- Email: [email protected]
The geomorphological features of Jordan
Geography and Natural Resources 29 (2008) 88–92
The geomorphological features of Jordan G. F. Umtsev Institute of the Earth Crust SB RAS, Irkutsk Received 27 June 2007
Abstract. The main landform features of Jordan are considered: elevated plains with step-like topography, ramp (scarp) of the eastern wall of the graben of the Dead Sea and of the Jordan river valley, and the shore area of the Dead Sea with its salt morphostructure. Jordan’s relief is compared with the western coast of the Red Sea and with the Western Ghats of the Indostanic Peninsula. Keywords: Jordan, Dead Sea, terrace plain, tableland, great scarp, shore area, intramontane depression.
Jordan is a country whose geomorphological descriptions sometimes employ a meaningless (but quite a rational – in this case) term ‘the highest depth lake level’ which was coined to characterize the lake terrace of the Dead Sea at -170 m absolute altitude below the ocean level. The present level of the Dead sea is at -405 m below the level of the world ocean and continues to decline because of much water intake from the Jordan river basin and, primarily, from the Sea of Tiberias that supplies fresh water to almost all territory of Israel via a well-developed pipeline system [1] (Fig. 1). On the other hand, Jordan lies in the extreme northwestern part of the Arabian peninsula, and its territory (mountains
and plains) is dominated by arid conditions of the morphogenesis. All this is of interest for the study of the country’s landforms. This report is based on this author’s observational data obtained as a result of several travels (in April 2007) in the western part of Jordan. Its territory is a superb area for the study not only of the relief but also of the recent geodynamics. The ruins of the ancient cities provide picturesque views of “pulled-up” columns or other deformations of the structures of a seismogenic origin [2, 3]. The location of Jordan in the Mediterranean region, combined with its climatic and historical characteristics, determines this country’s high recreational potential. This is exemplied by such wonderful places as Petra and vadi Ram which constitute also integral natural-historical monuments, and research areas. The economic potential of such places is of important signicance for the country. Geomorphological areas
Fig. 1. Staircase of desiccation terraces and portions of the high depth lake levels on the eastern shore of the Dead Sea.
Corresponding author. E-mail address: u[email protected] (G. F. Umtsev)
On the territory of Jordan, it is possible to identify two geomorphological areas: a system of grabens in the Gulf of Akaba – vadi Al-Araba – Dead Sea – Jordan valley, and a system of trans-Jordan volcanic plateaus, multi-staged plains, and uplands. The connecting link between the areas is provided by the eastern macro-slope (descent) of the Dead Sea’s graben, and by its extensions. This macro-slope can be regarded in all respects (geomorphological, physicalgeographical, and economic) as a special element. Its total altitude difference from the graben bottoms to the edge is normally 1200-1500 m, and in the southern part of the coun-
Copyright © 2008 IG SB, Siberian Branch of RAS. Published by Elsevier B.V. All rights reserved doi:10.1016/j.gnr.2008.04.017
G. F. Ufimtsev / Geography and Natural Resources 29 (2008) 88–92
89
Fig. 2. Longitudinal proles of the bottom of the Dead Sea’s graben. Valleys: 1 – Jordan river, 2 – top surface of western fringing, 3 – top surface of eastern fringing.
try it approaches 2000 m, where it rises signicantly above the edge of the rift side and is monolithic (Fig. 2). In the northern part, the western and eastern sides of the grabens have the same height, but it is where the “green belt” is located, which is most favorable for human life. It is likely that its existence and functioning is largely determined by two factors: the presence of a continuous transverse lowering of the Jordan valley on the western side along which the humid Mediterranean air masses penetrate along the eastward direction, as well as the presence of several continuous valley depressions (El-Yarmuk, Ez-Zarka, and El-Majib) on the eastern side along which the moisture-saturated air ascends as high as the edge of the scarp and the elevated part of the plateau and the uplands behind the edge. It is for that reason that the “green belt” seems to be more pronounced in northwestern Jordan, although the eastern edge of the grabens is the tallest in the south (see Fig. 2). The plateau of Trans-Jordan The elevated country to the east of Jordan and the Dead Sea, previously known as Trans-Jordan) is difcult to dene geographically. In general it is a at territory gradually descending to the east. In its northern part there occur plains of volcanic accumulation (lava plateaus with a very weak erosion incision). Most of the terrestrial surface, however, is composed of chalky limestones which occur either subhorizontally (and one can speak of an elevated staged plain in this case) or are saturated with small discontinuous folds, which permits such plains to be classed as upland formations. Without considering the areas of the volcanic plateau we can say that Trans-Jordan is an elevated at surface with clearly pronounced staged topography, all features of which are well dened to the south of Amman (Fig. 3). Two stages of topography are clearly seen here. The lower of them represents either a gently sloping undulating plain with a convex prole or a nearly at plain whose monotony is disturbed by broad, unclearly outlined, declivities a few
tens of meters deep. They occur at the upper parts of large valleys which in the west cross the descending band toward the Dead Sea’s graben. The surface of these lowlands produces some level, a peculiar kind of stage of topography in its early development, and the declivities themselves can be dened, according to their geomorphological position, as depressions behind the edge of the descending graben side. An identically extensive declivity can also be found to the north of Amman near irbid, where it is bounded from the edge of the graben of the Jordan river valley by a ridge of low hills, he eastern slopes of which form a low (a few tens of meters in height), gently sloping lineament-shaped scarp extending submeridionally. The declivity has a at bottom, while in the depression behind the “ramp” to the south of Amman in the upper part of the El-Majib river basin the bottom is structured in a more complicated way: relatively narrow blind creeks are incised into the hilly surface to produce something like the intermediate stage of topography. The main surface of the elevated country to the south of Amman, however, constitutes alternating gently-sloping undulating or at plains, and the at plains include areas re-
Fig. 3. Multistage topography to the south of the city of Amman .
