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Page Contents
We have tried to place the Faiyum in the geological history of Egypt as a whole, the geomorphology of the Western Desert and the evolution of the modern Nile. This section deals with the Faiyum itself in more detail. There are four main topics:
Issawi et al start in the Oligocene. The tilting of the African Plate sets rivers flowing westward and northwards. They and their tributaries cut valleys with steep, high, escarpments into the Eocene limestone plateau of what is now the Western Desert, eventually excavating Bahariya and the depressions to the south of it. The process is illustrated in Map 6. In contrast, the rivers draining the newly rising Red Sea Mountains spread thick layers of fossiliferous sand and gravel over the region which is now the Faiyum. These Oligocene fluvial sediments are stripped off in succeeding periods, especially the late Miocene, when the Mediterranean dries up and north flowing rivers cut deep canyons down towards the sea bed. The cutting continues until the Faiyum is carved out of the Eocene limestone bedrock. When the sea returned, the Faiyum gradually filled with sediment. A second phase of excavation then begins. The sediment is removed in the successive layers described below. At the end of the Pleistocene, the Holocene lake is formed and a Nile connection cut. The history of the Faiyum is then the history of the Nile floods.
5.2 The Geography of the Faiyum Map 1, below, shows the Faiyum to be a rounded triangular depression. Depending on what boundary you choose, it covers about 1700km2. The brackish Lake Qarun is located to the north of the depression. It is about 200km2 in extent. Its surface is currently about 45m below sea level and it is about 8m deep. It contains the small island of Geziret el Qarun. Approximately 8m of lake bottom sediment overlies the Eocene bedrock. “The maximum extent of the mid Holocene lake approximates the lake area bounded by the 20m contour” (Hassan 1986). This approximates the area covered by Nile silts on Map 2, below, now under cultivation.
0m asl
The steep northern escarpment of the Oligocene Gebel Qatrani formation rises to 350m and is capped by an Oligocene basaltic sill. It overlies the Eocene Qasr el Sagha formation. Both are clearly visible on the geological map. Beyond the scarp to the north is the Miocene Northern Desert. Along the northern lake shore is a narrow band of dunes. To the south, the Faiyum is separated from the smaller Wadi Rayyan depression by a ridge running roughly along the 40m contour.
The Faiyum is separated from the Nile Valley by a ridge running south from the Giza plateau. The ridge is approximately 10km wide at its northern boundary, but narrows to 2.5km in the south. It is outlined approximately on Map 2, above, by the 40m contour It is broken by the Nile connection at the Hawara canal. Both ridges, Qasr el Sagha, and the depression floor, have been carved out of the Eocene bedrock of the plateau. Today, the lake is fed by the drainage of irrigation waters from Lake Nasser. Its area is controlled by pipes which drain excess water into Wadi Rayyan. This has meant a cessation of silt deposition and increasing soil salinity.
5.3 Three Phases of Deposition and Degradation We suggested that, if the Western Desert had been stripped uniformly from the high ground in the south to the sea in the north Map 5 would show a set of more or less horizontal bands, with the oldest sediments exposed in the south. Asking why this is not, in fact, the case gives some insight into the history of the desert. Something similar is true of the Faiyum. If the Faiyum had been cut down and gouged out like an open cast mine, always moving from top to bottom, you would expect to find the strata laid out in a set of closed concentric rings around the lake, with the oldest sediments at the bottom. At first sight the map shows something like this. But, at second sight, it is obvious that
Asking why this is so gives some insight into the geological history of the depression. We approach it at two levels. The complex sequence of degradation and aggregation since the Oligocene are described below. But complex sequences have left a complex geological map. It helps in understanding the jigsaw shown on Map 2 to divide the sedimentation into three periods, each starting after a period of excavation. The earlier sediments exposed in each excavation appear on Map 2 in more or less concentric broken circles , surrounding the lake
Issawi, Ossman and Meibed begin the story at 350m above sea level on Gebel Qatrani, in the Oligocene. It is a combination of previous workers’ results, their own extensive field work and Issawi and McCauley’s Gilf River theory.
5.5 The Geological Formations of the Faiyum Inside the Depression Different texts distinguish the different formations in slightly differing ways. The following tabulations tries to document any formation which the archaeologist is likely to encounter in the literature. It follows Sandford and Arkell in distinguishing four Eocene formations. From the Oligocene to the Holocene it follows Issawi. The sample of Holocene lake shore deposits is taken from Hassan 1986. The main formations are:
Outside the Depression The formations which run broadly north to south, along the eastern flank of the ridge separation the Faiyum from the Nile Valley, are outside the depression itself, but are intimately related to the geological history of the Faiyum. The material consists of sands, gravels, and other typical floodplain and river bottom sediments. They are coarse, with large pebbles, indicating fast flowing waters. Map 2 classifies them simply as “Pliocene and Pleistocene.” They derive, in the main, from two sources:
Sandford and Arkell’s beautiful map identifies a series of small Pliocene deposits, running east to west, which are probably overlaid by the floodplain sediments of the Prenile in the east.
