جستجوی مقالات مرتبط با کلیدواژه « Badland » در نشریات گروه « جغرافیا »

Among the various forms of water erosion, badland erosion is one of the most important emerging factors in water resources and its sustainability. The purpose of this study is to zoning of e badland erosion in the kelerz Basin in Garmsar. For this purpose environmental factors including geological formations, elevation classes, slope, slope direction and vegetation were compared using pairwise comparisons. Also, pairwise comparisons between sub-basins were performed in each of the five criteria mentioned above, and by calculating the multiplication of the total weight of the criteria and sub-basins relative to each other, the priority of each sub-basin was determined. In parallel with the above steps, the area distribution map was mapped using Landsat 8 OLI satellite imagery and Google Earth imagery and was monitored and modified with the help of field surveys and operations to eventually overlap sub-basin priority maps with the existing erosion status map. The accuracy of the proposed model was evaluated. The results of the overlap of the badland Distribution layer with the Erosion Intensity Layer show that sub-basins 2, 3, 4 and 12 have a 100% correlation between the rank calculated in the study with the rank obtained from the frequency ratio. Also sub-basins 1, 5, 9, 10 and 11 with amplitude difference of maximum 2 rank imply high accuracy of calculations. The results also show that sub-basins 12 and 9 have the highest intensity of badland erosion. The sub-basins 11, 4, 6 and 7 are characterized by high erosion and sub-basin 10 with moderate erosion and the rest of the sub-basins are evaluated with low erosion.

The "badland" term refers to regions that have soft and poorly consolidated material outcrops, limited vegetation, reduced or no human activity and a wide range of geomorphic processes (Martinez- Morillo and Nadal- Romero, 2018). A specific character of these landscapes is their high rates of evolution. Although, these landscapes may be observed in any climate, but they commonly are seen in arid and semiarid areas. Lithology plays a key role in their formation. The most common lithologies creating badlands are mud rocks and marine marls (Faulkner, 2013), because such factors as fine particles and richness in Na+ cause their particles to be dispersed and become prone to erosion and piping. The main particles in badland- forming lithologies include clays and silts, since they are suitable for weathering, dispersion, piping and slope instability (Faulkner, 2016). Clay particles play a major role in permeability, contraction- expansion capacity, slaking, fissility and weathering profile of the materials creating badlands. Two- layer clays such as montmorillonite are more susceptible to dispersion than other clays. There are four main type of badland, which include calanchi, biancane, pinnacle and pseudokarstic. The kind of badland formed in a specific area depends on such diverse factors as lithology, tectonic activity, climate, as well as topographic slope. Pseudokarstic badlands are much less common than the other three types, mainly because they need vertical and horizontal pipes for development. These badlands have several apparent similarities with true karsts and this is why they are called pseudokarstic. The prerequisite for formation of these badlands is development of pipes. Intensified erosion at the mouth of vertical pipes creates funnel- shaped depressions similar to miniature solution dolines. Enlargement of horizontal pipes may cause their roofs to collapse and collapse depressions take form. At a larger scale, it is possible that the entire roof of a horizontal pipe to collapse and a collapse gully will form.

In this study, the following investigations were undertaken. 1. Field investigation for discovering the characteritics of studied badlands. 2. The landforms constituting these landscapes were identified. 3. The hydrological system of the badlands was investigated. 4. The processes creating this landscape were studied. 5. A model for formation of the studied badlands is presented. 6. Morphomeric measuremens of landforms were undertaken. 7. The studied pseudokarstic badlands are compared with true karsts.

The study area lies at at a distance of about 85 km at the east of Kerman city. The playa surface on which the badland landscape has formed gently slopes towards the north and is 9.1 km in length and 1.7 km in average length.The south Golbaf playa is situated at the southern part of NNW-SSE trending Golbaf tectonic valley. This valley in bounded from the west and the east, respectively, by Abbarik and Sekonj mountains. The average amounts of annual precipitation and temperature in south Golbaf playa are about 110 mm and 17 ºC, respectively. Therefore, it expriences a dry climate .The south Golbaf playa is a small pull-apart basin created by tectonic tension and subsidence resulting from right-step condition in Golbaf fault zone (Walker and Jackson, 2002). Actually, this playa is the product of silt, clay and some sand deposition by incoming ephemeral streams.