90
G. F. Ufimtsev / Geography and Natural Resources 29 (2008) 88–92
sembling takyrs in Central Asia. On this at surface there are island mountains, plateaus, and small low-mountain elevations forming the upper stage of topography (see Fig. 3). Among the elevations forming residual rocks occupying large areas, one can distinguish two main morphological types. One includes low-mountain and hilly-mountain ridges in the form of combinations of convex hills usually supported by a gently-sloping undulating plain of the lower stage. The slopes of the elevations are small and moderate in steepness, not exceeding 100 m in height. A typical feature is a rather fractional distribution into separate dome-shaped tops, with some poorly pronounced staged structure of their top level occurring in some places. It can be suggested that such elevations occur on territories where the thickness of chalky limestones has considerable folding deformations. The other type of elevations includes typical tableland massifs with a at top surface bounded by convex and steep (in the upper part) slopes. Often there occur rocky borders produced in relatively stable subhorizontal layers. These elevations have almost no internal dissection and have a massive appearance (see Fig. 3), while the steeply sloping hollows dissect only their lateral slopes and do not penetrate into the inner parts of these residual rocks of the upper stage of topography. The main morphological feature of the plateaus implies that their convext bounds are combinations of steep slopes supported by gently sloping surfaces, typical rudiments usually of a few hundred meters in width. The surfaces of the elevations are fractionally dissected in some places by forking (in a complicated manner) shallow gullies, the longest of wwhich are continued by steep hollows along the slopes. All this endows the staged morphological landscape with the typical appearance as reported by L. King [4]. Some of the island mountains seem to be small replicas of the asforementioned elevations. If they are at top formations, then they are usually bounded by steep slopes. In other cases, however, there occur typical conical island mountains supported by the surrounding pediment (see Fig. 3). And some groups of closed (at their feet) small mountains seem to occur at local dislocations of chalky limestone layers. This staged morphological landscape of the elevated Trans-Jordan country strikingly resembles the Deccan landscape in the western part of the Indostanic Peninsula [5], although both the climatic conditions and the geological structure of these regions in South Asia differ greatly. A feature common to them implies that, morphologically, both Deccan and the territory of Jordan represents obliquely uplifted blocks, counter-elevations of the rift systems. Whilst the aforementioned territories refer to different development stages of the rifts and splitting of the continents, the morphological characteristics of their topography are strikingly similar. The only difference is that behind the scarp of the Western Ghats of the Indostanic Peninsula the staged relief occurs mainly on rocks of the foundation of the old platform; therefore, there are no at-top plateaus of the upper stage of topography.
The eastern coast of the Dead Sea Along the eastern coast and on the shore of the Dead Sea, in the lower part of the side of the rift valley, there occur also other interesting landforms in the extremely arid climatic situation. The coastal zone of the Dead Sea is characterized by two typical features. One (mentioned above) is the presence of a large number (as many as 10 or more) narrow (not broader that 3-4 m) terrace platforms separated by escarpments as tall as 1.5 m and forming some kind of terrace staircase: vivid evidence of a rapid, if not catastrophic, fall of the Dead Sea table occurring in recent years (see Fig. 1). A staircase of narrow terraces is observed throughout the eastern coast of the Dead Sea, although their number changes. While on the eastern coast they represent narrow platform, in the northern termination of the Dead Sea the width of the upper terraces can reach several tens of meters. The narrowing of the terrace platforms to the present-day shoreline can be regarded as evidence for an acceleration of the process of water table lowering in the lake. The other salient feature of the shore area is the presence of salt accumulations covering large areas. The eastern shore of the lake is characterized by typical elements “salt” morphostructure in the form of low-lying salt terraces and “mushrooms”, while on the eastern shore, salt accumulations in the form of sinter or incrustations with a bulgy surface cover the stony material of beaches and benches several meters wide thus forming a characteristic white band. In addition, on the cliffs overhanging the shore there are frequent clusters of salt stalactites many tens of centimeters long. One further feature of these salt accumulations is that (also under the water surface near the shore) are continued in the form of a narrow band, with white salt wedges penetrating deep into the lake and representing areas in which the salt mass ows down. In this case we can speak of the underwater salt antifestoons in the shore zone of the Dead Sea. The differences in salt morphostructure of its western and eastern coasts seem to be determined by the windward location of the eastern coast undergoing a large storm inuence resulting in a rapid evaporation of water in the shore zone. The typical arid mountains and lake terraces adjacent to them tower above the coastal zone of the Dead Sea. Of signicant importance for the fractional dissection of the slopes are the narrow rock crevices , or slits as we suggested in the description of the mountains along the western coast of the Dead Sea [7, 8], since they have mostly a denudation origin (temperature weathering, including desquamation), and only afterwards some of them are used by water ows which expand these crevices and transform them to gorges. On the eastern coast of the Dead Sea, such is the valley of the El-Majib river which in its outow part is not more than 15-20 m wide, where the subvertical walls conne the rock bed of the water stream with a highly uneven ow rate. In their original form, the slits mostly are narrow (a few meters) passes which can be superimposed by residual denudation arches or collapsed block masses,
