Prace Geograficzne, z. 118

Redaktorzy: Skiba S., Krzemień K.
Rok wydania: 2008
Język publikacji: angielski

ISSN 1644-3586

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Prefacje
Autor: Stefan Skiba, Kazimierz Krzemień
Strony: 7-8
Morphostructural and geomorphological outline of Morocco
Autor: Abdellah Laouina
Strony: 9-14
Summary - read more..
The paper bears the characteristic of the surface relief of Morocco. This relief is connected with the mode of closing of the Mediterranean Sea by the African continent. The closure of the Mediterranean Sea is built by Hercynides. In the Mesozoic and in early Paleogene they were folded, what resulted in formation of the mountain ridges separated by intramontane basins, in which sedimentation took place. In the Oligocene and later in the Neogene periods as well, the tectonic movements yielded formation of two mountain ridges: Rif mountains in the north and Atlas Mountains in the south. The Moroccan plains extending in the west-east direction widespread from 300 to 400 km and they accommodate the extension of the mountain ridges, which are the basis of the regional division. The Moroccan surface relief may be divided into three parts: the mountainous one comprising Atlas and Rif Mts, the Atlantic one consisting of plains and elevated denudation flats, and the largest one of eastern Morocco and Sahara that includes platforms more or less distinctly separated by mountains (Figure 1). Four morphostructural units may be distinguished in Morocco. The first one comprises the area most stable tectonically in the past, which extends from Mauretania in the south to the zone of the southern Atlas Mts in the north. It includes the ridge of Antiatlas, flats and hamadas of Presahara, as well as the whole Atlantic zone of Sahara. The second unit includes mainly meridional ridges of the Atlas Mts. They are built from rocks of various age. Their uplift took place in early Paleogene. The uplifted and fractured sediments underwent numerous deformation and erosion cycles. The third unit, Meseta, consists of plains and uplifted flats of the Atlantic Moroccan coast as well as elevated Moroccan-Oranian plains extending to the east from the Middle Atlas Mts. These areas are built from rocks folded in late Paleozoic (Hercynian orogenesis), which till the Middle Triassic remained stable. In the old massifs, in which the large-scale uplift took place, extensive areas of accumulation formed. Depressions originated by subsidence became basins filled by sediment beds of frequently large thickness.The Rif unit, occurring northernmost, was the area of the marine sedimentation till Miocene. The subsequent orogenic movements caused the overthrusting of the beds to the south, toward the southern Rif groove, which separates the Rif unit and the Meseta and Atlas units. This young unit of the flysch type was eroded and denudated most intensively.
Recent erosion measurements in Morocco
Autor: Abdellah Laouina, Miloud Chaker, Rachida Nafaa, Antonio Ferreira, Simone Van Dijck
Strony: 15-22
Summary - read more..
The paper describes selected investigations concerning the progress of erosion in various regions of Morocco which were carried out from 1990 onwards by a group of geomorphologists sponsored by UNESCO. It was found that the intensity of erosion, especially in recent years, is linked to fast socio-economic development and incorrect management of the exploitation of natural resources. Extensive grazing, deforestation and expansion of agriculture on frequently unsuitable soils are of great importance here. These activities caused a decrease in the infiltration of precipitation water into the subsoil, thus soils became less humid and ground water resources decrease. Simultaneously increased runoff causes mud accumulation and pollution in man-made water reservoirs, which play an important role in water supply during dry periods. The first studies in this project were made in the forest of Mamora and in the region of Bou Khouali - Tanecherfi (eastern Morocco) in the years 1990-1995. They assessed the process of soil erosion and its intensity. On the basis of the results obtained it was found that type of soil and kind of land use were the main factors influencing the process of soil degradation; these factors being characteristic for individual regions of different climate. The second set of studies described were carried out in the regions of Tatoft and Benslimane in the years 1996-1999 as a part of the MEDCHANGE (INCO-MED) project in cooperation with Aveiro University. These studies concerned surface flow and erosion rate determined with the use of precipitation simulators. It was recognized that the smallest surface flow occurs in natural oak forests, however this is twice as high when there is grazing in the forest, and four times higher in those areas where trees were cut down and the resulting clearfell areas are used as pasture. Moreover, the studies have shown that the total amount of mineral and organic material which has been eroded depends to a large degree on the intensity of the surface flow, though this relation is not linear. Even scarce plant cover, e.g. matorral (shrubland), n an area being considered is an important factor causing compacting of the soil and retention of the mineral sediment. The third group of investigations were experiments performed in the region of Sehoul, close to Rabat City in the years 2000-2003 in the project CLIMED (INCO-MED ICA3-2000-30005) in cooperation with Aveiro University and concerning hydrologic reaction and bottom transport. Erosion connected with rainfall was recognized by means of the hydrologic model LISEM. It was found that the surface flow depends on a low infiltration capacity of the dusty-clayey soils occurring in the drainage area investigated, low soil humidity retention due to the limited thickness of the soil layer or the presence of an impermeable bed and scarce vegetation in wastelands and pastures.