5.6 The Hydrology of the Faiyum Until modern times the Faiyum was a stage in an energy cycle, which transported water from the ocean, to the Equatorial Lakes, and the Ethiopian Highlands then, via the Nile and Bahr Yusef, to the Faiyum - and returned it by evaporation from the surface of Lake Qarun. It was the variations in the summer monsoon which were responsible for variations in the Holocene lake levels. The sources of energy driving the cycle were solar radiation and gravity. Around the lake itself, wind played a large part in the creation of beaches and the desiccation of exposed shorelines. But, overwhelmingly, the medium by which energy was transmitted from one stage of the cycle to another was water. The flows and their long-term variations are shown schematically in the diagram below:
The quantity of water carried through the cycle varied seasonally with the Nile floods, and over longer periods of time, giving several hundred-year long variations in average flood levels. Variations in the Area of the Lake The effect of both variations on Lake Qarun was amplified by the Bar Yusef sill. The extent of the lake surface in different periods is obviously important for the archaeology of the Faiyum. The extent and depth of Lake Qarun was a function of
Since the climate of the Faiyum varied little, “Exit” can be taken as constant for any given lake surface area. For any given inflow, the surface area is determined by the level of the lake at the beginning of the inflow and the contours of the lake margins. On lakes with gently sloping beaches, small variations in the volume of water produce large variations in the area of land submerged. Even the relatively steep cultivable margins of Lake Qarun would have amplified variations in Nile flood levels, in terms of variations in the available land. For similar reasons, increases and decreases in the extent of the lake may have been sudden. Ball (1939) and Hassan (1981) have made calculations of evaporation rates, variations in surface area and variations in depth, for seasonal and long period variations in water entry, taking account of the Bahr Yusef sill. The calculations confirm that the pattern of fluctuations shown in Hassan’s field work are broadly consistent with historical records. Ball estimates an addition to surface areas, from an average Nile flood, of 5.2km2, and a loss of 3.78km2 from evaporation. Assuming no backflow, this means that Lake Qarun could fill to cover 2000km2, a size consistent with Herodotus, in 35 years. Hassan also shows that there are good correlations between his estimates of lake levels and Butzer’s estimates on the levels of Lake Rudolph in Ethiopia. The Nile Connection The Connection with the Nile is via the Bahr Yusef, an old braid of the Nile which enters the Faiyum through the Hawara channel at Lahun. The link with the Nile was made at the end of the Pleistocene. Said suggests that a stream draining the eastern rim of the depression cut backwards, in the location of a previous Pleistocene channel. The process has left a sill at about 28m above the lowest point of the depression. It has played a key part in the entry and exit of flood waters. When the flood waters were higher than the sill, the river discharged into the lake. When the lake surface was higher than 17m below sea level, and when the Nile was receding, the lake discharged back into the lake.
Lake Qarun, at the north and lowest part of the Faiyum depression, has had a long legacy of change throughout archaeological time, and has both increased and decreased at different stages, which has caused some confusion to early archaeologists who assumed that the lake had simply decreased over time, and did not envisage fluctuations. Today it covers 214sq km, stretching for 40km from east to west, and has one sandy island called Geziret el-Qarun. Understanding Lake Qarun’s status at different times is of fundamental importance to archaeologists: “the Holocene history of the lake is characterized by a number of fluctuations which are of the utmost importance for the understanding of the history of occupation around the lake” (Hendrickx and Vermeersch 2000 p.36). Wendorf and Schild (1976) have suggested a sequence for the lake as follows:
A more recent proposal by Fekri Hassan (1986 p.492), based on his work in the Western Faiyum and the Biyahmu area, proposes the following sequence:
The lake was at its maximum in August and at its minimum in March. Hassan concludes “The lake and its vegetated shores must have thus stood in marked contrast to its desert setting. Fed by the Nile from distant sources, the lake was an allogernic geomorphic feature. With an outlet and subject to intense evaporation under arid climate its survival was dependent on the annual replenishment by the Nile waters” (Hassan 1986, p.493). Just as the Nile Valley inhabitants were dependent on the Nile, so were Faiyum inhabitants dependent on the river for replenishing the lake. A detailed analysis of the lake is out of the scope of this project but is covered in depth in Hassan’s 1986 paper.