G. F. Ufimtsev / Geography and Natural Resources 29 (2008) 88–92
where the jammed rock blocks cover the upper parts of the rock crevices. According to the sections in the roadside hollows, the sediments of the high terraces on the eastern coast of the Dead Sea are composed of terrigenous formations and, not infrequently, of calcareous soils: for the highest depth lake level (-170 m) there are also indications of stromatolites [3]. Terrigenous formations of the lake levels (horizontal-layered sand-pebble material) can lean against subvecrtical rear rock walls, near the scarps of which there can occur rounded blocks one meter or more in size. Sections of such a kind are typical of the areas of the coast, where the graben has a steep side, with calcareous platforms emerging in places of its attening or in the presence of tectonic steps. Near thermal springs, to the north of the El-Majib valley, the dingles show travertine pendants, and walls with stalactites. The salient features of morphosculprure of the arid mountains are particularly clearly pronounced near the ruins of Petra, along vadi Musa and the broad Sika slit leading t them. As a matter of fact, this area can be useful for the study of arid mountains as a research site and hence deserves a special description. Topography of the western ramp of the upland Curious landforms of the upper part of the ramp of the plateau on the side of the graben of the Dead Sea and the Jordan valley are observed northwestward of Amman around the cities of Jarish, Irbid, and Um Kais, where the ramp is traversed by the valleys of Az-Zara, Yarmuk, El-Arab, and other rivers. The “green belt” of increased humidication is fully manifest just here. However, whilst there are natural and articial forest stands, the soil-vegetation cover of the territory is patchy, and on the terrestrial surface there occurs a stony pavement in the form of near-lying or closely packed limestone blocks. Its general character usually depends on the occurrence of relatively rm layers; therefore, the pavement must be continuous if the terrestrial surface is shielded, or must have a complicated lacy pattern on the slopes. The upper part of the ramp is characterized by low-mountain moderately dissected topography, the contrasts and relative altitudes of which are enhanced along the sides of the main valleys (Fig. 4). This area is dominated by slopes with a convex prole, which might be directly associated with increased (for this region) humidication of the ramp near the top. Another interesting landform in the upper part of the ramp toward the Jordan valley is the presence of a young incision into the broad early-generation valleys. Between the cities Irbid (on the rim of the ramp) and Um Kais (where the ramp begins to increase in steepness) the young incision represents a system of V-shaped narrow valleys as deep as 100 m or more, which undercut the slopes of moderate or small steepness or valley pediments. But the main salient feature of the upper part of the ramp is the presence of large declivities (depressions) of two kinds. One includes broad fuzzy declivities behind the rim
91
Fig. 4. Morphological landscapes of the upper part of the ramp to the Dead Sea’s graben and the Jordan valley. a – low mountains near the city of Jarash; b – intramontane depression to the south of Um Kais.
of the ramp toward the graben of the Dead Sea and the Jordan valley. The depressions occupy considerable areas, and their boundaries in the east are fuzzy unless the declivities are bounded by residual rocky elevations of the upper stage of topography. On the side of the rim of the ramp, elements bounding these declivities are represented by clusters of low (a few tens of meters) scarps of the hillsides, such as observed near the city of Irbid, for example. In the uppermost part of the ramp the depressions are shaped as intramontane expansions of extended valleys. Their depth is normally greater than the mean level of the ramp, by at least200-250 m. A typical example of such structures is provided by the intramontane depression to the south of the city of Um Kais (see Fig. 4), surrounded by massive lowlands with at top surfaces. The bottom of this declivity shows also fractionally dissected topography represented by hilly mountains, where their portions at a top level near the borders include gently sloping surfaces of the type of pediments connected with the sides of the depression through angular convex bends. These landforms all indicate that the bottom of the intramontane depression was produced by the formation of a local level of valley pediments, and by a subsequent small erosion incision which, as mentioned above, is generally typical of the upper part of the western ramp of the plateau toward the grabens of the Dead Sea and Jordan. A similar situation can also be observed along the valley of the Ez-zarka river to the north of Amman, where in the bottom of the intramontane depression the pediments are connected with the level of a high river terrace and are conjugated with it. The bottom of the large intramontane depression near the northern part of Amman also includes gently convex hills whose tops seem to merge together into a common subhorizontal level, with the slopes of the surrounding low mountains towering above it. This depression (and also, by the way, the other depressions described above) is a closed one, because the valley leaving it is almost not traceable at rst glance. It is a sharp narrowing; furthermore, it is partly hid-