Physical geography of the Coude du Dra region
Autor: Maciej Dłużewski, Kazimierz Krzemień
Strony: 23-36
Summary - read more..
Situated on the border between the Antiatlas and the Sahara Desert, the Coude du Dra was chosen for this study because of its great diversity of natural environments that influences the lives of the local population. The environment owes its variety to the geological and relief structures and to the transitional character of the climate. Depending on the season the region comes under the influence of either Mediterranean or very dry climates. The consequences of this transitional character are discussed further in the paper.
Soils of the southern part of Morocco
Autor: Stefan Skiba
Strony: 37-42
Summary - read more..
Soils of the discussed area have been formed in the arid climatic conditions where evaporation prevails over precipitation. Those are the soils of the aridic and dry desert areas. Gypsisols prevail, also Calcisols can be found. Vast areas of the regions are covered by dune formations where initial Arenosols occur. Within the oasis where agricultural soils are subject to irrigation Solonchaks can be found. The existing described agricultural value of the discussed soils (Categories I-IV) is at present of very little use because of the strong desertification processes that take place in the investigation area.
Properties of the desert soils of the Mhamid area
Autor: Stefan Skiba, Michał Skiba
Strony: 43-50
Summary - read more..
Research has been carried out in the area situated on the border of the Antiatlas Mountains on vast and geologically and geomorphologically differentiated region of the Sahara Desert. Typical soil profiles of the investigated desert soils (Gypsisols, Arenosols, Solonchaks) have been shown and described. For the chosen soils and dunes a mineral composition analysis has been made. In the mineral composition quartz together with calcium minerals (gypsum, calcite) prevail. In the soils and dunes of the Iriqui Lake area also feldspars and micas can be found as well as ferruginous lithoclasts.
Reasons for development of the dune fields in the Coude du Dra region
Autor: Maciej Dłużewski
Strony: 51-64
Summary - read more..
The development of the dune fields in the region of Coude du Dra, occurring to the south of the Antiatlas, along the Moroccan border with Algeria, is described in this paper. The determination of the reasons for expansion of the dune fields was the aim of the studies presented here. The evaluation of the rate of expansion was made on the basis of the analysis of the topographical maps, satellite images and field investigations. Since 1932, the surface of the dune field has increased ca. 30 times. To estimate the causes of such a dynamic development of the dune fields, the source areas of the dune material were determined on the basis of the analyses of the sediment textural features, mainly the mineral and lithologic composition. It was found that local alluvial sediments in the Oued (Wadi) Dra valley and lacustrine beds (mainly of the Iriqui Lake) are the sources of the majority of the dune sediments in the Coude du Dra region. This is evidenced by great mineralogical conformity of the dune and basement sediments, namely the significant contents of the ferruginous-clayey particles forming in local, periodical water reservoirs. Large content of this component in dune sediments, combined with its very low resistance to mechanical abrasion, indicates that the dune material underwent short aeolian process and passed a limited distance from its source. After recognition of the source areas, the features of the natural environment of these areas were evaluated, taking into account especially those which are of special importance for the deflation process. It was found that the water table lowering is the most important change of the natural environment, which influenced during last several tens of years the distinct increase of the deflation process. Other features of the natural environment like the surface relief, climatic conditions or vegetation did not influence essentially the dynamic development of the dune fields in this region. Only today the distinct morphometric borders, especially in the north and in the south, may limit further expansion of the dune field in these directions. The construction of the dam system on the Oued Dra supplying water to the described region is the main reason for the ground water table lowering, thus resulting in drying of the surface sediments and making them ready to deflate. Change of the causes of the dune fields development from the factors determined by gradual climate changes to the factors connected with the local human activity influenced essentially the increase of the rate of the dune fields development in the region of Coude du Dra.