If we accept Issawi and McCauley’s version of the evolution of the Egyptian landforms, and Issawi et al’s account of the stages of degradation of the depression, we are very close to understanding the origin of the Faiyum and its present day geology. However, there are some unresolved issues. There seems to be little problem with the origin of Bahariya and the depressions to the south. They have been carved from Eocene limestone, through a one-way process of degradation. Solution of the limestone by carbonic acid, the creation of solution cavities, collapse of roves and rock faces, as suggested by Said, seem eminently plausible and supportive of Issawi’s account. Reduction of the floor levels below the rim levels by wind erosion also seems plausible. With the Faiyum, things are not so simple. Being near the sea margin it has been subject to several periods of aggradation and degradation. Only in the late Miocene was it primarily limestone which was degradated. After that the special factors at work in the southern depressions no longer apply in the same way. It is not clear in Issawi et al how the re-excavation of the Faiyum was accomplished, following the Pliocene transgression and silting up. Perhaps the reduction from 110m above sea level to 40m above sea level itself requires no special explanation. Issawi et al assert that, below 40m above sea level, no connection could be made with the Nile Valley, presumably because of the height of the eastward ridges. But it is not obvious why the process of deflation could not have cut a deep channel into the ridge, as Said’s Prenile did in the Pleistocene, below the Hawara channel. The next problem is why, at 40m above sea level, there was a lake and not a valley. Any fluvial process would have difficulty producing a hollow surrounded by a rim. Perhaps rivers degrading the Faiyum to this level became blocked, leaving a type of moraine. The fall from 40m above sea level to -45 is equally puzzling. In Issawi et al’s account, the Faiyum enters the Quarternary as a stagnant lake at 40m above sea level. To get to -45 m above sea level, there either has to have been an agent which could remove sediment over a rim, or one which excavated conventionally and became blocked at its point of exit. Said’s “turbulent Prenile” cuts a channel at Hawara to -17m above sea level. This could be an exit route for material, down to that level. But the channel was subsequently blocked with sediment, as was, presumably, the depression behind it. And, at -17m asl, we still have 28m to go. None of this detracts from the information that has been acquired. Our understanding of the topography of Egypt , the evolution of the Western Desert, and the origin of the Faiyum has been radically transformed by the discoveries of modern technology and the work of Said, Issawi and their colleagues. But the Faiyum has not yet given up all of its secrets.
5.9 Physical Environment and Human Occupation The Epipalaeolithic or Terminal Palaeolithic occupation studied by Hassan was situated on high ground adjacent to a bedrock basin, and existed during a period when “the lake level was fluctuating widely.” The environmental basis of their economy was almost certainly silts deposited by annual flooding and shallow fish-filled basins. For much of the Neolithic a key feature of the environment seems to have been marsh areas, fed by the lake, whose extent and position varied considerably. Settlements were almost certainly seasonal, moving with the movement of the marshes. Fishing was again a major source of food, along with farming (arable and some pastoral) and hunting. Settlement patterns also correlate with the recently established series of climatic shifts. Following the period of moister weather which accompanied the Terminal Palaeolithic, a drier period began in the early Neolithic in the 6th Millennium b.p. This probably initiated the movement of desert peoples into the Fayum as proposed by Butzer and others. Studies at the Qarunian site FS2 indicate that the lake was subject to fluctuations and that seasonally-filled basins appeared and eventually evaporated, which would have been fished when present but point to a seasonal occupation because this source would no longer have been available when evaporated. Studies at the Neolithic site FS2 again indicate lake fluctuations, and again point to a seasonal way of life
5.10 Technical Implications for the Archaeologist The environmental history of the Faiyum, as presently understood, has a number of technical implications:
Such comparisons are outside the scope of this paper. However, first impressions are that differences between the Faiyum sites and floodplain sites are much less than might at first appear. And levels of contact in the prehistoric period were much greater than might have been expected given the harsh desert surrounding of the Faiyum.
The notes on Geology and Geomorphology have been compiled from materials collected for a proposed Internet site dealing with the prehistory of Egypt at the undergraduate level. See Part 4 for details of this project. The sources are all listed in the Bibliography, but for convenience are classified below: Textbooks and Introductory Texts Brown A.G. 1997 Pincauze, D.F. 2000 Rapp, G. and Hill C.L. 1998 Sampsell, B.M 2003 Van Andel T.H. 1994 Vivian, C. 2000
Dictionaries Kearey, P. 2001 Whittow J. 2000
Technical Hantar, G. Issawi, B. and McCauley, J. 1993 Said, R. (ed.) 1990 Said, R. 1993 Said, R. 1990 Sandford K.S. and Arkell W.J. 1929
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Map 2: Schematic Geology of the Faiyum