92
G. F. Ufimtsev / Geography and Natural Resources 29 (2008) 88–92
den by a side ridge. It seems likely that such narrow valleys are the beginning of river valleys abounding in gorges, and vadis occurring in the lower half of the western ramp of the plateau toward the grabens. The origin of the rear declivities behind the rim of the ramp and intramontane depressions in its upper half can be hypothesized differently. The declivities were obviously produced with the involvement of denudation processes; specically the bottoms of the intramontane depressions are becoming deep through the formation of valley pediments. There also a subsequent erosion incision which seems to extend over the entire western ramp of the plateau. Conceivably the intramontane depressions are inherent in geographical nodes, or areas in which several relatively long valleys merge together. This is true for at least the intramontane depression near Um Kais. The presence of a lineament-shaped scarp on the western termination of the declivity behind the rim near the city of Irbid is suggestive of the operation of recent tectonics in the formation of structures of this kind. It is a more complicated matter to resolve the questionconcerning the origin of the intramontane depressions in the upper part of the western ramp of the plateau. The morphological landscape of the upper part of the western ramp of the plateau toward the grabens is represented by an upland, with a typical, multiply convex, prole. This distinguishes it drastically from the typically arid “ruin” rocky mountains of the lower part of the ramp as observed near Petra or on the eastern coast of the Dead Sea. The contrast of morphological landscapes is particularly clearly pronounced in the area of vadi Musa and Petra, where the upper parts of the valleys (within the “green belt”) are surrounded by gently-sloping undulating low mountains, while the lower parts include rock ruins with intermittent groups of desquamation hills, arid “towns of huts” [7, 8]. Furthermore, the soil cover of the upper part of the ramp, combined with red-color loose structures are generally small in thickness or alternate with stony pavements, which is also an indication of stable arid conditions of the morphogenesis. Conclusion Trans-Jordan is an elevated country in the form of a combination of plateaus and upland landscapes. It represents an obliquely uplifted block, the arm of the counter-elevation of the Dead Sea – Jordan valley graben, as the emergence of the inter-continental Red Sea rift on the mainland which is also accompanied by obliquely-uplifted arms [9]. This series can be continued with the Western Ghats that accompany the system of grabens on the shelf, and on the continental slope along the western coast of the Indostanic Peninsula [5]. The aforementioned forms of planetary morphotectonics line up in a sequence; however, it does not manifest itself in morphosculptural features. The Trans-Jordan elevated country, with its staged at topography, seems to be replicated in the morphological landscape of Deccan, while the western
boundary of the Red Sea rift is dominated by arid mountains with a complex system of waterless vadi-valleys. This suggests the conclusion that the start and end elements of this morphotectonic sequence have staged at topography (in an arid and monsoon climate), whereas the middle element is characterized by mountains. The western rear boundary of Egypt’s Eastern Desert that is formed by the Nile valley, does not seem to be responsible for this situation; the waterless vadi-valleys penetrate deep into the western area on the side of the Red Sea coast, while the Western Ghats on the Indostanic Peninsula represent typical one-sided mountains, the “great escarpment”, and its draining rivers do not reach Deccan. Jordan is also dominated by upland topography; however, a large number of valleys cross the escarpment-ramp toward the graben. The presence of staged topography is common to Jordan and Indostan, and some of these forms seem to include some sequence of the morphogenesis, however: 1) the uplifting of the arm of the inland rift, and the intrusion of the upper parts of the main valleys to its at surface; 2) fractional dissection of the arm of the inter-mainland rift by a desnse network of valleys functioning either as river valleys or as waterless vadi-valleys, and 3) the new uplifting phase of the edge of the continental massif above the shelf basins and grabens where the coastal river basins still drain only the lateral great escarpment above the coast. This work was done with support from the Russian foundation for Basic Research (05-05-64173). References 1. Israel, the Palestine Territories. General Geographical Map, scale 1:500 000. Moscow: FGUP “Kartograya”, 2005. 2. Korzhenkov A. M. and Mazor U. Structural reconstruction of seismic events: The ruins of ancient cities as petried seismographs. 3. Sixth International Symposium on Eastern Mediterranean Geology incorporating the Ninth International Conference of Jordanian Geologists Association. Ed. K. Moumani, K. Shawabkeh, A. Al-Malabeh, M. Abdelghafoor. Amman, 2007, 356 p. 4. King L. The Earth’s Morphology (Study and Synthesis of Information on the Earth’s Relief). Moscow: Progress, 1967, 559 p. 5. Umtsev G. F. Geomorphological observations in Goa (western Indostanic Peninsula). Geograya i prirodnye resursy, 2007, No. 2, pp. 140-145. 6. Umtsev G. F. Geomorphological characteristics of Egypt’s Eastern Desert Geograya i prirodnye resursy, 2005, No. 3, pp. 137-145. 7. Umtsev G. F. The arid mountains. Geomorfologiya, 2006, No. 2, pp. 21-33. 8. Lot A. In Search of the Tassili n’Ajjer Frescos. Leningrad: Iskusstvo, 1973, 110 p. 9. Umtsev G. F. Morphotectonics of Eurasia. Irkutsk: Izd-vo Ikr. un-ta , 2002, 494 p.