Extorted forms of aeolian accumulation in the Coude du Dra region
Autor: Elżbieta Mycielska-Dowgiałło, Maciej Dłużewski, Lidia Dubis, Barbara Woronko
Strony: 65-78
Summary - read more..
Two types of the extorted aeolian accumulation forms i.e. nebkhas and Tamarix cones, occur in the Coude du Dra region. The first ones are small sandy forms, usually of the height of several tens of centimetres and a significant elongation accordant to the wind direction. The second ones are forms several metres high, without observable elongation and with distinct layered structure. In the years 2000-2006 the studies comprised two kinds of the nebkhas. One kind was formed by accumulation around the halophyte arfej (Rhantherium suaveolens) growing in the area of the dried Lake Iriqui. Another kind formed around the grassy plant drinn (Aristida pungens) growing in numerous pits being the oxbow lakes of the braided bed of Oued (Wadi) Dra. The studied forms show great diversity, although both formed in similar climatic conditions. After a five-hour storm when the wind velocity exceeded 14 m per second, the change of morphology of the nebkhas accumulated behind the grass drinn was obserwed. From a uniform morphologically shape new forms developed with a depression caused by deflation directly behind the plant obstacle. Formation of the Tamarix cones is connected with accumulation of sediment around the Tamarix shrubs during low sandy-dusty storms, especially in their final parts, when the finest grains fall. This accumulation is frequently accompanied by rainfall. In the years 2005-2005 both nebkhas and Tamarix cones were significantly degraded. Some of the studied nebkha fields disappeared due to complete degradation of plants, which forced originally the material accumulation. The Tamarix cones were degraded in part as well. This is connected with lowering of the ground water table down to 3-4 m and more below the ground surface (outside the main bed of Oued Dra) and in the region of the Tamarix cones occurrence even deeper than 10 m. Degradation of the extorted forms of the aeolian accumulation caused expansion of the dune fields.
The source of the Aeolian sediments in the Coude du Dra region
Autor: Andrzej Barczuk, Maciej Dłużewski
Strony: 79-92
Summary - read more..
Determination of the source of material building the dunes of the Coude du Dra region was the aim of the performed studies. To estimate the source areas, the selected textural features, especially the mineralogical and lithologic composition of the dune sand basement sediments were studied. This composition was determined by means of the microscope analysis of the granular preparations. On the basis of the obtained results one found that the dunes of the Coude du Dra region have high content of the components of low resistance to the deteriorating factors of transport and weathering processes. Only in the north-eastern part of the area and in the apical parts of the highest dune forms there occur the sediments with high content of the resistant minerals, mainly quartz. The results indicated also the insignificant difference in the mineral and lithologic composition of the sediments of the basement and those of the dunes. This allowed the conclusion that the source of the dune sediments occur in the close neighbourhood of the dunes. This yielded from the presence of numerous components of relatively coarse fraction and low resistance, transported mainly by saltation, which is the mode favouring intensive mechanic abrasion. They are mainly clayey-ferruginous clasts, moreover feldspars and carbonate rock grains. Moreover, the feldspars are well preserved and frequently of automorphic habit and certain feldspars occur as perfect crystals with sharp edges, which could not be preserved during a long transport. The close source of the dune material and short period of the dune formation were confirmed by the analysis of the composition of the heavy mineral fraction. On the basis of the obtained results one found that first of all the local sediments accumulated in stagnating water were the source of the dune material, mainly the sediments of the Iriqui Lake and numerous pits without water outflow, occurring in the area of the broad there valley of Oued (Wadi) Dra. This is indicated by a very high content of clayey-ferruginous clasts, which formed during the periodic water flow transporting to local, ephemeral basins fine detritic material coloured in red by dispersed iron compounds, forming commonly under strongly oxidizing desert conditions.
Surface features of sand grains from the Coude du Dra region (Morocco)
Autor: Barbara Woronko
Strony: 93-102
Summary - read more..