The material on which the studied badlands are formed is a loam deposit equivalent with mud rock. This material is fit for occurrence of badlands. Its minerals include gypsum, quartz, calcite, dolomite, albite, chlorite and montmorillonite. The exchangeable sodium percentage (ESP) value of these mud rocks is higher than 10, indicating a dispersible material suitable for piping.There are a set of landforms which constitute the studied badlands. They include: erosion gullies, funnel- shaped depressions, collapse depressions and collapse gullies. The main processes operating on these badlands include weathering, erosion, slope failure, shrink and swell, dissolution, transport and precipitation. The main product of weathering is a thin regolith covering the loams. The operating processes acting on these badlands include rain splash, sheet wash, rill erosion and bank erosion in gullies. Additionally, tunnel erosion operates in the pipes which cause them to be enlarged. Pipe collapse, solifluction and creep are other processes affecting these badlands.The studied badlands have formed from erosion of muds deposited in a pull apart basin which was formed as a result of right- step condition in two segments of the Gowk active fault. The thicknesses of these muds is 20m at maximum. This flat depositional environment became an erosional environment as a result of the depression being filled of muds and, the consequent overflowing of floods from the northwestern border of the depression. The resulting steep segment played as a knickpoint which moved backwards into the playa's flat environment, and incision of water courses. Incision of the playa surface created erosion gullies. The gullies devided the playa into a number of separated blocks which became dried as a result of drainage by erosion gullies. Drainage, ultimately, led to contraction of muds and creation of dessication fissures. Penetration of surface runoffs into these fissures, and the consequent erosion, created the pipe system. Also, intensified erosion at the mouth of vertical pipes created the funnel- shaped depressions. Morphometrically, the average depth and diameter of depressions are 1.6 and 2.8 meters, respectively. The studied pseudokarstic badlands have several similarities and differences with true karsts.

The studied pseudokarstic badlands have formed in mud rocks deposited in a small and shallow tectonic basin at 85 Km east of Kerman city, SE Iran. This environment shifted from depositional to erosional, as a result of being filled of sediments which caused overflow of the floods from a point at the north of the basin. The steep gradient resulting from overflowing played as a knickpoint which migrated upstreain. This led to erosion of playa surface by the passing flows. As a result, the playa deposits became dry and a network of contraction fissures were formed in them. The arrival of surface runoff into these fissures was led to depevopment of the pipe system.