The geomorphological features of Jordan G. F. Umtsev Institute of the Earth Crust SB RAS, Irkutsk Received 27 June 2007
Abstract. The main landform features of Jordan are considered: elevated plains with step-like topography, ramp (scarp) of the eastern wall of the graben of the Dead Sea and of the Jordan river valley, and the shore area of the Dead Sea with its salt morphostructure. Jordan’s relief is compared with the western coast of the Red Sea and with the Western Ghats of the Indostanic Peninsula. Keywords: Jordan, Dead Sea, terrace plain, tableland, great scarp, shore area, intramontane depression.
Jordan is a country whose geomorphological descriptions sometimes employ a meaningless (but quite a rational – in this case) term ‘the highest depth lake level’ which was coined to characterize the lake terrace of the Dead Sea at -170 m absolute altitude below the ocean level. The present level of the Dead sea is at -405 m below the level of the world ocean and continues to decline because of much water intake from the Jordan river basin and, primarily, from the Sea of Tiberias that supplies fresh water to almost all territory of Israel via a well-developed pipeline system [1] (Fig. 1). On the other hand, Jordan lies in the extreme northwestern part of the Arabian peninsula, and its territory (mountains
and plains) is dominated by arid conditions of the morphogenesis. All this is of interest for the study of the country’s landforms. This report is based on this author’s observational data obtained as a result of several travels (in April 2007) in the western part of Jordan. Its territory is a superb area for the study not only of the relief but also of the recent geodynamics. The ruins of the ancient cities provide picturesque views of “pulled-up” columns or other deformations of the structures of a seismogenic origin [2, 3]. The location of Jordan in the Mediterranean region, combined with its climatic and historical characteristics, determines this country’s high recreational potential. This is exemplied by such wonderful places as Petra and vadi Ram which constitute also integral natural-historical monuments, and research areas. The economic potential of such places is of important signicance for the country. Geomorphological areas
Fig. 1. Staircase of desiccation terraces and portions of the high depth lake levels on the eastern shore of the Dead Sea.
Corresponding author. E-mail address: u[email protected] (G. F. Umtsev)
On the territory of Jordan, it is possible to identify two geomorphological areas: a system of grabens in the Gulf of Akaba – vadi Al-Araba – Dead Sea – Jordan valley, and a system of trans-Jordan volcanic plateaus, multi-staged plains, and uplands. The connecting link between the areas is provided by the eastern macro-slope (descent) of the Dead Sea’s graben, and by its extensions. This macro-slope can be regarded in all respects (geomorphological, physicalgeographical, and economic) as a special element. Its total altitude difference from the graben bottoms to the edge is normally 1200-1500 m, and in the southern part of the coun-
Copyright © 2008 IG SB, Siberian Branch of RAS. Published by Elsevier B.V. All rights reserved doi:10.1016/j.gnr.2008.04.017
G. F. Ufimtsev / Geography and Natural Resources 29 (2008) 88–92
89
Fig. 2. Longitudinal proles of the bottom of the Dead Sea’s graben. Valleys: 1 – Jordan river, 2 – top surface of western fringing, 3 – top surface of eastern fringing.
try it approaches 2000 m, where it rises signicantly above the edge of the rift side and is monolithic (Fig. 2). In the northern part, the western and eastern sides of the grabens have the same height, but it is where the “green belt” is located, which is most favorable for human life. It is likely that its existence and functioning is largely determined by two factors: the presence of a continuous transverse lowering of the Jordan valley on the western side along which the humid Mediterranean air masses penetrate along the eastward direction, as well as the presence of several continuous valley depressions (El-Yarmuk, Ez-Zarka, and El-Majib) on the eastern side along which the moisture-saturated air ascends as high as the edge of the scarp and the elevated part of the plateau and the uplands behind the edge. It is for that reason that the “green belt” seems to be more pronounced in northwestern Jordan, although the eastern edge of the grabens is the tallest in the south (see Fig. 2). The plateau of Trans-Jordan The elevated country to the east of Jordan and the Dead Sea, previously known as Trans-Jordan) is difcult to dene geographically. In general it is a at territory gradually descending to the east. In its northern part there occur plains of volcanic accumulation (lava plateaus with a very weak erosion incision). Most of the terrestrial surface, however, is composed of chalky limestones which occur either subhorizontally (and one can speak of an elevated staged plain in this case) or are saturated with small discontinuous folds, which permits such plains to be classed as upland formations. Without considering the areas of the volcanic plateau we can say that Trans-Jordan is an elevated at surface with clearly pronounced staged topography, all features of which are well dened to the south of Amman (Fig. 3). Two stages of topography are clearly seen here. The lower of them represents either a gently sloping undulating plain with a convex prole or a nearly at plain whose monotony is disturbed by broad, unclearly outlined, declivities a few
tens of meters deep. They occur at the upper parts of large valleys which in the west cross the descending band toward the Dead Sea’s graben. The surface of these lowlands produces some level, a peculiar kind of stage of topography in its early development, and the declivities themselves can be dened, according to their geomorphological position, as depressions behind the edge of the descending graben side. An identically extensive declivity can also be found to the north of Amman near irbid, where it is bounded from the edge of the graben of the Jordan river valley by a ridge of low hills, he eastern slopes of which form a low (a few tens of meters in height), gently sloping lineament-shaped scarp extending submeridionally. The declivity has a at bottom, while in the depression behind the “ramp” to the south of Amman in the upper part of the El-Majib river basin the bottom is structured in a more complicated way: relatively narrow blind creeks are incised into the hilly surface to produce something like the intermediate stage of topography. The main surface of the elevated country to the south of Amman, however, constitutes alternating gently-sloping undulating or at plains, and the at plains include areas re-
Fig. 3. Multistage topography to the south of the city of Amman .
