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Mapping and Landscape Interpretation of Al Madinah Province, Western Saudi Arabia

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posted on 17.09.2018, 08:52 authored by Ghizayel Ragaullah D. Almuhammadi
In relation to the Kingdom of Saudi Arabia, there is very little environmental and geomorphological information. This is especially so in the western region, represented by Al Madinah Province, which remains poorly understood. Therefore, in this study, the never before studied landscape in the east of Al Madinah Province was mapped and interpreted, using multiple approaches in the investigation, in what is considered an important and advanced step in mapping and interpreting landscape. Such approaches contributed to gathering the largest amount of data on this area relating to both the past and present, which provided a clearer and more comprehensive understanding than what had existed for this desert environment in the east of Al Madinah Province. These approaches included: First, using remote sensing, ASTER GDEM and Landsat 8 multispectral image processing techniques (principle component analysis, band ratioing, and false colour composites) alongside field and laboratory reflectance measurements ASD HH2, helped in understanding the spectral characteristics of deposits, and as such describe composition and mixing of sediments in the image, and infer how sediment is weathered and transported around the study area. This contributed to interpreting the landscape, including provenance, sediment movement, and locations of deposition that have contributed to the principal geomorphological features found in the area. This study demonstrates the relationship between laboratory spectral reflectances, and that of Landsat 8 imagery showing a strong positive correlation (R2=0.84 to 0.89). Consequently, Landsat 8 surface reflectances data was used effectively in mapping different geomorphological units (sand dunes, sand sheets, sand ramps, wadi deposits, slopes, Qa, sabkha, intermountaneous basins, Sahuq plateau, and East Al Madinah plateau) on spectral bases using maximum likelihood supervised classification with overall accuracy of 80.84%. A spectral transect passing through East Al Madinah plateau showed the spectral characteristics of sediments regarding their grain size. Landsat 8 PCA colour composite was found to be the most effective for visual interpreting and describing sediments composition and mixing, and inferred the geomorphic processes within the study area. In some cases, field spectral measurements might be more effective than laboratory measurements giving reliable spectral signature more comparable with satellite imagery, especially for dikes and similar longitudinal features. Second, field observations with sediments analysis and OSL dating were used to identify the ages of palaeogeomorphic and palaeoenvironmental conditions. This allows the geomorphological history to be initially interpreted. Moreover, for this otherwise unstudied area, the extent of spatial and regional changes could be ascertained. The results of OSL dating support the existence of wet periods in Al Madinah at 34.2±2.5 ka in Marine Isotope Stage (MIS) 3, and in the early Holocene (9.9±0.6 – 11.6±1.0 ka). These results show that the monsoon rainfall belt extended to latitudes 25° N and 26° N, not just 23° - 24° N. The monsoon rainfall belt did not move from Southern to Northern Arabia over 1800 years, it took place at the same time, in southern, western, eastern, and central areas of the Arabian Peninsula.



McLaren, Sue; Powell, Mark

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Department of Geography

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University of Leicester

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