 million years old, is exposed anywhere in the country, and geologists infer the older layers from deep boreholes in Syria, Israel and Jordan. Those wells show thick sandy deposits from the Paleozoic, when the land that became Lebanon lay on the northern margin of the supercontinent Gondwana, with the Arabian Plate at about 30° south of the equator. A stratigraphic break across the region records the Hercynian orogeny, the mountain-building that followed the collision of Gondwana and Laurussia.
In the Permian and Triassic, a strip of crust broke away from Gondwana’s northern edge and drifted towards Eurasia, opening a new ocean, the Neo-Tethys, behind it. The Levant Basin, which runs from the deep Mediterranean floor inland beneath Lebanon, began to subside at this time and received its final rifting in the Late Jurassic. The sea that flooded it left the oldest rocks you can touch in Lebanon today. The most prominent is the Kesrouane Formation, a succession of shallow-marine dolomite about 1,300 m thick. On top of it sits the Bhannes Formation, a complex of basalt mixed with shale, marl and carbonate, evidence that volcanoes erupted through the Jurassic seafloor; some geologists link them to a mantle plume beneath the Levant. Then came the Bikfaya Formation, a thick limestone that weathers into sheer cliffs.
These Jurassic limestones and dolomites, with the Cretaceous limestones laid on top of them, are why 70% of Lebanon’s exposed rock is limestone karst. Qurnat as Sawda’ itself, the summit of the Makmel range in Bsharri District, is a limestone and dolomite massif. So is the plateau near Tannourine where the Baatara gorge waterfall drops 255 m into the Balaa Pothole, a shaft in Jurassic limestone that meltwater falls through past three natural rock bridges. The chasm was described to European science in 1952 by the French biospeleologist Henri Coiffait and mapped in the 1980s by the Spéléo Club du Liban.
Cretaceous Sandstone, Amber and the Fish Beds of Haqel
Near the end of the Jurassic, during the Kimmeridgian stage, the sea pulled back westward and the exposed limestone was eroded. When deposition resumed in the Early Cretaceous, what is now Lebanon lay on a tropical or subtropical coast, and rivers spread sand across it. These sands, known to geologists as the Grès du Liban, hold one of the world’s most important deposits of amber. Resin produced in coastal, possibly estuarine, forests between about 130 and 125 million years ago, in the Hauterivian stage, trapped small organisms as it hardened. It is among the oldest amber anywhere with a significant number of fossil inclusions, and up to 300 sources of it had been found by 2010. The same sandstone contains poor-quality lignite that was occasionally mined, too sulphur-rich to be worth much.
Later in the Cretaceous, Lebanon sank beneath open sea again, and marls full of foraminifera piled up on the old coastline. In the Cenomanian stage, about 98 million years ago, fine limy mud on the seafloor near Haqel in Byblos District buried marine animals and preserved them as fossils. In 1991 Haqel opened Lebanon’s first natural history museum for marine fossils, built on the finds of local collector Rizkallah Nohra. The Cretaceous ended with the Chekka Formation, white chalk and marly limestone with bands of chert and phosphate that continues into the Paleocene. The Chekka and the older Maameltain Formation still feed the country’s cement works.
The Dead Sea Transform Splits Mount Lebanon from the Anti-Lebanon
The event that turned layers of seafloor into mountains began far to the south, with the opening of the Red Sea in the Eocene and Oligocene. As Arabia pulled away from Africa, a new plate boundary formed along the eastern Mediterranean: the Dead Sea Transform, a system of faults running about 1,000 km from the Marash triple junction in south-eastern Turkey to the northern end of the Red Sea. Both plates move roughly north-north-east, but Arabia moves faster, so the two sides of the fault slide past each other; offset river terraces and other markers show about 105 km of total movement. The fault system developed between the Oligocene and the late Miocene, and almost the entire Oligocene is missing from Lebanon’s rock record, with Miocene rocks lying directly on Eocene ones.
In Lebanon the fault takes a kink, known as the Lebanon restraining bend. Where a sliding fault bends, the two sides jam against each other, and the crust on both flanks is squeezed upward. That compression lifted Mount Lebanon on the west and the Anti-Lebanon on the east, two ranges that geologists believe once formed a single mountain block. Between them, the Beqaa Valley sank as a trough about 177 km long and 9.6 to 16 km wide. The main strand of the fault in Lebanon, the Yammouneh Fault, bounds Mount Lebanon, while its counterpart in the Anti-Lebanon, the Serghaya Fault, runs about 150 km to the eastern side of Mount Hermon. In the Miocene the land rose, the shoreline retreated, and basalt flowed across parts of Lebanon and Syria.
The valley floor filled as fast as the mountains rose. Gravity surveys in the late 1990s suggested the sediment beneath the Beqaa is up to 9 km thick, and Miocene river gravels alone are up to 600 m deep over the limestone. Today the plain sits at an average of about 900 m, with lake and river deposits capped by Pliocene and Quaternary alluvial fans spreading out from both ranges. Offshore, the Mediterranean nearly dried out during the Messinian Salinity Crisis at the end of the Miocene, leaving up to 2 km of salt in the Levant Basin. The Anti-Lebanon, higher in the south, climbs to Mount Hermon, whose summit straddles the Lebanon–Syria border. Its southern slopes run into the Golan Heights, and a small area there, the Shebaa Farms, is claimed by Lebanon, a position Syria supports, while Israel, which has held it since 1967, treats it as part of the Golan.
The resulting pattern of parallel ranges and trough is part of a much larger feature that runs through the Jordan Valley to the Red Sea; our explainer on what a rift valley is sets the Beqaa in that wider context.
Snowmelt, Karst Rivers and Caves: Jeita, the Kadisha and the Litani
Over the last five million years, water has done most of the shaping. In the Pliocene the sea still reached into low ground, leaving around 450 m of sediment and basalt north of Tripoli and in the Beqaa. Within the last 2.5 million years, carbonate and quartz sands known locally as ramleh built up along the coast, and red terra rossa clays settled in the areas now occupied by Beirut and Tripoli.
Lebanon receives about 80% of its precipitation between November and March, much of it as snow on the high ranges. On Qurnat as Sawda’, patches of old snow can survive into summer. Because limestone dissolves, meltwater sinks underground and re-emerges as large springs, feeding 11 rivers in Mount Lebanon and two in the Anti-Lebanon. The Kadisha River has cut the deep Kadisha Valley below the Makmel range, where the Cedars of God grow above 2,000 m; downstream it becomes the Nahr Abu Ali and reaches the sea at Tripoli. At Afqa the Adonis River begins as a waterfall on a 180 m bluff that forms a natural amphitheatre.
The Jeita Grotto shows the process from the inside. North of Beirut in the Nahr al-Kalb valley, two connected limestone caves run for nearly 9 km. The lower cave, which carries an underground river that supplies drinking water to more than a million people, was rediscovered in 1836 by the American missionary William Thomson; the dry upper galleries, 60 m higher, were found in 1958 and hold what is described as the world’s largest known stalactite.
In the Beqaa, the Orontes rises from springs near Labweh and flows north, falling 600 m through a gorge on its way into Syria, while the Litani rises west of Baalbek, runs south down the valley, then swings west through the mountains to reach the sea north of Tyre, carrying an average of 0.92 km³ of water a year.
The plates have not stopped. On 9 July 551, an earthquake of about magnitude 7.5 on this plate boundary triggered a tsunami that wrecked the coastal towns of Byzantine Phoenicia, and the Roum Fault near Beirut remains seismically active. The same slow collision that raised these mountains also explains why Lebanon’s borders follow ridges and valleys so closely, as our guide to the countries that border Lebanon shows.