90
G. F. Ufimtsev / Geography and Natural Resources 29 (2008) 88–92
sembling takyrs in Central Asia. On this at surface there are island mountains, plateaus, and small low-mountain elevations forming the upper stage of topography (see Fig. 3). Among the elevations forming residual rocks occupying large areas, one can distinguish two main morphological types. One includes low-mountain and hilly-mountain ridges in the form of combinations of convex hills usually supported by a gently-sloping undulating plain of the lower stage. The slopes of the elevations are small and moderate in steepness, not exceeding 100 m in height. A typical feature is a rather fractional distribution into separate dome-shaped tops, with some poorly pronounced staged structure of their top level occurring in some places. It can be suggested that such elevations occur on territories where the thickness of chalky limestones has considerable folding deformations. The other type of elevations includes typical tableland massifs with a at top surface bounded by convex and steep (in the upper part) slopes. Often there occur rocky borders produced in relatively stable subhorizontal layers. These elevations have almost no internal dissection and have a massive appearance (see Fig. 3), while the steeply sloping hollows dissect only their lateral slopes and do not penetrate into the inner parts of these residual rocks of the upper stage of topography. The main morphological feature of the plateaus implies that their convext bounds are combinations of steep slopes supported by gently sloping surfaces, typical rudiments usually of a few hundred meters in width. The surfaces of the elevations are fractionally dissected in some places by forking (in a complicated manner) shallow gullies, the longest of wwhich are continued by steep hollows along the slopes. All this endows the staged morphological landscape with the typical appearance as reported by L. King [4]. Some of the island mountains seem to be small replicas of the asforementioned elevations. If they are at top formations, then they are usually bounded by steep slopes. In other cases, however, there occur typical conical island mountains supported by the surrounding pediment (see Fig. 3). And some groups of closed (at their feet) small mountains seem to occur at local dislocations of chalky limestone layers. This staged morphological landscape of the elevated Trans-Jordan country strikingly resembles the Deccan landscape in the western part of the Indostanic Peninsula [5], although both the climatic conditions and the geological structure of these regions in South Asia differ greatly. A feature common to them implies that, morphologically, both Deccan and the territory of Jordan represents obliquely uplifted blocks, counter-elevations of the rift systems. Whilst the aforementioned territories refer to different development stages of the rifts and splitting of the continents, the morphological characteristics of their topography are strikingly similar. The only difference is that behind the scarp of the Western Ghats of the Indostanic Peninsula the staged relief occurs mainly on rocks of the foundation of the old platform; therefore, there are no at-top plateaus of the upper stage of topography.
The eastern coast of the Dead Sea Along the eastern coast and on the shore of the Dead Sea, in the lower part of the side of the rift valley, there occur also other interesting landforms in the extremely arid climatic situation. The coastal zone of the Dead Sea is characterized by two typical features. One (mentioned above) is the presence of a large number (as many as 10 or more) narrow (not broader that 3-4 m) terrace platforms separated by escarpments as tall as 1.5 m and forming some kind of terrace staircase: vivid evidence of a rapid, if not catastrophic, fall of the Dead Sea table occurring in recent years (see Fig. 1). A staircase of narrow terraces is observed throughout the eastern coast of the Dead Sea, although their number changes. While on the eastern coast they represent narrow platform, in the northern termination of the Dead Sea the width of the upper terraces can reach several tens of meters. The narrowing of the terrace platforms to the present-day shoreline can be regarded as evidence for an acceleration of the process of water table lowering in the lake. The other salient feature of the shore area is the presence of salt accumulations covering large areas. The eastern shore of the lake is characterized by typical elements “salt” morphostructure in the form of low-lying salt terraces and “mushrooms”, while on the eastern shore, salt accumulations in the form of sinter or incrustations with a bulgy surface cover the stony material of beaches and benches several meters wide thus forming a characteristic white band. In addition, on the cliffs overhanging the shore there are frequent clusters of salt stalactites many tens of centimeters long. One further feature of these salt accumulations is that (also under the water surface near the shore) are continued in the form of a narrow band, with white salt wedges penetrating deep into the lake and representing areas in which the salt mass ows down. In this case we can speak of the underwater salt antifestoons in the shore zone of the Dead Sea. The differences in salt morphostructure of its western and eastern coasts seem to be determined by the windward location of the eastern coast undergoing a large storm inuence resulting in a rapid evaporation of water in the shore zone. The typical arid mountains and lake terraces adjacent to them tower above the coastal zone of the Dead Sea. Of signicant importance for the fractional dissection of the slopes are the narrow rock crevices , or slits as we suggested in the description of the mountains along the western coast of the Dead Sea [7, 8], since they have mostly a denudation origin (temperature weathering, including desquamation), and only afterwards some of them are used by water ows which expand these crevices and transform them to gorges. On the eastern coast of the Dead Sea, such is the valley of the El-Majib river which in its outow part is not more than 15-20 m wide, where the subvertical walls conne the rock bed of the water stream with a highly uneven ow rate. In their original form, the slits mostly are narrow (a few meters) passes which can be superimposed by residual denudation arches or collapsed block masses,