The analysis of grain surface character, especially of quartz grains, allows to obtain precious information on environmental conditions which shaped the grains and thus can inform about the sediment source. Results of such an analysis performed on grains from the dunes of the Coude du Dra erg showed that the grains underwent heavy chemical weathering processes such as dissolution and re-precipitation of silica on the grain surfaces. This is inferred from intensive crusting of the grains. Only limited amount of the grains exhibits effects of aeolian abrasion. Majority of the grains is angular or sub-angular and only few grains are well or very well rounded. This shows that the sediment was not transported for a long distance and the sediment source for this growing erg is local. Only very few grains which are very well rounded can represent another sediment source.
The geomorphological role of episodic rivers based on the example of the Oueds el Mut and el Feija (AntiAtlas Mountains, Morocco)
Autor: Bogdana Izmaiłow, Kazimierz Krzemień
Strony: 103-118
Summary - read more..
The paper discusses the results of a 2001-2005 field investigation into episodic river channels in the southern Antiatlas mountain range. Because of the size of the study area the investigation concerned only a few selected fluvial systems. The characteristics of the channels in the designated areas were based on the qualitative and quantitative properties of the river channels, the erosion and accumulation landforms present as well as on the kind and quantity of rubble and coarse sediments. Five channel types were identified and described. In general terms the role of the episodic streams draining the northern and southern slopes of Djebel Bani varies. Investigation of the channels and tracks of water flow shows that only the largest oueds on the southern slope carry material to the base of Djebel Bani and the sediment in those river channels is better sorted. On the northern slope clastic material is deposited in Oued el Feija. Aeolian activity can clearly be seen on the alluvial fans which form at the ends of smaller oueds as well as within bigger oueds, and yet the aeolian activity does not mask the fluvial forms.
Natural and anthropogenic factors of the development of Erg Chebbi
Autorzy: Andrzej Barczuk, Maciej Dłużewski, Lidia Dubis
Strony: 119-134
Summary - read more..
Estimation of the factors determining the development of Erg Chebbi, especially the influence of the human activity on the increase of the deflation intensity in the source areas, were the aim of the studies presented in this paper. This erg, occurring in the south-eastern part of Morocco along the border with Algeria, is formed by 13 star dunes and complex transversal dunes, the latter developed in the margins of the erg, mainly in its eastern and southern parts. On the basis of the textural analysis of the dune and basement material, the degree of aeolization of the sediments and their source areas were determined. The results of the investigations indicated high degree of eolization and allochthonous source of the sediments which formed the dunes in Erg Chebbi. This is evidenced by high uniformity of the dune material within individual forms and in the erg as a whole, moreover by relatively large grain diameter, good sorting, negative values of the skewness index suggesting absence of the local fine-grain material supply and generally low participation of the local material poorly resistant to abrasion in the dune sediments. Taking into account the climatic conditions (mainly the wind velocity and direction) it was found that the areas of the vast hamadas, i.e. Guir in the east and north-east, and Kem-Kem in the west and south-west are the main source regions of the material building the star dunes in Erg Chebbi. These areas are largely not populated, and recently did not suffer any sudden changes of the natural conditions. Desertification of the source areas may be connected with the global climate changes and only in this context one may discuss the indirect human influence on the development of Erg Chebbi. Initial accumulation of the dune material was connected with the surface morphology of this area. Erg Chebbi formed in the lowest part of the depression, where two factors forcing sedimentation of the material transported by wind were present - this means the shallow or surface-reaching ground water and vegetation connected with these water conditions. The obtained results indicate as well the significant difference of the textural features of the dune sediments occurring in the surroundings of Erg Chebbi and the basement sediments. The dunes form a system with a distinct, linear shape connected with the network of the river beds. The source of the material of these dunes is connected with the material transported formerly by rivers, which subsequently became episodic rivers. One found that the present-day absence of flow in the river beds, which are source of material for these dunes, is connected with the decrease of precipitation and degradation of the plant assemblages, the latter resulting in poorer retention of water, and only in slight degree - with decrease of water supply caused by the local human activity. On the basis of the performed studies one also found that the fast change of certain environmental factors in the area of Erg Chebbi, resulting from strong recent anthropopression, was not in the past and is not presently of any real importance for the development of this dune field.