Assessment of Salt weathering in Siwa Oasis
(The Western Desert of Egypt)
Abstract
Salt weathering is a negative aspect that causes marked deterioration and hazards in Siwa Oasis. Salt weathering primarily results from both mechanical and chemical deterioration of rocks. In recent years many parts of Siwa Oasis have suffered immensely from salt weathering activities such as archaeological sites, roads, cultivated and urban areas. Human activities are a main cause for secondary salinization particularly in the last decades as a result of unplanned development programs. LAND SAT- TM, SPOT, IKONOS and QUIKBIRD images in addition to GIS techniques were apply to record the varying degrees of development of salt weathering. They were used to detect, analyze and assess the negative environmental features of salt weathering. Cartographic representation of this feature was produced from multi-dates data, digital maps and field investigation. A comprehensive map of such hazards is produced and represents a contribution in this connection.
This study explains the reasons of how salt weathering activity in Siwa varies according to its different accelerating processes. The detected changes explain that the total surface area surrounding the saline lakes (salt flats) have increased from 1933 to 2002 by some 20.55km2. The hazard map shows that salt weathering activity vary considerably from one local to another thus manifesting a special rate of their spatial distribution. The most intense activities occur around the margins of saline lakes, in low areas, where the ground surface is affected by the capillary rise from shallow saline groundwater. The total area affected by salt weathering reaches 32.82 % of the Oasis area. The highly exposed area suffering from salt weathering equals 39.1km2 representing 9.57%of the total area of Siwa.