G. F. Ufimtsev / Geography and Natural Resources 29 (2008) 88–92
where the jammed rock blocks cover the upper parts of the rock crevices. According to the sections in the roadside hollows, the sediments of the high terraces on the eastern coast of the Dead Sea are composed of terrigenous formations and, not infrequently, of calcareous soils: for the highest depth lake level (-170 m) there are also indications of stromatolites [3]. Terrigenous formations of the lake levels (horizontal-layered sand-pebble material) can lean against subvecrtical rear rock walls, near the scarps of which there can occur rounded blocks one meter or more in size. Sections of such a kind are typical of the areas of the coast, where the graben has a steep side, with calcareous platforms emerging in places of its attening or in the presence of tectonic steps. Near thermal springs, to the north of the El-Majib valley, the dingles show travertine pendants, and walls with stalactites. The salient features of morphosculprure of the arid mountains are particularly clearly pronounced near the ruins of Petra, along vadi Musa and the broad Sika slit leading t them. As a matter of fact, this area can be useful for the study of arid mountains as a research site and hence deserves a special description. Topography of the western ramp of the upland Curious landforms of the upper part of the ramp of the plateau on the side of the graben of the Dead Sea and the Jordan valley are observed northwestward of Amman around the cities of Jarish, Irbid, and Um Kais, where the ramp is traversed by the valleys of Az-Zara, Yarmuk, El-Arab, and other rivers. The “green belt” of increased humidication is fully manifest just here. However, whilst there are natural and articial forest stands, the soil-vegetation cover of the territory is patchy, and on the terrestrial surface there occurs a stony pavement in the form of near-lying or closely packed limestone blocks. Its general character usually depends on the occurrence of relatively rm layers; therefore, the pavement must be continuous if the terrestrial surface is shielded, or must have a complicated lacy pattern on the slopes. The upper part of the ramp is characterized by low-mountain moderately dissected topography, the contrasts and relative altitudes of which are enhanced along the sides of the main valleys (Fig. 4). This area is dominated by slopes with a convex prole, which might be directly associated with increased (for this region) humidication of the ramp near the top. Another interesting landform in the upper part of the ramp toward the Jordan valley is the presence of a young incision into the broad early-generation valleys. Between the cities Irbid (on the rim of the ramp) and Um Kais (where the ramp begins to increase in steepness) the young incision represents a system of V-shaped narrow valleys as deep as 100 m or more, which undercut the slopes of moderate or small steepness or valley pediments. But the main salient feature of the upper part of the ramp is the presence of large declivities (depressions) of two kinds. One includes broad fuzzy declivities behind the rim
91
Fig. 4. Morphological landscapes of the upper part of the ramp to the Dead Sea’s graben and the Jordan valley. a – low mountains near the city of Jarash; b – intramontane depression to the south of Um Kais.
of the ramp toward the graben of the Dead Sea and the Jordan valley. The depressions occupy considerable areas, and their boundaries in the east are fuzzy unless the declivities are bounded by residual rocky elevations of the upper stage of topography. On the side of the rim of the ramp, elements bounding these declivities are represented by clusters of low (a few tens of meters) scarps of the hillsides, such as observed near the city of Irbid, for example. In the uppermost part of the ramp the depressions are shaped as intramontane expansions of extended valleys. Their depth is normally greater than the mean level of the ramp, by at least200-250 m. A typical example of such structures is provided by the intramontane depression to the south of the city of Um Kais (see Fig. 4), surrounded by massive lowlands with at top surfaces. The bottom of this declivity shows also fractionally dissected topography represented by hilly mountains, where their portions at a top level near the borders include gently sloping surfaces of the type of pediments connected with the sides of the depression through angular convex bends. These landforms all indicate that the bottom of the intramontane depression was produced by the formation of a local level of valley pediments, and by a subsequent small erosion incision which, as mentioned above, is generally typical of the upper part of the western ramp of the plateau toward the grabens of the Dead Sea and Jordan. A similar situation can also be observed along the valley of the Ez-zarka river to the north of Amman, where in the bottom of the intramontane depression the pediments are connected with the level of a high river terrace and are conjugated with it. The bottom of the large intramontane depression near the northern part of Amman also includes gently convex hills whose tops seem to merge together into a common subhorizontal level, with the slopes of the surrounding low mountains towering above it. This depression (and also, by the way, the other depressions described above) is a closed one, because the valley leaving it is almost not traceable at rst glance. It is a sharp narrowing; furthermore, it is partly hid-