Piping is a subsurface form of erosion which involves the removal of subsurface soils in pipe-like erosional channels to a free or escape exit. Although it is one of the coolest and rarest Erosion phenomena that can be formed in any weather conditions، but generally it develops in geological formation with low infiltration capacity and high soluble minerals. Piping materials are commonly highly erodible. However the situation is not fully understood، especially in terms of geomorphology. Compared with surface soil erosion by water، subsurface erosion (piping) is generally less studied and harder to quantify. However، wherever piping occurs، it is often a significant or even the main sediment source (Verachtert et. al.، 2011). This erosion process might occur at any crack that exists in the earth structure، due to differential settlements، seismic movements، tension stresses، or holes caused by dry roots or gnawing animals (rabbits، rats، and etcetera). The erosion starts at any point where the seepage water discharges and works toward the reservoir، gradually enlarging the seepage channel. Field scientists studying badland processes in Mediterranean and Semi-arid climates require assurances that the material in which gullies are presented is not dispersive (Faulkner، 2010). Piping materials are commonly highly erodible. Factors that are involved in Piping formation may include several categories. They are divided to bedrock، soil، climatic and biological factors. Material properties have a significant effect on erosion. When soils are dispersive، piping is very frequently a significant geomorphological agent. To fully interpret badland form and function in rapidly erosion Mediterranean and semi-arid climatic contexts، therefore، field scientists embarking upon any investigation into the gully processes involved require assurances that the material in which the gullies are presented is not dispersive (Faulkner، 2010). Piping can be responsible for accelerated subsurface sediment transport. Subsurface piping pathways can extend for some distance as either continuous features or as a system of interconnected features that form extensive، branched networks. As the pipe enlarges، flow in the conduit becomes increasingly concentrated and turbulent. Collapse of these subsurface conduits and networks can lead to the development of karst-like (“pseudokarst”) topography (ZIEMER، 1992:188، after Halliday، 1960) and the development of gully networks (ZIEMER، 1992:188، after Higgins، 1984; Swanson et al.، 1989). ‘‘Internal erosion’’ is similar to backwards erosion piping in that tractive forces remove soil particles. However، internal erosion is due to flow along pre-existing openings such as cracks in cohesive material or voids along a soil-structure contact. By this definition، internal erosion is not due to the dynamics of intergranular flow and the hydraulics of the problem is quite different than for backwards erosion (Lane، 1934). Soil piping is an important، but little studied. Piping must be understood in order to design for environmentally sound land use. Research that has been done، are stressed mainly on surface erosion and the dynamics of water in the gully. Recent studies indicate that (1) gully erosion represents an important sediment source in a range of environments and (2) gullies are effective links for transferring runoff and sediment from uplands to valley bottoms and permanent channels where they aggravate off site effects of water erosion (Poesen et. al. 2003:51). The study of erosion forms in marls demonstrated that is a drift relationship between erosion forms and some soil chemical properties and includes different sort of erosion (Esmaeilzadeh، 2002). North of Oman Sea is located in the Makran region، this zone is composed of seabed sediments، sediments of surface waters and ophiolites. During Eocene to Oligocene، South Makran coverd by the high thickness of flysch type sediments (Alaee Taleghani، 2003). Badland hills are the major part of Makran Flysch formation at Sirik and Jask County; the main geomorphologic forms of these foothills، is Piping (Fig 1). The aim of this study is to find out Piping erosion in Makran Flysch formation is affected from which of sediment characteristics at Sirik and Jask County. Study Area: The study area is located at 25o38’-26o23’N 57o4’-58o7’E، in Sirik and Jask County، Hormozgan Province، south of Iran at the north of Oman Sea (Fig 2). In general the region under research could be assumed a dry land with very low rain. From geological aspect، this area affected by Makran region general construction and mainly composed of shale، marl and sandstone layers. The formation of this region began on Tertiary (Neogene) and has been continued in the Quaternary period. The geological structure of this area is mainly east-westward and it is located in Coastal Makran sub division that mainly composed of marl. In this region abundance of blinded holes has led to Piping erosion on green marl sediments in Makran flysch formation. Piping erosion has more extensive in areas where marls sediment thickness increases (Fig 3). Research data were including sediment characteristics such as lime and gypsum percentages، calcium، magnesium، sodium and potassium levels، pH، Ec، soil texture and type of clay minerals. Maps of geology and topography، Satellite Imagery، Aerial Photos، laboratory equipment and computer software such as ILWIS، ArcGIS and Minitab also were used as a tools. The methods can be divided into several sections: A) Geomorphologic studies: Distribution map of Badland hills with and without Piping erosion was determined by using of available documents and expedition results. B) Choosing the sediment sampling sites: With the help of networking، samples sites (20 controls and 30 samples)، were identified in landforms map. Then، given the limits of costs، 4-5 points were randomly assigned in a manner that could be statistically processed. C) Sampling: Sediment sampling was conducted by referring to the field. Before sampling، in order to mitigate the effects of climatic factors، 15 cm of the surface layer were taken aside. D) Laboratory works: Sediment samples were transferred to the laboratory and characteristics such as lime and gypsum percentages، calcium، magnesium، sodium and potassium levels، pH، Ec، soil texture and type of clay minerals were identified. E) Statistical analysis: Laboratory results analyzed with appropriate statistical test data in Minitab program. Sediment characteristics of controls and samples such as lime and gypsum percentages، calcium، magnesium، sodium and potassium levels، pH، Ece and soil texture were obtained from the laboratory results. These characteristics were statistically analyzed and compared. According to 1. Piping erosion is related to pH، Ece، clay، silt and sand percentage، lime percentage and calcium، sodium and potassium ions، at the significant level of %1. 2. Piping erosion is related to gypsum percentage and magnesium ion at the significant level of %5. 3. The electrical conductivity (Ece)، silt and sand percentages، lime and gypsum percentages، magnesium، calcium، sodium and potassium ions، are directly related to Piping. 4. Soil pH، soil saturation (sp) and clay percentages، are inversely related to Piping. Among sedimentological characteristics which studied in Makran flysch formation، the electrical conductivity of soil، silt، lime and gypsum percentages، also magnesium، calcium، sodium and potassium ions have been led to Sensitivity and soil acidity (pH)، soil saturation percentage (SP) and clay percentage have been led to resistance from Piping. The present study in the Sirik and Jask county area، Hormozgan province، Iran، shows that electrical conductivity، clay، silt and sand percentage، also calcium، potassium، sodium ions and lime percentage، ordinarily are the most affective factors on Piping erosion. In the next ranks، it affected by gypsum percentage and magnesium ion content. Among these factors، electrical conductivity، silt، lime and gypsum percentage، also magnesium، calcium، sodium and potassium ions have been led to Sensitivity and soil acidity (pH)، soil saturation percentage (SP) and clay percentage have been led to resistance from Piping.

This paper presents the processes and forms that are shaped in loess deposit in the south and east of Aghband. The study area is the Centre of agriculture of Golestan- province. Therefore the investigation of erosion outcrops such as gully erosion, badland and landslide in the study area is important. Another important processes are  the characteristics of arid and semi arid climate as well as other natural factors involved. Using the laboratory methods which were carried out on soils of the study area has shown that the presence of limestone, silt, clay and gips of the loess- deposit has led to the forming of Gully erosion in arid- central part, piping in semi- arid- part and landslide in humid sourthern part and badland topography in  most parts of northern and southern parts of the study area.