92
G. F. Ufimtsev / Geography and Natural Resources 29 (2008) 88–92
den by a side ridge. It seems likely that such narrow valleys are the beginning of river valleys abounding in gorges, and vadis occurring in the lower half of the western ramp of the plateau toward the grabens. The origin of the rear declivities behind the rim of the ramp and intramontane depressions in its upper half can be hypothesized differently. The declivities were obviously produced with the involvement of denudation processes; specically the bottoms of the intramontane depressions are becoming deep through the formation of valley pediments. There also a subsequent erosion incision which seems to extend over the entire western ramp of the plateau. Conceivably the intramontane depressions are inherent in geographical nodes, or areas in which several relatively long valleys merge together. This is true for at least the intramontane depression near Um Kais. The presence of a lineament-shaped scarp on the western termination of the declivity behind the rim near the city of Irbid is suggestive of the operation of recent tectonics in the formation of structures of this kind. It is a more complicated matter to resolve the questionconcerning the origin of the intramontane depressions in the upper part of the western ramp of the plateau. The morphological landscape of the upper part of the western ramp of the plateau toward the grabens is represented by an upland, with a typical, multiply convex, prole. This distinguishes it drastically from the typically arid “ruin” rocky mountains of the lower part of the ramp as observed near Petra or on the eastern coast of the Dead Sea. The contrast of morphological landscapes is particularly clearly pronounced in the area of vadi Musa and Petra, where the upper parts of the valleys (within the “green belt”) are surrounded by gently-sloping undulating low mountains, while the lower parts include rock ruins with intermittent groups of desquamation hills, arid “towns of huts” [7, 8]. Furthermore, the soil cover of the upper part of the ramp, combined with red-color loose structures are generally small in thickness or alternate with stony pavements, which is also an indication of stable arid conditions of the morphogenesis. Conclusion Trans-Jordan is an elevated country in the form of a combination of plateaus and upland landscapes. It represents an obliquely uplifted block, the arm of the counter-elevation of the Dead Sea – Jordan valley graben, as the emergence of the inter-continental Red Sea rift on the mainland which is also accompanied by obliquely-uplifted arms [9]. This series can be continued with the Western Ghats that accompany the system of grabens on the shelf, and on the continental slope along the western coast of the Indostanic Peninsula [5]. The aforementioned forms of planetary morphotectonics line up in a sequence; however, it does not manifest itself in morphosculptural features. The Trans-Jordan elevated country, with its staged at topography, seems to be replicated in the morphological landscape of Deccan, while the western
boundary of the Red Sea rift is dominated by arid mountains with a complex system of waterless vadi-valleys. This suggests the conclusion that the start and end elements of this morphotectonic sequence have staged at topography (in an arid and monsoon climate), whereas the middle element is characterized by mountains. The western rear boundary of Egypt’s Eastern Desert that is formed by the Nile valley, does not seem to be responsible for this situation; the waterless vadi-valleys penetrate deep into the western area on the side of the Red Sea coast, while the Western Ghats on the Indostanic Peninsula represent typical one-sided mountains, the “great escarpment”, and its draining rivers do not reach Deccan. Jordan is also dominated by upland topography; however, a large number of valleys cross the escarpment-ramp toward the graben. The presence of staged topography is common to Jordan and Indostan, and some of these forms seem to include some sequence of the morphogenesis, however: 1) the uplifting of the arm of the inland rift, and the intrusion of the upper parts of the main valleys to its at surface; 2) fractional dissection of the arm of the inter-mainland rift by a desnse network of valleys functioning either as river valleys or as waterless vadi-valleys, and 3) the new uplifting phase of the edge of the continental massif above the shelf basins and grabens where the coastal river basins still drain only the lateral great escarpment above the coast. This work was done with support from the Russian foundation for Basic Research (05-05-64173). References 1. Israel, the Palestine Territories. General Geographical Map, scale 1:500 000. Moscow: FGUP “Kartograya”, 2005. 2. Korzhenkov A. M. and Mazor U. Structural reconstruction of seismic events: The ruins of ancient cities as petried seismographs. 3. Sixth International Symposium on Eastern Mediterranean Geology incorporating the Ninth International Conference of Jordanian Geologists Association. Ed. K. Moumani, K. Shawabkeh, A. Al-Malabeh, M. Abdelghafoor. Amman, 2007, 356 p. 4. King L. The Earth’s Morphology (Study and Synthesis of Information on the Earth’s Relief). Moscow: Progress, 1967, 559 p. 5. Umtsev G. F. Geomorphological observations in Goa (western Indostanic Peninsula). Geograya i prirodnye resursy, 2007, No. 2, pp. 140-145. 6. Umtsev G. F. Geomorphological characteristics of Egypt’s Eastern Desert Geograya i prirodnye resursy, 2005, No. 3, pp. 137-145. 7. Umtsev G. F. The arid mountains. Geomorfologiya, 2006, No. 2, pp. 21-33. 8. Lot A. In Search of the Tassili n’Ajjer Frescos. Leningrad: Iskusstvo, 1973, 110 p. 9. Umtsev G. F. Morphotectonics of Eurasia. Irkutsk: Izd-vo Ikr. un-ta , 2002, 494 p.